Controlled and stereoselective polymerization of lactide: kinetics, selectivity, and microstructures.
Controlled and stereoselective polymerization of lactide: kinetics, selectivity, and microstructures.
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DOI：
10.1021/ja0347585
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发表时间：
2003-08
影响因子：
15
通讯作者：
Z. Zhong;P. Dijkstra;J. Feijen
中科院分区：
文献类型：
--
作者：
Z. Zhong;P. Dijkstra;J. Feijen
合成了基于手性或外消旋环己基salen配体（Jacobsen配体）的手性异丙醇铝，并将其用于丙交酯在甲苯中70 ℃的立体选择性开环聚合。动力学，选择性的催化剂，和所获得的聚乳酸的微观结构，使用不同的组合的丙交酯对映体和催化剂，进行了测定。在所有情况下，得到了分子量可控、多分散性低和限定端基的聚交酯。聚合反应在单体和催化剂中均为一级反应。（R，R）-环己基salenAlO（i）（i）Pr [（R，R）-1]使l-丙交酯的聚合显著快于d-丙交酯，速率常数比k（l）/k（d）为约14。使用（R，R）-1的外消旋-丙交酯的聚合产生结晶聚合物，基于分离的聚合物的光学纯度，可以计算出高达50%转化率的结晶聚合物的选择性因子为约5.5。通过（R，R）-1聚合l-丙交酯/d-丙交酯（摩尔比：80/20）混合物，得到全同立构-无规立构嵌段共聚丙交酯，其高度结晶，T（m）=约155 ℃。应用外消旋-环己基salenAlO（i）Pr [rac-1]聚合外消旋-丙交酯产生具有高T（m）=约185 ℃和高结晶度的全同立构立构嵌段聚丙交酯。
Chiral aluminum isopropoxides based on enantiopure or racemic cyclohexylsalen ligand (Jacobsen ligand) have been prepared and employed for stereoelective/stereoselective ring-opening polymerization of lactide in toluene at 70 degrees C. The kinetics, selectivity of the catalysts, and microstructure of the obtained polylactides, using different combinations of lactide enantiomers and catalysts, were determined. In all cases, polylactides of controlled molecular weight, low polydispersity, and defined end groups were obtained. The polymerizations are first-order in both monomer(s) and catalyst. (R,R)-CyclohexylsalenAlO(i)()Pr [(R,R)-1] polymerizes l-lactide significantly faster than d-lactide with a rate constant ratio k(l)/k(d) of approximately 14. The polymerization of rac-lactide using (R,R)-1 yields crystalline polymers, for which a selectivity factor of approximately 5.5 could be calculated up to 50% conversion based on the optical purity of the isolated polymers. The polymerization of a l-lactide/d-lactide (molar ratio: 80/20) mixture by (R,R)-1 furnishes an isotactic-atactic block copolylactide, which is highly crystalline with a T(m) = approximately 155 degrees C. Polymerization of rac-lactide applying rac-cyclohexylsalenAlO(i)()Pr [rac-1] yields isotactic stereoblock polylactides with a high T(m) = approximately 185 degrees C and a high degree of crystallinity.