Stereospecific cationic RAFT polymerization of bulky vinyl ethers and stereoblock poly(vinyl alcohol) via mechanistic transformation to radical RAFT polymerization of vinyl acetate
Stereospecific cationic RAFT polymerization of bulky vinyl ethers and stereoblock poly(vinyl alcohol) via mechanistic transformation to radical RAFT polymerization of vinyl acetate
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DOI：
10.1016/j.giant.2021.100047
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发表时间：
2021-02-10
期刊：
影响因子：
7
通讯作者：
Kamigaito, Masami
中科院分区：
文献类型：
--
作者：
Uchiyama, Mineto;Satoh, Kotaro;Kamigaito, Masami
在阳离子聚合中同时控制分子量和立构规整度仍然具有挑战性。在这里，我们提出了一种立体定向活性阳离子聚合的新方法，将阳离子可逆加成断裂链转移（RAFT）聚合与硫代羰基硫代化合物以及大体积乙烯基醚与路易斯酸催化剂的立体定向阳离子聚合相结合。在这个组合系统中，分子量由生长的阳离子和休眠二硫代氨基甲酸酯链端之间的RAFT过程控制，而立构规整度由基于路易斯酸催化剂衍生的庞大侧基和反阴离子的空间位阻的立体有择传播控制。在此，我们证明了这种方法在各种大体积乙烯基醚（例如叔丁基、苄基、三甲基甲硅烷基和叔丁基二甲基甲硅烷基乙烯基醚）的阳离子聚合中的可用性，使用二硫代氨基甲酸酯和BF3中心点OEt2或EtAlCl2在甲苯中于-78℃下进行。 从一系列大体积乙烯基醚中获得了具有受控分子量和二硫代氨基甲酸酯链端基团的聚（乙烯醇），并转化为具有高熔融温度（T-m 类似于 230 ℃）的分子量受控的全同立构聚（乙烯醇）（mm >= 70%）。此外，通过将三甲基硅乙烯基醚的立体定向阳离子RAFT聚合转化为乙酸乙烯酯的自由基RAFT聚合，通过机械转化合成了全同立构-b-无规立构立体嵌段PVA（mm/mr/rr = 75/25/5和23/48/29，T-m类似于210℃）。 二苯基二硫代氨基甲酸酯作为常见的 RAFT 试剂，然后同时对甲硅烷基和乙酰基进行脱保护。
The simultaneous control of molecular weight and tacticity in cationic polymerization remains challenging. Here, we propose a new approach for stereospecific living cationic polymerization by combining cationic reversible addition-fragmentation chain transfer (RAFT) polymerization with thiocarbonylthio compounds and stereospecific cationic polymerization of bulky vinyl ethers with Lewis acid catalysts. In this combined system, the molecular weight was controlled by the RAFT process between the growing cationic and dormant dithiocarbamate chain ends, whereas the tacticity was controlled by stereospecific propagation based on the steric hindrance of bulky side groups and counteranions derived from the Lewis acid catalysts. Herein, we demonstrate the availability of this approach in the cationic polymerization of various bulky vinyl ethers, such as tert-butyl, benzyl, trimethylsilyl, and tert-butyldimethylsilyl vinyl ether, using dithiocarbamates and BF3 center dot OEt2 or EtAlCl2 in toluene at -78 degrees C. Isotactic-rich poly(vinyl ether)s with controlled molecular weights and dithiocarbamate chain-end groups were obtained from a series of bulky vinyl ethers and were converted into molecular-weight-controlled isotactic poly(vinyl alcohol) (mm >= 70%) with a high melting temperature (T-m similar to 230 degrees C). Furthermore, isotactic-b-atactic stereoblock PVA (mm/mr/rr = 75/25/5 and 23/48/29, T-m similar to 210 degrees C) was synthesized by mechanistic transformation from the stereospecific cationic RAFT polymerization of trimethylsilyl vinyl ether into the radical RAFT polymerization of vinyl acetate using diphenyl dithiocarbamate as the common RAFT agent followed by simultaneous deprotection of the silyl and acetyl groups.