Physically crosslinkable adhesive copolymer

Abstract

A polymerizable composition comprising a (meth)acrylate copolymer having pendent photoinitiator groups and a high T.sub.g monomer or macromer is described. The resulting copolymer is physically crosslinking and is of the formula I: (I). ##STR00001##

Claims

1. An adhesive copolymer of the formula: ##STR00012## wherein M.sup.acryl represents acrylate ester monomer units and subscript a is non-zero; M.sup.PI* represents the residue of monomer units having pendent photoinitiator groups and subscript b is non-zero; M.sup.polar represents monomer units having polar functional groups and subscript c is zero or non-zero; M.sup.other represents other monomer units and subscript d is zero or non-zero; M.sup.HighTg represent a high T.sub.g group and subscript e is at least one, wherein said copolymer comprises: (a) from 70 to 99 parts by weight of polymerized monomer units acrylic ester monomers; (b) from 0.5 to 10 parts by weight of polymerized monomer units derived from of an monomer having a photoinitiator group; (c) from 0 to 10 parts by weight of polymerized polar monomer units; (d) from 0 to 10 parts by weight of polymerized monomer units derived from at least one other monomer; and (e) from 1 to 5 parts by weight of grafted high T.sub.g monomer units, which are monomers that when homopolymerized produce a polymer having a Tg of 50 C.; the sum of monomer units being 100 parts by weight.

2. The adhesive copolymer of claim 1 wherein said copolymer comprises 1 to 5 parts by weight of acid-functional monomer units.

3. An adhesive copolymer of the formula: ##STR00013## wherein M.sup.acryl represents (meth)acrylate ester monomer units and subscript a is non-zero; M.sup.PI* represents the residue of monomer units having pendent photoinitiator groups and subscript b is non-zero; M.sup.polar represents monomer units having polar functional groups and subscript c is zero or non-zero; M.sup.other represents other monomer units and subscript d is zero or non-zero; M.sup.HighTg represent a high T.sub.g group having a Tg of 50 C. and subscript e is at least one, and wherein subscript e is 2 to 10 times that of subscript b.

4. The adhesive copolymer of claim 1 comprising 90 to 95 parts by weight of acrylate ester monomers.

5. The adhesive copolymer of claim 1 wherein the high T.sub.g group M.sup.HighTg is derived from polymerized high T.sub.g monomers.

6. The adhesive copolymer of claim 1 wherein M.sup.HighTg is a high T.sub.g macromer.

7. The adhesive copolymer of claim 6 wherein the high T.sub.g macromer is a styrene macromer, a poly(methyl methacrylate) macromer or a macromer derived from a high T.sub.g monomer.

8. The adhesive copolymer of claim 1 wherein M.sup.PI* is derived from monomers of the formula ##STR00014## where; X.sup.1 is O or NR.sup.1, R.sup.1 is independently H or C.sub.1-C.sub.4 alkyl; PI is a photoinitiator group; R.sup.10 is a divalent (hetero)hydrocarbyl linking group connecting the (meth)acryloyl group with the PI group.

9. The adhesive copolymer of claim 8 wherein the PI group is an alpha-cleavage type photoinitiator group.

10. The adhesive copolymer of claim 1, wherein the copolymer comprises from 0.5 to 10 parts by weight of polymerized monomer units, M.sup.PI*, derived from of a monomer having a photoinitiator group.

11. The adhesive copolymer of claim 5 wherein the high T.sub.g monomer is selected from t-butyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, stearyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, benzyl methacrylate, 3,3,5 trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl acrylamide, and propyl methacrylate or combinations.

12. The adhesive copolymer of claim 1, wherein at least 10% of the M.sup.highTg monomer units have a subscript e of at least 10.

13. A polymerizable composition comprising a (meth)acrylate copolymer having pendent photoinitiator groups and a high T.sub.g macromer of the formula: X(Y).sub.nZ wherein X is a polymerizable vinyl or acrylate group; Y is a divalent linking group where n can be zero or one; and Z is a monovalent polymeric moiety having a T.sub.gthan 30 C.

14. The polymerizable composition of claim 13 wherein the (meth)acrylate copolymer having pendent photoinitiator groups is of the formula:
[M.sup.Acryl].sub.a-[M.sup.PI].sub.b-[M.sup.polar].sub.c-[M.sup.other].sub.d, wherein M.sup.acryl represents (meth)acrylate ester monomer units and subscript a is at least one; M.sup.PI represents monomer units having pendent photoinitiator groups and subscript b is at least one; M.sup.polar represents monomer units having polar functional groups and subscript c is zero or non-zero; M.sup.other represents other monomer units and subscript d is zero or non-zero.

15. The polymerizable composition of claim 13 wherein the high T.sub.g macromer is selected from oligomeric styrene, methystyrene, poly(methyl methacrylate) and macromers of high T.sub.g monomers.

16. The polymerizable composition of claim 13 comprising 70-95 wt. % of said (meth)acrylate copolymer having pendent photoinitiator groups and 5-30 wt. % of a macromers of high T.sub.g monomers.

17. The polymerizable composition of claim 13 wherein MN comprises interpolymerized monomers of the formula: ##STR00015## where; X.sup.1 is O or NR.sup.1, R.sup.1 is independently H or C.sub.1-C.sub.4 alkyl; PI is a photoinitiator group; R.sup.10 is a divalent (hetero)hydrocarbyl linking group connecting the (meth)acryloyl group with the PI group.

18. The polymerizable composition of claim 17 wherein the photoinitiator groups of the photoinitiator monomer M.sup.PI is an alpha-cleavage type photoinitiator group.

Description

EXAMPLES

(1) TABLE-US-00001 TABLE 1 Materials Designation Description and Source AA Acrylic acid, available from Sigma Aldrich, St. Louis, MO EtOAc Ethyl acetate, available from Sigma Aldrich, St. Louis, MO HOSTAPHAN Primed polyester film available from Mitsubishi, 3SAB Greer, SC, under the trade designation HOSTAPHAN 3SAB IBoA Isobornyl acrylate, available from Sigma Aldrich, St. Louis, MO IOA Isooctylacrylate (CAS Number: 29590-42-9), available from 3M Co., St. Paul, MN VAZO 67 2,2-azobis-(2-methylbutyronitrile) (CAS Number: 13472-08-7), available from DuPont, Wilmington, DE, under the trade designation VAZO 67 VAZPIA 2-[4-(2-hydroxy-2-methylpropanoyl)phen- oxy]ethyl-2-methyl-2-N-propenoylamino propanoate (disclosed in U.S. Pat. No. 5,506,279), available from 3M Co., St. Paul, MN, under the trade designation VAZPIA
Test Methods
90 Angle Peel Adhesion Strength Test

(2) Peel adhesion strength was measured at a 90 angle using an IMASS SP-200 SLIP/PEEL TESTER (available from IMASS, Inc., Accord Mass.) at a peel rate of 305 mm/minute (12 inches/minute) using the procedure described in ASTM International standard, D3330, Method F. Test panels of either stainless steel or soda-lime glass were prepared by wiping the panels with a tissue wetted with the corresponding solvents shown in Table 2 using heavy hand pressure to wipe the panel 8-10 times. The test panels were wiped two more times with clean tissues wetted with the solvent. The cleaned panel was allowed to dry. The adhesive tape was cut into strips measuring 1.27 cm20 cm ( in.8 in.) and the strips were rolled down onto the cleaned panel with a 2.0 kg (4.5 lb.) rubber roller using 2 passes. The prepared samples were stored at 23 C./50% RH for 24 hours before testing. Two samples were tested for each example and averaged values were expressed in Oz/inch. Failure mode was noted and recorded as: cohesive (COH, i.e., the adhesive split leaving residue on both the tape and test surface); adhesive (ADH, i.e., the adhesive peeled cleanly from the test surface); or 2-B 2-Bond (2-B, i.e., the adhesive peeled away from the backing).

(3) TABLE-US-00002 TABLE 2 Peel Adhesion Test Panel Materials Material Solvent SS - Stainless Steel Heptane Glass - Soda-lime glass Heptane
Static Shear Strength Test

(4) Static shear strength was evaluated as described in the ASTM International standard, D3654, Procedure A-at 23 C./50% RH (relative humidity) using a 500 g load. Tape test samples measuring 1.27 cm15.24 cm ( in.6 in.) were adhered to 1.5 inch by 2 inch stainless steel (SS) panels using the method to clean the panel and adhere the tape described in the peel adhesion test. The tape overlapped the panel by 1.27 cm2.5 cm. and the strip was folded over itself on the adhesive side, and then folded again. A hook was hung in the second fold and secured by stapling the tape above the hook. The weight was attached to the hook and the panels were hung in a 23 C./50% RH room. The time to failure in minutes was recorded. If no failure was observed after 10,000 minutes, the test was stopped and a value of >10,000 minutes was recorded. The mode of failure described in the peel adhesion test was also noted.

(5) Percent Gel Test

(6) The percent gel content of samples was determined as described in the ASTM International standard, D3616-95. A round test specimen measuring 63/64 inch (25 mm) in diameter was die-cut from a tape coated with the polymer and cured. The specimen was placed in a mesh basket measuring 1 inch (3.8 cm) by 1 inch (3.8 cm). The basket with the specimen was weighed to the nearest 0.1 mg and placed in a capped jar containing sufficient toluene to cover the sample. After 24 hours the basket (containing the specimen) was removed, drained and placed in an oven at 120 C. for 30 minutes. The percent gel was determined by calculating weight % (wt. %) of the remaining, unextracted portion to the original sample. A disc of the uncoated polyester backing material of the same size as the specimen was also die-cut and weighed. The weight percent gel (wt. % gel) was calculated according to the equation:

(7) $\mathrm{wt}.\%\mathrm{gel}=100\frac{\begin{array}{c}(\mathrm{unextracted}\mathrm{sample}\mathrm{wt}.\mathrm{after}\mathrm{extraction}-\\ \mathrm{uncoated}\mathrm{backing}\mathrm{wt}.)\end{array}}{\left(\mathrm{original}\mathrm{sample}\mathrm{wt}.-\mathrm{uncoated}\mathrm{backing}\mathrm{wt}.\right)}$
Molecular Weight Determination by Gel Permeation Chromatography (GPC)

(8) Molecular weight and polydispersity (MW/MN) of polymer samples were characterized by using gel permeation chromatography (GPC, Manufacturer: Waters Corporation (Milford, Mass.)). The instrument consists of a pump (model#: 1515), an auto sampler (model#:2707), a UV detector (model#: 2489), and a refractive index detector (model#: 2414). Polymer sample solutions were prepared by dissolving dry polymers in tetrahydrofuran (THF) at 1.0 weight percent and were filtered with 0.2 micron Teflon syringe filters. The molecular weight calculations were based upon a calibration made of narrow dispersity polystyrene (PS) molecular weight standards.

(9) Preparation of Base PSA Polymer Solution

(10) PSA copolymers were prepared by radical polymerization with three monomers IOA, AA, and VAZPIA. The monomers were mixed with a reaction solvent (EtOAc) with a concentration of 30% (solid %) and thermal radical initiator (VAZO 67, 0.3 wt. % of total solids) in an amber, narrow necked pint bottles at room temperature. The solutions were de-aerated by purging with nitrogen gas for 10 minutes at room temperature. The bottles were capped tightly and put in an Atlas launderometer at 60 C. for 24-48 hours. The bottles were then cooled to room temperature and the polymer solutions were used for further evaluations. Detailed monomer compositions were as summarized in Table 3.

(11) TABLE-US-00003 TABLE 3 Base PSA Polymer IOA, AA, IOA/AA VAZPIA Wt. % Solids Solution wt. % wt. % Weight Ratio (wt. %) in EtOAc A 90 10 90/10 0 30 B 89.1 9.9 90/10 1 30 C 87.75 9.75 90/10 2.5 30 D 85.5 9.5 90/10 5 30

Examples 1-11

(12) Base PSA polymer solutions (A, B, C, and D), as prepared in the previous section, were used for preparing PSA coating solutions. Example 1, 3, 5, 7 solutions were made with the base PSA polymer solutions A, B, C, D, respectively, without any further treatments. Example 2, 4, 6, 8 were also made with base PSA polymer A, B, C, D, respectively but they were mixed with 20 pph of isobornyl acrylate added to the base PSA polymer solution and UV irradiated for 20 min. Example 9, 10, 11 were made with polymer C (VAZPIA, 2.5 wt. %) and 20 pph isobornyl acrylate, but the UV irradiation time for each sample was different, with irradiation times of 5, 10 and 60 minutes for Example 9, 10, and 11, respectively. Detailed composition and UV irradiation times were as summarized in Table 4.

(13) TABLE-US-00004 TABLE 4 Final Isobornyl UV Solution solution Base Acrylate, irradiation, Visual wt. Example polymer pph minutes Appearance % solid Ex. 1 A 0 0 Transparent 30 Ex. 2 A 20 20 Transparent 34 Ex. 3 B 0 0 Transparent 30 Ex. 4 B 20 20 Slightly hazy 34 Ex. 5 C 0 0 Transparent 30 Ex. 6 C 20 20 Slightly hazy 34 Ex. 7 D 0 0 Transparent 30 Ex. 8 D 20 20 Slightly hazy 34 Ex. 9 C 20 5 Slightly hazy 34 Ex. 10 C 20 10 Slightly hazy 34 Ex. 11 C 20 60 Transparent 34

(14) For each of the prepared compositions of Ex. 1 to Ex. 11, the prepared composition was knife-coated onto a 6 inch (15 cm) by 25 inch (64 cm) strip of polyester film backing (HOSTAPHAN 3SAB) to a wet thickness of about 15 mils (380 micrometers). The coated film was dried in an oven set at 70 C. for 60 minutes to provide a tape having an adhesive coating thickness of 2 mils (51 micrometers), to provide corresponding tapes Examples 12-22.

(15) All tapes (Examples 12-22) were conditioned at 23 C., 50% RH for 24 hours before testing for shear strength and 90 peel adhesion. Shear test results and adhesion data are shown in Tables 5 and 6, respectively.

(16) TABLE-US-00005 TABLE 5 Coating Room temp Example solution shear (min) Failure Mode* Ex. 12 Ex. 1 341 COH Ex. 13 Ex. 2 354 COH Ex. 14 Ex. 3 136 COH Ex. 15 Ex. 4 1141 COH Ex. 16 Ex. 5 235 COH Ex. 17 Ex. 6 2205 COH Ex. 18 Ex. 7 340 COH Ex. 19 Ex. 8 >10000 None Ex. 20 Ex. 9 641 COH Ex. 21 Ex. 10 2158 COH Ex. 22 Ex. 11 >10000 None *COH = cohesive

(17) TABLE-US-00006 TABLE 6 Coating Stainless steel Glass adhesion Failure Example solution adhesion (N/dm) (N/dm) Mode* 23 Ex. 1 31.1 44.4 ADH 24 Ex. 2 27.5 44.1 ADH 25 Ex. 3 26.6 44.9 ADH 26 Ex. 4 18.2 35.7 ADH 27 Ex. 5 41.6 39.8 ADH 28 Ex. 6 41.5 40.9 ADH 29 Ex. 7 27.3 42.5 ADH 30 Ex. 8 16.1 40.9 ADH 31 Ex. 9 33.5 39.0 ADH 32 Ex. 10 25.1 38.5 ADH 33 Ex. 11 40.3 47.3 ADH *ADH = adhesive

(18) TABLE-US-00007 TABLE 7 Coating Mn by GPC, Mw by GPC, Wt. Example solution Kg/mol Kg/mol Polydispersity % gel 34 Ex. 1 167 397 2.4 <1 35 Ex. 2 197 447 2.3 <1 36 Ex. 3 41 153 3.8 <1 37 Ex. 4 58 285 4.9 <1 38 Ex. 5 48 154 3.2 <1 39 Ex. 6 76 491 4.3 <1 40 Ex. 7 48 157 3.3 <1 41 Ex. 8 59 261 4.4 <1 42 Ex. 9 73 323 4.4 <1 43 Ex. 10 75 416 5.4 <1 44 Ex. 11 76 524 6.9 <1

(19) This disclosure provides the following embodiments:

(20) 1. An adhesive copolymer of the formula:

(21) ##STR00009##
wherein M.sup.acryl represents (meth)acrylate ester monomer units and subscript a is non-zero; M.sup.PI* represents the residue of monomer units having pendent photoinitiator groups and subscript b is non-zero; M.sup.polar represents monomer units having polar functional groups and subscript c is zero or non-zero; M.sup.other represents other monomer units and subscript d is zero or non-zero; M.sup.HighTg represent a high T.sub.g group and subscript e is at least one.

(22) 2. The adhesive copolymer of embodiment 1 wherein said copolymer comprises: (a) from 70 to 99 parts by weight of polymerized monomer units acrylic ester monomers; (b) from 0.5 to 10 parts by weight of polymerized monomer units derived from of an monomer having a photoinitiator group; (c) from 0 to 10 parts by weight of polymerized polar monomer units; (d) from 0 to 10 parts by weight of polymerized monomer units derived from at least one other monomer; and (e) from 1 to 5 parts by weight of grafted high T.sub.g monomer units;
the sum of monomer units being 100 parts by weight.

(23) 3. The adhesive copolymer of any of the previous embodiments wherein said copolymer comprises 1 to 5 parts by weight of acid-functional monomer units.

(24) 4. The adhesive copolymer of any of the previous embodiments, wherein subscript e is 2 to 10 times that of subscript b.

(25) 5. The adhesive copolymer of any of embodiments 2-4 comprising 90 to 95 parts by weight of acrylate ester monomers.

(26) 6. The adhesive copolymer of any of the previous embodiments wherein the high T.sub.g group M.sup.HighTg is derived from polymerized high T.sub.g monomers.

(27) 7. The adhesive copolymer of any of the previous embodiments wherein M.sup.HighTg is a high T.sub.g macromer.

(28) 8. The adhesive copolymer of embodiment 7 wherein the high T.sub.g macromer is a styrene macromer, a poly(methyl methacrylate) macromer or a macromer derived from a high T.sub.g monomer.

(29) 9. The adhesive copolymer of any of the previous embodiments wherein M.sup.PI* is derived from monomers of the formula

(30) ##STR00010##
where; X.sup.1 is O or R.sup.1 is independently H or C.sub.1-C.sub.4 alkyl; PI is a photoinitiator group; R.sup.10 is a divalent (hetero)hydrocarbyl linking group connecting the (meth)acryloyl group with the PI group.

(31) 10. The adhesive copolymer of embodiment 9 wherein the PI group is an alpha-cleavage type photoinitiator group.

(32) 11. The adhesive copolymer of any of embodiments 2-10, wherein the copolymer comprises from 0.5 to 10 parts by weight of polymerized monomer units, M.sup.PI*, derived from of an monomer having a photoinitiator group.

(33) 12. The adhesive copolymer of any of embodiments 1-11 wherein the high T.sub.g monomer is selected from t-butyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, stearyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, benzyl methacrylate, 3,3,5 trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl acrylamide, and propyl methacrylate or combinations.

(34) 13. The adhesive copolymer of any of the previous embodiments wherein 0.01 to 10 percent of the monomer units are substituted by grafted high T.sub.g groups.

(35) 14. The adhesive copolymer of any of the previous embodiments wherein the weight percent of the grafted high T.sub.g groups in the grafted copolymer is 5-30 wt. %.

(36) 15. The adhesive copolymer of any of the previous embodiments, wherein at least 10% of the M.sup.HighTg monomer units have a subscript e of at least 10.

(37) 16. A polymerizable composition comprising a (meth)acrylate copolymer having pendent photoinitiator groups and a high T.sub.g monomer or macromer.

(38) 17. The polymerizable composition of embodiment 16 wherein the (meth)acrylate copolymer having pendent photoinitiator groups is of the formula:
[M.sup.Acryl].sub.a[M.sup.PI].sub.b[M.sup.polar].sub.c[M.sup.other].sub.d,
wherein M.sup.acryl represents (meth)acrylate ester monomer units and subscript a is at least one; M.sup.PI represents monomer units having pendent photoinitiator groups and subscript b is at least one; M.sup.polar represents monomer units having polar functional groups and subscript c is zero or non-zero; M.sup.other represents other monomer units and subscript d is zero or non-zero.

(39) 18. The polymerizable composition of any of embodiments 16-17 wherein the high T.sub.g macromer is of the formula:
X(Y).sub.nZ
wherein X is a polymerizable vinyl or acrylate group; Y is a divalent linking group where n can be zero or one; and Z is a monovalent polymeric moiety having a T.sub.g than 30 C.

(40) 19. The polymerizable composition of any of embodiments 16-18 wherein the high T.sub.g macromer is selected from oligomeric styrene, methystyrene, poly(methyl methacrylate) and macromers of high T.sub.g monomers.

(41) 20. The polymerizable composition of any of embodiments 16-19 comprising 70-95 wt. % of said (meth)acrylate copolymer having pendent photoinitiator groups and 5-30 wt. % of a high T.sub.g monomers.

(42) 21. The polymerizable composition of any of embodiments 16-20 wherein MPI comprises interpolymerized monomers of the formula:

(43) ##STR00011##
where; X.sup.1 is O or R.sup.1 is independently H or C.sub.1-C.sub.4 alkyl; PI is a photoinitiator group; R.sup.10 is a divalent (hetero)hydrocarbyl linking group connecting the (meth)acryloyl group with the PI group.

(44) 22. The polymerizable composition of embodiment 21 wherein the photoinitiator groups of the photoinitiator monomer M.sup.PI is an alpha-cleavage type photoinitiator group.