Perfectly alternating copolymerization of CO2 and epichlorohydrin using cobalt(III)-based catalyst systems.
Perfectly alternating copolymerization of CO2 and epichlorohydrin using cobalt(III)-based catalyst systems.
复制标题
DOI：
10.1021/ja206425j
复制
发表时间：
2011-09
影响因子：
15
通讯作者：
Guang Wu;Sheng-Hsuan Wei;Wei-Min Ren;Xiao‐Bing Lu;Tie Xu;D. Darensbourg
中科院分区：
文献类型：
--
作者：
Guang Wu;Sheng-Hsuan Wei;Wei-Min Ren;Xiao‐Bing Lu;Tie Xu;D. Darensbourg
通过两种单体的交替共聚将二氧化碳和环氧化物选择性转化为可生物降解的聚碳酸酯代表了二氧化碳在化学合成中潜在的大规模利用的一些最充分研究和创新的技术。在大多数情况下，这些方法的以前的研究集中在使用脂肪族末端环氧化物或氧化环己烯衍生物，只有很少的报道涉及从含有吸电子基团的环氧化物如氧化苯乙烯合成CO（2）共聚物。本文中，我们报告了使用二元和双官能（salen）钴（III）基催化剂体系，通过CO（2）与环氧氯丙烷的偶联来生产具有99%以上碳酸酯键的CO（2）共聚物。通过原位红外测量作为温度的函数来进行比较动力学研究，以评估用于生产环状碳酸酯与涉及两种电子上不同的环氧化物：环氧氯丙烷和环氧丙烷的共聚物的活化屏障。对于表氯醇/CO（2）方法，共聚物与环状碳酸酯形成之间的相对小的活化能差异（45.4kJ/mol）部分地解释了与环氧丙烷/CO（2）情况（53.5kJ/mol）相比共聚物的选择性合成更困难。通过电喷雾电离质谱直接观察二元（salen）考克斯/MTBD（X = 2，4-二硝基苯酚盐和MTBD = 7-甲基-1，5，7-三氮杂双环[4.4.0]癸-5-烯）催化剂体系中增长的聚合物链物种证实了共聚过程的完全交替性质。这一观察结果与对照实验相结合，表明可能的中间体涉及MTBD在CO（2）/环氧氯丙烷共聚过程。
Selective transformations of carbon dioxide and epoxides into biodegradable polycarbonates by the alternating copolymerization of the two monomers represent some of the most well-studied and innovative technologies for potential large-scale utilization of carbon dioxide in chemical synthesis. For the most part, previous studies of these processes have focused on the use of aliphatic terminal epoxides or cyclohexene oxide derivatives, with only rare reports concerning the synthesis of CO(2) copolymers from epoxides containing electron-withdrawing groups such as styrene oxide. Herein we report the production of the CO(2) copolymer with more than 99% carbonate linkages from the coupling of CO(2) with epichlorohydrin, employing binary and bifunctional (salen)cobalt(III)-based catalyst systems. Comparative kinetic studies were performed via in situ infrared measurements as a function of temperature to assess the activation barriers for the production of cyclic carbonate versus copolymer involving two electronically different epoxides: epichlorohydrin and propylene oxide. The relative small activation energy difference between copolymer versus cyclic carbonate formation for the epichlorohydrin/CO(2) process (45.4 kJ/mol) accounts in part for the selective synthesis of copolymer to be more difficult in comparison with the propylene oxide/CO(2) case (53.5 kJ/mol). Direct observation of the propagating polymer-chain species from the binary (salen)CoX/MTBD (X = 2,4-dinitrophenoxide and MTBD = 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene) catalyst system by means of electrospray ionization mass spectrometry confirmed the perfectly alternating nature of the copolymerization process. This observation in combination with control experiments suggests possible intermediates involving MTBD in the CO(2)/epichlorohydrin copolymerization process.