Biodegradation of poly(vinyl alcohol) and vinyl alcohol block as biodegradable segment

The biodegradation of poly(vinyl alcohol) (PVA) and the vinyl alcohol block as a biodegradable segment was evaluated for the design of biodegradable water-soluble functional polymers using PVA-assimilating aerobic and anaerobic microbes. PVA having a number-average molecular weight <((M)over bar n)> between 90000 and 530 (corresponds to the vinyl alcohol heptamer of the PVA oligomer) was equally and substantially biodegraded by the aerobic microbes. No difference in the biodegradability of PVA was observed for molecular weights above the heptamer of the vinyl alcohol monomer units. The isotactic moieties of PVA were preferentially biodegraded compared to the atactic or syndiotactic moieties. That is, the biodegradability was increased with increasing isotactic content of the PVA. PVA having a <(M)over bar n> of 2200 and 14000 was also biodegraded by the anaerobic microbes. However, the anaerobic biodegradation rate was slower than that under aerobic conditions. Also, the lower molecular weight fractions of PVA tended to biodegrade more rapidly under anaerobic conditions. The minimum structure of the vinyl alcohol block, which is accepted as a substrate for PVA-assimilating microbes and PVA-dehydrogenase, is estimated to be an isotactic-type vinyl alcohol block having a chain length of 3 monomer units. A significant increase in the biodegradability of the poly(sodium carboxylate) containing vinyl alcohol blocks was observed for a vinyl alcohol block length of more than about 3.