Phase-segmented non-isocyanate elastomers

Abstract

Elastomers are prepared from a reaction mixture that contains a polyene compound, an epoxy resin, a thiol curing agent and a basic catalyst. The polyene compound has an average of at least two groups containing aliphatic carbon-carbon double bonds capable of reaction with a thiol group. At least one of said aliphatic carbon-carbon double bonds is separated from each other said aliphatic carbon-carbon double bond by an aliphatic spacer group having a weight of at least 500 atomic mass units. These elastomers are typically phase-separated materials having good elongation and tensile properties.

Claims

1. A process for forming an elastomeric polymer, comprising a) forming a reaction mixture containing 1) at least one ene-terminated polyether having a molecular weight of 4,000 to 8,000, 2 to 6 aliphatic carbon-carbon double bonds capable of reaction with a thiol group, wherein at least one of said aliphatic carbon-carbon double bonds is separated from each other said aliphatic carbon-carbon double bond by an aliphatic spacer group having a weight of at least 1000 atomic mass units, 2) from 20 to 150 parts by weight, per 100 parts by weight of component 1), of at least one epoxy resin having an average of at least 1.5 epoxide groups per molecule and an epoxy equivalent weight of up to 1000, 3) at least one curing agent having at least two thiol groups, 4) at least one basic catalyst, and b) curing the reaction mixture to form the polymeric elastomer.

2. The process of claim 1, wherein the epoxy resin has an epoxy equivalent weight of up to 250.

3. The process of claim 2, wherein the curing agent includes at least one polythiol compound that contains from 2 to 4 thiol groups, or a mixture of two or more polythiol compounds that each contain 2 to 4 thiol groups, and the polythiol compound(s) have a thiol equivalent weight of 50 to 250.

4. The process of claim 2 wherein the base catalyst includes at least one tertiary amine compound, at least one cyclic amidine catalyst, at least one tertiary phosphine compound or a mixture of any two or more thereof.

5. The process of claim 2, wherein the reaction mixture further includes at least one thermally-decomposable free radical initiator compound.

6. The process of claim 2, wherein the curing agent provides 0.75 to 1.25 equivalents of thiol groups per equivalent of epoxide and ene groups present in the reaction mixture.

7. The process of claim 2 wherein the terminal aliphatic carbon-carbon double bonds are vinyl (—CH═CH.sub.2) groups.

8. The process of claim 2 wherein the terminal aliphatic carbon-carbon double bonds are acrylate groups.

9. The process of claim 2, wherein step b) is performed at a temperature of 0 to 180° C.

10. The process of claim 2, wherein step b) includes a free-radical reaction of the ene-terminated polyether and a thiol curing agent, and a base-catalyzed reaction between the epoxy resin and a thiol curing agent.

11. An elastomeric polymer made in accordance with claim 1.

12. The elastomeric polymer of claim 11, which has an elongation to break of at least 50% and a tensile strength of at least 3500 kPa.

13. The elastomeric polymer of 12, which has a continuous phase having a glass transition temperature of no greater than −20° C. and a disperse phase having a glass transition temperature of at least 20° C., wherein the continuous phase includes a reaction product of the ene-terminated polyether and a portion of the thiol curing agent, and the disperse phase includes a reaction product of the epoxy resin and the thiol curing agent.

14. An elastomeric polymer which has a continuous phase having a glass transition temperature of no greater than −20° C. and a disperse phase having a glass transition temperature of at least 20° C., wherein the continuous phase includes a reaction product of an ene-terminated polyether having a molecular weight of 4,000 to 8,000, 2 to 6 aliphatic carbon-carbon double bonds capable of reaction with a thiol group, wherein at least one of said aliphatic carbon-carbon double bonds is separated from each other said aliphatic carbon-carbon double bond by an aliphatic spacer group having a weight of at least 1000 atomic mass units, and a thiol curing agent, and the disperse phase includes a reaction product of an epoxy resin and a thiol curing agent.

15. The elastomeric polymer of claim 14, which has an elongation to break of at least 50% and a tensile strength of at least 3500 kPa.

16. The elastomeric polymer of claim 15, which has an elongation to break of at least 100%.

Description

EXAMPLES

(1) A. Synthesis of Acrylate-Terminated Polyether

(2) 74.5 g (428 mmol) toluene diisocyanate (TDI, 80/20 mixture of 2,4- and 2,6-isomers) is charged to a dry 2 L 4-neck round bottom flask equipped with overhead stirring, temperature control probe, addition funnel, and nitrogen inlet. The flask and its contents are heated to 80° C., and 827 g (207 mmol) of a 4000 molecular weight, nominally difunctional poly(propylene oxide) diol having 7 μeq/g of terminal unsaturation is added. The solution is stirred for 30 minutes after the diol is added. A drop of dibutyltin dilaurate is added and the reaction stirred for an additional 2 hours. The product is an isocyanate-terminated prepolymer having an isocyanate content of 2.04% by weight, as determined by titration.

(3) 881.2 grams of the prepolymer is brought to a temperature of 45° C. 54.3 g (467.6 mmole) of hydroxyethylacrylate (95%) and a drop of dibutyltin diluarate are added. The reaction mixture is stirred at 45° C. until no measurable isocyanate groups remain as observed by FT-IR. The resulting product is a polyether capped with two terminal acrylate (—O—C(O)—CH═CH.sub.2) groups per molecule.

(4) B. Production of Phase-Segmented Elastomer

(5) 150.00 g of the acrylate-terminated polyether produced in A above and 100.00 g of a 180 epoxy equivalent weight diglycidyl ether of bisphenol A (D. E. R. 383, from The Dow Chemical Company) are mixed on a high-speed laboratory mixture until homogeneous. Separately, 84 g trimethylolpropane tris(mercaptopropionate) (Sigma Aldrich technical grade) is mixed with 318 mg (0.33 mole-% based on thiol groups) of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, Sigma Aldrich technical grade). The thiol/catalyst mixture is then mixed with the acrylate-terminated prepolymer/epoxy resin mixture on the high speed mixer to produce a clear mixture. These proportions of starting materials provides about 1.15 equivalents of thiol groups per combined equivalents of acrylate and epoxide groups. A portion of the mixture is poured into a mold warmed to 50° C. The filled mold is then placed in a 50° C. oven overnight. A tack-free plaque is obtained. The cured plaque contains 25% by weight cured epoxy resin, calculated as described before.

(6) The plaque has a tensile strength of 8950 kPa (about 1300 psi) and an elongation at break of 138% (each as measured per ASTM D1708). The Shore A hardness is 90.

(7) A 10 mg sample of the cured plaque is evaluated by differential scanning calorimetry by equilibrating the sample at −90° C. and heating to 200° C. at the rate of 10° C./minute. Two glass transition temperatures are elicited, one at about −50° C. and a second one at about 25° C.

(8) A 10 cm×10 cm section of the cured plaque is placed in distilled water and heated at 70° C. for 14 days. The sample is then dried and its tensile strength, elongation and Shore A hardness are measured. The tensile strength is 7764 kPa (1126 psi), a reduction of only 13%. Elongation is 186%. Shore A hardness is not materially changed. The sample gains only 2.5% in mass, which is consistent with little reaction with and/or absorption of water.

(9) This system also cures at room temperature to form an elastomer having similar properties, although longer curing times are needed.

Examples 2-5

(10) To produce Example 2, 150.00 g of an acrylate-terminated polyether as in Example 1A above and 100.00 g of a 180 epoxy equivalent weight diglycidyl ether of bisphenol A (D. E. R. 383, from The Dow Chemical Company) are mixed on a high-speed laboratory mixture until homogeneous. Separately, 84 g trimethylolpropane tris(mercaptopropionate) (Sigma Aldrich technical grade) is mixed with 0.45 mole-% (based on trimethylolpropane tris(mercaptopropionate)) of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, Sigma Aldrich technical grade). The thiol/catalyst mixture is then blended with the acrylate-terminated prepolymer/epoxy resin mixture on the high speed mixer to produce a clear blend. About 20 grams are poured into a scintillation vial, which is sealed and placed in a block of insulating foam. The temperature of the reaction mixture is monitored with a thermocouple to determine the peak temperature generated by the exothermic curing reaction, as well as the time required to reach the peak exotherm temperature. The peak exotherm temperature of 110° C. is reached after about 10 minutes.

(11) Example 3 is performed in the same manner, except the amount of DBU catalyst is reduced to 0.33 mole-%. The peak exotherm temperature of 85° C. is reached after about 20-25 minutes. This indicates a much slower cure at this lower catalyst level, compared to Example 2.

(12) For Example 4, the DBU catalyst is replaced with 1 mole-% dimethylphenyl phosphine (DMPP). The peak exotherm temperature of 111° C. is reached after about 6 minutes. For Example 5, the DBU catalyst is replaced with 0.5 mole-% DMPP. The peak exotherm temperature of 118° C. is reached after about 2½ minutes. In these experiments, DMPP is found to provide a much faster cure than the DBU.

Examples 6-8

(13) Example 2 is repeated three times, each time replacing the DBU catalyst with 1,4-diazabicyclo[2.2.2]octane (DABCO). For Examples 6-8, 0.33, 0.25 and 0.22 mole-percent, respectively, of the triethylenediamine catalyst (based on the polythiol) are used. At each of these levels, the triethylenediamine catalyst provides an induction period in which little or no exotherm is seen, followed by a rapid increase in temperature indicative of a strong curing reaction. For Example 6, very little exotherm is seen for almost 15 minutes, and then the temperature rises rapidly to a peak exotherm of 111° C. after about 21 minutes. For Example 7, the temperature does not reach 40° C. for almost 60 minutes, and the peak exotherm of about 87° C. is seen after about 62 minutes. For Example 8, the time to reach 40° C. is over 80 minutes and the peak exotherm temperature of about 72° C. is seen after almost 110 minutes.

Example 9

(14) 200.00 g of an acrylate-terminated polyether as produced in Example 1A above and 100.00 g of a 180 epoxy equivalent weight diglycidyl ether of bisphenol A (D. E. R. 383, from The Dow Chemical Company) are mixed on a high-speed laboratory mixture until homogeneous. Separately, 64.96 g of pentaerythritol tetra(mercaptoacetate) (Sigma Aldrich technical grade) is mixed with 300 mg of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, Sigma Aldrich technical grade). The thiol/catalyst mixture is then mixed and cured in the manner described in Example 1B.

(15) The plaque has a tensile strength of 6550 kPa (950 psi) and percent elongation at break of 164% (as measured per ASTM D1708). The Shore A hardness is 70.

(16) As with Example 1, this sample is also curable at room temperature.

Example 10

(17) 304.7 grams of an isocyanate-terminated prepolymer as described in Example 1A is brought to a temperature of 45° C. 9.25 g of allyl alcohol and a drop of dibutyltin diluarate are added. The reaction mixture is stirred at 45° C. until no measurable isocyanate groups remain as observed by FT-IR. The resulting product is a polyether capped with two terminal allyl ether (—O—CH.sub.2—CH═CH.sub.2) groups per molecule.

(18) A phase-segmented elastomer is made in the general manner described in Example 2, using as ingredients 15 g of the allyl-terminated polyether, 10.00 g of a 180 epoxy equivalent weight diglycidyl ether of bisphenol A (D. E. R. 383, from The Dow Chemical Company), 8.35 g trimethylolpropane tris(mercaptopropionate) (Sigma Aldrich technical grade), 32 mg (1 mole-% based on trimethylolpropane tris(mercaptopropionate) of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, Sigma Aldrich technical grade) and 333 mg of t-butyl peroxide. The mixture is cured overnight at 80° C. in an oven.

(19) The t-butyl peroxide decomposes at the curing temperature to form free radicals. As a result, this system is believed to engage in both a free radical cure (between the ene groups and thiol groups) and a base-catalyzed cure (between the epoxy groups and the thiol groups. Some of the ene/thiol reaction also may be base-catalyzed. The product has a tensile strength of 9200 kPa (1335 psi) and an elongation to break of 200%. The material exhibits two glass transition temperatures, one at 34° C. and one at about −50° C.

(20) Micrographs are taken of the resulting elastomer using atomic force microscopic methods. A two-phase material is seen, in which the cured epoxy resin is mainly in the form of 0.5-1 mm phases dispersed in a continuous phase which consists mainly of the polyether.

(21) This system is also curable at room temperature.

Examples 11-14

(22) An acrylate-terminated polyether having an equivalent weight per terminal acrylate group of 1947 is made in the general manner described in Example 1A. Elastomer Examples 11-14 are made from this acrylate-terminated polyether, using formulations as set forth in Table 1 below. In each case, the acrylate-terminated polyether is mixed with the epoxy resin in a high-speed laboratory mixture, and then a mixture of the thiol and catalyst are stirred in. A portion of the resulting reaction mixture is poured into a mold warmed to 50° C. The filled mold is then placed in a 50° C. oven overnight. A tack-free plaque is obtained. Tensile strength, elongation, tensile modulus and Shore A hardness are as reported in Table 1.

(23) TABLE-US-00001 TABLE 1 Parts by weight Ingredient Ex. 11 Ex. 12 Ex. 13 Ex. 14 Acrylate-terminated 20 20 15 35 polyether DER 383 Epoxy 4.1 6.667 9.59 35 resin Trimethylolpropane 4.39 6.29 8.1 28.22 tri(thiopropionate) DBU catalyst 0.017 0.024 0.031 0.107 Properties Tensile Str, kPa 2650 (385) 3300 (477)  6975 (1012) 11,175 (1621) (psi) Elongation, % 187 159 122 120 Tensile Modulus, 3515 (510) 4710 (683) 10915 (1583)  26025 (3775) kPa (psi) Shore A hardness 63 N.D. 79 89

(24) These systems are also curable at room temperature.

Examples 15-18

(25) An acrylate-terminated polyether having an equivalent weight per terminal acrylate group of 1947 is made in the general manner described in Example 1A. Elastomer Examples 15-18 are made from this acrylate-terminated polyether, using formulations as set forth in Table 2 below. In each case, the acrylate-terminated polyether is mixed with the epoxy resin in a high-speed laboratory mixture, and then a mixture of the thiol and catalyst are stirred in. A portion of the resulting reaction mixture is poured into a mold warmed to 50° C. The filled mold is then placed in a 80° C. oven overnight. Tensile strength, elongation, tensile modulus and Shore A hardness are as reported in Table 2.

(26) TABLE-US-00002 TABLE 2 Parts by weight Ingredient Ex. 15 Ex. 16 Ex. 17 Ex. 18 Acrylate- 20 50 35 35 terminated polyether DER 383 Epoxy 4.1 31.97 35 65 resin Trimethylol- 1.97 6.29 14.11 14.39 propane tri(thio- propionate) Ethylene glycol 2.19 13.50 12.65 12.91 di(thio- propionate) DBU catalyst 0.055 0.278 0.291 0.198 Properties Tensile Str, kPa 3010 (437) 9045 (1312) 10570 (1533) 19300 (2800) (psi) Elongation, % 453 354 300 258 Tensile Modulus, 1965 (285) 6075 (881) 14730 (2137) 36400 (5281) kPa (psi) Shore A N.D. N.D. 80-85 N.D. hardness Tear Strength, N.D. N.D. 30 N.D. N/mm

(27) The abrasion resistance of elastomer Example 17 is evaluated for 1000 cycles on a Taber abrader equipped with 1 kg weight and H22 wheels. Example 17 loses less than 100 mg of mass.

(28) These systems are all curable at room temperature.

Examples 19-21

(29) An acrylate-terminated polyether having an equivalent weight per terminal acrylate group of 1230 is made in the general manner described in Example 1A, by capping a 2000-molecular weight poly(tetramethylene oxide) diol with toluene diisocyanate to form an isocyanate-terminated prepolymer, and then capping the isocyanate groups with hydroxyethylacrylate.

(30) Elastomer Examples 19-21 are made from this acrylate-terminated polyether, using formulations as set forth in Table 3 below. In each case, the acrylate-terminated polyether is mixed with the epoxy resin in a high-speed laboratory mixture, and then a mixture of the thiol and catalyst are stirred in. A portion of the resulting reaction mixture is poured into a mold warmed to 50° C. The filled mold is then placed in a 50° C. oven overnight. A tack-free plaque is obtained. Tensile strength and elongation are as reported in Table 3.

(31) TABLE-US-00003 TABLE 3 Ingredient Ex. 19 Ex. 20 Ex. 21 Acrylate-terminated 20 20 20 polyether DER 383 Epoxy resin 0 2.22 13.33 Trimethylolpropane 2.70 3.80 12.0 tri(thiopropionate) DBU catalyst 0.014 0.014 0.045 Properties Tensile Str, kPa (psi) 3268 (474) 3668 (532)   7095 (1029) Elongation, % 378 686 188 Tensile Modulus, kPa (psi) 2820 (409) 1489 (216) 19,954 (2894) Shore A hardness N.D. 75 85

(32) As before, these systems are all curable at room temperature.

Examples 22-25

(33) An acrylate-terminated polyether having an equivalent weight per terminal acrylate group of 1230 is made in the general manner described in Example 1A, by capping a 2000-molecular weight poly(tetramethylene oxide) diol with toluene diisocyanate to form an isocyanate-terminated prepolymer, and then capping the isocyanate groups with hydroxyethylacrylate.

(34) Elastomer Examples 22-25 are made from this acrylate-terminated polyether, using formulations as set forth in Table 4 below. In each case, the acrylate-terminated polyether is mixed with the epoxy resin in a high-speed laboratory mixture, and then a mixture of the thiol and catalyst are stirred in. A portion of the resulting reaction mixture is poured into a mold warmed to 50° C. The filled mold is then placed in a 50° C. oven overnight. A tack-free plaque is obtained. Tensile strength and elongation are as reported in Table 4.

(35) TABLE-US-00004 TABLE 4 Parts by weight Ingredient Ex. 22 Ex. 23 Ex. 24 Ex. 25 Acrylate-terminated 20 20 20 20 polyether Diglycidyl ether of 1,4- 1.05 2.22 5.0 8.57 butane diol Pentraerythritol 3.26 4.67 8.03 12.35 tetra(thiopropionate) DBU catalyst 0.013 0.015 0.014 0.015 Properties Tensile Str, kPa (psi) 3565 (517) 1730 (251) 1565 (227) 1165 (169) Elongation, % 350 313 322 174

(36) As before, these systems are curable at room temperature.

Examples 26-29

(37) Elastomer Examples 26-29 are made from an acrylate-terminated polyether, using formulations as set forth in Table 5 below. In each case, the acrylate-terminated polyether is mixed with the epoxy resin in a high-speed laboratory mixture, and then a mixture of the thiol and catalyst are stirred in. A portion of the resulting reaction mixture is poured into a mold warmed to 50° C. The filled mold is then placed in a 50° C. oven over about three days. A tack-free plaque is obtained in each case. Tensile strength and elongation are as reported in Table 5.

(38) TABLE-US-00005 TABLE 5 Parts by weight Ingredient Ex. 26 Ex. 27 Ex. 28 Ex. 29 Acrylate- 55 55 50 50 terminated polyether DER 383 epoxy 36.67 36.67 33.33 33.33 resin Trimethylolpropane 22.96 15.308 25.05 20.88 tri(thiopropionate) (2,3-di((2- 5.00 10.01 0 0 mercaptoethyl) thio)1-propanethiol Fatty acid thiol 0 0 6.90 17.24 DBU catalyst 0.116 0.116 0.210 0.105 Properties Tensile Strength, 7825 (1135) 7720 (1120) 4675 (678) 6785 (984) kPa (psi) Elongation, % 107 104 201 174 Shore A hardness 84 85 76 78 Hard segment Tg, 38 41 28 32 ° C.

Examples 30-33

(39) An acrylate-terminated polyether having an equivalent weight per terminal acrylate group of 2496 is made in the general manner described in Example 1A, by capping a 6000 molecular weight 20% ethylene oxide capped poly(propylene oxide)triol with TDI to form an isocyanate-terminated prepolymer, and then capping the isocyanate groups with hydroxyethylacrylate.

(40) Elastomer Examples 30-33 are made from this acrylate-terminated polyether, using formulations as set forth in Table 6 below. In each case, the acrylate-terminated polyether is mixed with the epoxy resin in a high-speed laboratory mixture, and then a mixture of the thiol and catalyst are stirred in. A portion of the resulting reaction mixture is poured into a mold warmed to 50° C. The filled mold is then placed in an 50° C. oven overnight. A tack-free plaque is obtained. Tensile strength and elongation are as reported in Table 7.

(41) TABLE-US-00006 TABLE 6 Parts by weight Ingredient Ex. 30 Ex. 31 Ex. 32 Ex. 33 Acrylate-terminated 15 10 15 15 polyether DER 383 Epoxy Resin 9.59 6.39 15.0 15 Trimethylolpropane 3.94 5.26 5.93 11.87 tri(thiopropionate) Ethylene glycol 3.53 0 5.32 0 di(thiopropionate) DBU catalyst 0.059 0.036 0.088 0.082 Properties Tensile Str, kPa (psi) 2695 (391) 4315 (626) 5655 (820) 7620 (1105) Elongation, % 195 129 243 114 Shore A hardness 70 80 79 89

Examples 34-39

(42) An acrylate-terminated polyether having an equivalent weight per terminal acrylate group of 1968 is made in the general manner described in Example 1A, by capping a 4000 dalton poly(propylene oxide) diol with a 20% ethylene oxide cap with TDI to form an isocyanate-terminated prepolymer, and then capping the isocyanate groups with hydroxyethylacrylate.

(43) Elastomer Examples 34-39 are made from this acrylate-terminated polyether, using formulations as set forth in Table 7 below. In each case, the acrylate-terminated polyether is mixed with the epoxy resin and varying amounts of poly(propylene oxide) based diacrylate (as in Example 1) in a high-speed laboratory mixture, and then a mixture of the thiol and catalyst are stirred in. A portion of the resulting reaction mixture is poured into a mold warmed to 50° C. The filled mold is then placed in an 50° C. oven overnight. A tack-free plaque is obtained in each case. Tensile strength and elongation are as reported in Table 7.

(44) TABLE-US-00007 TABLE 7 Parts by weight Ex. 34 Ex. 35 Ex. 36 Ex. 37 Ex. 38 Ex. 39 Ingredient Acrylate- 0 12.5 25 33 50 100 terminated 20% EO polyether Example 1 100 87.5 75 67 50 0 (100% PO) DER 383 Epoxy 100 100 100 100 100 100 Resin Trimethylolpro- 80.6 80.6 80.6 80.6 80.6 80.6 pane tri(thiopro- pionate) DBU catalyst 0.3 0.3 0.3 0.3 0.3 0.3 Properties Tensile Str, 11.7 11.8 12.8 13.6 11.0 10.7 MPa (psi) (1694) (1716) (1858) (1978) (1591) (1559) Elongation, % 125 129 140 153 145 154 Shore A 89 89 90 90 hardness

(45) These systems are also curable at room temperature.

Examples 40-43

(46) Example 40 is prepared by mixing 6 grams of an acrylate-terminated polyether as prepared in Example 1B above, 4 grams of a low molecular weight polyene compound having the structure:

(47) ##STR00004##
and 10 grams of the D. E. R. 383 epoxy resin until homogeneous. Separately, 9.86 g trimethylolpropane tris(mercaptopropionate) is mixed with 37 mg of DBU. The mixture are combined and cured as described in Example 1.

(48) Example 41 is prepared in the same manner, except dimethylphenylphosphine is substituted for the DBU catalyst.

(49) Example 42 is prepared in the same manner as Example 40, except the amount of acrylate-terminated polyether is increased to 8 grams and the amount of the low molecular weight polyene compound is reduced to 2 grams.

(50) Example 43 is prepared in the same manner as Example 42, except dimethylphenylphosphine is substituted for the DBU catalyst.

(51) Results of physical property measurement are as indicated in Table 8.

(52) TABLE-US-00008 TABLE 8 Ex. 40 Ex. 41 Ex. 42 Ex. 43 Tensile Str, 12.1 (1761) 13.7 (1981) 12.2 (1773) 13.0 (1881) MPa (psi) Elongation, 161 165 151 176 % Tensile  147 (23,300)  170 (24600)  106 (15400)  162 (23500) Modulus, MPa (psi)

Examples 44 and 45

(53) An acrylate-terminated prepolymer is made and capped with hydroxyethylacrylate as described in Example 1A to form an ene-terminated polyether. This material is used to make Example 44 as described below.

(54) A ene-terminated polyether is made in the same fashion, except the polyether in this case is higher unsaturation (140 μeq/g), 4000 molecular weight poly(propylene oxide)diol. This material is used to make Example 45 as described below.

(55) To make each of Examples 44 and 45, 75 parts of the acrylate-terminated polyether and 50 parts of a 180 epoxy equivalent weight diglycidyl ether of bisphenol A (D. E. R. 383, from The Dow Chemical Company) are mixed on a high-speed laboratory mixture until homogeneous. Separately, 99.4 parts of 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol and 0.6 parts of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, Sigma Aldrich technical grade) are mixed. The acrylate-terminated prepolymer/epoxy resin mixture is then mixed with the thiol/catalyst mixture at a 6.45:1 weight ratio on the high speed mixer to produce a clear mixture. A portion of the mixture is poured into a mold warmed to 50° C. The filled mold is then placed in a 50° C. oven overnight. A tack-free plaque is obtained.

(56) Example 45 has a tensile strength of 2.7 MPa and an elongation to break of 154%. Example 44 has a tensile strength of 3.5 MPa and an elongation to break of 277%. The higher tensile strength of Example 44 compared to Example 45 is believed to be due to the use of the low unsaturation polyether polyol starting material. The lower quantity of monofunctional species in the polyether polyol, and hence in the ene-terminated polyether, is believed to reduce the occurrence of chain defects in the cured elastomer, which increases tensile strength and in this case increases elongation as well.