Novozym-435 catalyzed ring-opening polymerization of a macrocyclic carbonate

Biodegradable aliphatic polycarbonates have attracted great attentions as an important kind of biomedical materials. In this study metal-free ring-opening polymerization of 14-membered dimmer, cyclobis (tetramethylene carbonate) [(TeMC)(2)] was attempted at 75 degrees C in toluene and in the presence of porcine pancreas lipase (PPL), candida rugosa lipase (Lipase AYS) or immobilized lipase Novozyme-435 to afford poly(tetramethylene carbonate). It was found that Novozyme-435 exhibited comparatively high catalytic activity with Sn(Oct)(2) while PPL and AYS exhibited no obvious activity to the polymerization of (TeMC)(2) with respect to the conversion and molecular weight. Optimal reaction conditions including monomer concentration and Novozyme-435 concentration were explored in an effort to positively influence the Outcome of the ring-opening polymerization. The polymerization rate was markedly increased with increasing the enzyme concentration A region exists around toluene/(TeMC)(2) (mL/g) ratio of 4:1 where Novozyme-435-catalyzed polymerizations could result in higher molecular weight and monomer conversion. It is interesting to point out that in the absence of toluene, the solid-phase polymerization could also occur at predetermined temperature of 75 degrees C, which was much lower than the melting point of (TeMC)(2) (T-m = 170 similar to 172 degrees C). The result of kinetic studies of polymerization showed that Novozym-435-catalyzed polymerization of (TeMC), did not behave living characteristics reported for that of E-caprolactone. The experimental data also indicated that the immobilized lipase Novozyme-435 could be repeatedly used with high activity.