Initiation of radical polymerization by peroxyacetates: Polymer end‐group analysis by electrospray ionization mass spectrometry
Initiation of radical polymerization by peroxyacetates: Polymer end‐group analysis by electrospray ionization mass spectrometry
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过氧乙酸酯引发自由基聚合：通过电喷雾电离质谱法进行聚合物端基分析
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发表时间：
2007
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通讯作者：
Philipp Vana
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作者：
M. Buback;H. Frauendorf;F. Günzler;Philipp Vana
采用电喷雾电离质谱（ESI-MS）对以过乙酸叔丁酯（TBPA）、过乙酸叔戊酯（TAPA）、过乙酸1，1，3，3-四甲基丁酯（TMBPA）和过乙酸1，1，2，2-四甲基丙酯（TMPPA）为引发剂的MMA自由基溶液聚合产物聚甲基丙烯酸甲酯（PMMA）的端基进行了分析。的类型和相对浓度的自由基的物种，实际上启动大分子的生长，被确定。在大多数情况下，这些物质不同于来自过氧乙酸酯热分解的初级自由基。傅里叶变换离子回旋共振质谱法（FT-ICR MS）用于明确的峰归属。甲基羰基氧基自由基，这是由所有过氧乙酸酯的分解形成的，被发现进行脱羧产生引发甲基自由基。TAPA和TMPPA衍生的烷氧基自由基主要发生β-断裂，TMBPA衍生的烷氧基自由基还发生1，5-氢转移反应。由TBPA产生的叔丁氧基自由基在分解成甲基自由基和丙酮之前经历显著的链转移反应。在使用苯作为相对惰性溶剂的情况下，叔丁氧基自由基表现出转移到单体，产生聚合物分子，其不携带任何引发剂衍生的端基。通过使用均三甲苯作为共溶剂，少量的星星聚合物通过叔丁氧基自由基从均三甲苯的三个单独的甲基基团的多个氢夺取而生成。这种端基和聚合物拓扑结构修饰的简单过程对于在技术过程中容易调节聚合物粘度可能是有吸引力的。© 2007 Wiley Periodicals，Inc.聚合物科学杂志A部分：聚合物化学45：2453-2467，2007
End-groups of poly(methyl methacrylate) from radical solution polymerization of MMA using tert-butyl peroxyacetate (TBPA), tert-amyl peroxyacetate (TAPA), 1,1,2,2- tetramethylpropyl peroxyacetate (TMPPA), and 1,1,3,3-tetramethylbutyl peroxyacetate (TMBPA) as the initiators were analyzed via electrospray ionization mass spectrometry (ESI-MS). The type and the relative concentration of the radical species, which actually initiate macromolecular growth, are determined. In the majority of cases, these species differ from the primary radicals from thermal decomposition of the peroxyacetates. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was applied for unambiguous peak assignment. The methylcarbonyloxyl radical, which is formed by the decomposition of all peroxyacetates, was found to undergo decarboxylation yielding an initiating methyl radical. TAPA- and TMPPA-derived alkoxyl radicals mainly show β-scission, TMBPA-derived alkoxyl radicals additionally undergo a 1,5-hydrogen-shift reaction. The tert-butoxyl radicals produced from TBPA undergo pronounced chain-transfer reaction prior to their decomposition into methyl radicals and acetone. In the case of using benzene as a relatively inert solvent, the tert-butoxyl radicals exhibit transfer to monomer yielding polymer molecules, which do not carry any initiator-derived end-groups. By using mesitylene as a cosolvent, small amounts of star polymer were generated via multiple hydrogen abstraction by tert-butoxyl radicals from the three individual methyl groups of mesitylene. This uncomplicated procedure of modification of end-group and polymer topology may be attractive for facile adjustment of polymer viscosity in technical processes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2453–2467, 2007