THEORETICAL PREDICTION OF WEIGHT-LOSS AND MOLECULAR-WEIGHT DURING RANDOM CHAIN SCISSION DEGRADATION OF POLYMERS

The number-average molecular weight and weight loss of a polymer are p redicted by considering that oligomeric substances are produced by ran dom chain scission degradation and they are removed upon being formed. Model calculation shows that the higher the degree of polymerization of the extractable oligomers, the faster the rate of weight loss and t he slower the rate of the decrease in the number-average molecular wei ght of the remaining polymer. When the weight change of poly(3-hydroxy butyrate-co-4-hydroxybutyrate) due to hydrolysis was monitored experim entally, it was found to be consistent with the theoretical prediction , only if the oligomers, whose degree of polymerization was less than 60, were dissolved. The observed weight loss of the polymer was interp reted to be caused by the fragmentation rather than the dissolution of the oligomers. As the number of broken bonds increased, the weight fr action of the monomer due to degradation approached one, while that of the oligomers due to degeneration approached zero after reaching a ma ximum. The lower the degree of polymerization of the oligomers, the hi gher the number of broken bonds of the maximum weight fraction. (C) 19 97 Elsevier Science Ltd.