醇铁化合物引发丙交酯开环聚合的研究

分别以乙醇铁、正丙醇铁、异丙醇铁、正丁醇铁为引发剂进行D,L-丙交酯和L-丙交酯的本体开环聚合,研究了在130℃的聚合温度下引发剂用量和聚合时间对聚合反应的影响.结果表明这些醇铁化合物对丙交酯开环聚合都有较好的引发作用;聚合36h,单体转化率可达90%以上.单体转化率在引发剂/单体摩尔比为1/1000时最高,然后随引发剂用量增加和聚合时间延长而降低.乙醇铁表现出最高的引发活性,聚合产物的相对粘均分子量最高可达7·28×104聚(D,L-丙交酯)]和19·00×104聚(L-丙交酯)].醇盐配体对聚合产物的分子量和分子量分布影响显著,随醇铁配体体积增大,聚合产物的分子量逐渐降低,分子量分布也逐渐加宽.1H和13C-NMR分析表明醇铁对L-丙交酯的开环聚合没有发生消旋化,对D,L-丙交酯的开环聚合有一定的等规加成选择性.MALDI-TOF MS分析指出D,L-丙交酯在开环聚合过程中发生了分子间的酯交换反应,用13C-NMR评价了各醇铁引发体系在聚合过程中的酯交换程度.但基于谱峰分辨原因,醇铁配体对立构加成选择性和酯交换的影响的规律性不明显.

FERRIC ALKOXIDES-INITIATED RING-OPENING POLYMERIZATION OF LACTIDES

Ferric ethoxide,ferric n-propoxide,ferric iso-propoxide and ferric n-butoxide were used as initiators respectively for bulk ring-opening polymerization of lactides.The effects of initiator content and polymerization time on the polymerization were investigated.It was showed that these ferric alkoxides were efficient initiators for the ring-opening polymerization of lactides with higher than 90% of monomer conversions polymerized at 130℃ for 36 h.Maximum molecular weights were achieved at 1/1000 of initiator/monomer mole ratio for the four ferric alkoxides and then decreased gradually with increasing the amount of initiator and prolonging polymerization time.Poly(D,L-lactide) and poly(L-lactide) with the maxium viscosity-arerage molecular weights (M_v) of 7.28×10~4 and 19.00×10~4 respectively were synthesized by using ferric ethoxide as initiator.It was found that the ligands of the ferric alkoxides had significant influence on the molecular weight and molecular weigth distribution of the polymerization products.With increasing the volume of the ligands of the ferric alkoxides,the molecular weight decreased and the molecular weight distribution broadened. ~1H and ~13 C-NMR analyses indicated that the ferric alkoxides studied here had no racemization on the ring-opening polymerization of L-lactide,but exhibited isotactic stereoselectivity addition on the ring-opening polymerization of D,L-lactide.Intermolecular tranesterification took place during polymerization of D,L-lactide for the four ferric alkoxides as evidenced by the results of MALDI-TOF MS analysis, and quantitative evaluations by ~13 C-NMR were made for the four initiation systems.However,no regularity of ligands of the ferric alkoxieds on both of isotactic stereoselectivity addition and intermolecular tranesterification was found due to incomplete resolution of the ~13 C-NMR spectra.