Cocrystallization in copolymers of α-olefins I—Copolymers of 4-methylpentene with linear α-olefins

Abstract

The helical chain conformations in homopolymers of isotactic olefins, branched and unbranched, are shortly discussed with a view to predicting the degree to which cocrystallization may occur in random copolymers due to isomorphism of monomer units, and particularly in relation to copolymers of 4-methylpentene with linear α-olefins, pentene, hexene, octene, decene and octadecene. In accordance with prediction, it is shown that copolymers with pentene and hexene show a high degree of isomorphism and cocrystallization. Copolymers with the higher α-olefins show increasing disruption of the poly-4-methylpentene crystallinity with side-chain length and comonomer content, but octene and decene units can enter the poly-4-methylpentene crystal lattice to some extent, while octadecene units do not. Degrees of crystallinity, lattice parameters and melting points have been measured, and crystal phases in pentene copolymers are discussed. Although the polymerization conditions were designed to give random copolymers, evidence is adduced to show that copoly-merization has taken place but not entirely randomly; chains of varying composition and degrees of blocking are undoubtedly present.