THERMAL REARRANGEMENTS OF POLYBUTADIENES WITH DIFFERENT VINYL CONTENTS

In the reported experiments, a study was made of the loss of double bonds in equibinary (1,4-1,2) polybutadiene (EB) and in polybutadienes with 30% 1,2, 70% 1,4 (FI), and 10% 1,2, 90% 1,4 (DI) double-bond content, when heated in vacuum under nonpyrolytic conditions (temperature range 220-280 degree C). These polymers were found to undergo second-order loss of 1,2 unsaturation with similar activation energies (E//a equals 34. 0 plus or minus 3 kcal/mole), by analogy to the previously reported thermally induced loss of double bonds in 1,2-polybutadiene (VB) (E//a equals 33. 6 plus or minus 3 kcal/mole). The loss of 1,2 double bonds in the various polybutadienes with different vinyl contents is accompanied by substantial methyl production, ranging from about one methyl group formed for every 4-5 vinyl units lost in VB, to one methyl for every two vinyls lost in EB, and to almost one methyl for each vinyl lost in DI or CB. Mechanisms are proposed for the thermally induced loss of 1,2 and 1,4 unsaturation in various polybutadienes and for the accompanying methyl production.