Enzyme-catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures. (1) Such polymerizations may allow the polymer to retain functionality that would be destroyed under normal polymerization conditions. (2) The selectivity provided by enzyme catalysts may permit polymers, including optically active polymers, to be prepared that are either not accessible or accessible only with difficulty by other methods. (3) The characteristics of the enzyme and the mild polymerization conditions may permit formation of polymers having highly regular sizes and backborn structures. (4) There should be environmental advantages in using enzymes as polymerization catalysts. Because the polymers have been formed biologically, they should also be susceptible to biodegradation.
This study describes an enzyme catalyzed polycondensation to prepare a chiral (AA-BB)x polyesters of several repeat units. Polymerization of bis(2,2,2-trichloroethyl) glutarate (BB) with 1,4-butanediol using the enzyme porcine pancreatic lipase (PPL) as a catalyst is detailed. The polycondensation were carried out at ambient temperature. Consumption of the starting diol and diester progresses at different rate by the fact nearly all of the diol has been consumed, but almost 30% of diester is still present after 5hr. The biocatalytic activity of lipase from different sources and the effects of chain length and nature of diol were studied in above transesterification reaction. Bis(2,2,2-trichloroethyl) glutarate (BB) and 1,4-butanediol were best accepted as substrate by the lipase from porcine pancreatic. The reaction was also catalyzed to some extent by the lipase from Humicola lanuginos and psudomonas sp. There was no direct correlation between the hydrolytic activity and the transesterification activity of tested lipases. In the series of short-chain diols ($C_2-C_4$) the transesterification reaction with Bis(2,2,2-trichloroethyl) glutarate (BB) was fastest with 1,4-butanediol, although the differences were relatively small and the reaction was much slower with secondary alcohol than with primary alcohol. For the long-chain diols (PEG-300-PEG-1000) the reaction was fastest with PEG-400 and the slower the reaction rate, the longer the length diols except for PEG-400. With PEGs only the monoesterification product was obtained.
The effects of organic solvent and reaction temperature were also studied. PPL functioned well in relatively hydrophilic organic solvent such as THF, ether and acetonitrile. The reaction rate was accelerated as the reaction temperature was raised to 20-60℃ while Mn value of the reaction product was not affected by the reaction temperature. End group analysis by NMR provived Mn values of 1500-4000 daltons.
