Controlling Polymer Composition in Organocatalyzed Photoredox Radical Ring-Opening Polymerization of Vinylcyclopropanes
Controlling Polymer Composition in Organocatalyzed Photoredox Radical Ring-Opening Polymerization of Vinylcyclopropanes
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DOI：
10.1021/jacs.9b07230
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发表时间：
2019-08-21
影响因子：
15
通讯作者：
Miyake, Garret M.
中科院分区：
文献类型：
--
作者：
Chen, Dian-Feng;Boyle, Bret M.;Miyake, Garret M.
尽管自由基聚合是合成组成和性质不同的聚合物的最常用方法之一，但自由基加成的内在反应性和选择性挑战了控制聚合过程和制备具有特定微观结构的聚合物的能力。乙烯基环丙烷(VCP)可以通过自由基开环聚合生成具有线型(L)或环型(C)重复单元的聚合物，为控制聚合物结构和改变聚合物性能提供了机会。在这里，我们首次报道了各种官能化VCP单体的有机催化光氧化还原自由基开环聚合，其中实现了高单体转化率和时空可控，以制备具有可预测的相对分子质量和低分散性的聚(VCP)。通过控制聚合浓度和温度，实现了L或c含量的可调，从而可以进一步研究与这两种不同组成相关的热和粘弹性材料性能。出乎意料的是，光氧化还原催化实现了后聚合修饰，将L含量转化为c含量。实验和计算相结合的研究表明，环戊烷和环己烷重复单元可能形成分子内自由基环化途径。
Although radical polymerizations are among the most prevalent methodologies for the synthesis of polymers with diverse compositions and properties, the intrinsic reactivity and selectivity of radical addition challenge the ability to impart control over the polymerization propagation and produce polymers with defined microstructure. Vinylcyclopropanes (VCPs) can be polymerized through radical ring-opening polymerization to produce polymers possessing linear (l) or cyclic (c) repeat units, providing the opportunity to control polymer structure and modify the polymer properties. Herein, we report the first organocatalyzed photoredox radical ring-opening polymerization of a variety of functionalized VCP monomers, where high monomer conversions and spatial and temporal control were achieved to produce poly(VCPs) with predictable molecular weight and low dispersity. Through manipulating polymerization concentration and temperature, tunable l or c content was realized, allowing further investigation of thermal and viscoelastic materials properties associated with these two distinct compositions. Unexpectedly, the photoredox catalysis enables a postpolymerization modification that converts l content into the c content. Combined experimental and computational studies suggested an intramolecular radical cyclization pathway, where cyclopentane and cyclohexane repeat units are likely formed.