Thermal rearrangements in polypentenamer and polyoctenamer

Experiments were conducted to show that polypentenamer and polyoctenamer, in common with 1,4-polybutadiene, undergo anaerobic thermal cis-trans isomerization at temperatures as low as 200 degrees C. Their activation energies for isomerization are comparable to that of polybutadiene. The relative rate constants are found to decrease in the order: polybutadiene, polypentenamer, polyoctenamer. When heated in a vacuum at 200 to 270 degrees C, polypentenamer exhibits a loss of double bonds. This disappearance of unsaturation has no counterpart in polybutadiene or polyoctenamer. In polypentenamer, a mechanism for a thermally-induced ring closure that is different from the one shown for the cyclization-depolymerization of various unsaturated polymers is evident. The cyclization-depolymerization process does cause a loss of double bonds in polybutadiene and polyoctenamer at temperatures greater than or equal to 275 degrees C.