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首页> 外文期刊>Journal of Applied Polymer Science >Controlled and stereospecific polymerization of rac-lactide with a single-site ethyl aluminum and alcohol initiating system
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Controlled and stereospecific polymerization of rac-lactide with a single-site ethyl aluminum and alcohol initiating system

机译：用单中心乙基铝和醇引发体系控制外消旋乳酸的立体定向聚合

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A single-site ethyl aluminum complex, [2,2-diethyl-1,3-propylenebis(3,5-di-tert-butyl-salicylideneimi- nato)] ethyl aluminum (2), with a geminal diethyl substitutent on the diamino bridge was synthesized by the reaction of AlEt3 with 1 equiv of N,N'-(2,2-diethyl-1,3-propylene)bis(3,5-di-tert-butylsalicylideneimine). X-ray diffraction showed that complex 2 contained a five-coordinate aluminum atom with a distorted trigonal bipyramidal geometry in the solid state. H-1-NMR and C-13-NMR spectra indicated that the two conformational enantiomers of 2 tautomerized quickly on the NMR timescale in solution. In the presence of isopropyl alcohol, the ring-opening polymerization (ROP) of rac-lactide with complex 2 produced a crystalline stereoblock polylactide (PLA). The stereoblocks contained an average of 12 units (L = 12) of enantiomerically pure lactic acid. There was a linear relationship between the monomer conversion and number-average molecular weights of the polymer. An induction period was observed for the polymerization. The induction period increased with decreasing concentration of catalyst 2 and isopropyl alcohol. In the presence of poly(ethylene glycol) (PEG), a PLA/PEG/PLA stereocomplex was prepared directly by the ROP of rac-lactide with complex 2, which was confirmed by NMR, gel permeation chromatography, wide-angle X-ray diffraction, and differential scanning calorimetry. (c) 2005 Wiley Periodicals, Inc.
机译：单中心乙基铝配合物，[2,2-二乙基-1,3-丙烯双（3,5-二叔丁基-水杨基亚胺基）]乙基铝（2），在二氨基上具有双乙基取代基通过AlEt 3与1当量的N，N′-（2，2-二乙基-1，3-丙烯）双（3，5-二叔丁基水杨亚胺）的反应合成桥。 X射线衍射表明，配合物2含有五个配位的铝原子，其固态具有扭曲的三角双锥体几何形状。 H-1-NMR和C-13-NMR光谱表明，在溶液中的NMR时间尺度上，两个2的构象对映异构体快速互变异构。在异丙醇的存在下，rac-丙交酯与配合物2的开环聚合（ROP）产生结晶的立体嵌段聚丙交酯（PLA）。立体嵌段平均包含12个对映体纯乳酸（L = 12）。单体转化率与聚合物的数均分子量之间存在线性关系。观察到聚合的诱导期。诱导期随催化剂2和异丙醇浓度的降低而增加。在聚乙二醇（PEG）的存在下，通过外消旋丙交酯与复合物2的ROP直接制备PLA / PEG / PLA立体复合物，并通过NMR，凝胶渗透色谱法，广角X射线证实衍射和差示扫描量热法。 （c）2005年Wiley Periodicals，Inc.

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