CONFIGURATIONAL STRUCTURES OF LACTIC-ACID STEREOCOPOLYMERS AS DETERMINED BY C-13-LABELED (H-1)-NMR
CONFIGURATIONAL STRUCTURES OF LACTIC-ACID STEREOCOPOLYMERS AS DETERMINED BY C-13-LABELED (H-1)-NMR
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DOI：
10.1016/0032-3861(83)90080-0
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发表时间：
1983-01-01
期刊：
影响因子：
4.6
通讯作者：
GRANGER, P
中科院分区：
文献类型：
--
作者：
CHABOT, F;VERT, M;GRANGER, P
调查了13C{1H}n.m.r。用不同的方法得到了一系列聚乳酸立体聚合物的光谱，即由锌粉引发的l-、RAC-和中位丙交酯的开环聚合，或不同比例的l-雄丙交酯的共聚，或L-乳酸的缩合聚合。用分辨率增强技术解决了由羰基碳原子的立体敏感性引起的共振。根据构型序列讨论了由此得到的精细结构。根据伯努利统计假设重复单元的单次相加和成对相加，将峰值强度与理论立体序列分布进行了比较。三联体、四联体和五联体立体序列的模型均与实验线的面积不符。结果表明，由于熔体中酯键的酯交换作用，聚乳酸中的立体序列发生了重新分布。通过丙交酯开环聚合得到的聚合物中的最终立体序列分布与成对加成机理和酯交换反应引起的重分布有关。
Investigations are made of the13C{1H} n.m.r. spectra of a series of poly(lactic acid) stereocopolymers obtained by different means, i.e. ring-opening polymerization ofl-,rac- andmeso-lactides initiated by powdered Zn, or copolymerization ofl- andrac-lactides in different proportions, or condensation polymerization ofrac-lactic acid. Resonances arising from the stereosensitivity of the carbonyl carbon atoms have been resolved using the resolution enhancement technique. The fine structures thus obtained are discussed in terms of configurational sequences. Comparison is made of the peak intensities with theoretical stereosequence distributions obtained when assuming single and pair additions of repeating units according to the Bernoullian statistics. Neither of the models for triad, tetrad and pentad stereosequences agrees with the area of the experimental lines. It is shown that redistribution of stereosequences in poly(lactic acid) occurs because oftransesterification at the ester bonds in the melt. The final stereosequence distribution in the polymers obtained by ring-opening polymerization of lactides is discussed in relation to the pair-addition mechanism and to the redistribution due totransesterification reactions.