RELEASE OF DISORDERED XANTHAN OLIGOMERS UPON PARTIAL ACID-HYDROLYSIS OF DOUBLE-STRANDED XANTHAN

Double stranded xanthan was subjected to acid hydrolysis and was found to yield xanthans with partly truncated sidechains and decreasing mol ecular weight. The depolymerisation kinetics of xanthan deviated from that of dispersed single-stranded polymers by revealing an initial reg ime in which the xanthan preparation showed only minor decrease in mol ecular weight (referring to the intact polypentamer repeating unit). S ubsequently, a move rapid degradation occurred. In the latter phase an oligomeric fraction yielding an overall bimodal molecular weight dist ribution, also started to appear in the molecular weight distribution. This oligomeric fraction. was shown to have the same chemical composi tion as the vest of the sample. Experimental determination of the mass per unit length suggests that the partly hydrolysed xanthans also pos sessed the basic duplex structure of intact xanthan. These data can be accounted for by taking the cooperative nature of the dimerisation oc curring on pairing two xanthan chains into account in a Monte Carlo mo del for depolymerisation of duplex polymers.