The anionic ring-opening polymerization of cyclic imines

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One important class of polymers is polyimines. Polyimines have a wide range of applications such as CO2 capture and non-viral gene-transfection. Despite their many applications, the use of these polymers is limited due to difficulties in controlling the polymerization. To increase the feasibility of polyimines in the aforementioned high-value applications, the research in this dissertation focuses on controlled routes to produce linear polyimines using living anionic ring-opening polymerization (AROP). The early work of this dissertation focuses on an AROP route to linear polyethylenimine (LPEI). Due to the insolubility of p(N-sulfonylaziridine)s (i.e. non-2-substituted) in all common solvents, this was achieved using a copolymerization strategy. Utilizing two N-sulfonylaziridines, N-(methanesulfonyl)aziridine (MsAz) and N-(sec-butylsulfonyl)aziridine (sBsAz), with similar reactivities, a soluble random copolymer with narrow molecular weight distributions is produced. Removal of the sulfonyl groups of p(MsAz-r-sBsAz) affords the first example of LPEI by living, controlled AROP. The later work in this dissertation focuses on the AROP of N-sulfonylazetidines in route to linear poly(trimethylenimine) (LPTMI). Initially, the polymerization of N-(methanesulfonyl)azetidine (MsAzet) was investigated. The kinetics of this polymerization were studied, and the reaction found to be first order with respect to monomer and the number of active chain ends remains constant throughout the polymerization. Interestingly, activation occurs at the methanesulfonyl group, leading to polymer branching. This branching precludes p(MsAzet) from being a precursor to LPTMI. By more judicial selection of N-sulfonylazetidine monomers, a living, controlled AROP approach to LPTMI was achieved by copolymerizing two similar N-sulfonylazetidines, N-(p-tolylsulfonyl)azetidine (pTsAzet) and N-(o-tolylsulfonyl)azetidine (oTsAzet), to produce a statistical copolymer. Copolymerization was required as the homopolymers resulting from these monomers were insoluble in all common solvents. The copolymerization is living and controlled, producing polymers with narrow molecular weight distributions. The kinetics of the copolymerization, and the reactivity ratios of the two monomers, were studied and the sulfonyl groups of the polymer were removed to provide the first example of LPTMI by living, controlled AROP. Finally, the high barrier to polymerization of N-sulfonylazetidines was utilized to produce block copolymers, containing no homopolymer impurities, in a closed system in which all monomers are present in solution at the time of initiation.

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Chemistry, Polymer chemistry, Organic chemistry