NOVOZYM-435 CATALYZED RING-OPENING POLYMERIZATION OF A MACROCYCLIC CARBONATE

Abstract

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(T_m=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 e-caprolactone.The experimental data also indicated that the immobilized lipase Novozyme-435 could be repeatedly used with high activity.