Fuchise Keita, Igarashi Masayasu, Sato Kazuhiko, Shimada Shigeru
Interdisciplinary Research Center for Catalytic Chemistry , National Institute of Advanced Industrial Science and Technology (AIST) , 1-1-1 Higashi , Tsukuba , Ibaraki 305-8565 , Japan . Email:
Chem Sci. 2018 Feb 19;9(11):2879-2891. doi: 10.1039/c7sc04234e. eCollection 2018 Mar 21.
Organocatalytic controlled/living ring-opening polymerization of cyclotrisiloxanes, such as hexamethylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane, and 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane, using water as an initiator and strong organic bases, such as amidines, guanidines, phosphazene bases, and proazaphosphatrane, as catalysts produced a variety of polysiloxanes with controlled number-average molecular weights ( = 2.64-102.3 kg mol), narrow polydispersity ( = 1.03-1.16), and well-defined symmetric structures. Controlled syntheses of statistical copolymers and triblock copolymers were achieved by copolymerizations of two cyclotrisiloxanes. Various terminal functionalities were successfully introduced by the end-capping reaction of propagating polysiloxanes using functional chlorosilanes. Kinetic investigations demonstrated that the polymerization proceeded through the initiator/chain-end activation mechanism, namely activations of water in the initiation reaction and of terminal silanols in propagating polysiloxanes in the propagation reaction. Catalytic activities of strong organic bases were revealed to depend on their Brønsted basicity and efficiency of the proton transfer in the initiation and propagation reactions. Guanidines possessing an R-N[double bond, length as m-dash]C(N)-NH-R' unit, in particular 1,3-trimethylene-2-propylguanidine, showed excellent performance as a catalyst. In this system, even non-dehydrated solvents are usable for the polymerization.
以水为引发剂，使用强有机碱（如脒、胍、磷腈碱和氮杂环磷三烯）作为催化剂，对环三硅氧烷（如六甲基环三硅氧烷、1,3,5-三甲基-1,3,5-三苯基环三硅氧烷、1,3,5-三甲基-1,3,5-三乙烯基环三硅氧烷和1,3,5-三甲基-1,3,5-三（3,3,3-三氟丙基）环三硅氧烷）进行有机催化可控/活性开环聚合反应，得到了多种具有可控数均分子量（=2.64-102.3 kg/mol）、窄多分散性（=1.03-1.16）和明确对称结构的聚硅氧烷。通过两种环三硅氧烷的共聚反应实现了统计共聚物和三嵌段共聚物的可控合成。使用功能性氯硅烷对增长的聚硅氧烷进行封端反应，成功引入了各种末端官能团。动力学研究表明，聚合反应通过引发剂/链端活化机制进行，即在引发反应中活化水，在增长反应中活化增长的聚硅氧烷中的末端硅醇。结果表明，强有机碱的催化活性取决于其布朗斯特碱性以及引发和增长反应中质子转移的效率。具有R-N=C(N)-NH-R'单元的胍，特别是1,3-三亚甲基-2-丙基胍，作为催化剂表现出优异的性能。在该体系中，甚至未脱水的溶剂也可用于聚合反应。
