Toughened polymer networks with organosilane and organogermanium crosslinkers and uses thereof

Abstract

Disclosed herein are toughened polymer networks comprising organosilane and organogermanium crosslinkers, methods of making the same, and uses thereof.

Description

[0001] DUKE-44295.601

[0002] TOUGHENED POLYMER NETWORKS WITH ORGANOSILANE AND ORGANOGERMANIUM CROSSLINKERS AND USES THEREOF CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and the benefit of U. S. Provisional Patent Application No. 63 / 748,198, filed on January 22, 2025, the disclosure of which is incorporated herein by reference in its entirety.

[0003] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0004] This invention was made with government support under CHE-2116298 awarded by the National Science Foundation. The government has certain rights in the invention.

[0005] FIELD

[0006] Provided herein are toughened polymer networks comprising organosilane and organogermanium crosslinkers, methods of making the same, and uses thereof.

[0007] BACKGROUND

[0008] The end of life for many polymer networks is mechanical failure, exemplified by the tearing of a contact lens. The macroscopic observation of a crack propagating through the polymer network arises from the breaking of bonds within the individual polymer strands and junctions that compose the network. The bond scission is typically a homolysis reaction forming two macroradicals. The strategic design and placement of mechanically labile functional groups (e.g., cyclobutane mechanophore) in the crosslinks of a polymer network can counterintuitively toughen an elastic network (Sakai et al. ACS Macro Lett. 2020, 9 (8), 1108-1113; Du et al. Nat Commun 2022, 13 (1), 3231; Wang et al Science 2023, 380 (6651), 1248-1252); the same scissile mechanophore placed in the main strand of a network results in a weaker network (Wang et al. J. Am. Chem. Soc. 2021, 143 (10), 3714—3718). Structureactivity relationships and accompanying molecular dynamics simulations in poly(methoxyethylacrylate) elastomers supported a mechanism for reactivity-guided molecular fracture paths that were directed around, rather than through, the primary polymer strands within the network when sufficiently reactive mechanophores are used as pendant cross-linkers (Beech et al. ACS Macro Lett. 2023, 12 (12), 1685-1691). The magnitude of the effect depends on both the length of the primary strands (longer strands lead to greater mechanophore toughening) and on the force-coupled scissile reactivity of the crosslinker (Wang 2021).DUKE-44295.601

[0009] SUMMARY

[0010] Disclosed herein are organosilane and organogermanium mechanophores that are reactive enough to improve the tear resistance of poly(alkyl)acrylate polymers, such as poly(methoxyethylacrylate) elastomers, when incorporated as a crosslinker. While the mechanical properties of polysiloxanes are well-studied, comparatively little work has focused on the mechanical properties of hybrid carbosilane polymers in which some carbon atoms have been systematically replaced with silicon atoms, or on hybrid polymers in which some carbon atoms have been systematically replaced with germanium atoms.

[0011] In one aspect, disclosed herein is a polymeric material comprising a crosslinker, wherein the crosslinker comprises a moiety of formula (I):

[0012]

[0013] wherein:

[0014] X is Si or Ge; and

[0015] R1and R2are each independently selected from C1-C4 alkyl.

[0016] In some embodiments, X is Si. In some embodiments, X is Ge. In some embodiments, R1and R2are each methyl.

[0017] In some embodiments, the crosslinker comprises a moiety of formula:

[0018]

[0019] In some embodiments, the crosslinker comprises a moiety of formula:

[0020]

[0021] In some embodiments, the crosslinker in the polymeric material is derived from a compound of formula (II):

[0022]

[0023] wherein:

[0024] X is Si or Ge;

[0025] R1and R2are each independently selected from C1-C4 alkyl; and

[0026] R3and R4are each independently selected from hydrogen and methyl.

[0027] In some embodiments, X is Si. In some embodiments, X is Ge. In some embodiments, R1and R2are each methyl. In some embodiments, R3and R4are each hydrogen.DUKE-44295.601

[0028] In some embodiments, the compound of formula (II) is:

[0029]

[0030] In some embodiments, the compound of formula (II) is:

[0031]

[0032] In some embodiments, the polymeric material is an acrylate polymeric material. In some embodiments, the polymeric material comprises one or more (meth)acrylate monomers selected from alkyl (meth)acrylates, hydroxyalkyl (meth)acrylates, alkoxyalkyl (meth)acrylates, cycloalkyl (meth)acrylates, and aromatic (meth)acrylates.

[0033] In some embodiments, the polymeric material comprises one or more alkyl (meth)acrylates selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, iso-decyl (meth)acrylate, heptadecyl (meth)acrylate, dodecyl (meth)acrylate, 2-propylheptyl (meth)acrylate, and stearyl (meth)acrylate. In some embodiments, the alkyl (meth)acrylate is ethyl acrylate.

[0034] In some embodiments, the polymeric material comprises one or more alkoxyalkyl (meth)acrylates selected from the group consisting of 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, l-methyl-2-methoxy ethyl (meth)acrylate, ethylene glycol methyl ether (meth)acrylate, diethylene glycol methyl ether (meth) acrylate, and triethylene glycol methyl ether (meth)acrylate. In some embodiments, the alkoxyalkyl (meth)acrylate is 2-methoxyethyl (meth)acrylate.

[0035] In another aspect, disclosed herein is a method of toughening a polymeric material, comprising:

[0036] incorporating a crosslinker into the polymeric material, wherein the crosslinker comprises a moiety of formula (I):

[0037]

[0038] wherein:

[0039] X is Si or Ge; and

[0040] R1and R2are each independently selected from C1-C4 alkyl.DUKE-44295.601

[0041] In some embodiments, X is Si. In some embodiments, X is Ge. In some embodiments, R1and R2are each methyl.

[0042] In some embodiments, the crosslinker comprises a moiety of formula:

[0043]

[0044] In some embodiments, the crosslinker comprises a moiety of formula:

[0045]

[0046] In some embodiments, the crosslinker is a compound of formula (II):

[0047]

[0048] wherein:

[0049] X is Si or Ge;

[0050] R1and R2are each independently selected from C1-C4 alkyl; and

[0051] R3and R4are each independently selected from hydrogen and methyl.

[0052] In some embodiments, X is Si. In some embodiments, X is Ge. In some embodiments, R1and R2are each methyl. In some embodiments, R3and R4are each hydrogen.

[0053] In some embodiments, the compound of formula (II) is:

[0054]

[0055] In some embodiments, the compound of formula (II) is:

[0056]

[0057] In some embodiments, the incorporating step comprises:

[0058] (a) providing a mixture comprising a monomer, the crosslinker, and an initiator; and (b) initiating polymerization to form the polymeric material.

[0059] In some embodiments, the polymeric material is an acrylate polymeric material. In some embodiments, the polymeric material comprises one or more (meth)acrylate monomers selected from alkyl (meth)acrylates, hydroxyalkyl (meth)acrylates, alkoxyalkyl (meth)acrylates, cycloalkyl (meth)acrylates, and aromatic (meth) acrylates.DUKE-44295.601

[0060] In some embodiments, the polymeric material comprises one or more alkyl (meth)acrylates selected from the group consisting of methyl (meth) acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, iso-decyl (meth)acrylate, heptadecyl (meth)acrylate, dodecyl (meth)acrylate, 2-propylheptyl (meth)acrylate, and stearyl (meth)acrylate. In some embodiments, the alkyl (meth)acrylate is ethyl acrylate.

[0061] In some embodiments, the polymeric material comprises one or more alkoxyalkyl (meth)acrylates selected from the group consisting of 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, l-methyl-2-methoxy ethyl (meth)acrylate, ethylene glycol methyl ether (meth)acrylate, diethylene glycol methyl ether (meth)acrylate, and triethylene glycol methyl ether (meth)acrylate. In some embodiments, the alkoxyalkyl (meth)acrylate is 2-methoxyethyl (meth)acrylate.

[0062] In some embodiments, the polymerizing step comprises reversible additionfragmentation chain transfer (RAFT) polymerization. In some embodiments, the mixture further comprises a chain transfer agent, the initiator is a photoinitiator, and step (b) comprises exposing the mixture to UV light to incorporate the moiety of formula (I) into the polymeric material and form the toughened polymeric material.

[0063] In some embodiments, the polymerizing step comprises free-radical polymerization. In some embodiments, the polymeric material has an increased toughness compared to a corresponding polymeric material having a crosslinker comprising a moiety of formula (I), wherein X is C. In some embodiments, the polymeric material has a tearing energy, as determined by the Thomas-Rivlin method, that is at least 50% greater than a tearing energy of a corresponding polymeric material having a crosslinker comprising a moiety of formula (I), wherein X is C.

[0064] In another aspect, disclosed herein is an article of manufacture comprising a polymeric material disclosed herein (e.g., a polymeric material comprising a crosslinker, wherein the crosslinker comprises a moiety of formula (I)).

[0065] In another aspect, disclosed herein is an article of manufacture comprising a polymeric material prepared according to a method disclosed herein (e.g., a method comprising incorporating a crosslinker into the polymeric material, wherein the crosslinker comprises a moiety of formula (I)).

[0066] In another aspect, disclosed herein is a method of producing an article of manufacture comprising a polymeric material disclosed herein (e.g., a polymeric material comprising aDUKE-44295.601

[0067] crosslinker, wherein the crosslinker comprises a moiety of formula (I)), comprising sequentially depositing layers of the polymeric material onto a surface, to thereby form the article of manufacture.

[0068] BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A-1C show: (FIG. 1A) Force-induced changes in ground state geometry distort the carbosilane towards the transition state geometry, thereby reducing the energetic barrier to Si-C bond homolysis. (FIG. 1B) Silyl and alkyl motifs studied in this manuscript, labeled with calculated bond dissociation energies (BDE) in kcal mol1. Geometry optimization: B3LYP-D4 / def2-SVP. BDEs evaluated: B3LYP-D4 / def2-TZVP. (FIG. 1C) Chemical structure of crosslinkers 1-3.

[0069] FIG. 2 shows a schematic depicting the cleavage of a scissile silane mechanophore and non-scissile ring-opening of mechanophore gDCC in response to sonication.

[0070] FIG. 3 shows a plot of ring opening of gDCC versus scission cycle with slopes of linear fits a

[0071]

[0072] s for P1-P3.

[0073] FIG. 4 shows synthesis of RAFT MEA networks N1-N3, MEA = 2-methoxyethyl acrylate; DDMAT = 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid; 2,4,6-trimethylbenzoyldiphenyl phosphine oxide as PI = photoinitiator.

[0074] FIGS. 5A-5D show: (FIG. 5A) Rheological frequency sweeps (oscillatory strain at 0.5%) of N12, N22and N32; (FIG. 5B) stress-strain curves of notched samples of N12, N22and N32under pure shear state for tear tests under strain rate of 0.25 % / s; (FIG. 5C) Tearing energies, T, for N12, N22and N32(T(N12) to T(N22) or T(N32)), p <.0001, t test; T(N22), T(N32), are not statistically significant to each other); (FIG. 5D) Tearing energies, T, for N1, N2 and N3 with different crosslinking densities.

[0075] FIG. 6 shows additive manufacturing of networks.

[0076] FIGS. 7A-7D show representative stress-strain curves for: (FIG. 7A) NU-3D, N21-3D and (FIG. 7B) N1i, N2i; (FIG. 7C) statistics of strain at break and critical stress for (a) and (b); (FIG. 7D) Young’s moduli for NU, N2i, NU-3D, and N21-3D.

[0077] FIGs. 8A-C show N1-3D network prints of (FIG. 8A) cylinder-hole print optimization model, (FIG. 8B) channel optimization model with varying channel widths (1000, 500, 250, and 100 pm), and (FIG. 8C) a model of a cat lying down.

[0078] FIGS. 9A-9B show: (FIG. 9A) Tearing energy, T, measured by pure-shear tear tests for poly-methoxy ethylacrylate (PMEA) networks prepared with different crosslinkers; (FIG.DUKE-44295.601

[0079] 9B) Chemical structures of the crosslinkers used and PMEA. p-values are indicated as: ns, p > 0.05; ****,p < 0.0001.

[0080] FIGS. 10A-10C show: (FIG. 10A) Chemical structures of ethyl acrylate / methoxyethyl acrylate copolymers and the crosslinkers studied, r (%) denotes the ethyl acrylate content in the copolymer; (FIGS. 10B-10C) Tearing energy, T, measured by pure-shear tear tests for copolymer networks with varying r, prepared using either the SiMe2 or control crosslinker at (FIG. 10B) 1.5% and (FIG. 10C) 4% crosslinker loading.

[0081] DETAILED DESCRIPTION

[0082] As has been disclosed in the context of cyclobutane mechanophore-derived materials, a scissile mechanophore will weaken a single polymer strand but counterintuitively toughen a polymer network if incorporated in crosslinks (Wang et al. Science 2023, 380 (6651), 1248— 1252; Wang et al. J. Am. Chem. Soc. 2021, 143 (10), 3714-3718). At the single strand level, a scissile mechanophore cleaves at lower force, resulting in chain scission. In a network with a scissile mechanophore placed only in the crosslink, selective mechanochemical scission cleaves crosslinks rather than load-bearing primary chains, resulting in network toughening.

[0083] Disclosed herein is a structural design that allows for placement of the same organosilane or organogermanium motif, such as a SiMe2 or GeMe2 motif, both in a network crosslink and in a single strand. In one embodiment, the bis(acetoxymethyl)silane motif (Scheme I) meets this need as the same substructure could be embedded into a network by radical copolymerization of 1 and 2-methoxyethyl acrylate (MEA) or into a single strand by polycondensation of diol 4 and glutaric acid (GA).DUKE-44295.601

[0084] Scheme 1. Network and Strand Design: the bis(acetoxymethyl)silane is a structural motif used in polymer networks and linear polymers synthesized from either crosslinker 1 or diol 4

[0085] (Itsfacs^

[0086] strand

[0087] HO 'Si OH

[0088] Me" Me

[0089] 4

[0090]

[0091] GA Definitions

[0092] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0093] Definitions of specific terms, including certain functional groups and chemical terms, are described in more detail below. For purposes of this disclosure, the chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 75thEd., inside cover, and specific functional groups are generally defined as described therein. Additionally, general principles of organic chemistry, as well as specific functional moieties and reactivity, are described in Sorrell, Organic Chemistry, 2ndedition, University Science Books, Sausalito, 2006; Smith, March's Advanced Organic Chemistry: Reactions, Mechanism, and Structure, 7thEdition, John Wiley & Sons, Inc., New York, 2013; Larock, Comprehensive Organic Transformations, 3rdEdition, John Wiley & Sons, Inc., New York, 2018; and Carruthers, Some Modern Methods of Organic Synthesis, 3rdEdition, Cambridge University Press, Cambridge, 1987; the entire contents of each of which are incorporated herein by reference.

[0094] As used herein, the term “alkyl” refers to a radical of a straight or branched saturated hydrocarbon chain. The alkyl chain can include, e.g., from 1 to 24 carbon atoms (C1-C24 alkyl), 1 to 16 carbon atoms (C1-C16 alkyl), 1 to 14 carbon atoms (C1-C14 alkyl), 1 to 12 carbon atoms (C1-C12 alkyl), 1 to 10 carbon atoms (C1-C10 alkyl), 1 to 8 carbon atoms (C1-C8alkyl), 1 to 6 carbon atoms (Ci-C& alkyl), 1 to 4 carbon atoms (C1-C4 alkyl), 1 to 3 carbonDUKE-44295.601

[0095] atoms (C1-C3 alkyl), or 1 to 2 carbon atoms (C1-C2 alkyl). Representative examples of alkyl include, but are not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, 3-methylhexyl, 2,2-dimethylpentyl, 2,3-dimethylpentyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, and n-dodecyl.

[0096] As used herein, the term “alkoxy” refers to an alkyl group, as defined herein, appended to the parent molecular moiety through an oxygen atom. Representative examples of alkoxy include, but are not limited to, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, and tert-butoxy.

[0097] As used herein, the term “alkoxyalkyl” refers to an alkyl group, as defined herein, in which at least one hydrogen atom (e.g., one hydrogen atom) is replaced with an alkoxy group, as defined herein. Representative examples of alkoxyalkyl include, but are not limited to, methoxymethyl, 2-methoxyethyl, and 2-ethoxyethyl.

[0098] As used herein, the term “aryl” refers to a radical of a monocyclic, bicyclic, or tricyclic 4n+2 aromatic ring system (e.g., having 6, 10, or 1471 electrons shared in a cyclic array) having 6-14 ring carbon atoms and zero heteroatoms (“C6-C14 aryl”). In some embodiments, an aryl group has six ring carbon atoms (“Ce aryl,” i.e., phenyl). In some embodiments, an aryl group has ten ring carbon atoms (“C10 aryl,” e.g., naphthyl such as 1-naphthyl and 2-naphthyl). In some embodiments, an aryl group has fourteen ring carbon atoms (“C14 aryl,” e.g., anthracenyl and phenanthrenyl).

[0099] As used herein, the term “cycloalkyl” refers to a radical of a saturated carbocyclic ring system containing three to ten carbon atoms and zero heteroatoms. The cycloalkyl may be monocyclic, bicyclic, bridged, fused, or spirocyclic. Representative examples of cycloalkyl include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, adamantyl, bicyclo[2.2.1]heptanyl, bicyclo[3.2.1]octanyl, and bicyclo[5.2.0]nonanyl.

[0100] As used herein, the term “hydroxy” refers to an -OH group.

[0101] As used herein, the term “hydroxyalkyl” refers to an alkyl group, as defined herein, in which at least one hydrogen atom (e.g., one hydrogen atom) is replaced with a hydroxy group. Representative examples of hydroxyalkyl include, but are not limited to, hydroxymethyl, 2-hydroxyethyl, 3-hydroxypropyl, and 4-hydroxybutyl.

[0102] As used herein, the term “(meth)” designates optional methyl substitution. Thus, a term such as “(meth)acrylates” denotes both methacrylates and acrylates. For example, the term “methyl (meth)acrylate” refers to methyl acrylate and methyl methacrylate.DUKE-44295.601

[0103] Polymeric Networks

[0104] In one aspect, disclosed herein is a polymeric material comprising a crosslinker, wherein the crosslinker comprises a moiety of formula (I):

[0105]

[0106] R1R2(I)

[0107] wherein X is Si or Ge, and R1and R2are each independently selected from C1-C4 alkyl.

[0108] In some embodiments, X is Si. In some embodiments, X is Ge.

[0109] In some embodiments, R1and R2are each independently selected from C1-C2 alkyl. In some embodiments, R1and R2are each methyl.

[0110] In some embodiments, the crosslinker comprises a moiety of formula:

[0111]

[0112] In some embodiments, the crosslinker comprises a moiety of formula:

[0113]

[0114] In some embodiments, the crosslinker comprises a moiety of formula:

[0115]

[0116] In some embodiments, the crosslinker in the polymeric material is derived from (i.e., is based on the crosslinker of formula) (II):

[0117]

[0118] wherein X is Si or Ge, R1and R2are each independently selected from C1-C4 alkyl, and R3and R4are each independently selected from hydrogen and methyl.

[0119] In some embodiments, X is Si. In some embodiments, X is Ge.

[0120] In some embodiments, R1and R2are each independently selected from C1-C2 alkyl. In some embodiments, R1and R2are each methyl. In some embodiments, R3and R4are each hydrogen. In some embodiments, R3and R4are each independently selected from C1-C2 alkyl. In some embodiments, R3and R4are each methyl.

[0121] In some embodiments, the crosslinker in the polymeric material is derived from (i.e., is based on the crosslinker of formula):DUKE-44295.601

[0122]

[0123] In some embodiments, the crosslinker in the polymeric material is derived from (i.e., is based on the crosslinker of formula):

[0124]

[0125] In some embodiments, the crosslinker in the polymeric material is derived from (i.e., is based on the crosslinker of formula):

[0126]

[0127] In some embodiments, the polymeric material is an acrylate polymeric material. An acrylate polymeric material described herein can include one or more (meth)acrylate monomers. Any (meth)acrylate monomers can be used. In some embodiments, the polymers include at least one (meth)acrylate monomer selected from an alkyl (meth)acrylate, a hydroxyalkyl (meth)acrylate, an alkoxyalkyl (meth)acrylate, a cycloalkyl (meth)acrylate, and an aromatic (meth)acrylate.

[0128] For example, in some embodiments, the polymer comprises an alkyl (meth) acrylate monomer. Exemplary alkyl (meth)acrylates include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, iso-decyl (meth)acrylate, heptadecyl (meth)acrylate, dodecyl (meth)acrylate, 2-propylheptyl (meth)acrylate, and stearyl (meth)acrylate. In some embodiments, the polymer comprises an ethyl acrylate monomer.

[0129] In some embodiments, the polymer comprises a hydroxyalkyl (meth)acrylate monomer. Exemplary hydroxyalkyl (meth)acrylate monomers include, but are not limited to, hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0130] In some embodiments, the polymer comprises an alkoxyalkyl (meth)acrylate monomer. Exemplary alkoxyalkyl (meth)acrylate monomers include, but are not limited to, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 1-methyl-2-methoxyethyl (meth)acrylate, ethylene glycol methyl ether (meth)acrylate, diethylene glycol methyl etherDUKE-44295.601

[0131] (meth)acrylate, and triethylene glycol methyl ether (meth)acrylate. In some embodiments, the polymer comprises a 2-methoxyethyl acrylate monomer.

[0132] In some embodiments, the polymer comprises a cycloalkyl (meth)acrylate monomer. Exemplary cycloalkyl (meth)acrylate monomers include, but are not limited to, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-cyclohexylethyl (meth)acrylate, 3-cyclohexylpropyl (meth)acrylate, 2-norbornyl (meth)acrylate, and isobornyl (meth)acrylate.

[0133] In some embodiments, the polymer comprises an aromatic (meth)acrylate monomer. Exemplary aromatic (meth)acrylate monomers include, but are not limited to, benzyl (meth)acrylate, 2-phenylethyl (meth)acrylate, 3 -phenylpropyl (meth)acrylate, 4-phenylbutyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 3-phenoxypropyl (meth)acrylate, and any combination thereof.

[0134] The polymers can include at least two different (meth) acrylate monomers, such as any of the monomers described herein. For polymer can be a block copolymer (e.g., a diblock copolymer or a triblock copolymer), a random copolymer, a graft copolymer, or the like. In some embodiments, the polymer is a copolymer (e.g., a random copolymer) of an alkyl (meth)acrylate and an alkoxyalkyl (meth)acrylate. In some embodiments, the polymer is a copolymer (e.g., a random copolymer) of ethyl acrylate and 2-methoxyethyl acrylate.

[0135] The polymers disclosed herein, such as crosslinked acrylate polymers described herein, can be prepared by a number of methods including free radical polymerization methods and controlled radical polymerization methods, such as reversible addition fragmentation chain transfer polymerization (RAFT), atom transfer radical polymerization (ATRP), stable free radical polymerization (SFRP), nitroxide-mediated polymerization (NMP), and the like. In some embodiments, the acrylate polymers are prepared by reversible addition-fragmentation chain transfer (RAFT).

[0136] For example, in some embodiments, the acrylate polymer can be prepared by:

[0137] (a) controlled radical polymerization (e.g., RAFT) of a (meth)acrylate monomer, to form a pre-gel mixture comprising acrylate polymer chains; and

[0138] (b) crosslinking the acrylate polymer chains in the pre-gel mixture with a crosslinker comprising a moiety of formula (I).

[0139] In some embodiments, step (b) comprises crosslinking the acrylate polymer chains in the pre-gel mixture with a crosslinker of formula (II) disclosed herein. For example, in some embodiments, in step (b) the crosslinker is:DUKE-44295.601

[0140]

[0141] In some embodiments, in step (b) the crosslinker is:

[0142]

[0143] The controlled radical polymerization (e.g., RAFT) reaction is conducted using an initiator, which is an agent capable of producing a free radical. In some embodiments, the controlled radical polymerization (e.g., RAFT) is conducted using a photoinitiator. An initiator is a compound that decomposes into radicals which subsequently react with a monomer to initiate a free-radical polymerization reaction. Photoinitiators decompose by photochemical processes. Typical examples of photoinitiators include, but are not limited to: benzil, benzoin, acetophenone, benzophenone, camphorquinone, or derivatives thereof; monoacyl and bisacyl phosphine oxides; and a-ketoesters including a-ketoglutaric acid, ethyl pyruvate, and the like. For example, in some embodiments, the photoinitiator is a monoacyl or bisacyl phosphine oxide, such as 2,4,6-trimethylbenzoyldiphenyl phosphine oxide.

[0144] Combinations of photoinitiators can also be used. In some embodiments, the photoinitiator is an a-ketoester. In some embodiments, the photoinitiator is a-ketoglutaric acid.

[0145] In some embodiments, the controlled radical polymerization (e.g., RAFT) is conducted using a chain transfer agent. Representative chain transfer agents include, but are not limited to: trithiocarbonates such as 3,5-bis(2-dodecylthiocarbonothioylthio-1-oxopropoxy) benzic, 3-butenyl 2-(dodecylthiocarbonothioylthio)-2-methyl propionate, 2-(2-carboxyethylsulfanylthiocarbonylsulfanyl)-proprionic acid, 4-((((2-carboxyethyl)thio) carbonothioyl)thio)-4-cyanopentanoic acid, 2-cyanobutan-2-yl 4-chloro-3,5-dimethyl-1H-pyrazole-1-carbodithioate, 2-cyanobutanyl-2-yl 3,5-dimethyl-1H-pyrazole-1-carbodithioate, 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid, 2-(butylthiocarbonothioylthio)propanoic acid, 4-cyano-4-(ethylcarbonothioylthio) pentanoic acid, 4-cyano-4- [(dodecylsulf any lthiocarbonyl)sulfanyl]pentanol, cyanomethyl (3,5-Dimethyl-lH-pyrazole)-carbodithioate, cyanomethyl dodecyl trithiocarbonate, cyanomethyl [3-(trimethoxysilyl)propyl] trithiocarbonate, 2-cyano-2-propyl dodecyl trithiocarbonate, S,S-di benzyl trithiocarbonate, 2-(dodecyl-thiocarbonothioylthio)-2-methylpropionic acid, 2-(dodecyl-thiocarbonothioyl-thio)-2-methylpropionic acid, 3-azido-1-propanol ester, 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid, N-hydroxysuccinimide ester of 4-DUKE-44295.601

[0146] cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid, pentafluorophenyl ester of 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid, 2-(dodecylthiocarbonothioylthio)propionic acid, methyl 2-(dodecyl)-2-methylpropionate, pentaerythritol tetrakis[2-(dodecylthiocarbonothioylthio)-2-methylpropionate], phthalimidomethyl butyl trithiocarbonate, poly(acrylic acid) having a 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid end, poly(ethylene glycol)bis[2-(dodecylthiocarbonothioylthio)-2-methylpropionate], poly(ethylene glycol) methyl ether 4-cyano-4- [(dodecyl sul fan ylthiocarbonyl)sulfanyl]pent anoate, poly (ethylene glycol) methyl ether (4-cyano-4-pentanoate dodecyl trithiocarbonate), poly(ethylene glycol)methyl ether (4-cyano-4-pentanoate dodecyl tri thiocarbonate), poly (ethylene glycol)methyl ether (4-cyano-4-pentanoate dodecyl trithiocarbonate), polyethylene glycol) methyl ether 2-(dodecylthiocarbonothioylthio)-2-methylpropionate, polyethylene glycol)methyl ether 2-(dodecylthiocarbonothioylthio)-2-methylpropionate, poly(ethylene glycol)methyl ether (2-methyl-2-propionic acid dodecyl trithiocarbonate)L-lactide) 4-cyano-4-[(dodecylsulfanyl-thiocarbonyl)sulfanyl] pentonate, poly(L-lactide) 4-cyano-4-[(dodecylsulfanyl-thiocarbonyl)sulfanyl] pentonate, poly(D, L-lactide), 4-cyano-4-[ (dodecylsulf anyl-thiocarbonyl)sulfanyl] pentonate, polystyrene with an end of 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid, or 1,1,1 -tris[(dodecylthiocarbonothioylthio)-2-methylpropionate] ethane;dithiocarbamates such as benzyl 1H-pyrrole-1-carbodithioate, cyanomethyl diphenylcarbamodi thioate, cyanomethyl methyl(phenyl)carbamodithioate, cyanomethyl methyl(4-pyridyl)carbamodithioate, 2-cyanopropan-2-yl N-methyl-(pyridin-4-yl)carbamodithioate, methyl 2-[methyl(4-pyridinyl)carbamothioylthio] propionate, 1 -succinimidyl-4-cyano-4- [N-methyl-N-(4-pyridyl)carbamothioylthio] pentanoate; dithiobenzoates such as benzyl benzodithioate, cyanomethyl benzodithioate, 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid, N-succinimidyl ester of 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid, 2-cyano-2-propyl benzodithioate, 2-cyano-2-propyl 4-cyanobenzodithioate, ethyl 2-(4-methoxyphenylcarbonothioylthio)acetate, ethyl 2-methyl-2-(phenylthiocarbonylthio)propionate, ethyl 2-(phenylcarbonothioylthio)-2-phenylacetate, ethyl 2-(phenylcarbonothioylthio) propionate, 1 -(methoxycarbonyl)ethyl benzodithioate, 2-(4-methoxyphenylcarbonothioylthio) ethanoic acid, 2-nitro-5-(2-propynyloxy)benzyl 4-cyano-4-(phenylcarbonothioylthio)pentanoate, 2-(phenylcarbonothioylthio) propanoic acid, or 2-phenyl-2-propyl benzodithioate; and switchable RAFT agents such as cyanomethyl methyl(4-pyridyl)carbamodithioate, 2-cyanopropan-2-yl N-methyl-N-(pyridin-4-yl)carbamodithioate,DUKE-44295.601

[0147] methyl 2-[methyl(4-pyridinyl)carbamothioylthio]propionate, or l-succinimidyl-4-cyano-4- [N-methyl-N-(4-pyridyl) carbamothioylthio] pentanoate. In some embodiments, the chain transfer agent is 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid. In some embodiments, the chain transfer agent is 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid.

[0148] Methods of Use

[0149] The crosslinking compounds disclosed herein are mechanically weak, yet produce polymers that have improved strength and tear resistance. Accordingly, disclosed herein is a method of toughening a polymeric material, comprising incorporating a moiety of formula (I) into the polymeric material. The moiety of formula (I) can be incorporated, for example, by incorporating a crosslinker comprising a moiety of formula (I), such as a crosslinker of formula (II), into the polymeric material according to methods disclosed herein. The polymeric materials have improved toughness compared to the corresponding polymeric materials having carbon-based crosslinkers. For example, in some embodiments, the polymeric networks disclosed herein have improved toughness compared to corresponding materials polymeric materials comprising a crosslinker, wherein the crosslinker comprises a moiety of formula (I) described herein where X is carbon (e.g., a crosslinker of formula (II) wherein X is carbon).

[0150] The increased toughness can be reflected by, for example, increased tearing energy. As those skilled in the art appreciate, tearing energy can be determined by conducting a tear test according to the Thomas-Rivlin method, described in: Rivlin et al. Journal of Polymer Science 1953, 10 (3), 291-318; and Danielsen et al. Chem. Rev. 2021, 121 (8), 5042-5092; each of which is incorporated herein by reference in its entirety. According to such a test, unnotched and notched samples are stretched at a constant strain rate of 0.01 mm / s under pure shear state. Tearing energy, T, is calculated by

[0151] Γ = W(εp)h0

[0152]

[0153] where W(εp) is the energy density of the sample for crack propagation, and h0is the initial gap distance between clamps. The strain energy density

[0154]

[0155] W(εp) is calculated from the unnotched curves as the integration to the critical strain εpof the stress-strain curves. Accordingly, in some embodiments, disclosed herein are polymeric materials comprising a crosslinker of formula (I) disclosed herein (e.g., polymeric materials comprising a crosslinker of formula (II) disclosed herein), having increased tearing energy compared to polymericDUKE-44295.601

[0156] materials comprising a crosslinker, wherein the crosslinker comprises a moiety of formula (I) described herein where X is carbon (e.g., a crosslinker of formula (II) wherein X is carbon). In some embodiments, polymeric materials disclosed herein have a tearing energy that is at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 100% greater than the tearing energy of a corresponding polymeric material comprising a moiety of formula (I) described herein where X is carbon (e.g., a crosslinker of formula (II) wherein X is carbon).

[0157] The toughened polymer networks can be used in any application in which it would be useful or desirable to use a mechanically strong polymeric material. For example, such polymeric materials are often used in additive manufacturing processes (i.e., 3D printing), in materials used in artificial joints, in dental fillings, and in cosmetic applications such as nail polish. Accordingly, disclosed herein is an article of manufacture comprising a polymeric material disclosed herein (e.g., a polymeric material comprising a crosslinker, wherein the crosslinker comprises a moiety of formula (I)). Also disclosed herein is an article of manufacture comprising a polymeric material prepared according to a method disclosed herein (e.g., a method comprising incorporating a crosslinker into the polymeric material, wherein the crosslinker comprises a moiety of formula (I)).

[0158] In some embodiments, disclosed herein is a method of producing an article of manufacture comprising a polymeric material disclosed herein (e.g., a polymeric material comprising a crosslinker, wherein the crosslinker comprises a moiety of formula (I) described herein, for example wherein the crosslinker is a compound of formula (II) as described herein). In some embodiments, the method comprises an additive manufacturing method (e.g., 3D printing), and the method comprises sequentially depositing layers of the polymeric material onto a surface, to thereby form the article of manufacture. Exemplary methods of 3D printing may use, for example, a digital light processing (DLP) 3D printer, such as one known in the art.

[0159] Materials. All reagents were used without further purification unless otherwise specified. Dichloromethane (DCM) and tetrahydrofuran (THF) used in reactions were dried via an Innovative Technologies PureSolv solvent purification system. Other solvents used in reactions were reagent grade obtained from Sigma- Aldrich and used as received without further purification, except for dimethylformamide (DMF). DMF was stirred with excess drying agent, calcium hydride (Ca2H) and refluxed gently (100°C) for 2h under inert atmosphere. After 2h,DUKE-44295.601

[0160] the mixture was distilled under vacuum at room temperature, gradually heating to 50°C. The dry DMF was used immediately and then stored over molecular sieves. 2,2-Dimethylpropane-1,3-diol (99%), triethylamine (>99.5%), acryloyl chloride (>97%, stabilized by phenothiazine), 4-dimethylaminopyridine (>99%), glutaric acid (99%), N,N'-diisopropylcarbodiimide (99%), 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (98%) and 2,4,6-trimethylbenzoyldiphenyl phosphine oxide (97%) were purchased from Sigma- Aldrich. Acrylic anhydride (98%, stabilized with MEHQ) was purchased from Ambeed. 2-Methoxyethyl Acrylate (>98%, stabilized with MEHQ) was purchased from TCI. 3,3-Dichloro-1,2-cyclopropanedimethanol (gDCC)1and 4-(dimethylamino)pyridinium-4-toluenesulfonate (DPTS)2were synthesized based on previously published procedures.

[0161] Characterization and Instrumentation, ’ll.13C and29Si { ’ll } DEPT spectra were collected on a Bruker 500 MHz spectrometer at 25 °C. 'll and13C chemical shifts were calibrated by the residual solvent peaks relative to tetramethylsilane (TMS). Chemical shifts are reported in parts per million (δ) and coupling constants (J) are reported in Hz. Multiplicities are assigned as singlet (s), doublet (d), triplet (t), quartet (q) and multiplet (m). High-resolution mass spectra were performed on an Agilent LCMS-TOF-DART by Duke University’s Mass Spectrometry Facility. Flash chromatography was conducted in a Teledyne ISCO CombiFlash Rf 200 instrument using Silicycle SiliaFlash® F60 gel (40-63 pm particle size, 230-400 mesh) as the column media.

[0162] ThermogravimetrThermogravimetric analysis (TGA) was conducted using a TA Instruments Discovery TGA550 (TGA Instruments – Waters L.L.C, New Castle, DE). Size exclusion chromatography (SEC) was conducted in an Agilent 1260 Infinity LC instrument with two in-line columns (105Å, 7.5x300 mm, 5 μm, part number PL1110-6500) at a flow of 1.0 mL / min in THF with three inline detectors, respectively Wyatt Optilab T-rEX refractive index detector, Wyatt miniDAWN TREOS multiangle light scattering detector and Agilent 1260 Infinity UV detector. Molecular weights were determined by Wyatt miniDAWN TREOS multi-angle light scattering detector, in which refractive index increment (dn / dc) for each sample was calculated by the online Wyatt Astra software with known injection concentration and mass. Each sample was first prepared as a ~ 2mg / mL solution in THF and passed through a 0.22 μm PTFE syringe filter before injection. Rheological measurements were performed on an Anton Paar MCR 302 rheometer with an 8-mm parallel plate geometry. Uniaxial tensile tests and tearing tests were conducted on a TA Instrument RSA III Dynamic Mechanical Analyzer (force resolution: 0.0001 N, displacement resolution: 1 pm).DUKE-44295.601

[0163] Example 1

[0164] Small Molecule Synthesis

[0165] o

[0166] MeZMeDMF'<>c-2 hMe Me

[0167]

[0168] 1 Synthesis of Crosslinker 1. In a glovebox, a 100 mL oven dried Schlenk flask equipped with an adapter and stir bar was charged with anhydrous sodium acrylate (2.69 g, 28.6 mmol, 3.0 cquiv). Anhydrous DMF (H2O < 1.0 ppm, 20 mL, 0.5 M) was added via syringe to form a suspension. Dichloromethyl(dimethyl)silane (1.5 g, 9.54 mmol, 1.0 equiv.). was added via syringe. The flask was sealed with a rubber septum, removed from the glovebox, attached to Schlenk line and submerged in an oil bath. The flask was heated to 100 °C for 2 h under inert atmosphere. Note: if the DMF contained significant amounts of water (e.g., [H2O] ca. 60 ppm), longer reaction times were necessary that resulted in lower yields due to autopolymerization. The preparation of rigorously anhydrous DMF is described in the General Information.

[0169] After 2 h, the reaction was cooled to rt, and an aliquot was placed in a vial. The aliquot was diluted with 0.25 mL DI water and 0.25 mL ether, sealing and shaking the vial. The organic layer was pipetted into a separate pipet containing Na2SO4to another vial. The conversion was checked via TLC against the starting material, stained with KMnO4. 'H NMR was taken of the aliquot to check conversion. Both TLC andXH NMR showed full conversion of product.

[0170] To a large separatory funnel, 60 mL DI water and the reaction mixture were added. The aqueous layer was extracted with ether (3x 60mL). The combined organic layers were added back to the separatory funnel and was washed with DI water (5x 60mL) and brine (5x lOmL). The organic layer was collected and dried over Na2SO4. Solvent was removed under reduced pressure in a tared flask to give product. Residual DMF in the crude oil was removed with 3x15 mL of heptane on rotovap to give a clear, colorless oil (1.71 g, 79%).1H NMR (400 MHz, CDCl3, 298 K) δ = 6.37 (dd, J = 17.4, 1.5 Hz, 2H), 6.11 (dd, J = 17.4, 10.4 Hz, 2H), 5.80 (dd, J = 10.4, 1.5 Hz, 2H), 3.95 (s, 4H), 0.17 (s, 6H).13C NMR (101 MHz, CDCl3, 298 K) δ = 167.39, 131.00, 128.68, 56.01, 5.44.29Si NMR (79 MHz, CDCl3) δ = −0.76. HRMS-ESI (m / z): calculated for C10H16O4Si [M+Na]+, 251.0710; observed, 251.0712.

[0171] \ / 9 HO. x.. x X x.-. OH+<> x.. Ac(.

[0172] DCM, 0 °C to RT

[0173]

[0174] DUKE-44295.601

[0175] Synthesis of Crosslinker 2. In a 50 mL flame-dried round-bottom flask, 2,2-dimethylpropane-l,3-diol (1.1 g, 10.6 mmol) was added with 15 mL DCM. The solution was purged with nitrogen and the flask was placed in an ice bath. Then, 2.95 mL of triethylamine (21.2 mmol) was slowly added to the solution under stirring. Acryloyl chloride (1.71 mL, 21.2 mmol) was then added dropwise to the mixture and the reaction was stirred overnight at room temperature. The organic mixture was extracted subsequently with saturated NH4CI (aq.), DI water and brine. The organic layer was dried over with MgSO4. After filtration, the organic phase was concentrated. Flash column chromatography (SiO2, 0 ~ 25% EtOAc / hexane gradient eluent) gave the desired compound as a clear, colorless oil (1.8 g, 82% yield), ’ll NMR (500 MHz, CDCL, 298 K) 5 = 6.41 (d, J = 17.4 Hz, 2H), 6.13 (dd, J = 17.3, 10.5 Hz, 2H), 5.84 (d, J = 10.5 Hz, 2H), 4.00 (s, 4H), 1.02 (s, 6H).13C NMR (126 MHz, CDCl3, 298 K) δ = 166.21, 131.03, 128.43, 69.41, 35.02, 21.93 ppm. HRMS-ESI (m / z): calculated for C11H16O4[M+H]+, 213.1121; observed, 213.1127.

[0176] Me \ z Me Me Me 1. NaOAc, DMF, 100 °C, 95% SL HO., OH 2. HCl. MeOH, 70cC, 48 h

[0177]

[0178] 89% Synthesis of Diol 4 (Karimata et al. RSC Adv. 2016, 6 (97), 94803-94808; Evangelist! et al. Inorg. Chem. 2010, 49 (11), 4865-4880). A 100 mL oven dried Schlenk flask equipped with an adapter and stir bar was charged with anhydrous sodium acetate (2.35 g, 28.6 mmol, 3.0 equiv.). The flask was sealed with a rubber septum and was evacuated and filled with argon 3x. Anhydrous DMF (H2O < 1.0 ppm, 20 mL, 0.5 M) was added via syringe to form a suspension. Dichloromethyl(dimethyl)silane (1.5 g, 9.55 mmol, 1.0 equiv.). was added via syringe. The flask was submerged in an oil bath and heated to 100 °C for 2 h under inert atmosphere. Note: if the DMF contained significant amounts of water (e.g., [H2O] ca. 60 ppm), longer reaction times were necessary). The preparation of rigorously anhydrous DMF is described in the General Information.

[0179] To a large separatory funnel, 60 mL DI water and the reaction mixture were added. The aqueous layer was extracted with ether (3x 60mL). The combined organic layers were added back to the separatory funnel and was washed with DI water (5x 60mL) and brine (5x lOmL). The organic layer was collected and dried over Na2SO4. Solvent was removed under reduced pressure in a tared flask to give (dimethylsilanediyl)bis(methylene) diacetate as a clear, paleyellow oil. (1.85 g, 95%).1H NMR (400 MHz, CDCl3, 298 K) δ = 3.82 (s, 4H), 2.03 (s, 6H),DUKE-44295.601

[0180] 0.13 (s, 6H).13C NMR (101 MHz, CDCl3, 298 K) δ = 172.13, 55.85, 21.11, −5.54.29Si NMR (79 MHz, CDCl3) δ = −1.14.

[0181] To a tared 250 mL flask attached to a Schlenk line under argon equipped with a condenser and stir bar was added (dimethylsilanediyl)bis(methylene) diacetate (4.36 g, 21.4 mmol, 1.0 equiv.) via syringe through septum. Methanol (105 mL) was added via syringe through the septum. Concentrated hydrochloric acid (0.638 g, 17.5 mmol, 0.82 equiv.) was measured out in a tared scintillation vial with cap and diluted with methanol (2 mL). The condenser was removed under a positive nitrogen flow and the HC1 solution was added via glass pipette under argon high pressure. The condenser was replaced and the mixture was stirred at 70 °C for 48 h under nitrogen. The reaction was cooled to room temperature before removing methanol under reduced pressure. The crude product was purified by distillation ( 100 °C, vacuum) to yield a clear, colorless oil. Yield: 89%.1H NMR (400 MHz, CDCl3, 298 K) δ = 3.48 (s, 4H), 0.05 (s, 6H).13C NMR (101 MHz, CDCl3, 298 K) δ = 54.87, −6.36.29Si NMR (79 MHz, CDCl3) δ = −4.05.

[0182] Example 2

[0183] Polymer Synthesis and Network Preparation

[0184] Polymer Synthesis

[0185] Cl, ci I X. y 9 PIC. OP HO I ■*" HO' "''OH DCS#

[0186]

[0187] Synthesis of Pl. (Dimethylsilanediyl)dimethanol 4 (8.7 mg, 0.08 mmol), (1R, 2S)-rel- 3,3-dichloro-l,2-cyclopropanedimethanol (gDCC-diol) (65.0 mg, 0.38 mmol), glutaric acid (59.8 mg, 0.45 mmol), and 4-(dimethylamino)pyridinium-4-toluenesulfonate (DPTS) (47.9 mg, 0.16 mmol) were dried under high vacuum in a 40 °C oil bath for 48 h in a vial. Then, the vial was purged with N2 for 20 minutes. Anhydrous DCM (1.1 mL) was then added via syringe, and finally 200 μL of N,N'-diisopropylcarbodiimide (DIC) (1.36 mmol) was added dropwise. The solution was stirred at room temperature for 5-7 days to yield a product that was precipitated in MeOH and redissolved in DCM three times. A white polymer Pl (70 mg) was obtained. The silane monomer incorporation was determined by 500 MHz1H NMR.

[0188] Ci. Cl X q o DIC, DPTS o +■ / ... X A HO-, / V-OH MO'ZDCM

[0189]

[0190] DUKE-44295.601

[0191] Synthesis of P2. 2,2-Dimethylpropane-l,3-diol (7.7 mg, 0.07 mmol), gDCC-diol (65.0 mg, 0.38 mmol), glutaric acid (59.8 mg, 0.45 mmol), and DPTS (47.9 mg, 0.16 mmol) were dried under high vacuum in a 40 °C oil bath for 48 h in a vial. Then, the vial was purged with N2 for 20 minutes. Anhydrous DCM (1.1 mL) was added via syringe and 200 pL of DIC (1.36 mmol) was added dropwise to the solution. The solution was stirred at room temperature for 5-7 days to yield a product that was precipitated in MeOH and redissolved in DCM three times. A white polymer P2 (87 mg) was obtained. The propanediol monomer incorporation was determined by 500 MHz 'll NMR.

[0192] 9 QIC, OPTS O K> o

[0193] A

[0194]

[0195] Synthesis of P3. Propane- 1,3-diol (5.8 mg, 0.08 mmol), gDCC-diol (68.4 mg, 0.40 mmol), glutaric acid (62.9 mg, 0.48 mmol), and DPTS (50.5 mg, 0.17 mmol) were dried under high vacuum in a 40 °C oil bath for 48 h in a vial. Then, the vial was purged with N2 for 20 minutes. Anhydrous DCM (1.2 mL) and 200 pL of DIG (1.43 mmol) were added dropwise to the mixture. The solution was stirred at room temperature for 5-7 days to yield the product. The polymer was precipitated in MeOH and redissolved in DCM three times. A white polymer P3 (65 mg) was obtained. The propanediol monomer incorporation was determined by 500 MHz ’ll NMR.

[0196] Network

[0197] RAFT photocuring networks. 2-Methoxyethyl acrylate (MEA) monomer was first passed through a basic alumina column to remove the inhibitor. The pre-gel solution is prepared by mixing MEA (30 mmol), 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) (0.025 mmol), 2,4,6-trimethylbenzoyldiphenyl phosphine oxide (TPO as photoinitiator, 0.0125 mmol), crosslinker 1 or 2 (0.3*X mmol) and 300 pL of DMF, following the stoichiometry [MEA]:[C]: [DDMAT]: [PI] = 1: X / 100: 1 / 1200: 1 / 2400 (X = 0.5, 1 and 2). The solution was sonicated for 10 min to homogenize and then purged with nitrogen for 3 min. The solution was then transferred to a glass mold using a syringe under nitrogen atmosphere. The mold was then placed under a 365 nm lamp for 20 h to yield a polymer network film. The film was placed under vacuum chamber for 2-3 days to ensure solvent and unreacted species were completely removed. The dried film was then ready for subsequent mechanical and thermal characterizations.DUKE-44295.601

[0198] Example 3

[0199] Polymer and Network Characterization

[0200] Polymer Sonication

[0201] Ultrasound experiments were performed in anhydrous THF on a Vibracell Model VCX500 operating at 20 kHz with a 13.1 mm titanium tip probe from Sonics. A polymer solution at a concentration of 2.0 mg / mL was first placed in an ice bath and purged under N2 for 15 min in a Suslick cell. Pulsed ultrasound power was set at an amplitude of 30% (8.0 W / cm2), while maintaining the temperature at around 6-9 °C under nitrogen with a sonication pulse 1 second on, 1 second off. Aliquots at different time points, respectively 0, 2, 5, 10, 30, 60, 120 and 240 min, were taken for SEC and NMR analysis.

[0202] Cl, Cl

[0203] Sonication Hb, Hb

[0204] - H H H H HaH / a

[0205]

[0206] Ring opening determination and Scission Cycle calculation. The extent of gDCC ring opening reaction in the polymer chain was monitored through ’ll NMR spectra and determined by the equation below:

[0207] Ring Opening = 4∫ Ha / (4∫ Ha+∫ HgDCC)

[0208] , in which the integration of Harefers to the peak integration at chemical shift 6.12 ppm, and the integration of HgDCCrefers to the peak integration at the chemical shift 4.23 ppm. Meanwhile, the scission cycle is calculated by below equation:

[0209] Scission Cycle = [ln(Mn,0) - ln(Mn,t)] / ln2

[0210] in which Mn,0represents the number-averaged molecular weight before sonication, Mn,trepresents the number-averaged molecular weight at each time point (at t min).

[0211] Sonication experiments to determine

[0212]

[0213] P1-P3 polymer solutions were prepared with a concentration of 2 mg / mL in THF. Aliquots of 0.8 mL of the solution were taken at 2, 5, 10, 30, 60, 120 min and 240 min time points, of which 0.3 mL was filtered through a 0.22 pm PTFE filter and injected to a size-exclusion chromatography (SEC) for molecular weight analysis. The remaining solution was dried in a small vial and then washed with MeOH three times. After dried under vacuum, the sample was dissolved in CDCb for NMR analysis. By plotting the scission cycle and ring opening at each time point for each polymer, d>i can be obtained from the slope of the linear fit, which serves to numerically compare the relativeDUKE-44295.601

[0214] mechanical strengths of the incorporated units. Polymers with different molecular weights for P1-P3 were synthesized and further underwent sonication experiments so that, studies were repeated and investigated through a range of average molecular weights.

[0215]

[0216] Thermogravimetric analysis (TGA)

[0217] Thermal degradation studies for Pl - P3 were performed using a TA Instruments Discovery TGA550 (TGA Instruments - Waters L. L. C, New Castle, DE). To determine the temperature at the maximum mass loss rate (maj), 5-10 mg of polymers were placed onto a sample pan at a rate of 10 °C / min from 25 °C to 600 °C under N2 atmosphere. Tmaxfor each sample was determined from the peak of the first derivative of weight change with temperature.

[0218] Additive Manufacturing and Tensile Testing

[0219] Resins containing either crosslinker 1 or 2 were printed using an Asiga Freeform Max UV-405 printer equipped with a 405 nm light source. The light intensity of the printer was set to 20 mW / cm2, layer exposure was 3.5 s, and the layer thickness was 50 pm. After printing, all structures were promptly rinsed with isopropyl alcohol to remove uncured resin and left to dry for 2-3 days. Print models were designed on Autodesk Fusion 360 or downloaded from Thingiverse and processed for printing using Asiga Composer software.

[0220] Mechanical Testing

[0221] Rheology. Rheological frequency sweeps were conducted on an Anton Paar MCR 302 rheometer with an 8-mm parallel plate geometry. Samples for rheology were cut by an 8-mm biopsy punch from network films. Frequency sweep measurements were conducted at room temperature ~ 23 °C with a constant oscillatory strain of 0.5% in the frequency range of 0.01 -100 Hz. Three different samples cut from the film were tested for the measurement.

[0222] Tensile tests. Uniaxial tensile tests and tearing tests were performed on a TA Instrument RSA III Dynamic Mechanical Analyzer (force resolution: 0.0001 N, displacement resolution: 1 pm). Uniaxial tensile tests of samples were performed with a strain rate of 10% / s with samples cut into rectangular stripes of dimension ~3 mm (width)* 0.8 mm (thickness)* 25 mm (height). Five replicates were performed for each network material.

[0223] Tear tests. Tearing tests was also performed on a TA Instrument RSA III Dynamic Mechanical Analyzer (force resolution: 0.0001 N, displacement resolution: 1 pm). Samples were cut into wide rectangles of dimension 20 mm (width) * 0.8 mm (thickness) * 15 mm (height). Once samples loaded onto the clamps, the final geometry becomes 20 * 0.8 * 4 mm.DUKE-44295.601

[0224] For notched samples, a ~5 mm cut perpendicular to the pulling direction was cut by the edge. Tear tests were conducted with Thomas-Rivlin method (Rivlin et al. Journal of Polymer Science 1953, 10 (3), 291-318; Danielsen et al. Chem. Rev. 2021, 121 (8), 5042-5092) such that unnotched and notched samples were stretched at a constant strain rate of 0.01 mm / s under pure shear state. Tearing energy, T, was calculated by

[0225] Γ = W(εp)h0,

[0226]

[0227] where W(εp) is the energy density of the sample for crack propagation, and h0is the initial gap distance between clamps. The strain energy density W

[0228]

[0229] W(εp) is calculated from the unnotched curves as the integration to the critical strain εpof the stress-strain curves. Results of tear tests are shown in Table 1.

[0230] Table 1. Critical strain (εp), strain energy per unit volume at the crack (W(εp)) and tearing energy (Γ) for N1, N2, and N3 at various crosslinking densities.

[0231] εpW(εp) (103J / m3) Γ (J / m2) N10.50.465 ± 0.024 28.4 ± 2.6 112.0 ± 9.5 N20.50.413 ± 0.056 23.1 ± 5.5 92.8 ± 22.8

[0232] N30.50.417 ± 0.056 25.1 ± 5.2 98.7 ± 17.0 N110.289 ± 0.022 23.4 ± 3.3 93.4 ± 13.6

[0233] N2i 0.221 ± 0.015 14.6 ± 2.0 57.8 ± 8.1 N3i 0.211 ± 0.018 13.5 ± 2.2 53.6 ± 8.1. N120.153 ± 0.020 11.9 ± 2.8 46.7 ± 11.0

[0234] N220.112 ± 0.003 6.4 ± 0.4 24.9 ± 1.2

[0235] N320.118 ± 0.002 7.7 ± 0.5 28.3 ± 1.2

[0236] Results and Discussion

[0237] SiMe2 Weakens Individual Strands.

[0238] Linear polymer chains containing SiMe2, CMe2, or CH2 motifs were synthesized, and their scission under ultrasonication conditions was examined to establish if SiMe2 was more scissile than CMC2 / CI I2. The two alkyl controls CMe2 and CH2 were employed because if bond dissociation energy were a significant contributor to mechanochemically-coupled scission then CMe2 should be more scissile than CH2 due to the greater stability of the tertiary alkyl radical relative to the primary alkyl radical, as reflected in the ca. 5 kcal mol1difference in their BDE (FIG. lb). However, if reactivity is governed by geometric deformation, then the two alkyl chains should exhibit similar mechanochemical reactivity.

[0239] An internal competition approach to assess relative mechanochemical reactivity has been described in detail previously (Lee etai. J. Am. Chem. Soc. 2015, 137 (33), 10826-10832;DUKE-44295.601

[0240] Bowser et al. Polym. Chem. 2018, 9 (26), 3583-3593). A qualitative description is provided below. gem-Dichlorocyclopropane (gDCC) is a non-scissile mechanophore, which undergoes an intramolecular ring-opening rather than polymer backbone scission upon mechanical activation via ultrasonication. If a scissile mechanophore is incorporated into a polymer strand that also contains gDCC, the scissile mechanophore will cleave and dissipate mechanical force, resulting in less gDCC ring-opening per scission cycle (FIG. 2). The ring-opening ratio Φ can be quantified by

[0241]

[0242] NMR analysis via integration of the gDCC and vinyl chloride resonances (eq 1).

[0243] Ci Ci C:

[0244] ring opening < P = (eq 1) scission cycle —ln(Mn’°) (eq 2)

[0245]

[0246] A plot of ring opening Φ versus scission cycle (Lenhardt et al. J. Am. Chem. Soc. 2011, 133 (10), 3222-3225) (see equation 2) can be fit with a straight line, and the magnitude of the slope Φiis indicative of the relative mechanical reactivity of the most scissile bond in the chain. Scission cycle normalizes the degree of chain scission relative to initial number-average molecular weight (Ire et al. J. Am. Chem.. Soc. 2015, 137 (33), 10826-10832). If the most scissile bond is relatively mechanically robust, Φiwill have a larger value as more of the embedded gDCC mechanophores will undergo ring-opening prior to chain scission. However, the more mechanically scissile a mechanophore is, the sooner it will preferentially cleave and dissipate mechanical energy relative to gDCC ring-opening, resulting in a lower value of Φi.

[0247] Statistical copolymerization of glutaric acid (GA) and a mixture of gDCC and an appropriately functionalized diol (Scheme 2) yielded the desired copolymers Pl-3. Moore and Stupp’s room temperature carbodiimide polycondensation was employed (Moore et al. Macromolecules 1990, 23 (1), 65-70), which has previously been shown to yield statistical copolymers in the reaction of glutaric acid, gDCC diol, and diols containing Diels-Alder mechanophores (Wang et al. Chemical Communications 2019, 55 (81), 12263-12266). Forthe three polyesters Pl-3, high molecular weights were obtained and similar dispersities (Table 2). Similar amounts of diol were incorporated into the chain (ca. 7-8 mol%), as determined by ’ll NMR spectroscopy.DUKE-44295.601 a -"-'x / x xvHO & OH HO V OH HO " ‘OH Me Me Me Me 4 6 7 b Cl Cl

[0248]

[0249] ER2| t‘s ER?- CM<:2i P3 £R2« CH, Scheme 2. (a) Molecular structure of Diols 4, 6, and 7. (b) Statistical condensation polymerization of glutaric acid (GA) with diols gDCC and 4, 6 and 7. DIG = N, N’-diisopropylcarbodiimide; DPTS = 4-(dimethylamino)pyridinium-4-toluenesulfonate.

[0250] Table 2. Synthetic details and molecular weight characteristics of copolymers Pl-3.

[0251] Diol ER2[diol]:[gDCC]:[GA] Polymer mol% Yield Mn.o Mw / MnbdioF (%) (kg mol-1)bSiMe2(4) 0.071:0.421:0.508 Pl 7.1 64.7 66.8 1.21 CMe2(6) 0.078:0.416:0.506 P2 7.8 69.6 76.8 1.25 CH2(7) 0.073:0.412:0.515 P3 7.3 78.0 88.2 1.23

[0252]

[0253] aDetermined by

[0254]

[0255] NMR spectroscopy.bDetermined by size exclusion chromatography with multiangle light scattering detector (SEC-MALS).

[0256] Polymers were dissolved in THF at a concentration of 2 mg mL-1, and the polymer solution was then sonicated under pulsed ultrasound with 30% amplitude (8.0 W cm-2, 1s on / 1s off). NMR and GPC analysis were performed at discrete timepoints to calculate ring opening Φ and scission cycle using equations 1 and 2.

[0257] Ultrasonication experiments confirmed that placement of SiMe2 within a chain substantially weakened the strand relative to alkyl strands. For each polymer P1-P3, a plot of ring-opening versus scission cycle (FIG. 3) was generated and the slope Φicalculated (Table 3). The slope for silane-containing Pl was significantly lower than for alkane-linked P2 and P3, indicating that the most scissile bond in Pl is not only more mechanically reactive than A'DCC but also more reactive than the most scissile bond in P2 and P3. The apparent limiting molecular weight, obtained after 4 h sonication as the rate of change in molecular weight becomes negligible, also serves as a complementary indication of relative mechanical liability of molecules of interest in the polymer chains. The limiting MW of Pl is 23.9 kg mol1, whichDUKE-44295.601

[0258] is lower than 27.6 kg mol1and 26.2 kg mol1for P2 and P3, suggesting that Pl is more inclined to undergo scission.

[0259] Table 3. Ultrasonication results cP, and limiting molecular weight for P1-P5.

[0260] Polymer ΦiaLimiting MW (kg mol-1)bPl 0.24 23.9

[0261] P2 0.41 27.6

[0262] P3 0.44 26.2

[0263]

[0264] aDetermined from the slope of Φ versus scission cycle, as plotted in FIG 3.bLimiting molecular weight is determined from the molecular weight measured at sonication time of 4 h.

[0265] The cP, values obtained for P1-P3 decrease in the order Pl < P2 ~ P3, where CMe2 and CH2 are similar and SiMe2 much more scissile. This trend is not correlated with the bond dissociation energies in FIG. lb that decrease in the order Pl < P2 < P3 (81.0 < 82.1 < 86.9 kcal mol1) in correlation with the stability of the resulting radicals •SiMe2, •CMe2, and •CH2. Therefore, the sonochemical data support a rationale for mechanochemically coupled bond scission in which factors other than thermodynamic bond strength contribute to reactivity.

[0266] Polymer Network Synthesis and Characterization.

[0267] Having established that C-Si bonds in the backbone of a linear polymer undergo force-coupled homolysis more rapidly than C-C bonds, driven by minimizing geometric change between the starting material and transition state, network polymers were then synthesized. Side-chain cross-linked elastomeric networks were prepared via photoregulated reversible addition-fragmentation chain-transfer (RAFT) polymerization as shown in FIG. 4. The controlled polymerization of 2-methoxyethyl acrylate (MEA) monomers allows the average primary chain length of the networks to be tuned through the ratio of monomer and chain transfer agent, 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT), and the degree of crosslinking is controlled by the ratio of crosslinker (C) and monomer.

[0268] Nl, N2 and N3, which only differ in their crosslinkers, were first compared. Networks Nix, N2x and N3x were fabricated with the same ratio of [MEA]:[C]:[DDMAT]:[PI] = LX / 100: 1 / 1200: 1 / 2400 (X = 0.5, 1 and 2) at a fixed degree of polymerization of 1200, but differ in the identity of their bisacrylate crosslinkers 1, 2 or 3, respectively (FIG. 4). Network names Nix, N2x or N3Xdenote which crosslinker 1, 2 or 3 was used while the subscript X denotes the equivalents of crosslinker relative to MEA. Thus, Nlx-N3x are expected to yieldDUKE-44295.601

[0269] networks that are effectively identical except for any effects due to the mechanochemical lability of the crosslinkers. The expectation that the networks would be identical except for mechanochemical reactivity was confirmed in the frequency sweep rheology of Nl, N2and N3 (FIG. 5a for X=2), whose storage moduli (G’) were indistinguishable across frequencies from 0.1 to 100 Hz (FIG. 5a).

[0270] To evaluate if there is a toughening effect via the incorporation of mechanically weak carbosilane crosslinkers, tear tests were performed under a pure shear geometry (FIG. 6B. C). The tearing energy (T) of NI2 is 53.0 ± 7.4 J m“2, which is approximately 2-fold higher than that of N22, 24.9 ± 1.2 J m“2(p = 7.5 x 10’6, t test) and N32, 28.3 ± 1.2 J m~ (p = 1.9 x 10'5, t test), while neopentyl N2 was found to be indistinguishable from propyl N3. The differences in toughness (Γ(N12) > Γ(N22) ≈ Γ(N32)) are aligned well with the mechanosusceptibility of the crosslinkers derived from the sonication experiments, The toughest network NI2 is formed with the crosslinker 1 that gave the lowest <, whereas Γ of N2i– N3iare, like their corresponding Φivalues, effectively indistinguishable. These results Nl > N2 - N3 strongly suggest that bond dissociation energy is not a predictor of relative tearing energy in N1-N3, which would predict Nl > N2 > N3 (FIG. lb for BDE values). The similarity of the carbon crosslinkers to each other and the higher mechanochemical reactivity of Nl instead implicate Si’s distinctive properties as the source of both the strand weakening and network toughening effects, rather than thermodynamic bond strength.

[0271] The effect of crosslinking density on the toughness of these materials was further investigated (FIG. 5D). With the increase of crosslinking density from X ~ 0.5 to 2 at a fixed degree of polymerization, an overall decrease of material toughness for both N1-N3 was observed. However, the difference in tearing energies of Nl to N2-N3 became larger as the crosslinking density i ncreased, which was consistent with a previously reported trend.3

[0272] Additive Manufacturing and Tensile Testing

[0273] An extraordinarily small concentration of Si for C replacement resulted in significant toughening in the comparison of N1-N3. The crosslinker is incorporated at a concentration of 0.5, 1, or 2 mol% relative to MEA and only a single atom changed across crosslinkers 1 and 2.

[0274] This subtle structural change, as well as the straightforward synthesis of the scissile carbosilane mechanophore, suggested that crosslinker 1 might be suitable for applications requiring large scale or accessible starting materials. In particular, photo-curable resins based on acrylates, used in dental fillings and 3-D printed parts, routinely suffer from increased brittleness relative to cast or molded networks (Ligon- Auer et al. Polym. Chem. 2016, 7 (2), 257-286).DUKE-44295.601

[0275] A digital light processing (DLP) 3D printer was used to demonstrate the additive manufacturing of SiMe2networks, highlighting their processability and ability to achieve complex geometries. While the cast formulations were prepared via RAFT polymerization, free radical polymerization was used for the printing process due to its rapid kinetics, resulting in shorter curing times per layer and enhanced resolution (FIG. 6) (Bagheri et al. Polymer Chemistry 2020, 11 (3), 641-647; Schwartz el al. MRS Bulletin 2022, 47 (6), 628-641). Resins were formulated with ratios of [MEA]:[C]:[PI] = 1:0.01:0.003, utilizing phenylbis(2,4,6-trimethylbenzoyljphosphine oxide (BAPO) as the radical initiator to create networks N1-3D and N2-3D for crosslinkers 1 and 2, respectively. Both of the resins were successfully printed in a DLP printer to afford samples for mechanical testing.

[0276] The mechanical properties of 3D-printed elastomers (N11-3D and N21-3D) were characterized by tensile tests (FIG. 7) as a comparison to RAFT polymerized N11and N21described earlier in FIG. 5. 3D-printed carbosilane-crosslinked network N11-3D exhibited higher strength and stretchability compared to its carbon-crosslinked analog N21-3D (FIG. 7a), mirroring the results obtained from molded RAFT networks (FIG. 7b). This speaks to the generality of the carbosilane weakening effect across both controlled and free radical synthetic methods. As a comparison of the manufacturing method, N11-3D and N21-3D overall had lower critical stress (σb) and strain at break (εb) compared to Nli and N2i (FIG. 7c), respectively, while maintaining similar Young’s moduli (FIG. 7d). The relatively inferior ductility of 3D printed vs. bulk RAFT polymerized samples has been previously attributed to either heterogeneities due to the uncontrolled free radical polymerization in the 3D printing manufacturing, an inherent feature of additive manufacturing, or to shrinkage stress as a result of the fast photopolymerization (Ligon-Auer 2016; Zhang et al. Polym. Chem. 2018, 9 (13), 1530-1540).

[0277] The N11-3D resin was further evaluated for its printability using the DLP printer. FIG.

[0278] 8a illustrates a cylinder-hole print optimization model that shows excellent resolution. Additionally, a channel optimization model with varying channel widths was printed to assess the resolution of these features. As shown in FIG. 8b, line-space arrays of 250 pm were achievable, while features at 100 pm were not resolved. Finally, a model of a cat lying down was printed (FIG. 8c), demonstrating that larger features can be achieved with good print fidelity and without the need for support structures or increased exposure times. Similar objects printed using crosslinker 2 showed significant flaking and curling, indicating that carbosilane 1 may be more attractive for printing applications than alkyl 2.DUKE-44295.601

[0279] Conclusions

[0280] Disclosed in Examples 1-3 is the synthesis and polymerization of a simple carbosilane sacrificial crosslinker 1. Linear polymer strands incorporating the structural motif of 1 are more mechanochemically scissile than carbon-based strands, despite similar thermodynamic bond strengths. When the carbosilane is incorporated into the crosslinks of a poly(methoxyethylacrylate) network, the mechanochemical lability of the crosslinks results in in a doubling of the network toughness in both well-defined networks prepared by photocontrolled RAFT polymerization and in 3D printed networks prepared by free radical polymerization.

[0281] These observations highlight that opportunities for the constructive application of mechanochemistry to polymer network optimization may be broader than is commonly realized. Here, a doubling of tearing energy is achieved with a compositional change that borders on the negligible, the single atom substitution of C for Si. The substitution itself is chemically minimal: the substitution of one tetrahedral center of low electronegativity for another. In addition, trivially low levels of substitution are required to achieved measurable and meaningful changes in toughness. In some networks, only 1 out of every 980 atoms is replaced - the other 979 are the same atoms in the same place. Advantages of carbosilane crosslinker 1 relative to other sacrificial crosslinkers include its one-step synthesis from commercially available starting materials and the minimal structural perturbation relative to conventional hydrocarbon network components.

[0282] The impacts of these insights are wide-ranging. The simple structure of 1 is distinctive relative to what in comparison might be regarded as “designer” mechanophores based on strain release, cycloreversion, or unusually weak covalent bonds. Complex designs and multistep syntheses are clearly not requirements for mechanophore effects to be realized. The expedient synthesis of 1 and its demonstrated suitability for additive manufacturing suggests potential for large scale applications.

[0283] Example 4

[0284] Synthesis and Characterization of Ge-Containing Crosslinker and Polymer Networks

[0285]

[0286] DUKE-44295.601

[0287] The GeMe2 compound shown above and networks containing the compound were prepared and tested using procedures equivalent to those used for the SiMe2, CMe2, and CH2 networks reported herein.

[0288] Ge-Containing Network Preparation. Before use, 2-methoxyethyl acrylate (MEA) was passed through a basic alumina column to remove the inhibitor. The pre-gel solution was prepared by mixing MEA (30 mmol), 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT, 0.025 mmol), 2,4,6-trimethylbenzoyldiphenyl phosphine oxide (TPO, photoinitiator, 0.0125 mmol), the GeMe2crosslinker, and 250 μL of DMF, using the stoichiometry [MEA]:[C]: [DDMAT]: [PI] = 100:2:0.8:0.4. The mixture was sonicated for 15 min to homogenize and purged with nitrogen for 3 min, then transferred to a glass mold. The mold was irradiated under a 365 nm lamp under a nitrogen flow for 20 h to yield a polymer network film. The film was then placed under vacuum for 3 days to ensure complete removal of residual solvent and unreacted species.

[0289] Tear tests. Tearing testing was performed on a TA Instruments RSA III Dynamic Mechanical Analyzer (force resolution: 0.0001 N; displacement resolution: 1 pm). Samples were cut into wide rectangles (20 mm x 0.8 mm x 15 mm; width x thickness x height), and the final clamped geometry was 20 mm x 0.8 mm x 4 mm. For notched samples, a ~5 mm edge cut perpendicular to the pulling direction was introduced. Unnotched and notched specimens were stretched under pure shear using the Thomas-Rivlin method at a constant displacement rate of 0.01 mm / s. The tearing energy, T, was calculated as T = W(ep)ho.

[0290] Results are shown in FIGS. 9A-9B, and show that PMEA networks prepared with SiMe2and GeMe2crosslinkers exhibit substantially higher tearing energy than networks prepared with CMe2and CH2analogs. No significant difference is observed between SiMe2and GeMe2, or between CMe2and CH2.

[0291] Example 5

[0292] Preparation and Characterization of Crosslinked Copolymer Networks Polymer networks were prepared as follows. 2-Methoxy ethyl acrylate (MEA), ethyl acrylate (EA), and 1,4-butanediol diacrylate (BDA, control) were passed through a basic alumina column to remove inhibitor before use. Networks with varying copolymer composition were prepared by defining r as the mole fraction of EA in the total monomer feed, r (%) = [EA] / ([EA]+[MEA]), with r = 0, 33, 67, and 100. Networks were prepared using either 1.5% or 4% crosslinker loading (SiMe2 crosslinker or the BDA control). The pre-gel solution was prepared by mixing the monomer (total 25 mmol), DDMAT (0.021 mmol), TPO (0.0104DUKE-44295.601

[0293] mmol), the crosslinker, and 250 μL of DMF, using the stoichiometry [MEA]:[C]:[DDMAT]:[PI] = 1: X / 100: 1 / 1200: 1 / 2400 (X = 1.5 or 4). The pre-gel mixtures were sonicated for 15 min to homogenize and purged with nitrogen for 3 min, then transferred to a glass sandwich mold. The molds were irradiated under a 365 nm lamp for 20 h under a nitrogen flow to yield polymer network films, followed by vacuum treatment for 3 days to remove solvent and unreacted species. Tear tests were performed as described in Example 4.

[0294] Results are shown in FIG. 10, and show that at constant crosslinker loading, the EA / MEA backbone composition was varied to assess strand-dependent mechanophore behavior. The results were considered in the context of two composition-dependent contributions chain entanglements and viscous dissipation. At 1.5% crosslinker loading, a significant SiMe2to control difference in Γ is observed at r = 0, but this difference decreases with increasing r and becomes negligible at high r (r = 100). At 4% loading, T increases with r and the SiMe2to control separation grows with increasing r, with the largest difference at high r (still under investigation).

Claims

DUKE-44295.601CLAIMS1. A polymeric material comprising a crosslinker, wherein the crosslinker comprises a moiety of formula (I):wherein:X is Si or Ge; andR1and R2are each independently selected from C1-C4 alkyl.

2. The polymeric material of claim 1, wherein X is Si.

3. The polymeric material of claim 1, wherein X is Ge.

4. The polymeric material of any one of claims 1-3, wherein R1and R2are each methyl.

5. The polymeric material of any one of claims 1-4, wherein the crosslinker comprises a moiety of formula:

6. The polymeric material of any one of claims 1-4, wherein the crosslinker comprises a moiety of formula:

7. The polymeric material of any one of claims 1-6, wherein the crosslinker in the polymeric material is derived from a compound of formula (II):O X OI \R3R1R2wherein:X is Si or Ge;R1and R2are each independently selected from C1-C4 alkyl; andDUKE-44295.601R3and R4are each independently selected from hydrogen and methyl.

8. The polymeric material of claim 7, wherein X is Si.

9. The polymeric material of claim 7, wherein X is Ge.

10. The polymeric material of any one of claims 7-9, wherein R1and R2are each methyl.

11. The polymeric material of any one of claims 7-10, wherein R3and R4are each hydrogen.

12. The polymeric material of claim?, wherein the compound of formula (II) is:

13. The polymeric material of claim 7, wherein the compound of formula (II) is:

14. The polymeric material of any one of claims 1-13, wherein the polymeric material is an acrylate polymeric material.

15. The polymeric material of claim 14, wherein the polymeric material comprises one or more (meth)acrylate monomers selected from alkyl (meth)acrylates, hydroxyalkyl (meth)acrylates, alkoxyalkyl (meth)acrylates, cycloalkyl (meth)acrylates, and aromatic (meth)acrylates.

16. The polymeric material of claim 15, wherein the polymeric material comprises one or more alkyl (meth)acrylates selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octylDUKE-44295.601(meth)acrylate, iso-decyl (meth)acrylate, heptadecyl (meth)acrylate, dodecyl (meth)acrylate, 2-propylheptyl (meth)acrylate, and stearyl (meth)acrylate.

17. The polymeric material of claim 16, wherein the alkyl (meth)acrylate is ethyl acrylate.

18. The polymeric material of any one of claims 14-17, wherein the polymeric material comprises one or more alkoxyalkyl (meth)acrylates selected from the group consisting of 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth) acrylate, l-methyl-2-methoxyethyl (meth)acrylate, ethylene glycol methyl ether (meth)acrylate, diethylene glycol methyl ether (meth)acrylate, and triethylene glycol methyl ether (meth)acrylate.

19. The polymeric material of claim 18, wherein the alkoxy alkyl (meth)acrylate is 2-methoxyethyl (meth)acrylate.

20. A method of toughening a polymeric material, comprising:incorporating a crosslinker into the polymeric material, wherein the crosslinker comprises a moiety of formula (I):wherein:X is Si or Ge; andR1and R2are each independently selected from C1-C4 alkyl.

21. The method of claim 20, wherein X is Si.

22. The method of claim 20, wherein X is Ge.

23. The method of any one of claims 20-22, wherein R1and R2are each methyl.

24. The method of any one of claims 20-23, wherein the crosslinker comprises a moiety of formula:DUKE-44295.60125. The method of any one of claims 20-23, wherein the crosslinker comprises a moiety of formula: / \ / 26. The method of any one of claims 20-25, wherein the crosslinker is a compound of formula (II):wherein:X is Si or Ge;R1and R2are each independently selected from C1-C4 alkyl; andR3and R4are each independently selected from hydrogen and methyl.

27. The method of claim 26, wherein X is Si.

28. The method of claim 26, wherein X is Ge.

29. The method of any one of claims 26-28, wherein R1and R2are each methyl.

30. The method of any one of claims 26-29, wherein R3and R4arc each hydrogen.

31. The method of claim 26, wherein the compound of formula (II) is:

32. The method of claim 26, wherein the compound of formula (II) is:

33. The method of any one of claims 20-32, wherein the incorporating step comprises:DUKE-44295.601(a) providing a mixture comprising a monomer, the crosslinker, and an initiator; and (b) initiating polymerization to form the polymeric material.

34. The method of any one of claims 20-33, wherein the polymeric material is an acrylate polymeric material.

35. The method of claim 34, wherein the polymeric material comprises one or more (meth)acrylate monomers selected from alkyl (meth)acrylates, hydroxyalkyl (meth)acrylates, alkoxyalkyl (meth)acrylates, cycloalkyl (meth) acrylates, and aromatic (meth)acrylates.

36. The method of claim 35, wherein the polymeric material comprises one or more alkyl (meth)acrylates selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (mcth)acrylatc, n-hcxyl (mcth)acrylatc, 2-cthylhcxyl (mcth)acrylatc, octyl (meth)acrylate, iso-decyl (meth)acrylate, heptadecyl (meth)acrylate, dodecyl (meth)acrylate, 2-propylheptyl (meth)acrylate, and stearyl (meth)acrylate.

37. The method of claim 36, wherein the alkyl (meth) acrylate is ethyl acrylate.

38. The method of any one of claims 34-37, wherein the polymeric material comprises one or more alkoxyalkyl (meth)acrylates selected from the group consisting of 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, l-methyl-2-methoxyethyl (meth)acrylate, ethylene glycol methyl ether (meth)acrylate, diethylene glycol methyl ether (meth)acrylate, and triethylene glycol methyl ether (meth)acrylate.

39. The method of claim 38, wherein the alkoxyalkyl (meth)acrylate is 2-methoxyethyl (meth)acrylate.

40. The method of any one of claims 20-39, wherein the polymerizing step comprises reversible addition-fragmentation chain transfer (RAFT) polymerization.

41. The method of claim 40, wherein the mixture further comprises a chain transfer agent, the initiator is a photoinitiator, and step (b) comprises exposing the mixture to UV light toDUKE-44295.601incorporate the moiety of formula (I) into the polymeric material and form the toughened polymeric material.

42. The method of any one of claims 20-39, wherein the polymerizing step comprises free-radical polymerization.

43. The method of any one of claims 20-42, wherein the polymeric material has an increased toughness compared to a corresponding polymeric material having a crosslinker comprising a moiety of formula (I), wherein X is C.

44. The method of any one of claims 20-43, wherein the polymeric material has a tearing energy, as determined by the Thomas-Rivlin method, that is at least 50% greater than a tearing energy of a corresponding polymeric material having a crosslinker comprising a moiety of formula (I), wherein X is C.

45. An article of manufacture comprising the polymeric material of any one of claims 1-19.

46. An article of manufacture comprising a polymeric material prepared according to a method of any one of claims 20-38.

47. A method of producing an article of manufacture comprising the polymeric material of any one of claims 1-19, comprising sequentially depositing layers of the polymeric material onto a surface, to thereby form the article of manufacture.

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