Claims
- 1. An impact modifier for a thermoset polymer comprising a terepolymer formed by the reaction of an acrylamide monomer, a rubber formable monomer and a nitrile monomer in combination with a mercapto modifier wherein said acrylamide monomer comprises an N-(R-oxymethyl) acrylamide wherein R is selected from the group consisting of C.sub.3 to C.sub.22 alkyl, ether, aldehyde, ketone, amide, ester, carboxylic acid, phthalimide and imide other than phthalimide said rubber formable monomer is selected from the group consisting of isoprene, butadiene, alkyl esters of methacrylic acid and chloroprene and said nitrile monomer is selected from the group consisting of acrylonitrile and methacrylonitrile and wherein said mercapto modifier comprises a modifier selected from the group consisting of mercapto C.sub.3 -C.sub.10 alkyl acids and C.sub.1 -C.sub.10 alkyl ester derivatives thereof.
- 2. The composition claimed in claim 1 wherein said terpolymer comprises 65 to 75% rubber formable monomer, 20 to 30% nitrile monomer and 4 to 10% acrylamide monomer.
- 3. The composition claimed in claim 2 wherein said terpolymer has a number average molecular weight less than about 12,000.
SUMMARY OF THE INVENTION
This is a division of application Ser. No. 099,253, filed Sept. 21, 1987, now U.S. Pat. No. 4,812,521.
The usefulness of thermosetting polymers as matrices for reinforced structural composites is seriously limited by their brittleness and susceptibility to crack initiation and propagation. When an epoxy resin is employed as the matrix for a fiberglass reinforced composite, high concentration of internal cracking occurs during cyclic load testing. Once initiated such cracks readily propagate along the fibers in regions of high fiber density.
To inhibit or prevent internal cracking various modifiers have been added to resins. For a number of years thermoplastics such as polyesters and polymethylmethacrylate have been enhanced by the addition of low concentrations of elastomeric polymers as small discrete particles suspended throughout the resin matrix.
Subsequently epoxy resins have been modified by the inclusion of small particles of liquid, butadiene nitrile rubbers, primarily hydroxy, carboxy, amine and vinyl terminated polymers This work was initially conducted at MIT (see McGarry, F. J. and Sultan, J., "Toughening Mechanisms in Polyester Resins and Composites" R67-66 December 1967 and McGarry, F. J. and Willner, A., "Toughening of an Epoxy Resin by an Elastomeric Second Phase" R68-68 March 1968). This work was primarily conducted with the Hycar brand carboxy terminated butadiene nitrile rubbers (CTBN) and the Hycar CTBNX rubber.
Butadiene nitrile rubbers with carboxyl groups at both ends of the chain, butadiene nitrile rubbers with terminal carboxyl groups as well as intermediate pendent carboxyl groups and butadiene nitrile rubbers which have no carboxyl groups but unsaturated carbon to carbon bonds interspersed along the chain were tested for impact modification of epoxy resins. It was found that only the carboxyl terminated polymers and the butadiene nitrile rubbers with intermediate pendent carboxyl groups provided toughening. See McGarry and Willner, "Crack Toughened Epoxy Resin Formulations" papers presented at the ACS 155th meeting, April 1968 at page 512.
There are of course a wide range of liquid rubbers. As indicated not all of these function as impact modifiers. The noncarboxylated butadiene nitrile rubbers including hydroxy and amine terminated polymers apparently provide limited modifying effect. There are also many examples of hydroxy terminated butadiene nitrile liquid rubbers as for example shown in Siebert U.S. Pat. No. 3,551,471. This is presented by way of example. These have not been shown to be effective epoxy impact modifiers. It has been proposed that only liquid polymers with terminal reactive carboxyl groups provide impact modification.
Another liquid polymer is disclosed in Melchior U.S. Pat. No. 4,529,558 which is assigned to the assignee of the present invention. This patent along with various related patents discloses a liquid heat curable polymer formed from rubber monomers such as isoprene or butadiene, acrylonitrile monomer and a potential acid catalyzed cure site monomer, N-(R-oxymethyl)acrylamide. This is a random terpolymer. It lacks any reactive carboxyl group as well as uniformly positioned reactive terminal groups. It is disclosed that these polymers can be used for preparation of gaskets when coated on a substrate such as metal, paper, cloth, nylon or the like. It is intended to be a solventless liquid heat curable polymer.
The present invention is premised on the realization that the polymers of the type disclosed in Melchior U.S. Pat. No. 4,529,558 comprising a liquid rubber formed from N-(R oxymethyl) acrylamide, diene, and nitrile effectively impact modify epoxy and epoxy novolak thermoset resins.
The invention is further premised on the realization that further modification is imparted by an effective degree of self reaction of the dispersed rubbery polymer with an acid catalyst prior to cure of the thermoset resin.
Further, substantial improvement of impact modification is obtained where at least some of the acrylamide portion of the polymer includes an acid or ester moiety.
Other advantages of the present invention will be appreciated in light of the following detailed description.
US Referenced Citations (4)
Foreign Referenced Citations (4)
| Number |
Date |
Country |
| 0236183 |
Jul 1959 |
AUX |
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May 1984 |
EPX |
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| 1179252 |
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Divisions (1)
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Number |
Date |
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| Parent |
99253 |
Sep 1987 |
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Patent Grant
4939271
