Nanoporous polymer materials and simple methods for preparing them

Abstract

The present invention relates to novel nanoporous polymer materials and to a simple and direct method for preparing them by rapid mechanical deformation of highly entangled polymer articles above their glass transition temperature and subsequent rapid cooling at a temperature well below the glass transition temperature. The present invention further encompasses the use of such nanoporous polymer materials in a wide variety of applications.

Description

[Technical Field]

[0001] The present invention relates to novel nanoporous polymer materials and to a simple and direct method for preparing them by rapid mechanical deformation of highly entangled polymer articles above their glass transition temperature and subsequent quenching at a temperature well below the glass transition temperature. The present invention further encompasses the use of such nanoporous polymer materials in a wide variety of applications. [Background technology]

[0002] Nanoporous and microporous materials have attracted considerable attention over the past few decades as an important class of functional systems serving many purposes, including, but not limited to, advanced water treatment, gas separation, food processing, or modern filtration processes such as medical dialysis. To satisfy the desired purposes, well-defined barrier properties, achieved through good control of the nanoporous and microporous structure of these materials, are required. In addition to the aforementioned filtration and separation applications, their uniquely large absorption area or microscopically small reaction volume offers unique new scientific and technological possibilities, stemming from their extremely high surface area-to-volume ratio, where catalytic activity can be combined as needed within such materials.

[0003] Several reviews on nanoporous materials have summarized the above requirements in detail, as well as their applications and expected developments. See [1] Abetz, V., Kremer, K., Mueller, M., Reiter, G.: Functional macromolecular systems: Kinetic pathways to obtain tailored structures. Macromol. Chem. Phys. 220(2019) 8, [2] Ariga, K., Nishikawa, M., Mori, T., Takeya, J., Shrestha, LK, Hill, JP: Self-assembly as a key player for materials nanoarchitectonics. Science and Technology of Advanced Materials 20, 51~95(2019), and [3] Bates, FS, Fredrickson, GH: Block copolymers - designer soft materials. Phys. Today 52, 32~38(1999).

[0004] A widely adopted method for forming such porous materials uses block copolymers, in which a well-defined pore structure is obtained by ordering into a columnar or double gyroid structure and then removing one type of block or solvent. [1], [2], [4] Sankhala, K., Koll, J., Abetz, V.: Facilitated structure formation in isoporous block copolymer membranes upon controlled evaporation by gas flow. Membranes 10, 83 (2020), [5] Bang, J., Kim, SH, Drockenmuller, E., Misner, MJ, Russell, TP, Hawker, CJ: Defect-free nanoporous thin films from abc triblock copolymers. J. Am. Chem. Soc. 128, 7622~7629 (2006), [6] Hillmyer, MA: Nanoporous materials from block copolymer precursors. In: Abetz, V. (ed.) Block Copolymers See also [7] Bolton, J., Bailey, TS, and Rzayev, J.: Large Pore Size Nanoporous Materials from the Self-Assembly of Asymmetric Bottlebrush block copolymers. Nano. Lett., 998-1001 (2011).

[0005] Larger pores can be obtained by using bottlebrush polymers; see [8] Batys, P., Fedorov, D., Mohammadi, P., Lemetti, L., Linder, MB, Samalkorpi, M.: Self-assembly of silk-like protein into nanoscale bicontinuous networks under phase-separation conditions. Biomacromolecules 22, 690-700 (2021).

[0006] However, in all of the methods described above, the polymer film typically requires mechanical support from the substrate.

[0007] [9] Liu, J., Huang, R., Li, G., Kaplan, DL, Zheng, Z., Wang, X.: Generation of nano-pores in silk fibroin films using silk nanoparticles for full-thickness wound healing. Biomacromolecules 22(2), 546~556(2021),

[10] Escal'e, P., Rubatat, L., Billon, L., Save, M.: Recent advances in honeycomb-structured porous polymer films prepared via breath figures. Springer Nature 2021 LATEX template 20 Nanoporous free standing polymer films Eur. Polym. J. 48(6), 1001~1025(2012), and

[11] Meng, F., Doi, M., Ouyang, Z.: Cavitation in drying droplets of soft matter solutions. Phys. Rev. Lett. In 113(2014), porous materials are formed by polymer solvent phase separation induced by the rapid evaporation of nanodroplets of water or solvent in a vacuum.

[0008] The aforementioned procedure requires specially formulated polymers and highly controlled methods to obtain the desired structure, and therefore cannot currently be applied on a larger commercial scale.

[0009] Another, less sophisticated method involves swelling of polymer gels or adding nanoscale inclusions and subsequently immobilizing the swollen network structure to form microporous polymer systems; see

[12] DeBenedictis, EP, Zhang, Y., Keten, S.: Structure and mechanics of bundled semiflexible polymer networks. Macromolecules 53, 6123-6134 (2020) and

[13] Gu, Y., Zhao, J., Johnson, JA: Polymer networks: From plastics and gels to porous frameworks. Angew. Chem. Int., 59th edition, 5022-5049 (2020).

[0010] In such gels, the structure and stability are determined by both chemical bonding and entanglement, i.e., non-crossing of the chains.

[0011] US2013 / 0157035A1 presents a method for forming a porous polyethylene film, the method comprising several stretching and shrinking steps in a given temperature regime.

[0012] WO2016 / 085709A1 discloses a method for preparing porous polyolefins by biaxial stretching a polyolefin film containing nano-inclusion additives incompatible with the polymer matrix.

[0013] In US2022 / 0362720A1, a porous film of cyclic polyolefin polymer is produced by adding isopropanol, a non-solvent that induces phase separation, to a polymer film containing tetrahydrofuran.

[0014] US2022 / 0362984A1 discloses the preparation of a porous polymer film by stretching a polymer film that contains a cavity-forming agent such as calcium carbonate or polymer particles that are not miscible with the base polymer of the film.

[0015] In both Rizzo et al., "Syndiotactic Polystyrene Films: Orientation and Structural Changes Upon Biaxial Drawing," Macromolecular Chemistry and Physics, vol. 212, no. 13, 2011, pp. 1419–1426

[14] and Rizzo et al., "Crystalline orientation and molecular transport in nanoporous syndiotactic polystyrene films," Macromolecular Symposia, vol. 185, no. 1, 2002, pp. 65–75

[15] , thermally unstable modified forms (γ, δ, and ε) of syndiotactic polystyrene are disclosed, which form helical structures with intercrystalline cavities or nanopores. In the recognized δ modified form, the distance between such helical polymer chains is defined as 8.7 angstroms or 0.87 nm, and the interplane distance is defined as 10.5 angstroms or 1.05 nm.

[14] The density of the bulk polymer found on page 66 is 0.977 g / cm³. 3 This is because the density of the bulk polymer is 1.05 g / cm³. 3Considering the presence of , it exhibits a maximum porosity of 7.5%. Furthermore, the preparation of the δ-modified material in

[14] and

[15] is carried out by extruding an amorphous film at 290°C, and then in a second step, by slowly biaxially stretching at 105–110°C at a rate of 10%. The resulting still amorphous film is then tempered at 230°C for 15 minutes and finally exposed to carbon disulfide vapor for 3 days. After evaporation of the carbon disulfide in a vacuum, the porous δ-modified material was obtained in particular (see [1, p.1420, right column]). The introduction and conclusion of

[15] also describe that the formation of the porous modified material is made possible by the formation of solvent inclusion compounds and the removal of the solvent. In summary, while references

[14] and

[15] disclose porous polymer structures, these structures are not formed and preserved by rapid stretching and cooling, but only after a complex process involving the formation and breakdown of solvent inclusion compounds. Furthermore, the resulting cavities or pores are significantly smaller than those of the present invention, as they have a size of 1 nm or less. [Prior art documents] [Patent Documents]

[0016] [Patent Document 1] US2013 / 0157035A1 [Patent Document 2] WO2016 / 085709A1 [Patent Document 3] US2022 / 0362720A1 [Patent Document 4] US2022 / 0362984A1 [Non-patent literature]

[0017] [Non-Patent Document 1] Abetz, V., Kremer, K., Mueller, M., Reiter, G.: Functional macromolecular systems: Kinetic pathways to obtain tailored structures. Macromol. Chem. Phys. 220(2019) 8 [Non-Patent Document 2] Ariga, K., Nishikawa, M., Mori, T., Takeya, J., Shrestha, LK, Hill, JP: Self-assembly as a key player for materials nanoarchitectonics. Science and Technology of Advanced Materials 20, 51–95(2019) [Non-Patent Document 3] Bates, FS, Fredrickson, GH: Block copolymers-designer soft materials. Phys. Today 52, 32–38 (1999) [Non-Patent Document 4] Sankhala, K., Koll, J., Abetz, V.: Facilitated structure formation in isoporous block copolymer membranes upon controlled evaporation by gas flow. Membranes 10, 83 (2020) [Non-Patent Document 5] Bang, J., Kim, SH, Drockenmuller, E., Misner, MJ, Russell, TP, Hawker, CJ: Defect-free nanoporous thin films from abc triblock copolymers. J. Am. Chem. Soc. 128, 7622~7629 (2006) [Non-Patent Document 6] Hillmyer, MA: Nanoporous materials from block copolymer precursors. In: Abetz, V. (ed.) Block Copolymers II. Advances in Polymer Science, Vol. 190, pp. 137-181. Springer [Non-Patent Document 7] Bolton, J., Bailey, TS, Rzayev, J.: Large Pore Size Nanoporous Materials from the Self-Assembly of Asymmetric Bottlebrush block copolymers. Nano. Lett., 998~1001 (2011) [Non-Patent Document 8] Batys, P., Fedorov, D., Mohammadi, P., Lemetti, L., Linder, MB, Sammalkorpi, M.: Self-assembly of silk-like protein into nanoscale bicontinuous networks under phase-separation conditions. Biomacromolecules 22, 690~700(2021) [Non-Patent Document 9] Liu, J., Huang, R., Li, G., Kaplan, DL, Zheng, Z., Wang, X.: Generation of nano-pores in silk fibroin films using silk nanoparticles for full-thickness wound healing. Biomacromolecules 22(2), 546~556(2021) [Non-Patent Document 10] Escal'e, P., Rubatat, L., Billon, L., Save, M.:Recent advances in honeycomb-structured porous polymer films prepared via breath figures. Springer Nature 2021 LATEX template 20 Nanoporous free standing polymer films Eur. Polym. J. 48(6), 1001~1025(2012) [Non-Patent Document 11] Meng, F., Doi, M., Ouyang, Z.: Cavitation in drying droplets of soft matter solutions. Phys. Rev. Lett. 113(2014) [Non-Patent Document 12] DeBenedictis, EP, Zhang, Y., Keten, S.: Structure and mechanics of bundled semiflexible polymer networks. Macromolecules 53, 6123~6134(2020) [Non-Patent Document 13] Gu, Y., Zhao, J., Johnson, JA: Polymer networks: From plastics and gels to porous frameworks. Angew. Chem. Int. 59th edition, 5022~5049 (2020) [Non-Patent Document 14] Rizzo et al., "Syndiotactic Polystyrene Films: Orientation and Structural Changes Upon Biaxial Drawing," Macromolecular Chemistry and Physics, Vol. 212, No. 13, 2011, pp. 1419-1426. [Non-Patent Document 15] Rizzo et al., "Crystalline orientation and molecular transport in nanoporous syndiotactic polystyrene films," Macromolecular Symposia, Vol. 185, No. 1, 2002, pp. 65-75. [Non-Patent Document 16] Physical Properties of Polymers, 2nd edition, 2007 Springer Science and Business Media LLC, edited by James E. Mark, Chapter 25, page 447: LJ Fetters, DJ Lohse, and RH Colby, "Chain Dimensions and Entanglement Spacings" [Non-Patent Document 17] Ferry, JD. Viscoelastic Properties of Polymers, 3rd edition, Wiley, New York (1980) [Non-Patent Document 18] Yu Cang, Jiaqi Liu, Meguya Ryu, Bartlomiej Graczykowski, Junko Morikawa, Shu Yang, George Fytas, “On the origin of elasticity and heat conduction anisotropy of liquid crystal elastomers at gigahertz frequencies”, Nat. Comm. 13, 5248(2022) [Non-Patent Document 19] Penciu, RS, Kriegs, H, Petekidis, G, Fytas, G, Economou, "Phonons in colloidal systems", J. Chem. Phys. 118, 5224 (2003) [Non-Patent Document 20] F.Kargar, AAABalandin Nat.Photonics 15, 720~731(2021) [Non-Patent Document 21] W. W. Greassley, "Polymeric Liquids & Networks: Dynamics and Rheology", Taylor & Francis 2008 [Non-Patent Document 22] Brunauer, S., Emmett, PH, Teller, E.: Adsorption of gases in multimolecular layers. Journal of the American Chemical Society 60(2), 309–319(1938) [Overview of the project] [Problems that the invention aims to solve]

[0018] Therefore, despite the advances made so far through various methods as described above, there is still a need to provide an easily implementable and direct route, particularly from readily available raw material polymers to stable, support-free nanoporous films. [Means for solving the problem]

[0019] According to one aspect of the present invention, 1) A polymer article is brought to a glass transition temperature T g A step of stretching in at least one direction at a temperature at least 5K, preferably at least 10K higher, to form nanopores, and then 2) The stretched polymer article is subjected to a glass transition temperature T g A process of cooling to a temperature 10K lower or lower than that. A method for preparing a nanoporous polymer material comprising at least, Steps 1) and 2) are carried out together within a time interval short enough to preserve, at least partially, the nanopores formed in step 1). A method for preparing nanoporous polymer materials is provided herein.

[0020] Another aspect of the present invention relates to a porous polymer material that can be obtained according to the method described above.

[0021] The present invention further includes the use of the nanoporous polymer material according to the present invention as a protective coating, an optical coating, or a part thereof, for example, as a membrane for filtration or separation tasks, and as a catalyst support. [Brief explanation of the drawing]

[0022] [Figure 1] Examples 1-4 show the polymer mass distribution of polystyrene used to prepare nanoporous polymer materials, specifically nanoporous polymer films. [Figure 2] The sequence of steps for preparing the nanoporous polymer film of the present invention according to Examples 2-4 is shown. [Figure 3] The image shows a photograph of the central portion of the cap-like structure obtained in Example 4, which will be used for further analysis. [Figure 4] The image shows an SEM image of the fracture surface of a biaxially expanded nanoporous polystyrene film according to Example 4. More specifically, the fracture surface of the film is shown in a top view at low magnification. [Figure 5] The image shows an SEM image of the fracture surface of a biaxially expanded nanoporous polystyrene film according to Example 4. Specifically, it shows the fracture surface of the film viewed from above at low magnification, followed by a zoomed-in view of the same region. [Figure 6] The image shows an SEM image of the fracture surface of a biaxially expanded nanoporous polystyrene film according to Example 4. A zoomed-in view of the same region is shown in detail. [Figure 7] The SEM image of the fracture surface of the biaxially expanded nanoporous polystyrene film according to Example 4 is shown. [Figure 8] This shows how the SFM experiment was performed. A nanoporous polymer film was left in the holder of a microtome, with the film protruding approximately 100 μm from the holder surface. The polymer surface was cut by a diamond microtome. [Figure 9]The high-resolution SFM topography image of the nanoporous polystyrene film obtained by Example 4 is shown. A granular structure with a characteristic diameter reduced to 10 nm is observed. [Figure 10] The high-resolution SFM topography image of the nanoporous polystyrene film obtained by Example 4 is shown. A granular structure with a characteristic diameter reduced to 10 nm is observed. [Figure 11] The longitudinal (CL) and transverse (CT) sound velocities, measured by BLS, are shown for the polymer articles, i.e., the untreated polymer film according to Example 1 and the nanoporous polymer films according to Examples 2-4, corresponding to their porosity and effective density. [Figure 12] The longitudinal sound velocity (CL) at various temperatures, measured by BLS, is shown for polymer articles, i.e., the untreated polymer film according to Example 1 and the nanoporous polymer films according to Examples 2-4. The gray rectangle indicates the region of the glass transition temperature (Tg). [Figure 13] The porosity of polymer articles, i.e., the untreated polymer film according to Example 1 and the nanoporous polymer films according to Examples 2-4, at various temperatures as measured by BLS is shown. The gray rectangles indicate the region of the glass transition temperature Tg. [Figure 14] Examples 1-4 show the frame, effective Young's modulus (EPS and Eeff), and bulk modulus (KPS and Keff) corresponding to the porosity of the polymer films. [Figure 15] Examples 1-4 show the frame, effective shear modulus (GPS and Geff), and Poisson's ratio corresponding to the porosity of the polymer films. [Figure 16] The cumulative pore volume corresponding to the pore size obtained from the BET experiment for Example 4 is shown. [Figure 17] This shows the experimental setup used for the BLS experiment. [Figure 18] The polarized BLS spectrum of a nanoporous polymer film recorded using the scattering geometry of Figure 19 is shown in Example 4. [Figure 19]A schematic diagram of the transmission geometry used in the BLS experiment is shown. The phonon wave vector q||=ks-ki, where ks and ki are the wave vectors of scattered and incident light in the (nanoporous) polymer film, is directed inward into the film plane when the scattering angle θ is half the incident angle α. In addition to inelastic scattering at q||, the wave vector qBS from the backscattered incident beam due to ki can also be selected. [Figure 20] The master curve for polystyrene with Mn=200kDa and a reference temperature of 433K is shown, with the storage modulus G' (shown as a star) and the loss modulus G'' (shown as a circle) and the first intersection 1 / τd as the reciprocal of the reptile unraveling time. This was used to calculate the suitable time range for step 1 for polystyrene with Mn=1037kDa, as adopted in Examples 1-4. Region A represents polymer flow, B represents the rubber state, C represents partial flow, and D represents the glassy state. [Figure 21] The image shows an SEM image of the fracture surface of a biaxially expanded nanoporous PMMA film according to Example 5, zoomed in in exactly the same way as in the polystyrene example. [Figure 22] The image shows an SEM image of the fracture surface of a biaxially expanded nanoporous PMMA film according to Example 5, zoomed in in exactly the same way as in the polystyrene example. [Modes for carrying out the invention]

[0023] The present invention also encompasses all combinations of preferred embodiments or parameter ranges of all levels disclosed below, either in combination with each other or in combination with the broadest disclosed parameter range or embodiment.

[0024] Wherever used herein, the terms “including,” “for example,” “e.g.,” “etc.,” and “like,” respectively, mean “including but not limited to” or “not limited to, for example.”

[0025] Polymer articles As used herein, the term "polymer article" refers to any polymer article that can be stretched in at least one dimension. This includes, among other things, polymer films and hollow polymer articles, so-called preforms, used in blow molding. A preferred polymer article is a polymer film.

[0026] As used herein, “polymer film” usually refers to a polymer article, where the spatial elongation of the polymer article in each of two dimensions (hereinafter also referred to as x and y dimensions) is at least 20 times, preferably at least 50 times, greater than that in a third dimension, the latter also referred to as film thickness, and the film thickness is in the range of 100 nm to 2.0 mm, preferably 100 nm to 1000 μm, more preferably 500 nm to 800 μm, for example, 1 to 800 μm or 10 to 500 μm or 10 to 200 μm.

[0027] As used herein, “polymer article” or “polymer film” refers to an article or film comprising at least 85 wt.% of at least one polymer, preferably at least 90 wt.%, more preferably at least 95 wt.%, and more preferably at least 98 wt.%, the remainder being a compound selected from the group of known polymer additives, including, if any, flame retardants, antioxidants, anti-aging agents such as antioxidants, anti-ozone degradation agents, heat stabilizers and light stabilizers, processing aids such as lubricants, hydrocarbon waxes and fatty acids, plasticizers, tackifiers, colorants, antistatic agents, antimicrobial agents, and deodorants.

[0028] As used herein, the term “bulk material” refers to a polymer article or a material made into a nanoporous polymer material obtained after carrying out the method of the present invention.

[0029] The bulk material used in the method of the present invention to produce polymer articles is typically and preferably a commercially available polymer.

[0030] Typically, bulk materials exhibit a porosity of less than 1.0%, preferably 0.5% or less, and more preferably 0.1% or less.

[0031] As used herein, a nanoporous polymer material or, in a preferred embodiment, a nanoporous polymer film typically refers to a polymer material or polymer film having pores in the nanometer range, i.e., 1 to 1000 nm, preferably 1 to 200 nm, and having a porosity of 5.0% or more, preferably 10.0% or more.

[0032] Preferably, the bulk material and thus polymer article used for the method of the present invention contains no blowing agent, foaming agent, or other porogenic agent whatsoever.

[0033] As used herein, “pore-forming agent” is i) By the release or formation of the gaseous compound under the reaction conditions of step 1), and / or ii) By forming an inert inorganic template material under the reaction conditions of step b), or by being an inert inorganic template material, iii) Furthermore, in one embodiment, by forming solvent domains that leave cavities or nanopores during subsequent evaporation, for example, evaporation in a vacuum. This shows any material that can form pores.

[0034] In another preferred embodiment, the bulk material and therefore polymer article employed for the method of the present invention contains no nano-inclusion agents whatsoever.

[0035] As used herein, “nano-inclusion agent” refers to any material that can be dispersed in a polymer article or polymer film in the form of discrete domains, having a nanoscale size of 1 nm to 1000 nm and being partially incompatible with further components of the bulk material, and in particular with at least one polymer of the bulk material.

[0036] In one embodiment, the polymer article, and in a preferred embodiment, the polymer film, are homogeneous.

[0037] In another embodiment, the nanoporous polymer material, and in a preferred embodiment, the nanoporous polymer film, is homogeneous.

[0038] As used herein, “homogeneous” means the compatibility of all components in a bulk material that do not form regions of phase separation.

[0039] In preferred embodiments, the polymer article employed in the method of the present invention and the resulting porous polymer material are support-free. As used herein, “support-free” means the absence of a support substrate, such as a metal foil or other rigid support, which retains substantially its rigidity when exposed to the conditions of the method according to the present invention.

[0040] The glass transition temperature of bulk materials is 40°C or higher, preferably 50°C or higher, such as 50°C or 250°C, 50°C or 210°C, or 50°C or 150°C, and more preferably 70°C or higher, such as 70°C or 250°C, 70°C or 210°C, or 70°C or 150°C.

[0041] In the context described above, the use of the term "bulk material" encompasses the possibility of evaluating the glass transition temperature of a bulk material or a polymer article, such as a polymer film employed in the method of the present invention.

[0042] Unless otherwise specified, the glass transition temperature for bulk materials is measured by differential scanning calorimetry in accordance with DIN EN11357-2:2020.

[0043] Unless otherwise specified, the melting point of (semi-crystalline) bulk materials or polymer articles is measured according to DIN 53736.

[0044] The polymer in bulk materials and thus polymer articles may be homopolymers or copolymers, i.e., polymers comprising repeating units derived from two or more monomers.

[0045] The polymer may be linear or branched, and the average number of branching points is in the range of greater than 0 and 1 or less per 100 monomer units of the polymer. A preferred polymer is a linear polymer.

[0046] In one embodiment, the polymer of the bulk material may or may not be crosslinked, as defined below, and is preferably not crosslinked.

[0047] When a bulk polymer is crosslinked, the term "crosslinked" refers to a polymer in which polymer chains are joined together by covalent chemical bonds, typically via crosslinking molecules or crosslinking groups, to form a network polymer, thereby having an average number of crosslinks greater than 0 and 1 or less per 100 monomer units of the polymer, preferably greater than 0 and 0.5 or less per 100 monomer units of the polymer.

[0048] Number average molecular weight [M] of bulk polymer n Typically and preferably, 200 kg / mol or more, for example, 200 kg / mol to 100,000 kg / mol or 200 kg / mol to 50,000 kg / mol, preferably 500 kg / mol or more, for example, 500 kg / mol to 100,000 kg / mol or 500 kg / mol to 50,000 kg / mol or 500 kg / mol to 20,000 kg / mol, and more preferably 800 kg / mol or more, for example, 800 kg / mol to 100,000 kg / mol or 800 kg / mol to 50,000 kg / mol or 800 kg / mol to 20,000 kg / mol.

[0049] In another embodiment, the number-average molecular weight [M] of the polymer of the bulk material. n ] is typically 20M e For example, 20M e ~2,000Me or 20M e ~500M e where M e is defined as the entanglement molecular weight as defined and disclosed for various polymers in

[16] Physical Properties of Polymers, 2nd Edition, 2007 Springer Science and Business Media LLC, edited by James E. Mark, Chapter 25, page 447: L. J. Fetters, D. J. Lohse, and R. H. Colby, "Chain Dimensions and Entanglement Spacings".

[0050] As shown in that document, the entanglement molecular weight is given by the following equation M e = ρRT / G e (where ρ is the density of the bulk material, R is the Boltzmann constant, T is the absolute temperature, and G e is the plateau modulus for each polymer (see also Equation 25.6 in

[16] and its explanation)). can be calculated according to this formula.

[0051] The plateau modulus G e can be obtained, for example, from the literature or as the minimum value of tanδ from the rheology master curve at a given temperature (see also

[17] Ferry, J. D. Viscoelastic Properties of Polymers, 3rd Edition, Wiley, New York (1980)).

[0052] Suitable polymers include thermoplastic polyimides such as acrylonitrile-butadiene-styrene and those derived from phthalimide, cellulose acetate, cellulose acetate-butyrate, cellulose diacetate, cellulose propionate, cyclic olefin copolymers such as copolymers of ethylene and norbornene or dicyclopentadiene, ethylene vinyl alcohol copolymer (EVOH), polystyrene, polyamide 11, polyamide 12, polyamide 46, polyamide 6, polyamide 66, polyesters such as polybutylene terephthalate, polyethylene terephthalate, polyethylene terephthalate glycol, poly(meth)acrylates such as polymethyl methacrylate, poly Examples include polycarbonates such as arylate, bisphenol A, tetramethylbisphenol A, bisphenol S, 1,1,1-tris(4-hydroxyphenyl)ethane, dihydroxydiphenyl sulfide, or 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane polycarbonate, polyetheretherketones, polyethersulfones, perfluoroalkoxyalkanes, polylactic acid, polymethacrylamide, polyphenylene ether, polyphenylene sulfide, polyphenylene sulfone, polysulfone, polyvinyl chloride, styrene-acrylonitrile (SAN), and styrene-maleic anhydride (SMA).

[0053] Generally, polymers may be crystalline, semi-crystalline, or amorphous, with amorphous and semi-crystalline polymers being preferred. In one embodiment, the polymer is amorphous.

[0054] Preferred polymers include polystyrene, polymethyl methacrylate, and polycarbonate, with polystyrene and polymethyl methacrylate being more preferred, and atactic polystyrene being even more preferred.

[0055] Glass transition temperature T gIt is obvious and well known to those skilled in the art that the required T depends on the type of polymer used, its average molecular weight, and the amount and type of additives present in the bulk material. However, the composition of the bulk material and the polymer article or polymer film can be adjusted to meet the required T g Satisfying the minimum value or range is an easy task for those skilled in the art.

[0056] Unless otherwise specified, the mass-average molecular weight or number-average molecular weight is measured by gel permeation chromatography according to DIN 55672.

[0057] PDI itself is not important. However, pore formation is promoted as PDI decreases.

[0058] Polydispersity index (PDI) [M w / M n For example, ] may be in the range of 1.00 to 10.00, preferably 1.01 to 5.00, more preferably 1.01 to 3.00 or 1.01 to 2.00, even more preferably 1.01 to 1.10, and even more preferably 1.03 to 1.08.

[0059] Computer simulations of a high molecular weight model system with a PDI height of approximately 1.80 performed during the process of the present invention showed stable pore formation with pore sizes close to those obtained from monodisperse model simulations.

[0060] However, in order to obtain a stable and desired porous form, the total amount of compounds having a molecular weight of less than 200 kg / mol in the bulk material should be 15 wt.% or less, preferably 10 wt.% or less, and more preferably 5 wt.% or less.

[0061] In another embodiment, 20M in bulk material e The total amount of compounds having a molecular weight less than 15 wt.% is preferably 10 wt.% or less, and more preferably 5 wt.% or less, in order to obtain a stable and desired porous form.

[0062] To avoid misunderstanding, such compounds include, for example, not only the polymer additives mentioned above, but also the polymer portion of the bulk material having a molecular weight of less than 200 kg / mol, or another polymer having a molecular weight of less than 200 kg / mol.

[0063] In step 1), the polymer article, preferably a polymer film, reaches a glass transition temperature T g Nanopores are formed by stretching in at least one direction at a temperature at least 5K, preferably at least 10K, higher than the specified temperature.

[0064] In a more preferred embodiment, the polymer article has a glass transition temperature T g Nanopores are formed by stretching in at least one direction at a temperature at least 20k higher than that.

[0065] In one embodiment, the temperature during step 1) is the glass transition temperature T g A temperature at least 5K, preferably at least 10K, and more preferably at least 20K higher than the decomposition temperature or the glass transition temperature T with respect to the selected bulk material. g If it exists at a higher temperature, it is between the melting point and either of the other temperatures.

[0066] Glass transition temperature T g If a higher melting point exists, the temperature during step 1) is the glass transition temperature T. g The glass transition temperature is preferably in the range from a temperature 5K, preferably 10K, more preferably at least 20K higher than the melting point to a temperature 10K lower than the melting point. g It is preferable that the temperature is in the range from 20K higher than the melting point to 20K lower than the melting point.

[0067] If there is no melting point, the temperature during step 1) is the glass transition temperature T g From a temperature 20K higher than that, the glass transition temperature T g It is preferable that the temperature range is 150K higher or lower than the decomposition temperature and 20K lower than the decomposition temperature.

[0068] As used herein, the decomposition temperature refers to the temperature at which 5.0% of the mass of a bulk material or polymer article is lost within 6 hours, as measured by thermogravimetric analysis (TGA).

[0069] In one embodiment, the temperature during step 1) is the glass transition temperature T g The glass transition temperature T is 20K higher than that. g It is in a temperature range up to 120K higher than that.

[0070] In one embodiment, prior to step 1), the polymer article and, in a preferred embodiment, the polymer film are subjected to a glass transition temperature T before stretching. g Exposure to a temperature at least 5K, preferably at least 10K, more preferably at least 20K higher, for, for, for 1 to 30 minutes, preferably 30 to 5 minutes, more preferably 30 to 3 minutes, allows for the equilibrium and removal of any strains that are potentially present at the molecular scale.

[0071] The stretching may be carried out uniaxially (in one direction) or in two directions (biaxially), preferably in directions perpendicular to each other or in more than two directions.

[0072] Polymer articles, particularly polymer films, tend to deform due to uneven strain when stretched in only one direction, a deformation often referred to as necking. Since necking can hinder proper pore formation, it should be avoided by applying appropriate means. Therefore, in preferred embodiments of unidirectional stretching, necking is at least substantially reduced or avoided by means known to the extent of the condition.

[0073] In this context, "substantially" means that the dimensional loss in the direction perpendicular to the stretching is less than 50% of the dimensional loss that would occur if no appropriate means were applied.

[0074] In the case of polymer articles and polymer films, suitable means include fastening by, for example, frames, holders, clamps, clips, or other fastening means arranged to substantially or entirely hold the shape in a direction perpendicular to the stretching direction.

[0075] The stretching of polymer articles and, in preferred embodiments, polymer films may be carried out in batches, i.e., article by article, or, in particular, continuously in the case of polymer films.

[0076] Stretching can be carried out by any method or apparatus known to those skilled in the art. This includes longitudinal stretching by a general roll-to-roll method, particularly in the case of polymer films, in which the film is placed under desired tension by the winding roll traveling at a greater radial speed than the feed roll. In this case, necking can be avoided, for example, by applying clamps to prevent transverse shrinkage, i.e., necking.

[0077] Stretching, especially in the case of polymer films, can be carried out by a general roll-to-roll method in which the winding roll travels at the same speed as the feed roll (to prevent necking) and clamps are applied for lateral stretching, so that the winding roll is wider than the feed roll.

[0078] Biaxial stretchers for polymer films are commercially available, for example, as the Karo IV from Bruckner Maschinenbau GmbH in Germany.

[0079] These methods are presented herein as examples of continuous processes and serve that purpose.

[0080] In one embodiment, longitudinal and transverse stretching may be carried out sequentially or simultaneously, preferably simultaneously, i.e., biaxial stretching may be carried out.

[0081] In another embodiment, stretching is carried out by an extension frame to which the polymer article is attached. Such a frame may be, for example, secondary, rectangular, or angled with a movable part.

[0082] In another embodiment, the polymer article is installed as a barrier between two pressurizable chambers or between the ambient atmosphere and one pressurizable chamber, and is stretched by exposure to a pressure difference.

[0083] As used herein, the term “pressurizable chamber” refers to any chamber that can be pressurized to above or below ambient pressure by appropriate means such as a vacuum pump, compressor, and other devices of similar nature.

[0084] These methods are presented herein as examples of batch processes and serve that purpose.

[0085] Multiaxial stretching may be carried out on any type of polymer article through known blow molding procedures such as extrusion blow molding, injection blow molding, and injection stretch blow molding. Specific examples include bubble or double bubble film extrusion.

[0086] Stretching is carried out such that, for example, the stretching rate of the polymer article and, in a preferred embodiment, the polymer film, is at least 1.05, preferably at least 1.20, for example, 1.20 to 3.50 or 1.20 to 4.00 or 1.20 to 5.00, and more preferably at least 1.50, for example, 1.50 to 3.50 or 1.50 to 4.00 or 1.50 to 4.00. In the case of unidirectional stretching, for example, a stretching rate of 1.20 means that the length of the polymer article and, in a preferred embodiment, the polymer film after stretching is 20% greater than that of the state before stretching. In this case, in a preferred embodiment, necking (i.e., a "stretching" rate in the direction perpendicular to the stretching, less than 1.00) is completely avoided.

[0087] When stretching is carried out in more than one direction, for example, the surface area of ​​the polymer article and, in a preferred embodiment, the polymer film is increased by at least 1.10 times, preferably at least 1.40 times, for example 1.40 to 25.00 times, or 1.40 to 20.00 times, or 1.40 to 16.00 times, or 1.40 to 10.00 times, more preferably at least 2.00 times, for example 2.00 to 25.00 times, or 2.00 to 20.00 times, or 2.00 to 16.00 times, or 2.00 to 10.00 times.

[0088] As used herein, the term “surface area” refers to the macroscopic surface area that defines the overall outer size or dimensions of a polymer article without considering the increase in inner surface area due to nanopore formation.

[0089] The stretching time may be, for example, 1 second to 60 minutes, preferably 30 seconds to 45 minutes, or 5 minutes to 30 minutes.

[0090] In one embodiment, stretching may be achieved, for example, with a constant force during the stretching time, or with a constant expansion rate per unit time, or with any other strain profile over the stretching time, with stretching with a constant force being preferred.

[0091] It is known to those skilled in the art that the dimensional and time or speed limitations of stretching depend on the polymer film material, as well as the initial thickness of the film, in addition to the temperature and thermal properties of the polymer film material used. However, depending on the desired porosity of the final nanoporous film, these parameters can be easily determined by a few orientation experiments.

[0092] The polymer article may be formed into any desired shape during stretching, or it may maintain its original shape.

[0093] During the stretching of polymer articles, particularly polymer films, whether uniaxial, biaxial, or multiaxial, the thickness, especially the film thickness, can typically be freely adjusted to a thickness smaller than that before stretching.

[0094] In step 2), the stretched polymer article, preferably a polymer film, reaches a glass transition temperature T g Preferably at a temperature 10K lower than or equal to the glass transition temperature T of the bulk material. g It is cooled to a temperature 20K lower than that.

[0095] In one embodiment, in step 2), the stretched polymer article, preferably a polymer film, is subjected to a glass transition temperature of 77K and the bulk material T g A temperature in the range of at least 20K lower than the boiling point of liquid nitrogen at atmospheric pressure and the glass transition temperature T of the bulk material, preferably 77K, i.e., the boiling point of liquid nitrogen at atmospheric pressure and the glass transition temperature T of the bulk material. g A temperature in the range of at least 50K lower than, more preferably 77K and the glass transition temperature T g It is cooled to a temperature in the range of at least 100K lower than that.

[0096] Cooling can be carried out by any method or apparatus known to those skilled in the art. This includes exposing the stretched polymer article to a stream of cold air or other gas, and bringing the stretched polymer article into contact with a cooled surface or a cooled liquid coolant that does not substantially dissolve the nanoporous polymer material. Furthermore, such liquid coolants include liquid nitrogen or other liquid materials that are gaseous at 20°C.

[0097] In one embodiment, the stretched polymer article, and in a preferred embodiment, the stretched polymer film, is immersed in liquid nitrogen in step 2).

[0098] Typically, the time taken to perform step 2) is 15 minutes or less, for example, 50 milliseconds to 15 minutes or 1 second to 15 minutes, preferably 1 minute or less, for example, 50 milliseconds to 1 minute or 1 second to 1 minute, more preferably 10 seconds or less, for example, 50 milliseconds to 10 seconds or 50 milliseconds to 10 seconds.

[0099] Steps 1) and 2) are carried out together within a time interval short enough to preserve, at least partially, the nanopores formed in step 1).

[0100] Typically, the time taken to carry out both steps 1) and 2) is 2 hours or less, for example, 30 seconds to 2 hours or 5 minutes to 2 hours, preferably 1 hour or less, for example, 30 seconds to 1 hour or 5 minutes to 1 hour, and more preferably 45 minutes or less, for example, 30 seconds to 45 minutes or 5 minutes to 31 minutes.

[0101] The degree of pore formation during stretching depends not only on the stretching conditions, but also on the structure and type of the bulk material or the polymer contained in the bulk material, and its glass transition temperature T g It will be apparent to those skilled in the art that all of these factors affect the most appropriate time range for carrying out process steps 1) and 2), as well as the process temperature used in step 1).

[0102] This time range can be easily determined by a slight orientation result, or it can be determined based on the rheological properties of the bulk material of the polymer article, or, in a preferred embodiment, the polymer film, employed in the method according to the present invention. The elongation shown above is also subject to the same principle.

[0103] Therefore, in another embodiment, the time taken to perform steps 1) and 2) is 1τ d ~100τ d Preferably 1τ d ~80τ d and more preferably 1τ d ~50τ d It is within the range of τ d The receptacle time of a polymer article is the receptacle time of the bulk material, also known as the relaxation time. The relaxation time is the reciprocal 1 / τ at the low-frequency intersection of the storage modulus G' and loss modulus G'' from a master curve obtained from measurements of the storage modulus G' and loss modulus G'' respectively using dynamic mechanical analysis (DMA) according to DIN EN ISO6721:2019. d It can be considered as such.

[0104] The method will be further outlined in the examples of polystyrene used for the present invention.

[0105] The method according to the present invention yields a stable, porous polymer material exhibiting numerous unprecedented features.

[0106] After performing steps 1) and 2), the porous polymer film or material maintains its porous structure and characteristics while having a maximum glass transition temperature T g The fact that it can be stored at a temperature 10K lower than that is an important finding.

[0107] In one embodiment, the nanoporous polymer material that can be obtained by carrying out the method of the present invention is measured by gas adsorption (BET) experiment at 77 K using liquid nitrogen according to DIN66131, with a density of 0.05 to 0.60 cm². 3 / cm 3 Pore ​​volume (V p ) or a porosity (Φ) of 5-60%, preferably 0.05-0.50 cm 3 / cm 3 Pore ​​volume (V p ) or a porosity (Φ) of 5-50%, more preferably 0.08-0.45 cm 3 / cm 3 Pore ​​volume (V p ) or a porosity (Φ) of 8-45%, with a layer more preferably 0.10-0.45 cm thick. 3 / cm 3 Pore ​​volume (V p ) or exhibits a porosity (Φ) of 10-45%.

[0108] The average pore size determined by the same method is typically in the range of 2 to 200 nm, preferably 2 to 100 nm, and more preferably 5 to 100 nm.

[0109] In one embodiment, the pores having a diameter of 2 to 20 nm in the nanoporous polymer material or polymer film according to the present invention account for 70% or more, preferably 80% or more, of the total pore volume.

[0110] In another embodiment, the pore size distribution of the porous polymer film or material is such that 50% of the total pore volume is 10 nm or less, preferably in the range between 2 nm and 10 nm.

[0111] In one embodiment, the nanoporous polymer film or material according to the present invention is determined according to the method described in detail in the examples, and is 20 to 1000 m 2 / g, preferably 50-1000m 2 BET ratio (SSA BET ) has.

[0112] The thickness of the porous polymer film obtained in a preferred embodiment of the present invention is typically within the range generally defined above for polymer films. However, it is obvious to those skilled in the art that stretching a polymer film typically reduces its thickness depending on the stretching conditions.

[0113] The main finding of this invention is that nanoporous polymer films and materials exhibit unexpectedly outstanding elastic properties.

[0114] To evaluate the elastic properties of polymer materials, Young's modulus, Poisson's ratio, bulk modulus, and shear modulus are typically examined.

[0115] Brillouin optical spectroscopy (BLS) was applied to provide a non-contact, non-invasive, zero-strain method for evaluating the elastic properties of the porous polymer film according to the present invention.

[0116] In particular, with BLS, there is absolutely no probe interference, and both the elastic modulus of the stretched chain and the polymer film porosity of the polymer material can be obtained as a result of the method according to the present invention. A method for obtaining the above values ​​is as follows:

[18] Yu Cang, Jiaqi Liu, Meguya Ryu, Bartlomiej Graczykowski, Junko Morikawa, Shu Yang, George Fytas, "On the origin of elasticity and heat conduction anisotropy of liquid crystal elastomers at gigahertz frequencies", Nat. Comm. 13, 5248(2022),

[19] Penciu, RS, Kriegs, H, Petekidis, G, Fytas, G, Economou, "Phonons in colloidal systems", J. Chem. Phys. 118, 5224(2003), and

[20] F. Kargar, AAABalandin Nat. Photonics 15, 720-731 (2021).

[0117] Therefore, all values ​​and comparisons shown below refer to values ​​obtained by BLS, as further explained in detail in the examples. It is important to note that BLS measurement provides the modulus of elasticity of the polymer frame within the porous polymer film, and not the modulus of elasticity measured by macroscopic tensile testing.

[0118] To calculate the modulus of elasticity when used for the following comparisons, the effective modulus of elasticity measured by BLS is the polymer volume fraction (1-V p The values ​​were multiplied by ), but please also refer to the data in the examples. It was found that nanoporous polymer materials and preferably nanoporous polymer films exhibit a slight decrease in elastic modulus due to porosity, for example, a decrease of approximately 10% at 43% porosity (see examples). This slight decrease in elastic modulus is due to the increased elastic modulus of the stretched polymer chains.

[0119] In a preferred embodiment, the relative Young's modulus increase rate RYMI for a given porosity in % units. x It is 0.50 or higher, RYMI x The calculation is as follows: RYMI x =(100 x (Young's modulus at x% porosity [GPa] / Young's modulus at 0% porosity [GPa] - 1)) / Porosity [%]

[0120] In one embodiment, the shear modulus G of the nanoporous polymer film is higher than the shear modulus of the bulk material, as measured by BLS.

[0121] In a preferred embodiment, the relative shear modulus increase rate (RSMI) for a given porosity in % units is used. x It is 0.40 or higher, RYMI x The calculation is as follows: RSMI x =(100 x (Shear modulus at x% porosity [GPa] / Shear modulus at 0% porosity [GPa] - 1)) / Porosity [%]

[0122] In one embodiment, the transverse and longitudinal sound velocity C of the porous polymer film T and C L This can be obtained with respect to Young's modulus as described above, and is higher than the speed of sound of bulk materials measured by BLS.

[0123] To determine whether the Young's modulus or shear modulus of a nanoporous polymer film is higher than that of the bulk material, the nanoporous polymer material or nanoporous polymer is heated to a temperature 50K higher than its glass transition temperature and maintained at that temperature for 60 minutes until the nanoporous structure disappears, and then subjected to BLS measurement at the same temperature as the nanoporous polymer material or nanoporous polymer film. To account for porosity, the effective modulus is as described above (1-V p It is multiplied by ).

[0124] While we do not wish to be constrained by theory, a brief explanation of the dynamics within the polymer material during the process may be helpful in understanding the process steps, pore formation, and subsequent stabilization.

[0125] The polymer article used in the method of the present invention is employed in step 1) at a temperature sufficiently higher than its glass transition temperature. Therefore, in practical terms, the polymer article exists as a highly entangled polymer molten body. The molten polymer chains typically exhibit Gaussian random walk behavior as the chains extend. Multiple polymer chains present in the molten body share the same given volume, forming a topological constraint of high average density. This results in characteristic chain lengths and entanglement lengths N. e , or entangled molecular weight M e Furthermore, it also results in polymer dynamics that follow a widely accepted tubular model. The topological constraints in the polymer chain, which increase with molecular weight, lead to very slow dynamics and slow polymer chain relaxation, i.e., high relaxation times. These high relaxation times, combined with temperature-dependent bead friction, make the topological constraints sufficiently long for the polymer process according to the present invention.

[0126] When a polymer article is stretched within a given time frame, the chain structure deforms overall, and local stresses within the chain are avoided by small-scale relaxation during this process, thus preventing strain-induced fracture. Subsequently, stable nanopores are formed in the polymer by competition between very slow, large-scale chain relaxation and the surface that minimizes surface tension.

[0127] The polymer chains extend beyond several nanopores, forming a stable, highly entangled network. To avoid complete chain relaxation in the molten material, the stretched polymer article is cooled in step 2) to a temperature well below the glass transition temperature, thereby "solidifying" and thus preserving the nanoporous structure obtained in step 1) with the extended polymer chains. These extended polymer chains are also presumed to contribute to the high degree of strengthening observed in the nanoporous polymer material and, in a preferred embodiment, the nanoporous polymer film of the present invention.

[0128] Purpose The nanoporous polymer material according to the present invention, which can be obtained according to the method of the present invention, is suitable for a wide variety of applications due to the unique properties described above. Accordingly, the present invention also includes the use of the nanoporous polymer material according to the present invention or the nanoporous polymer material that can be obtained according to the method of the present invention as a membrane in filtration, purification, and separation applications, a solid support for sensors and catalysts, a diffusion layer for gas sensors, a scaffold for tissue engineering, a low electrical constant material for microelectronic devices, a photonic bandgap material, and for other optical applications.

[0129] Accordingly, the present invention further encompasses films, solid supports for sensors and catalysts, diffusion layers, scaffolds, low electrical constant materials, photonic bandgap materials, and optical materials comprising the nanoporous polymer material according to the present invention.

[0130] The main advantage of the present invention is the possibility of producing nanoporous polymer materials with clearly defined, uniformly small pore sizes and unprecedented elastic properties without the need for foaming agents, bubblers, other pore-forming agents, nano-inclusion agents, or other chemical processes.

[0131] Furthermore, it requires neither a supporting substrate nor a matrix-forming compound. Instead, a known mechanical deformation procedure, combined with a specific temperature profile, yields a novel porous polymer material that is remarkably stable over the long term under ambient conditions.

[0132] The present invention is illustrated below by examples, but these examples are not intended to limit the scope of the present invention.

[0133] Experiment Section I. Chemical Substances and Methods 1. Scanning electron microscopy (SEM) SEM images were recorded using a LEO Gemini1530 SEM instrument. For SEM imaging, a sample approximately 5 mm in diameter was cut from the central cap-shaped region. This small piece was immersed in liquid nitrogen for several seconds and then brittle fractured into two pieces. The fracture surfaces were then mounted in a 90° cross-section SEM holder and examined. The sample surface was not sputtered with a conductive layer to avoid covering any small pores and to image the cleanest possible fracture surface. Typical imaging conditions were a working distance of 1.3 mm with an electron incidence energy of 250 eV using an in-lens secondary electron detector.

[0134] 2. Scanning force microscopy (SFM) SFM investigations were recorded using a Bruker Dimension Icon Atomic Force Microscope equipped with Scan Analyst. The experiment was conducted using the Peak Force Tapping Mode in Air with a Micro Cantilever from Nano and More, Germany, with the tip positioned at the polar tip of the cantilever, at a resonant frequency of 300 kHz, a spring constant of 26 N / m, and a back-side aluminum reflective coating.

[0135] 3 BET Porosity and BET surface measurements were performed using a Quantachrome Autosorb-1 porosimeter, after degassing each sample under vacuum at 423K for 20 hours, followed by physioadsorption using nitrogen (N2) at 77K. Specific surface area was calculated by applying the Brunauer-Emmett-Teller (BET) model.

[0136] 4. Brillouin light scattering (BLS) Brillouin light scattering (BLS) spectra were acquired using a standard scientific apparatus, including a continuous-wave (cw) laser, a tandem Fabry-Perot interferometer (TFPI) (JRS Scientific Instruments, Switzerland), a goniometer, and an avalanche photodiode (APD), as schematically shown in Figure 17.

[0137] Specifically, a solid-state Nd-YAG laser with λ=532nm operating at 100mW output, a beam splitter for the reference beam, a focusing lens, and a Glan-Thomson polarizer (Halle, Berlin) were mounted on the arm of the goniometer. Scattered light at a selected scattering angle θ due to the selected polarization determined by the analyzer was focused into an approximately 150mm pinhole located at the entrance of the piezoelectric scanning TFPI and detected by an avalanche photodiode connected to a multi-channel analyzer. A typical accumulation time for obtaining a BLS spectrum from a 50μm thick (nanoporous) polymer film was approximately 10 minutes. To maintain the TFPI stably over several days, the reference beam was used by means of a synchronized shutter during scanning of frequencies from the central Rayleigh line up to 0.6GHz. Therefore, strong elastic scattered light from the sample did not enter the APD detector.

[0138] To obtain the longitudinal sound velocity of the (nanoporous) polymer film, two scattered wave vectors q are shown in Figure 19. || = (4π / λ)sinα and q in backscattering with respect to the film refractive index n BS The BLS spectrum was recorded at θ=90° using a geometric configuration that allows simultaneous access to =4πn / λ.

[0139] Specifically, in Brillouin light scattering, the frequency of scattered light due to thermal phonon propagation depends on its wave vector q and sound velocity c in the medium, and is Doppler-shifted by ±f from the frequency of incident monochromatic light of wavelength λ (=532 nm). The probed q = ks - ki is defined by the scattered (ks) and incident (ki) light wave vectors and forms a scattering angle of 10° < θ < 150°, which is predetermined by the means of goniometer rotation around the optical axis (TFPI axis and incident laser convergence) of the incident laser beam of the sample cell; see

[20] Kargar, F., Balandin, AA: Brillouin-mandelstam light-scattering spectroscopy. Nat. Photon. 15, 720~731 (2021). The frequency shift f = ±cq / (2π) was resolved by a high-resolution tandem Fabry-Perot interferometer as described above. The formula q = (4πn / λ) / sin(θ / 2) generally depends on the refractive index (n), scattering angle (θ), and polarization of the probed phonon, and was selected based on the polarization combination of the incident and scattered light. Longitudinal (LA) and transverse (TA) acoustic phonons were probed for parallel (VV) and crossed (VH) polarization configurations, respectively. With respect to the scattering plane (ki, ks), the first letter (V) represents incident light polarized perpendicularly, while the second letter V(H) represents scattered light polarized perpendicularly (horizontally). Depending on the polarization of the probed phonon, the measured sound velocity from the BLS spectrum is in the longitudinal direction c L In the case of a solid, the lateral direction c T It can be either one of the two. The n dependence of q was avoided in a specific transmission geometry where the incident laser angle α = θ / 2 and q = ks - ki are directed within the (nanoporous) polymer film plane with size q|| = 4πsinα / λ. In the reflection geometry, q is directed perpendicular to the film plane with n perpendicular to the film plane, q⊥ = 4πp(n² - sinα² / λ). For temperature scanning measurements, the sample temperature was monitored with a platinum resistance temperature detector and controlled with a temperature controller. The sample was allowed to reach isothermal equilibrium for 20 minutes, and then the spectrum was recorded.

[0140] 5 Chemicals Monodisperse atactic polystyrene (PS) with a number-average molecular weight of 10³⁷ kg / mol, a mass-average molecular weight of 10⁸⁴ kg / mol, and therefore a polydispersity index Mw / Mn of 1.04 was used for all Examples 1–4. It was obtained from Sigma Aldrich (Germany). Figure 1 shows the mass distribution of polystyrene obtained from GPC experiments.

[0141] For Example 5, monodisperse polymethyl methacrylate (PMMA) with a number-average molecular weight of 1030 kg / mol, a mass-average molecular weight of 1070 kg / mol, and therefore a polydispersity index Mw / Mn of 1.04 was used. The glass transition temperature was 106°C. This was obtained from Agilent. [Examples]

[0142] II. Embodiment Examples 1-4 A 250 mg transparent polystyrene film was prepared by pressing polystyrene for 1 hour at a temperature of 433 K under a 20 kN load, which is a temperature sufficiently higher than the glass transition temperature Tg of 380 K.

[0143] To carry out step 1) according to the present invention, a polystyrene film made using a cyanoacrylate adhesive was attached to one end of a vacuum flange. The vacuum flange had an aperture with a diameter of 1.75 cm. The vacuum flange with the film attached was then placed in an oven and maintained at a temperature of 473 K for 2 minutes.

[0144] Subsequently, a vacuum of 50 hPa was applied for various durations, and then the stretched film was cooled to 77 K by immersing it in a bath containing liquid nitrogen as described in step 2) according to the method of the present invention. The time for performing step 2) was approximately 5 seconds or 0.13τ in each example. d It was estimated to be (see calculation below).

[0145] The resulting cap-like porous polymer film, shown in Figure 3, was stored at room temperature without any further precautions. As shown in Table 1 below, different degrees of elongation were obtained in the polymer film depending on the duration of vacuum pressure.

[0146] To measure the specific properties of the (porous) polymer films according to Examples 1-4, a small 5 mm diameter cutout was obtained from the top of the cap-like polymer film, as indicated by the black circle in Figure 3.

[0147] Figure 2 shows a schematic diagram of an experimental protocol for deforming a polystyrene film into a "hat" shape using a vacuum. This protocol involves preheating the polymer film to 473K (left), deforming the film into a "hat" shape by applying a pressure of 50mbar (center), and rapidly cooling the stretched film to 77K.

[0148] Table 1 summarizes the details of experiments with one unstretched film (Example 1 for comparison) and three nanoporous polymer films stretched to different degrees according to the present invention.

[0149] [Table 1]

[0150] Table 1 further shows the multiple relaxation times τ at 473K for the polystyrene used. d This is shown. As a reference, the master curve shown in Figure 20 was used, which is M200 kg / mol. n Polystyrene and τ relating to this polymer d, 433K This measurement was taken at a temperature of 433K for polystyrene, where the time interval is 1 / 0.16s = 6.25s.

[0151] To account for the higher drawing temperature of 473K in the first step, it is necessary to apply a time shift factor. This temperature shift factor is polymer-specific and can be determined experimentally by shifting the high-frequency side intersections at different temperatures shown in Figure 20, or by referring to the literature (e.g., see

[17] J.D. Ferry, "Viscoleastic properties of polymers", Wiley 3rd edition, 1980 and

[21] W.W. Greassley, "Polymeric Liquids & Networks: Dynamics and Rheology", Taylor & Francis 2008).

[0152] Here, the inventors have found that for polystyrene with M n = 200 Kg / mol, the temperature shift factor a T = 0.02393 at temperature T = 473K. τ d, 200kg / mol, 473K = a T x τ d, 200kg / mol, 433K = 6.25s x 0.02393 = 0.15s

[0153] In the second step, it is necessary to consider the change in relaxation time as a function of chain length or molecular weight (see

[18] ).

[0154] M n = 1,037 Kg / mol of polystyrene, for the polystyrene adopted in this example, the desired relaxation time is τ d, 1037kg / mol, 473K =(1037 / 200) 3.4 x τ d, 200kg / mol, 473K= 40.40s can be calculated from.

[0155] The relaxation times for other polymers can be easily obtained directly from the master curve, from the literature, or calculated as shown above if the polymer adopted at a specific drawing temperature has different literature values for temperature and molecular weight.

[0156] Example 5 To demonstrate the generality of the present invention, PMMA was used instead of PS in Example 5. A transparent PMMA film (250 mg) with a thickness of 112 μm was prepared to be fully equilibrated by pressing the PMMA for 1 hour at a temperature of 458 K under a load of 20 kN, i.e., at a temperature well above the glass transition temperature Tg of 379 K.

[0157] To carry out step 1) according to the present invention, the resulting PMMA film was attached to one end of a vacuum flange using a cyanoacrylate adhesive. The vacuum flange had an aperture with a diameter of 1.75 cm. The vacuum flange with the film attached was then placed in an oven and maintained at a temperature of 482 K for 5 minutes.

[0158] Subsequently, a vacuum of 15 hPa was applied for 26 minutes, and then the film stretched according to step 2) of the present invention was cooled to 77 K by immersion in a bath of liquid nitrogen. The time required to perform step 2) was estimated to be 5 seconds. It is important to note that the bead friction, i.e., the non-universal prefactor of viscosity at a temperature 100°C higher than the Tg for PMMA, is approximately 1000 times higher than in the case of polystyrene. Therefore, the relaxation time τd will be longer due to similar factors, given the same number of entanglements per chain. Thus, the expansion process for PMMA here was faster than the relaxation time of the PMMA chain. From this, it is demonstrated that the method according to the present invention is very robust and effective even for expansion rates much faster than those selected in Example 1.

[0159] The resulting cap-like porous PMMA polymer film was stored at room temperature without any further precautions. A small 5 mm diameter section from the top of the cap-like polymer film was obtained for SEM analysis. Figures 21 and 22 clearly show the porous structure, similar to that observed in polystyrene.

[0160] Characteristic evaluation: The porous polymer films from Examples 1-4 were analyzed and their properties were evaluated in detail.

[0161] SEM and SFM Figures 4 and 5 show the fracture surface of the film perpendicular to the expansion plane at different magnifications. In Example 4, if the sample was not acquired from the central cap-like region, the reduced film thickness (60 nm) can be obtained from the SEM image in Figure 5. In Figures 6 and 7, which show a zoomed-in view at a higher magnification, the porous structure of the polymer film can be seen over a wide area.

[0162] Scanning force microscopy (SFM) is a well-established tool for detailed analysis of surface structures. For SFM, the same fracture surface used in SEM was used and mounted in a 90° 8-container section SEM holder. SFM experiments were performed in tapping mode on surfaces cut with a diamond knife (Leica Microtome UC6, Diatome knife). The film was left in the microtome holder, protruding approximately 100 μm from the holder surface, as seen in Figure 8. All measurements were performed close to the center of the film. High-resolution SFM topography shows granular structures with characteristic diameters reduced to 10 nm, as seen in Figure 9. At lower magnifications, stripes are visible, which are caused by the roughness of the cutting knife blade (see Figure 10).

[0163] BET experiment To confirm and complement the porosity analysis of the expanded samples, gas adsorption (BET) experiments according to DIN66131 were performed on polymer films according to Examples 1-4 using 77K liquid nitrogen. For background information, see also

[22] Brunauer, S., Emmett, PH, Teller, E.: Adsorption of gases in multimolecular layers. Journal of the American Chemical Society 60(2), 309-319 (1938).

[0164] The results regarding the comparison of the cumulative pore volume between Example 1 (for comparison) and Example 4 according to the present invention are shown in Fig. 16.

[0165] The pore volume Vp of the porous polymer film of Example 4 is 0.552 cm 3 g -1 , which is equivalent to a porosity of 43%. On the other hand, this pore volume is about 1 / 70 times lower than that of the polymer film of Example 1, that is, about 0.008 cm 3 g -1 or a porosity of 0.7%.

[0166] The BET technique was developed to estimate the total surface area of solid powders. This technique does not directly measure either the pore size or the pore size distribution. Typically, the value of the total pore volume is obtained from the volume of nitrogen taken up at a pressure of 1013 hPa and a temperature of 77 K. Similarly, the value of the total surface area of the pores is obtained from the BET surface area measurement. Assuming cylindrical pores, the total pore volume Vp is calculated as Vp = πd2 l / 4, and the BET surface area is S(BET) = πdl. In the formula, d is the average pore diameter and l is the total length of the pores. Using the above two equations, the diameter d of the pores is calculated by eliminating the length l of the pores.

[0167] Table 2 shows the values obtained by weighing the 5 mm diameter cut-outs from the polymer films according to Examples 1 to 4 and calculating the density from the film thickness, mass, and BET values.

[0168] [Table 2]

[0169] Brillouin light scattering As seen in Fig. 18, the BLS spectrum obtained from the nanoporous polymer film according to Example 4 consists of two peaks. The first one is at a low frequency f corresponding to the scattering wave vector q || = 0.0167 nm -1 , and the second one is at a frequency f corresponding to the scattering wave vector q 90 =(c L / 2π)q ||The second is backscatter q BS =(0.0236n)nm -1 The higher frequency side of f BS =(c L / 2π)q BS It is located at two frequencies from c L And n are determined simultaneously, and from these, the elastic modulus M = ρc L 2 and porosity p=(n 2 -1) / (n PS 2 -1) was determined, where ρ is the density of the porous film, and n PS is the refractive index of polystyrene. This single experiment yields both the porosity and modulus of the same (nanoporous) polymer film.

[0170] A unique feature of the nanoporous polymer film according to the present invention is the stretching of polystyrene chains, demonstrated by a higher transverse sound velocity compared to bulk polystyrene (see Figure 11). In particular, this difference increases with porosity due to the stronger stretching of the polymer film (see Figure 12).

[0171] Table 3 shows the longitudinal and transverse sound velocities C measured by BLS for Examples 1-4. T and C L The values ​​for this are shown.

[0172] [Table 3]

[0173] Nanoporous polymer films are stable under ambient conditions, but the chains are T g When exposed to extremely high temperatures for extended periods, the material relaxes and returns to its equilibrium configuration, losing its porosity (see Figure 13).

[0174] Strengthening of the resulting nanoporous polymer film by stretching polystyrene chains also results in a higher Young's modulus E compared to bulk polystyrene, which increases relatively even as porosity increases. PS (See Figure 14) and a high shear modulus GPS (See Figure 15) This is demonstrated by (Table 4 and Table 5 and the relative modulus increase rate RYMI disclosed in the general description above. x and RSMY x (See reference).

[0175] [Table 4]

[0176] [Table 5]

Claims

1. 1) A polymer article is brought to a glass transition temperature T g A step of stretching in at least one direction at a temperature at least 5K, preferably at least 10K, more preferably at least 20K higher to form nanopores, and then 2) The stretched polymer article is brought to a glass transition temperature T g A step of cooling to a temperature 10K, preferably 20K, lower than the above. A method for preparing a nanoporous polymer material having a porosity of 5.0% or more, preferably 10.0% or more, comprising at least [a specific element], The polymer article is made from a bulk material comprising at least 85 wt.% of at least one polymer, preferably at least 90 wt.%, more preferably at least 95 wt.%, more preferably at least 98 wt.%, and having a glass transition temperature of 40°C or higher, preferably 50°C or higher, more preferably 70°C or higher. Steps 1) and 2) are carried out together within a time interval short enough to preserve, at least partially, the nanopores formed in step 1). A method for preparing nanoporous polymer materials.

2. The method according to claim 1, wherein the polymer article is a polymer film, preferably a polymer film having a film thickness of 100 nm to 2.0 mm, preferably 100 nm to 1000 μm, and more preferably 500 nm to 800 μm.

3. The method according to claim 1 or 2, wherein the bulk material and therefore the polymer article contain no foaming agents, foaming agents, other pore-forming agents, or nano-inclusion agents.

4. The number average molecular weight [M] of the polymer in the bulk material. n ] is 200 kg / mol or more, preferably 500 kg / mol or more, more preferably 800 kg / mol or more, or instead, M e If we define it as the molecular weight of the entangled molecules, then 20M e The method according to any one of claims 1 to 3.

5. The at least one polymer in the bulk material is acrylonitrile-butadiene-styrene, thermoplastic polyimide, cellulose acetate, cellulose acetate butyrate, cellulose diacetate, cellulose propionate, cyclic olefin copolymer, ethylene vinyl alcohol copolymer (EVOH), polystyrene, polyamide 11, polyamide 12, polyamide 46, polyamide 6, polyamide 66, polyester, for example polybutylene terephthalate, polyethylene terephthalate, polyethylene terephthalate glycol, poly(meth)acrylate, for example polymethyl methacrylate, polyarylate, polycarbonate, preferably bisphenol A, tetramethylbisphenol A, bisphenol S, The method according to any one of claims 1 to 4, wherein a polycarbonate of 1,1,1-tris(4-hydroxyphenyl)ethane, dihydroxydiphenyl sulfide, or 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; a polyetheretherketone, polyethersulfone, perfluoroalkoxyalkane, polylactic acid, polymethacrylamide, polyphenylene ether, polyphenylene sulfide, polyphenylene sulfone, polysulfone, polyvinyl chloride, styrene-acrylonitrile, and styrene-maleic anhydride (SMA) is selected from the group, and polystyrene, polycarbonate, and polymethyl methacrylate are preferred, and polystyrene is more preferred.

6. The polydispersity index (PDI) of the polymer in the bulk material [M w / M n The method according to any one of claims 1 to 5, wherein ] is in the range of 1.00 to 10.00, preferably in the range of 1.01 to 5.00, more preferably in the range of 1.01 to 1.50, even more preferably in the range of 1.01 to 1.10, and even more preferably in the range of 1.03 to 1.

08.

7. Less than 200 kg / mol in the bulk material, or 20 M instead. e The method according to any one of claims 1 to 6, wherein the total amount of compounds having a molecular weight of less than 15 wt.% is 15 wt.% or less, preferably 10 wt.% or less, and more preferably 5 wt.% or less.

8. The method according to any one of claims 1 to 7, wherein the stretching of the polymer article is carried out such that the expansion ratio in each stretching direction is at least 1.05, preferably at least 1.20, for example 1.20 to 3.50 or 1.20 to 4.00 or 1.20 to 5.00, more preferably at least 1.50, for example 1.50 to 3.50 or 1.50 to 4.00 or 1.50 to 4.

00.

9. The method according to any one of claims 1 to 8, wherein the time required to carry out both steps 1) and 2) is 2 hours or less, preferably 1 hour or less, and more preferably 45 minutes or less.

10. The time for performing both steps 1) and 2) is 1τ d to 100τ d , preferably 1τ d to 80τ d and more preferably 1τ d to 50τ d in the range, where τ d is the reptation relaxation time of the bulk material of the polymer article. The method according to any one of claims 1 to 8

11. A nanoporous polymer material that can be obtained by the method described in any one of claims 1 to 10.

12. A nanoporous polymer material, preferably having specifications such as the bulk material in one or more of claims 3 to 7, and having a porosity Φ of 5 to 60%, preferably 5 to 50%, more preferably 8 to 45%, when measured by gas adsorption (BET) at 77K using liquid nitrogen in accordance with DIN66131.

13. A nanoporous polymer material according to claim 11 or 12, wherein the nanoporous polymer material includes an average pore diameter of 2 to 200 nm, preferably 2 to 100 nm, and / or pores of the nanoporous polymer material having a diameter of 2 to 20 nm account for 70% or more, preferably 80% or more, of the total pore volume, and / or the pore diameter distribution of the porous polymer film is such that 50% of the total pore volume is 10 nm or less, preferably in the range between 2 nm and 10 nm.

14. Factor (1-V) that has a higher pore volume Vp than bulk material, as measured by BLS. p ) multiplied by Young's modulus and / or shear modulus and / or transverse and longitudinal sound velocity C T and C L Preferably, the Young's modulus and shear modulus, and the transverse and longitudinal sound velocity C are higher than those of the bulk material. T and C L A nanoporous polymer material according to any one of claims 11 to 13, which exhibits the following characteristics.

15. Solid supports, diffusion layers, scaffolds, low electrical constant materials, photonic bandgap materials, and optical materials for films, sensors, and catalysts, comprising the nanoporous polymer material according to any one of claims 11 to 14.

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