Chemical modification of polydienes, 3. Copolymers with polytetrahydrofuran by grafting‐from butadiene polymers

Polybutadienes of various microstructures and some butadiene copolymers were epoxidised to low levels (<1 mol‐%) with m‐chloroperbenzoic acid. The epoxide groups functioned as initiation sites for a “grafting‐from polymerization” of tetrahydrofuran (THF) catalysed by BF3. By conducting the reaction in dilute THF solution ([Monomeric unit] < 0,3 mol · 1−1) with a large excess of BF3 over epoxide groups, gel formation was avoided. The conversion of THF was less than 2% and the copolymers contained from 10 to 50% polytetrahydrofuran (PTHF) comprising graft chains of molar mass up to 43000 g · mol−1. The relative rate of grafting tended to decrease as the content of trans‐1,4 units in the backbone polymer increased, and, unusually, there was a small increase in volume during the graft copolymerization. The graft copolymers had a two‐phase morphology consisting of amorphous rubber and crystallites of PTHF. The latter function as physical crosslinks which break down above the melting point of PTHF, so that the materials behave as thermoplastic elastomers.