Effect of asymmetric centers on free radical polymerization and the properties of polymers: Methacrylyl alanine, methacrylyl glutamic acid, acrylyl glutamic acid, and their polymers
Effect of asymmetric centers on free radical polymerization and the properties of polymers: Methacrylyl alanine, methacrylyl glutamic acid, acrylyl glutamic acid, and their polymers
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不对称中心对自由基聚合及聚合物性能的影响：甲基丙烯酰丙氨酸、甲基丙烯酰谷氨酸、丙烯酰谷氨酸及其聚合物
DOI：
10.1002/pol.1961.1205416014
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发表时间：
1961
影响因子：
3.4
通讯作者：
H. Morawetz
中科院分区：
文献类型：
--
作者：
R. K. Kulkarni;H. Morawetz
甲基丙烯酰基-D-丙氨酸、甲基丙烯酰基-L-谷氨酸和丙烯酰基-L-谷氨酸与它们的对映体在二氧六环、0.1N盐酸水溶液和水中均聚或共聚，单体的中和度为90%。光学异构体的均聚和外消旋混合物的共聚在90%的中和度下以相同的速率进行，甲基丙烯丙氨酸在0.1NHCl和正丁醇中进行，而外消旋单体在0.1NHCl中的聚合速度略慢于纯光学异构体。均聚物在水中的光学活性随聚合介质的不同而不同，可能是由于立体调控程度的不同所致。当L含量为85%，D异构体含量为15%时，得到的共聚物的光学活性大多低于L均聚物的70%，这表明生长的链自由基偏向于单体单元空间构型的变化。并与胡椒-L-丙氨酸、胡椒-L-谷氨酸和异丁酰基-L-谷氨酸的光学活性随电离度的变化进行了比较。聚(甲基丙烯酰基-D-丙氨酸)的行为与其类似物相似，但甲基丙烯酰基和丙烯酰谷氨酸聚合物的旋光活性变化遵循与其类似物完全不同的复杂模式。结果的解释是基于这样的假设：(1)在聚合物中，本质上酸性较弱的γ羧基首先电离，因为它们的电离导致比α-羧基电离低的电荷密度；(2)聚合物主链的延伸通过改变侧链中的构象分布来影响旋光活性。人们认为，在所研究的情况下，螺旋的形成对聚合物和其类似物的旋光活性之间的差异没有显著的贡献。
Methacrylyl-D-alanine, methacrylyl-L-glutamic acid, and acrylyl-L-glutamic acid were homopolymerized or copolymerized with their enantiomorphs in dioxane, aqueous 0.1N HCl, and in water at 90% neutralization of the monomer. The homopolymerization of the optical isomer and copolymerization of racemic mixtures proceeded at identical rates for the first two monomers at 90% neutralization and for methacrylalanine in 0.1N HCl and in butanol, while with methacrylyl glutamic acid in 0.1N HCl the racemic monomer polymerized slightly more slowly than the pure optical isomer. The optical activities of the homopolymers in water varied with the polymerization medium, probably because of differences in the degree of stereoregulation. Optical activities of copolymers prepared from a mixture of the enantiomorphic monomers containing 85% of L and 15% of D isomer were mostly lower than 70% of that of the L homopolymer, which suggests that the growing chain radical has a bias toward an alternation of the steric configurations of the monomer units. Changes in the optical activities of the homopolymers with degree of ionization were compared with the behavior of pivalyl-L-alanine, pivalyl-L-glutamic acid, and isobutyryl-L-glutamic acid. Poly(methacrylyl-D-alanine) behaved in a manner similar to that of its analogue, but the changes in the optical activities of the methacrylyl- and acrylyl glutamic acid polymers followed a complex pattern quite different from that of their analogues. The results were interpreted on the assumption that (1) in the polymer the intrinsically more weakly acidic γ carboxyls ionize first since their ionization leads to a lower charge density than the ionization of α-carboxyl groups and (2) the extension of the polymer backbone affects the optical activity by modifying the conformational distribution in the side chains. It is not believed that, in the cases investigated, helix formation makes an appreciable contribution to the difference between the optical activities of the polymer and their analogues.