Bulk polymerizations of ε-caprolactone (CL) were conducted at 130 °C, in which the structure and amount of initiator were varied. Polymerization induction periods were observed and attributed to slow heat transfer and to the type of alcohol used as initiator. Induction periods persisted until virtually complete consumption of both ethylene glycol (EG) and 1,3-propanediol (PD). 1-Butanol displayed no detectable induction. ¹H NMR suggested that induction was a result of strong and unique interactions between the diols and stannous octoate, which lead to the formation of more stable, less reactive stannous alkoxides compared to stannous alkoxides derived from the polymer chain end. Only after virtually all free diol was consumed did chain propagation commence at the normal rate. The rate of polymerization was insensitive to the [CL]/[EG] ratios chosen for this study. The results were consistent with a mechanism in which stannous alkoxide initiator is formed in situ via reaction between stannous octoate and alcohol, and stannous alkoxide chain ends are the actively propagating species.

中文翻译：

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辛酸亚锡催化ε-己内酯本体聚合的动力学及机理

ε-己内酯（CL）的本体聚合反应是在130°C下进行的，其中引发剂的结构和数量都发生了变化。观察到聚合诱导期，并且归因于缓慢的热传递和用作引发剂的醇的类型。诱导期一直持续到乙二醇（EG）和1,3-丙二醇（PD）几乎完全消耗为止。1-丁醇未显示出可检测的诱导。^1个1 H NMR表明，感应是二醇与辛酸亚锡之间强而独特的相互作用的结果，与衍生自聚合物链端的亚锡醇盐相比，后者导致形成了更稳定，反应性更低的亚锡醇盐。只有在消耗掉几乎所有的游离二醇之后，链增长才以正常速率开始。聚合速率对本研究选择的[CL] / [EG]比不敏感。该结果与通过辛酸亚锡和醇之间的反应在原位形成烷氧基亚锡引发剂并且烷氧基亚锡链末端是活性繁殖物种的机理相一致。