Thiol-cured elastomeric epoxy resins

Abstract

Elastomers are formed by curing a reaction mixture that includes an polyepoxide-terminated polyether having a linear or branched polyether chain that has a molecular weight of at least 2000, at least two epoxide groups that has an epoxide equivalent weight of at least 400 2) a curing agent containing at least one polythiol compound having at least two thiol groups and an equivalent weight per thiol group of up to 500, and 3) at least one base catalyst.

Claims

1. A process for forming a phase-segregated elastomeric polymer, a) forming a reaction mixture containing 1) at least one polyepoxide-terminated polyether having a linear or branched polyether chain that has a molecular weight of at least 2000 and an epoxide equivalent weight of at least 400, which polyepoxide-terminated polyether is formed by the reaction of a polyether that has epoxy-reactive groups and an average molecular weight of 4,000 to 8,000 with an epoxy resin, 2) a curing agent containing at least one polythiol compound having at least two thiol groups and an equivalent weight per thiol group of up to 500, 3) at least one base catalyst and 4) from 10 to 150 parts by weight, per 100 parts by weight of component 1), of an epoxy resin having an average of at least 1.5 epoxide groups per molecule and an epoxy equivalent weight of up to 250 and b) curing the reaction mixture at a temperature up to 60° C. to form the phase-segregated elastomeric polymer that exhibits multiple glass transition temperatures, one of which is −20° C. or lower.

2. The process of claim 1, wherein the epoxy resin 4) includes a polyglycidyl ether of a polyphenol.

3. The process of claim 2, wherein the epoxy resin 4) includes an aliphatic epoxy resin having an epoxide equivalent weight of up to 250.

4. The process of claim 3 wherein from 0.1 to 1.5 equivalents of thiol groups are provided per equivalent of epoxy groups.

5. The process of claim 3, wherein the reaction mixture further contains from 10 to 150 parts by weight, per 100 parts by weight of component 1), of 5) a polyene compound having at least two carbon-carbon double bonds capable of engaging in a thiol-ene reaction and which has a weight of up to 250 per such carbon-carbon double bond.

6. The process of claim 1, wherein the polyether is a poly(oxypropylene) homopolymer or a copolymer of 1,2-propylene oxide and ethylene oxide wherein the ethylene oxide constitutes less than 20 weight percent of the weight of the oxides.

7. The process of claim 1, wherein the reaction mixture is cured at ambient temperature.

8. The process of claim 1 wherein the polymeric elastomer has an elongation to break of at least 50% and a Shore A hardness of 60 to 95.

9. The process of claim 5 wherein the polymeric elastomer has an elongation to break of at least 50% and a Shore A hardness of 60 to 95.

Description

EXAMPLES 1-6

(1) A. Production of Epoxy-Terminated Prepolymer:

(2) 49.6 kg of a 180 equivalent weight diglycidyl ether of bisphenol A (DER™ 383 liquid epoxy resin, available from The Dow Chemical Company) are mixed with a 52.3 kg of a 5000 molecular weight amine-terminated glycerin-initiated poly(propyleneoxide) (Jeffamine™ T5000, available from Huntsman Corp., amine hydrogen equivalent weight=952 g/mol). The mixture is degassed, and heated at 125° C. under nitrogen for three hours. The resulting product is a viscous liquid having a viscosity of 90,000 cPs at 25° C. and an epoxy equivalent weight of 412 g/mol. The product is a mixture contains about 70% by weight of an epoxy-terminated polyether corresponding to the reaction product of the amine-terminated polyether with the epoxy resin, and about 30% by weight of unreacted liquid epoxy resin.

(3) B. Production of Phase-Segmented Elastomer

(4) To produce Example 1, 21.8 g of trimethylolpropane tris(3-mercaptopropionate), 7.3 g of (2,3-di((2-mercaptoethyl)thio)1-propanethiol and 0.33 moles of DBU catalyst per mole of thiol groups are mixed on a high-speed laboratory mixer. Separately, 53.0 g of the product produced in A above is mixed with 22.7 g of an epoxy blend (Airstone 780 E, from The Dow Chemical Company) on a high-speed laboratory mixer until homogenous. The thiol/catalyst mixture is then mixed with the epoxy resin mixture to produce a clear mixture and allowed to cure at room temperature. 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 about 160° C. is reached after about 10 minutes.

(5) Example 2 is prepared in the same manner, except the amount of DBU catalyst is reduced to 0.20 mole-%. Example 2 cures similarly to Example 1.

(6) Example 3 is prepared in the same manner, except the amount of DBU catalyst is reduced to 0.15 mole-%. Example 3 cures slightly more slowly than Examples 1 and 2, and the exotherm produces a slightly lower temperature.

(7) Example 4 is prepared in the same manner, except the amount of DBU catalyst is reduced to 0.05 mole-%. The peak exotherm temperature of about 135° C. is reached after about 65 minutes.

(8) Example 5 is prepared in the same manner, except the catalyst is 0.15 mole-% of 1,4-diazabicyclo[2.2.2]octane. The peak exotherm temperature of about 140° C. is reached after about 30 minutes.

(9) Example 6 is prepared in the same manner, except the catalyst is 0.05 mole-% of 1,4-diazabicyclo[2.2.2]octane. The peak exotherm temperature of about 120° C. is reached after about 80 minutes.

EXAMPLE 7

(10) To produce Example 7, 24.6 g of trimethylolpropane tris(3-mercaptopropionate) and 0.33 moles of DBU catalyst per mole of thiol groups are mixed on a high-speed laboratory blender. Separately, 53.0 g of the product produced as in Example 1A above is mixed with 22.7 g of an epoxy blend (Airstone 780 E, from The Dow Chemical Company) on a high-speed laboratory mixer until homogenous. The thiol/catalyst mixture is then mixed with the epoxy resin mixture to produce a clear mixture, poured into a mold and allowed to cure at 50° C.

(11) The cured plaque has a tensile strength of 10.5 MPa (about 1520 psi), an elongation at break of 76% (as measured per ASTM D1708), a tensile modulus of 91.2 MPa (about 13200 psi), and a Shore A hardness of 72. 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 −58° C. and a second one at about 37° C.

EXAMPLE 8

(12) To produce Example 8, 16.5 g of trimethylolpropane trimercaptopropionate and 0.33 moles of DBU catalyst per mole of thiol groups are mixed on a high-speed laboratory blender. Separately, a portion of the product produced in Example 1A above is blended with a 180 equivalent weight diglycidyl ether of bisphenol A and a diglycidyl ether of 1,4-butane diol at a weight ratio of 72.5:22.5:5.0 to from a blend having a viscosity of 30,000 cPs at 25° C. The epoxy resin mixture and the trimethyolpropane trimercaptopropionate/catalyst mixture are blended at room temperature at a ratio of 2:1, and cured at 50° C. to form a plaque. The cured plaque has a tensile strength of 9.65 MPa (about 1400 psi) and an elongation at break of 155% (as measured per ASTM D1708), a tensile modulus of 33.2 MPa (about 4820 psi), and a Shore A hardness of 88. 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 −58° C. and a second one at about 28° C.

EXAMPLE 9

(13) To produce Example 9, 15.2 g of trimethylolpropane tris(3-mercaptopropionate) and 0.33 moles of DBU catalyst per mole of thiol groups are mixed on a high-speed laboratory blender. Separately, 24.4 g of the product produced in Example 1A above is mixed with 10.4 g of an epoxy blend (Airstone 780 E, from The Dow Chemical Company) on a high-speed laboratory mixer until homogenous to from a blend having a viscosity of 31,000 cPs at 25° C. The trimethyolpropane trimercaptopropionate/catalyst mixture is combined at room temperature with the epoxy resin mixture, poured into a mold and allowed to cure at 50° C.

(14) The cured plaque has a tensile strength of 7.65 MPa (about 1110 psi), an elongation at break of 110% (as measured per ASTM D1708), a tensile modulus of 28.7 MPa (about 4160 psi), and a Shore A hardness of 86. 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 −55° C. and a second one at about 28° C.

EXAMPLE 10

(15) To produce Example 9, 10.0 g of trimethylolpropane tris(3-mercaptopropionate), 3.3 g of 1,2-Bis[(2-mercaptoethyl)thio]-3-mercaptopropane and 0.33 moles of DBU catalyst per mole of thiol groups are mixed on a high-speed laboratory blender. Separately, 24.4 g of the product produced in Example 1A above is mixed with 10.4 g of an epoxy blend (Airstone 780 E, from The Dow Chemical Company) on a high-speed laboratory mixer until homogenous to from a blend having a viscosity of 31,000 cPs at 25° C. The trimethyolpropane trimercaptopropionate/catalyst mixture is combined at room temperature with the epoxy resin mixture, poured into a mold and allowed to cure at 50° C.

(16) The cured plaque has a tensile strength of 7650 kPa (about 1110 psi), an elongation at break of 110% (as measured per ASTM D1708), a tensile modulus of 28680 kPa (about 4160 psi), and a Shore A hardness of 87.