Initiation of free‐radical polymerization by peroxypivalates studied by electrospray ionization mass spectrometry
Initiation of free‐radical polymerization by peroxypivalates studied by electrospray ionization mass spectrometry
复制标题
电喷雾电离质谱研究过氧化新戊酸酯引发自由基聚合
DOI：
10.1002/pola.20264
复制
发表时间：
2004
期刊：
影响因子：
--
通讯作者：
Philipp Vana
中科院分区：
文献类型：
--
作者：
M. Buback;H. Frauendorf;Philipp Vana
通过使用电喷雾电离质量进行聚合物端基分析，研究了过氧化新戊酸叔丁酯 (TBPP)、过氧化新戊酸叔戊酯 (TAPP)、过氧化新戊酸 1,1,3,3-四甲基丁基过氧化新戊酸酯 (TMBPP) 或过氧化新戊酸 1,1,2,2-四甲基丙酯 (TMPPP) 在 90 °C 的甲苯溶液中引发甲基丙烯酸甲酯的自由基聚合光谱测定（ESI-MS）。结论性的峰分配允许测量在这些过氧化新戊酸盐热分解后实际引发大分子生长的片段的类型和浓度。发现新戊酰氧基部分经历瞬时脱羧，产生引发叔丁基。另一方面，烷氧基部分可以通过β-断裂反应生成不同类型的碳中心自由基（与酮一起），或者可以进行1,5-H-转移反应，通过该反应将氧中心自由基转化为碳中心羟基自由基。这种氢转移反应是在 TMBPP 的情况下发现的。令人惊讶的是，没有发现引发烷氧基自由基的证据，即使在通过 TBPP 引发的情况下也没有发现，其中中间体叔丁氧基自由基与溶剂甲苯进行快速链转移反应。
Initiation by tert-butyl peroxypivalate (TBPP), tert-amyl peroxypivalate (TAPP), 1,1,3,3-tetramethylbutyl peroxypivalate (TMBPP), or 1,1,2,2-tetramethylpropyl peroxypivalate (TMPPP) of radical polymerization of methyl methacrylate in toluene solution at 90 °C was studied via polymer end-group analysis using electrospray ionization mass spectrometry (ESI-MS). Conclusive peak assignments allowed for measuring the type and concentration of the fragments that actually initiate macromolecular growth after thermal decomposition of these peroxypivalates. It was found that the pivaloyloxy radical moiety undergoes instantaneous decarboxylation to yield an initiating tert-butyl radical. The alkoxy radical moiety, on the other hand, may generate, via β-scission reaction, different types of carbon-centered radicals (together with a ketone) or may undergo a 1,5-H-shift reaction, by which reaction an oxygen-centered radical is transformed into a carbon-centered hydroxy radical. This hydrogen shift reaction was found in case of TMBPP. Surprisingly, no evidence for initiating alkoxy radicals could be found, not even in case of initiation by TBPP, where the intermediate tert-butoxy radical undergoes a rapid chain-transfer reaction with the solvent toluene.