The polymerization of 1,4-pentadiene to [3.3.1]bicyclo-linked chains

1, 4-Pentadiene has been polymerized by Ziegler-Natta catalysts to give amorphous polymers which are up to 64 wt.-% soluble. The polymers all have residual unsaturation which is substantially less than one double bond per mer, some as low as 0.1 double bond per mer. The polymerizations proceed by an unusual double inter-, double intramolecular cyclopolymerization mechanism leading to the formation of [3.3.1] bicyclic repeat units. Some main-chain (internal) unsaturation as well as pendant-group (external) unsaturation is observed. The latter results from incompletely cyclized 1,4-pentadiene units. The former is due to some concurrent isomerization of 1,4- to 1,3 pentadiene, which then copolymerizes with the 1,4 diene. The extent of isomerization varied with the catalyst system used. The soluble polymer fractions were brittle for internal unsaturations of less than about 0.05 double bond per mer and were viscous for higher values. The insoluble fractions were brittle and are believed to be lightly crosslinked.