SYNOPSISThe synthesis of a series of novel cyano-containing copolymers is described. Alternating copolymers of acrylonitrile with vinyl esters are obtained by increasing the electrophilic character of the nitrile monomers by complexation with zinc chloride. Copolymers of methyl and ethyl a-cyanoacrylates with vinyl esters are prepared using radical initiators in the presence of 7% acetic acid as inhibitor for anionic polymerization. The copolymers of methyl a-cyanoacrylate with the vinyl esters have Tg's above 14OoC. Methyl vinylidene cyanide ( MVCN ) copolymerizes spontaneously with para-substituted styrenes to yield copolymers with high inherent viscosities and high Tg ( 160°C) and the copolymer of MVCN with vinyl acetate is also synthesized. The pyroelectric constantsp for these polymers were measured and the values of p for the copolymers of vinyl acetate with methyl PJ-dicyanoacrylate, methyl a-cyanoacrylate, or MVCN were in the same range as the well-studied vinylidene cyanide /vinyl acetate copolymer. A higher concentration of dipoles generally results in higher T i s and higher pyroelectric coefficients. 0 1992 John Wiley & Sons, Inc.
As an all-fiberglass reinforcement is progressively replaced by graphite fiber, the longitudinal composite fracture stress and strain decrease rapidly for all loading modes except shear, accompanied by a substantial increase in the tensile and compressive stiffness. Conversely, upon introducing some fiberglass into a graphite composite, its strength declines in proportion to the decrease in graphite fiber content. The maximum torsional shear stress is approximately 8 ksi for all combinations of glass and graphite. Most of the transverse mechanical properties decrease linearly upon progressive replacement of the fiberglass by graphite. The transverse torsional shear properties are about 20 percent lower than the longitudinal ones.
The magnitude of the flexural modulus, which depends not only on the graphite content but even more so on the distance of the graphitic plies from the center plane of the laminate, may be calculated by means of the existing theory of bidirectional laminates. It is concluded that the large increase in composite stiffness upon addition of a small amount of oriented graphite fiber is the most salient characteristic of glass-graphite hybridization.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.