MOLECULAR-WEIGHT DISTRIBUTION AND MASS CHANGES DURING POLYAMIDE HYDROLYSIS

Samples of polyamide 6, 11 and 12 have been hydrolysed at various temp eratures ranging from 80 to 120 degrees C in water baths of pH ranging from 0 to 4. The polymer degradation was monitored by steric exclusio n chromatography (SEC), viscometry and gravimetry. SEC data indicate t hat the polydispersity of the polyamides tested does not increase duri ng ageing. This can be considered as proof of the homogeneity of the r eaction. Average molecular weight data from SEC or viscometry appear t o be consistent with a random chain scission process, however gravimet ry (at least in the case of relatively soft conditions, for instance p H greater than or equal to 4) indicates a high monomer yield. These ap parently contradictory results are tentatively explained by the equili brated character of hydrolysis. Acid-amine pairs resulting from hydrol ysis events would recombine easily when both belong to macromolecular fragments. When one fragment is the monomer or a low oligomer, it can escape easily from the cage and the corresponding recombination yield is decreased. The monomer extraction by water complicates the gravimet ric behaviour, especially in the most severe hydrolysis conditions. (C ) 1997 Elsevier Science Ltd. All rights reserved.