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B(C6F5)3‑Catalyzed Group Transfer Polymerization of N,N-Disubstituted Acrylamide Using Hydrosilane: Effect of Hydrosilane and Monomer Structures, Polymerization Mechanism, and Synthesis of α‑End-Functionalized Polyacrylamides

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journal contribution
posted on 04.04.2016, 17:04 by Seiya Kikuchi, Yougen Chen, Kodai Kitano, Shin-ichiro Sato, Toshifumi Satoh, Toyoji Kakuchi
The tris­(pentafluorophenyl)­borane- (B­(C6F5)3-) catalyzed group transfer polymerization (GTP) of N,N-disubstituted acrylamide (DAAm) using a moisture-tolerant hydrosilane (HSi) as part of the initiator has been intensively investigated in this study. The screening experiment using various HSis suggested that dimethylethylsilane (Me2EtSiH) with the least steric bulkiness was the most appropriate reagent for the polymerization control. The chemical structure of the DAAms significantly affected the livingness of the polymerization. For instance, the polymerization of N,N-diethylacrylamide (DEtAAm) using Me2EtSiH only showed better control over the molecular weight distribution, while that of N-acryloylmorpholine (MorAAm) with a more obstructive side group using the same HSi afforded precise control of the molecular weight as well as its distribution. Given that the entire polymerization was composed of the monomer activation, the in situ formation of a silyl ketene aminal as the true initiator by the 1,4-hydrosilylation of DAAm, and the GTP process, the polymerization mechanism was discussed in detail for each specific case, e.g., the B­(C6F5)3-catalyzed polymerizations of DEtAAm and MorAAm and the polymerization of MorAAm using B­(C6F5)3 and Me3SiNTf2 as a double catalytic system. Finally, the convenient α-end-functionalization of poly­(N,N-disubstituted acrylamide) (PDAAm) was achieved by the in situ preparation of functional silyl ketene aminals through the 1,4-hydrosilylation of functional methacrylamides, which has no polymerization reactivity in the Lewis acid-catalyzed GTP, followed by the Me3SiNTf2-catalyzed GTP of DAAms.