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Organocatalytic Cationic Ring-Opening Polymerization of a Cyclic Hemiacetal Ester

阳离子聚合 聚合 化学 摩尔质量 单体 高分子化学 开环聚合 本体聚合 产量(工程) 催化作用 有机化学 聚合物 自由基聚合 材料科学 冶金
作者
Angelika E. Neitzel,Thomas J. Haversang,Marc A. Hillmyer
出处
期刊:Industrial & Engineering Chemistry Research [American Chemical Society]
卷期号:55 (45): 11747-11755 被引量:35
标识
DOI:10.1021/acs.iecr.6b03114
摘要

We report the bulk cationic ring-opening polymerization of renewably sourced 2-methyl-1,3-dioxan-4-one (MDO) to yield a polyester with hydrolytically and thermally sensitive linkages that facilitate degradation. Neat monomer was successfully polymerized using a variety of protic acids as catalysts. We discovered that, with these catalysts, the cationic polymerization of MDO proceeds via two distinct mechanistic routes, namely, the activated monomer (AM) and active chain-end (ACE) mechanisms. The kinetics of these competing mechanistic avenues were investigated by employing diphenylphosphoric acid (DPP) with or without an alcohol initiator. Without an exogenous initiator, the polymerization propagates via a dioxacarbenium ion that rapidly adds more MDO to produce high-molar-mass poly(2-methyl-1,3-dioxan-4-one) (PMDO). However, we found no clear relationship between [MDO]0/[protic acid]0 and resultant molar mass, suggesting that the ACE mechanism is not well-controlled. This conclusion was further supported by the production of cyclic PMDO arising from unimolecular backbiting reactions as the system approached equilibrium. With an exogenous alcohol initiator, the polymerization proceeds primarily via an AM mechanism and affords a mixture of linear PMDO and a small amount of macrocyclics derived from the competing ACE mechanism. Consistent with this interpretation of competing mechanisms, a linear relationship between theoretical and observed molar mass was observed when the initial ratio of monomer to added initiator was <80.
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