Synthesis and characterization of polymers of 1,4‐hexadienes

Abstract

AbstractThe homopolymerization of trans‐1,4‐hexadiene, cis‐1,4‐hexadiene, and 5‐methyl‐1,4‐hexadiene was investigated with a variety of catalysts. During polymerization, 1,4‐hexadienes undergo concurrent isomerization reactions. The nature and extent of isomerization products are influenced by the monomer structure and polymerization conditions. Nuclear magnetic resonance (NMR) and infrared (IR) data show that poly(trans‐1,4‐hexadiene) and poly(cis‐1,4‐hexadiene) prepared with a Et3Al/α‐TiCl3/hexamethylphosphoric triamide catalyst system consist mainly of 1,2‐polymerization units arranged in a regular head‐to‐tail sequence. A 300‐MHz proton NMR spectrum shows that the trans‐hexadiene polymer is isotactic; it also may be the case for the cis‐hexadiene polymer. These polymers are the first examples of uncrosslinked ozone‐resistant rubbers containing pendant unsaturation on alternating carbon atoms of the saturated carbon‐carbon backbone. Polymerization of the 1,4‐hexadienes was also studied with VOCl3‐ and β‐TiCl3‐based catalysts. Microstructures of the resulting polymers are quite complicated due to significant loss of unsaturation, in contrast to those obtained with the α‐TiCl3‐based catalyst. In agreement with the literature, there was no discernible monomer isomerization with the VOCl3 catalyst system.