POLYLACTONES .23. POLYMERIZATION OF RACEMIC AND MESO D,L-LACTIDE WITH VARIOUS ORGANOTIN CATALYSTS STEREOCHEMICAL ASPECTS
POLYLACTONES .23. POLYMERIZATION OF RACEMIC AND MESO D,L-LACTIDE WITH VARIOUS ORGANOTIN CATALYSTS STEREOCHEMICAL ASPECTS
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DOI：
10.1016/0032-3861(92)90459-a
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发表时间：
1992-01-01
期刊：
影响因子：
4.6
通讯作者：
TONNES, KU
中科院分区：
文献类型：
--
作者：
KRICHELDORF, HR;BOETTCHER, C;TONNES, KU
外消旋和中消旋D， l -丙交酯在90或120℃的二甲苯中或在120,150和180℃的散装条件下聚合。此外，在180℃下进行了外消旋D，L-丙交酯和L，L-丙交酯的批量共聚。以三丁基二甲氧基锡（Bu3SnOMe）、二丁基二甲氧基锡（Bu2Sn(OMe)2）和八酸锡（II）为引发剂。尽管产率很高，但两种氧化锡的分子量都很低。八酸锡（II）的分子量显著提高。基于四分体效应，用H-1和C-13核磁共振光谱分析了立体序列。讨论了信号分配。Bu3SnOMe和BU2Sn(OMe)2是有效的酯交换催化剂，即使在90℃下也会引起“背咬”降解。在所有由甲氧锡引发的聚合反应中，有两种趋势可以检测到：随着反应时间的延长和反应温度的升高，立体序列的随机性增加。相反，八酸锡（II）在低于或等于120℃时不会引起酯交换反应，甚至在180℃时，立体序列的随机化也很慢。
Racemic and meso D,L-lactide were polymerized at 90 or 120-degrees-C in xylylene or at 120, 150 and 180-degrees-C in bulk. Furthermore, copolymerizations of racemic D,L-lactide and L,L-lactide were conducted at 180-degrees-C in bulk. Tributyltin methoxide (Bu3SnOMe), dibutyltin dimethoxide (Bu2Sn(OMe)2) and Sn(II) octoate were used as initiators. Despite high yields only low molecular weights were obtained with both tin methoxides. Sn(II) octoate gave significantly higher molecular weights. The stereosequences were analysed by H-1 and C-13 n.m.r. spectroscopy on the basis of tetrad effects. The signal assignments are discussed. Bu3SnOMe and BU2Sn(OMe)2 are effective transesterification catalysts and cause 'back-biting' degradation even at 90-degrees-C. In all series of polymerizations initiated with tin methoxides two tendencies are detectable: increasing randomization of the stereosequence with increasing reaction time and with higher reaction temperatures. In contrast, Sn(II) octoate does not cause transesterification at less-than-or-equal-to 120-degrees-C and even at 180-degrees-C randomization of the stereosequences is slow.