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℃ 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℃

which was much lower than the melting point of (TeMC)2 (Tm=170～172℃).The result of kinetic studies of polymerization showed that Novozym-435-catalyzed polymerization of (TeMC)2 did not behave living characteristics reported for that of ε-caprolactone.The experimental data also indicated that the immobilized lipase Novozyme-435 could be repeatedly used with high activity.