Theoretical prediction of weight loss and molecular weight during random chain scission degradation of polymers

Abstract The number-average molecular weight and weight loss of a polymer are predicted by considering that oligomeric substances are produced by random 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 the slower the rate of the decrease in the number-average molecular weight of the remaining polymer. When the weight change of poly(3-hydroxybutyrate- co -4-hydroxybutyrate) due to hydrolysis was monitored experimentally, 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 interpreted to be caused by the fragmentation rather than the dissolution of the oligomers. As the number of broken bonds increased, the weight fraction of the monomer due to degradation approached one, while that of the oligomers due to degeneration approached zero after reaching a maximum. The lower the degree of polymerization of the oligomers, the higher the number of broken bonds of the maximum weight fraction. © 1997 Elsevier Science Ltd.

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