Dual Catalytic Ring-Opening Polymerization of Ethylene Carbonate for the Preparation of Degradable PEG.
Dual Catalytic Ring-Opening Polymerization of Ethylene Carbonate for the Preparation of Degradable PEG.
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DOI：
10.1021/acs.biomac.0c00360
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发表时间：
2020-05
影响因子：
6.2
通讯作者：
Nils von Seggern;Tamara Schindler;S. Naumann
中科院分区：
文献类型：
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作者：
Nils von Seggern;Tamara Schindler;S. Naumann
以一系列不同的Lewis碱(包括N-杂环烯烃、磷腈和氮碱)和简单的Lewis酸(如LiCl2、MgF2、BEt3)为催化剂，采用双催化体系，以五元环状乙烯碳酸酯(EC)为原料合成了聚醚碳酸酯S。聚合反应是在温度为160-200°C、催化剂负载量较低(有机碱用量为0.4-0.005摩尔-%)的条件下进行的，摩尔质量可达10000g/摩尔。动力学研究、凝胶渗透色谱、MALDI-TOF MS和核磁共振分析相结合的结果表明，聚合可以是高效的(吨高达>；17.000)，但仍会发生副反应，导致反应过程受到适度控制。与增加乙醚含量的传统方法不同，增加乙醚含量通常只能通过更高的温度和更长的反应时间(以大大减少摩尔质量为代价)，而双重催化方法揭示了选择Lewis酸作为这一性质的更有效调节参数。因此，尽管碳酸盐含量高达30%是可能的，但使用LiCl作为助催化剂可以提供高乙醚含量(90-99%，Mn=800-10000g/mol)的聚合物，这一发现似乎也适用于其他锂盐。因此，使用这种操作简单的装置和EC作为廉价的原料，可以一锅一步的方法制备本质上是可降解的聚乙二醇的共聚物。值得注意的是，所获得的低碳酸盐含量允许制备半结晶聚醚碳酸酯，进一步强调了材料的“类似聚乙二醇组分”。
A dual catalytic setup, consisting of a range of different Lewis bases (including N-heterocyclic olefins, phosphazenes and nitrogen bases) and simple Lewis acids (such as LiCl, MgF2, BEt3) was employed to prepare poly(ether carbonate)s from five-membered, cyclic ethylene carbonate (EC). Polymerizations were conducted under microwave irradiation at T = 160-200°C with low catalyst loading (0.4 - 0.005 mol.-% regarding organobases) in the bulk, enabling access to molar masses of up to 10 000 g/mol. A combination of kinetic investigation, GPC, MALDI-ToF MS and NMR analysis underlines that the polymerization can be highly effective (TON up to > 17.000) but side reactions still occur, resulting in a moderately controlled process. In contrast to traditional procedures, where increased ether contents can typically only be realized by higher temperatures and longer reaction times (at the cost of much reduced molar masses), the dual catalytic approach reveals choice of the Lewis acid as a more effective tuning parameter for this property. Thus, while carbonate contents of up to 30% are possible, application of LiCl as cocatalyst provides polymer with high ether content (90-99%, Mn = 800 - 10 000 g/mol), a finding that also seems to apply for other lithium salts. Thus, using this operationally simple setup and EC as a cheap feedstock, a copolymer which is essentially a degradable poly(ethylene glycol) can be prepared in a one-pot, one-step approach. Notably, the obtained low carbonate content allows for the preparation of semi-crystalline poly(ether carbonate), further underlining the "PEG-likeness" of the material.