BLOCK AND GRAFT-COPOLYMERS OF PIVALOLACTONE .4. TRIBLOCK AND BLOCK-GRAFT COPOLYMERS FROM PIVALOLACTONE AND ISOPRENE

Poly(pivalolactone-fc-isoprene-fe-pivalolactone) triblock copolymers and poly[(pivalolactoneb-isoprene-b-pivalolactone)-g-pivalolactone] block-graft copolymers have been synthesized by attaching poly(pivalolactone) segments to polyisoprenes. The triblock copolymers were made by reaction of, - dilithio-cis-l, 4-polyisoprene with carbon dioxide, conversion of the resulting lithium carboxylates to tetrabutylammonium salts, and use of salts to initiate polymerization of pivalolactone. For the block-graft copolymers, the dilithiopolyisoprene was first reacted with s-BuLi in the presence of tetramethylethylenediamines to introduce lithio sites randomly along the chain by metalation. The metalated polymer was then carboxylated followed by conversion of lithium carboxylates to tetrabutylammonium salts and use of the salts to initiate polymerization of pivalolactone. Both types of polymers were very strong, especially after orientation by drawing, and are highly resilient thermoplastic elastomers. Strength is ascribed to apparent “cross-linking” through crystalline domains of the poly(pivalolactone) segments, which form a separate phase in the polyisoprene major phase. The block-graft polymers have been spun into elastic fibers, which, after orientation, have shown resistance to stress decay equal to that of sulfur-cured natural rubber. From these results, it is concluded that the apparent “cross-links” formed by crystalline poly(pivalolactone) are just as effective as chemical cross-links. © 1979, American Chemical Society. All rights reserved.