Structural adhesives including menthyl (METH)acrylate

Abstract

Provided are polymerizable compositions comprising: menthyl (meth)acrylate; an ethylenically unsaturated monomer having polar content that is a vinyl functional polar monomer or a (meth)acrylate represented by the formula: CH2=CR1-(CO)-O-R5 wherein R1 is an H or a methyl group; (CO) is a carbonyl group C=O; R5 is an -R4-(X)p group or a polyether group; R4 is a linear or branched p+1 valent aliphatic group with at least two carbon atoms; X is a polar group comprising a hydroxyl group, a nitrogen-containing group, or an acid group; and p is an integer of 1 or greater; a compound including a (meth)acrylic moiety; a compound that upon at least partial curing of the polymerizable composition does not form a covalent bond with a compound comprising a (meth)acrylic moiety; and optionally a curing system. Bonded articles including the disclosed polymerizable compositions and methods of their preparation are described.

Description

[0001] STRUCTURAL ADHESIVES INCLUDING MENTHYL (METHjACRYLATE

[0002] BACKGROUND

[0003] Structural adhesives are known to be useful for bonding one substrate to another, e.g., a metal to a metal, a metal to a plastic, a plastic to a plastic, a glass to a glass. In some applications, structural adhesives are attractive alternatives to mechanical joining methods, such as riveting or spot welding, because structural adhesives distribute load stresses over larger areas rather than concentrating such stresses at a few points. Structural adhesives may also produce cleaner and quieter products because they can dampen mechanical vibrations and reduce noise. Additionally, structural adhesives can be used to bond a variety of materials, sometimes without extensive surface preparation (e.g., corona, flame, abrasion).

[0004] SUMMARY

[0005] In one aspect, provided are polymerizable compositions comprising: menthyl (methjacrylate; an ethylenically unsaturated monomer having polar content that is a vinyl functional polar monomer or a (methjacrylate represented by the formula:

[0006] CH2=CR1-(CO)-O-R5wherein R1is an H or a methyl group;

[0007] (CO) is a carbonyl group C=O;

[0008] R5is an -R4-(X)Pgroup or a polyether group;

[0009] R4is a linear or branched p+1 valent aliphatic group with at least two carbon atoms; X is a polar group comprising a hydroxyl group, a nitrogen-containing group, or an acid group; and p is an integer of 1 or greater; a compound including a (methjacrylic moiety; a compound that upon at least partial curing of the polymerizable composition does not form a covalent bond with a compound comprising a (methjacrylic moiety; and optionally a curing system.

[0010] In another aspect, bonded articles including the disclosed polymerizable compositions and methods of their preparation are described.

[0011] As used herein: the term "(methjacrylate" refers to "methacrylate" and / or "acrylate."

[0012] Features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims. DETAILED DESCRIPTION

[0013] Adhesives may be and are are often derived from acrylic monomers. To properly tune the mechanical properties of such adhesive compositions, the acrylic monomers may be selected based on their homopolymer’s characteristics, such as, for example, the glass transition temperature ("Tg"). Monomers having higher glass transition temperatures typically improve adhesion and rigidity of the final product and therefore, a monomer that can increase a material’s glass transition temperature is desirable in many compositions.

[0014] Compared to their acrylate counterparts, methacrylate monomers typically provide materials with higher glass transition temperatures. However, in many cases, combining acrylate and methacrylate monomers in a single curable resin is undesirable as it can have unpredictable effects on the polymerization kinetics with undesirable consequences for the resulting material's mechanical properties and performance.

[0015] Isobomyl methacrylate ("IBOMA") is commonly used as an acrylate monomer in adhesives, because when cured it provides materials with a higher glass transition temperature than that which is observed when the IBOMA has been replaced with other commercially available, acrylate monomers. However, commercial sources of IBOMA are typically contaminated with camphene and residual starting isobomyl alcohol. Camphene produces a distinct, unpleasant odor and can act as a chain transfer agent, thus lowering a cured material's molecular weight and resulting in a lower degree of conversion, ultimately increasing the cured material’s volatile organic content. Additionally, IBOMA is an allergen and unreacted residuals of IBOMA can be found in IBOMA-containing adhesives. As such, customers purchasing such acrylate adhesives are requesting IBOMA-free compositions.

[0016] Polymers are traditionally predominantly sourced from cmde-oil building blocks. As awareness of implications related to heavily relying on petroleum-based materials grows there is increasing interest in using non-petroleum sourced raw materials. Currently, there are few polymerizable, sustainably sourced raw materials that are commercially available. Furthermore, these limited sustainably sourced raw materials often utilize fatty acids or the like as a starting material, resulting in a limited set of properties obtainable when using these monomers in polymerizable resins. The present disclosure provides menthyl (meth)acrylate as an IBOA and IBOMA replacement.

[0017] As shown in Scheme 1, menthol, a terpene, can be converted into menthyl acrylate in one step. oteestlar Weight: 16S.27 Molecular Weight: 22:4.34

[0018] Scheme 1. Preparation of menthyl methacrylate Examples provided herein demonstrate that menthyl (meth)acrylate-comprising formulations may yield materials with comparable and / or improved performance relative to formulations containing IBO(M)A and that menthyl (meth)acrylate can be used as a renewably -derived monomer to replace IBO(M)A and / or petroleum-derived high Tg monomers in structural adhesive formulations and in bonded articles that include such menthyl (meth)acrylate-comprising formulations.

[0019] Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.

[0020] EXAMPLES

[0021] Unless otherwise noted or readily apparent from the context, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight.

[0022] Materials

[0023] Preparation of Menthv Methacrylate ("MTMA") Used in the Examples

[0024] To a 500 mL round bottom flask was added L-menthol (50.0 g, 0.320 mol, 1.00 equiv), DMAP (0.50 g, 0.032 mol, 0.1 equiv), and ethyl acetate (110 mL). Then methacrylic anhydride (47.25 mL, 0.632 mol, 1.00 equiv) was added using an addition funnel. After stirring at room temperature for 3 hours, the heat was increased to 55 °C and the reaction was allowed to stir for an additional 24 hours. The crude material was collected, concentrated, and purified using column chromatography (2x in hexane elutent). A clear colorless liquid was obtained after concentrating from the hexane column. Yield = 70.363 g.

[0025] Test Methods

[0026] Overlap Shear ("OLS") Testing: Nylon substrates (1 inch x 4 inches x 0.25 inch; 2.5 cm x 10 cm x 1.3 cm) and aluminum substrates (1 inch x 4 inches x 0.064 inch; 2.5 cm x 10 cm x 0.16 cm) were washed with isopropyl alcohol and air dried for at least 10 minutes. Structural adhesive base formulations and ACCELERATOR were loaded into a 10 / 1 cartridge, spun using a centrifuge for 1 min at 1500 rpm, and sealed with the appropriate cap. The adhesives were dispensed with a mixing nozzle and sprinkled with at least one glass bead 5-50 mils (Thomas Scientific, Swedesboro, NJ) over the substrate. Within one minute, a second matching substrate was applied to the sample, thus closing the bond. The bond area was 0.5 inches x 1 inch (1.3 cm x 2.5 cm) for aluminum and 0.25 inch x 1 inch (0.65 cm x 2.5 cm) for nylon. The bond was clamped with binder clips and allowed to sit at room temperature for 24 hours prior to testing. Dynamic overlap shear testing was performed at ambient temperature i.e., approximately 25 degrees Celsius using an MTS Sintech Tensile Tester (tensile tester from MTS Sintech, Eden Prairie Minnesota), specimens were loaded into the grips and the crosshead was operated at 2 inches per minute (5 cm / min) for Nylon substrates or operated at 0.1 inch per minute (2.54 mm per minute) for Aluminum substrates loading the specimen to failure. Stress at break was recorded in units of pounds per square inch (psi) and converted into megapascals MPa.

[0027] Tensile and Elongation ("T&E"): Base formulations and ACCELERATOR were loaded into a 10 / 1 cartridge, spun using a centrifuge for 1 min at 1500 rpm and sealed with the appropriate cap. The adhesives were dispensed with a mixing nozzle onto a knife coater equipped with a top and bottom liner and set to approximately 0.5 mm. Approximately 20 g of resin was dispensed onto one liner which was pulled through the knife coater such that the second liner covered the resin. The film was allowed to sit at ambient conditions for at least 24 h prior to testing. Tensile elongation testing was performed at ambient temperature using a Tensile Tester (tensile tester from MTS Sintech, Eden Prairie Minnesota), with a 30 kN loadcell. Specimens were cut using a type IV dogbone and were loaded into the grips at a distance of 2.5 inches (6.35 cm) and the crosshead was operated at 3.94 inch per minute (100 mm per minute), loading the specimen to failure. Stress at break was recorded in units of megapascals (MPa).

[0028] Dynamic Mechanical Analysis ("DMA") Test Method Temperature Ramp (US): Base formulations and ACCELERATOR were loaded into a 10 / 1 cartridge, spun using a centrifuge for 1 min at 1500 rpm and sealed with the appropriate cap. The adhesives were dispensed with a mixing nozzle onto a knife coater equipped with a top and bottom liner and set to approximately 0.5 mm. Approximately 20 g of resin was dispensed onto one liner which was pulled through the knife coater such that the second liner covered the resin. The film was allowed to sit at ambient conditions for at least 24 h prior to testing. The thickness of each film was measured. The films were mounted in the tensile grips of an DMA850 (TA Instruments, New Castle, DE, USA) with an initial grip separation of 12-16 mm. The measurement procedure was done to determine the precise grip separation with an initial / preload force of 0.1 N with a “Use Force Track” set to 150%. The samples were then tested at an oscillation of 0.2% strain and 1 Hz throughout a temperature ramp from at least -20 °C to 60 °C at a rate of 3 °C per minute. The temperatures at which the tan delta signal reached a maximum were recorded as the glass transition temperature ("Tg").

[0029] Example 1 ("EXI") and Comparative Examples 1 and 2 ("CE1 and CE2")

[0030] The stock formulation (Table 1) was prepared by combining all materials in a a polypropylene MAX 600 DAC cup (FlackTek, Inc., Landrum, SC). The cup was closed with a polypropylene lid and the mixture was high shear mixed at ambient temperature and pressure using a SPEEDMIXER (Hauschild SpeedMixer inc., Dallas Texas) for at least 30 s at 2000 revolutions per minute (rpm) until homogenous. The homogenous stock formulation was then divided into three MAX 600 DAC cups and a different monomer was added to each cup, as indicated in Table 2, to provide structural adhesive base formulations.

[0031] Table 1. Structural Adhesive Stock Formulation

[0032] Table 1. Structural Adhesive Base Formulations in Weight Percent

[0033] Results Each structural adhesive base formulation was tested according to general procedures described above. The results, shown in Table 3 below, demonstrate that MTMA can replace IBOMA in a liquid structural acrylic adhesive and that replacing IBOMA with MTMA provides a structural adhesive with similar mechanical properties and adhesion to nylon and aluminum. In contrast, formulations containing CHMA, an alternative hydrophobic monomer, have lower adhesion.

[0034] Table 2. Mechanical Testing Data All cited references, patents, and patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.

Claims

What is claimed is:

1. A polymerizable composition comprising: menthyl (meth)acrylate; an ethylenically unsaturated monomer having polar content that is a vinyl functional polar monomer or a (meth)acrylate represented by the formula: CH2=CR1-(CO)-O-R5wherein R1is an H or a methyl group;(CO) is a carbonyl group C=O;R5is an -R4-(X)Pgroup or a polyether group;R4is a linear or branched p+1 valent aliphatic group with at least two carbon atoms; X is a polar group comprising a hydroxyl group, a nitrogen-containing group, or an acid group; and p is an integer of 1 or greater; a compound including a (meth)acrylic moiety; a compound that upon at least partial curing of the polymerizable composition does not form a covalent bond with a compound comprising a (meth)acrylic moiety; and optionally a curing system.

2. The polymerizable composition of claim 1, wherein the at least one ethylenically unsaturated monomer having polar content is selected from the group consisting of a carboxylic acidcontaining (meth)acrylic monomer, a hydroxyl group-containing (meth)acrylic monomer, a glycidol ester-containing (meth)acrylic monomer, a phosphorate ester-containing (meth)acrylic monomer, a nitrogen-containing (meth)acrylic monomer, and combinations thereof.

3. The polymerizable composition of claim 1, wherein the compound including a (meth)acrylic moiety is a mono-functional (meth)acrylic monomer, a di-functional (meth)acrylic monomer, a tri- functional(meth)acrylic monomer, or a multi-functional (meth)acrylic monomer, and combinations thereof.

4. The polymerizable composition of claim 1, wherein the compound that upon at least partial curing of the polymerizable composition does not form a covalent bond with a compound comprising a (meth)acrylic moiety is selected from the group consisting of an organic filler, an inorganic filler particle, a plasticizer, a wax, a rheological additive, a toughening agent, and combinations thereof.

5. The polymerizable composition of claim 1, wherein the curing system comprises a free radical initiator selected from the group consisting of a cure initiator system, a redox initiator, a thermal initiator, a photoinitiator, and combinations thereof.

6. The polymerizable composition of claim 1, packaged as a one-part adhesive composition, or as a first part of a two-part adhesive composition, wherein the second part comprises at least part of the curing system.

7. The polymerizable composition of claim 1, at least partially cured, having a glass transition temperature in a range from 30 °C to 200 °C and a storage modulus at 25 °C of at least 200 MPa as determined by DMA.

8. The polymerizable composition of claim 1, wherein menthyl (meth)acrylate is present in an amount of 5 to 50 weight percent of the total composition.

9. An adhesive comprising the polymerizable composition of claim 1, at least partially cured with a curing system, wherein the adhesive bonds to at least one substrate providing an overlap shear strength of at least 3 MPa at room temperature.

10. The composition of claim 3, wherein the compound comprising (meth)acrylic moieties comprises divalent segments L and at least two X groups, wherein the divalent segments L are represented by the formula:L wherein each divalent segment L is respectively directly bonded to: i) two secondary N atoms, each directly bonded to a further divalent segment L or an X group, ii) two tertiary N atoms, each directly bonded to p further divalent segments L and (2-p) X groups, wherein p is 0, 1, or 2, or iii) a secondary N atom directly bonded to a further divalent segment L or an X group; and a tertiary N atom directly bonded to p further divalent segments L and (2-p) X groups, wherein p is 0, 1, or 2, wherein each ' independently represents an alkylene group having from 1 to 4 carbon atoms, with the proviso that at least some of the R1groups are -CH2-CH2-CH2-CH2-, wherein each n independently represents a positive integer, and wherein each X group is independently represented by the formulaCH2=C(R)-C(O)-O-V-W-C(O)- wherein each W is independently O, S, or NR2, wherein R2is hydrogen or alkyl having up to 4 carbon atoms, and wherein each V is independently alkylene that is optionally interrupted by at least one ether linkage or amine linkage and optionally substituted by hydroxyl.

11. The composition of claim 1, wherein the ethylenically unsaturated monomer having polar content is present in an amount of 0.1 to 50 percent by weight, based on the total weight of the acrylicfunctional compounds in the composition.

12. The composition of claim 1, wherein the compound including a (meth)acrylate moiety is present in an amount in a range from 1 percent by weight to 60 percent by weight, based on the total weight of (meth)acrylic -functional compounds in the composition.

13. An article bonded with the composition of claim 1, at least partially cured with a cure initiator system, wherein the article comprises a substrate, the substrate selected from the group consisting of a polyamide, a polycarbonate, a plastic, a metal, a glass, an epoxy composite, and combinations thereof.

14. A method of making a bonded article comprising a first substrate and a second substrate, the method comprising: combining the composition of claim 1 with a curing system to provide an adhesive composition; applying the adhesive composition on at least one of the first substrate or the second substrate; adhering the first substrate and the second substrate using the adhesive composition; and allowing the adhesive composition to at least partially cure to make the bonded article.

15. The method of claim 14, wherein at least one of the first substrate and the second substrate comprises a polyamide, a polycarbonate, a plastic, a metal, a glass, or an epoxy composite.

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