Control of Grafting Density and Distribution in Graft Polymers by Living Ring-Opening Metathesis. Copolymerization
Control of Grafting Density and Distribution in Graft Polymers by Living Ring-Opening Metathesis. Copolymerization
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DOI：
10.1021/jacs.7b00791
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发表时间：
2017-03-15
影响因子：
15
通讯作者：
Grubbs, Robert H.
中科院分区：
文献类型：
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作者：
Lin, Tzu-Pin;Chang, Alice B.;Grubbs, Robert H.
对聚合物序列和结构的控制对于理解结构性质关系和设计功能材料都是至关重要的。为了追求这些目标，我们开发了一种新的合成方法，可以通过活性开环复分解聚合(ROMP)轻松地控制接枝聚合物中的接枝密度和分布。在第三代复分解催化剂(G3)的作用下，设计了一种内、外去甲基降冰片烯基双芳酸酯(二甲基二甲醚、二乙基二乙基、二正丁基DBE)与降冰片烯官能化的聚苯乙烯(PS)、聚乳酸(PLA)或聚二甲基硅氧烷(PDMS)大单体的共聚反应。小分子双酯作为稀释剂，增加了接枝侧链之间的平均距离，产生了不同接枝密度的聚合物。接枝密度(侧链数目/降冰片烯主链重复数目)可以直接由大单体/稀释剂加料比控制。为了深入了解共聚物的序列和结构，根据末端共聚模型确定了自蔓延和交叉传播速率常数。这些动力学分析表明，大单体/稀释剂对与均匀匹配的自传播速率常数共聚有利于随机分布的侧链。随着大单体和稀释剂均聚速率之间的差异增大，竞聚率偏离1，导致梯度趋势增大。为了验证我们的方法的有效性，我们合成了一系列单分散聚合物(PLA(X)-RAN-DME1-x)(N)，它们具有不同的接枝密度(x=1.0，0.75，0.5，0.25)和总主链聚合度(n=167,133,100，67，33)。因此，这项工作中揭示的方法构成了一种强大的策略，用于合成跨越线性到瓶刷体系的聚合物，具有受控的接枝密度和侧链分布，这些分子属性决定了微观和宏观性质。
Control over polymer sequence and architecture is crucial to both understanding structure property relationships and designing functional materials. In pursuit of these goals, we developed a new synthetic approach that enables facile manipulation of the density and distribution of grafts in polymers via living ring-opening metathesis polymerization (ROMP). Discrete endo,exo-norbornenyl dialkylesters (dimethyl DME, diethyl DEE, di-n-butyl DBE) were strategically designed to copolymerize with a norbornene-functionalized polystyrene (PS), polylactide (PLA), or polydimethylsiloxane (PDMS) macromonomer mediated by the third-generation metathesis catalyst (G3). The small molecule diesters act as diluents that increase the average distance between grafted side chains, generating polymers with variable grafting density. The grafting density (number of side chains/number of norbornene backbone repeats) could be straightforwardly controlled by the macromonomer/diluent feed ratio. To gain insight into the copolymer sequence and architecture, self-propagation and cross-propagation rate constants were determined according to a terminal copolymerization model. These kinetic analyses suggest that copolymerizing a macromonomer/diluent pair with evenly matched self -propagation rate constants favors randomly distributed side chains. As the disparity between macromonomer and diluent homopolymerization rates increases, the reactivity ratios depart from unity, leading to an increase in gradient tendency. To demonstrate the effectiveness of our method, an array of monodisperse polymers (PLA(x)-ran-DME1-x)(n) bearing variable grafting densities (x = 1.0, 0.75, 0.5, 0.25) and total backbone degrees of polymerization (n = 167, 133, 100, 67, 33) were synthesized. The approach disclosed in this work therefore constitutes a powerful strategy for the synthesis of polymers spanning the linear-to-bottlebrush regimes with controlled grafting density and side chain distribution, molecular attributes that dictate micro- and macroscopic properties.