激进的
氢原子萃取
键裂
光化学
甲基丙烯酸甲酯
三重态
化学
电子顺磁共振
未成对电子
材料科学
分子
高分子化学
聚合物
核磁共振
聚合
有机化学
催化作用
物理
作者
Masayoshi Tabata,Hiroaki Yamakawa,Kenshi Takahashi,Junkichi Sohma
标识
DOI:10.1016/0141-3910(79)90025-9
摘要
Mechanisms of the conversion of poly(methyl methacrylate) (PMMA) radicals produced by ball-milling have been investigated by means of ESR. The spectrum observed after a short milling time (0·1 h) at 77 K in vacuum was resolved into the three components, a triplet, a nonet and a doublet. The nonet, the triplet and the doublet are ascribed to the three kinds of radical: respectively. On the other hand, it was found that the spectrum after milling for more than 18 h at 77 K in a vacuum consisted of the nonet and the doublet, which had been converted from the triplet. The conversion of the triplet to the doublet during long milling suggests inter- and/or intra-hydrogen abstraction by the radical responsible for the triplet. The doublet observed after milling for longer than 18 h did not change its line-shape up to 263 K but on further warming to 273 K for 0·1 h the spectrum changed to give a triplet component. This reproduction of the triplet was interpretated in terms of β-bond scission to the unpaired electron of the radical (C), due to the thermal treatment. The bond scission was confirmed by the observed decrease in the molecular weight after the heat treatment. The radical (B) formed by the β-scission abstracts the hydrogen in the PMMA parent molecule to produce a radical of the species (C). This cyclic reaction leads to a self-degradation.
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