B(C6F5)3-Catalyzed Group Transfer Polymerization of Acrylates Using Hydrosilane: Polymerization Mechanism, Applicable Monomers, and Synthesis of Well-Defined Acrylate Polymers

摘要

We demonstrated the B(C6F5)(3)-catalyzed group transfer polymerization (GTP) of acrylate monomers with hydrosilane by the in situ formation of silyl ketene acetals (SKAs) as the initiator by the B(C6F5)(3)-catalyzed 1,4-hydrosilylation of acrylate monomers and hydrosilane. In addition, this new GTP method was clarified in terms of the polymerization mechanism, scope and limitation of the acrylate monomers, the livingness of the polymerization, and the synthesis of statistic and block acrylate copolymers and omega-end-functionalized acrylate polymers. A mechanism involving six elementary reactions was proposed based on the specified analysis of the 1,4-hydrosilylation reaction and the usual GTP using a Lewis acid catalyst. The B(C6F5)(3)-catalyzed GTP using Me2PhSiH was applicable for not only various alkyl acrylates, such as the methyl, 2-ethylhexyl, cyclohexyl, and dicyclopentanyl acrylates, but also functional acrylates, such as the 2-methoxyethyl, 2-(2-ethoxyethoxy)ethyl, tetrahydrofurfuryl, allyl, triisopropylsilyl, and 2-(triisopropylsiloxy)ethyl acrylates. On the other hand, the isobornyl, tert-butyl, 2-methyl-2-adamantyl, 2-(dimethylamino)ethyl, and 2-oxotetrahydrofuran-3-yl acrylates were unsuitable GTP monomers because they showed low or even no polymerization property due to the deactivation of the B(C6F5)(3) catalyst or the in situ produced SKA initiator. The livingness for the GTP of suitable acrylates using Me2PhSiH was verified by the kinetic studies, which was applied to the random and block copolymerizations of two different acrylate monomers. Finally, the omega-end-functionalization of the nucleophilic propagating end of poly(n-butyl acrylate) was performed using electrophiles, such as benzaldehyde, N-benzylidenemethylamine, and N-benzylidenebenzylamine, as terminators.