大环碳酸酯的Novozym-435酶促开环聚合

研究了14元环的碳酸丁二酯二聚体在固定化脂肪酶Novozym-435催化下的开环聚合反应制备聚碳酸丁二酯.聚合在常压,75℃的甲苯溶液中进行,反应条件温和.详细探讨了反应条件诸如单体浓度,酶浓度对于聚合的影响.结果显示Novozym-435具有与异辛酸亚锡可比拟的高催化活性,同时可以回收重复使用.聚合动力学研究表明碳酸丁二酯的酶促甲苯溶液开环聚合和环状内酯的酶促甲苯溶液聚合有所不同,没有表现出活性聚合的特征.

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℃ 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 ε-caprolactone.The experimental data also indicated that the immobilized lipase Novozyme-435 could be repeatedly used with high activity.