STUDIES ON POLYESTER ELASTOMER .2. THERMAL-STABILITY OF POLYESTER POLYESTER BLOCK POLYMER

Block polymers were prepared from the reaction of epsilon-caprolactone (epsilon-CL) with poly(1,4-butylene terephtalate) (PBT), and the change in their blockcharacter in molten state was studied. It was found that the decrease in the melting point was small on treatment at 235-degrees-C, whereas that was very large at 250-degrees-C, which shows that the randomization seems not to proceed below the equilibrium temperature. From the polymer composition and the average chain length of the block polymers, it was assumed that their soft segments would have been decomposed, and thus the content of soft segments and their average chain length sharply decreased. The activation energy of the ester exchange reaction between hard and soft segments was estimated as 66.55 kcal/mol. The polymers were stable enough during the treatment for 3 b at 230-degrees-C. However, they showed a sharp decrease in viscosity when treated at 250-degrees-C for over 90 min. Long term thermal stability of the polymers under a nitrogen atmosphere was superior to that of polylactones which were not blocked at both end groups in terms of both weight loss and gel formation.