Photo-Induced Ligation of Acrylonitrile-Butadiene Rubber: Selective Tetrazole–Ene Coupling of Chain-End-Functionalized Copolymers of 1,3-Butadiene
journal contributionposted on 19.02.2016, 01:27 by Christoph J. Dürr, Paul Lederhose, Lebohang Hlalele, Doris Abt, Andreas Kaiser, Sven Brandau, Christopher Barner-Kowollik
A highly selective photo-induced nitrile imine mediated tetrazole–ene coupling (NITEC) of chain-end-functionalized nitrile–butadiene rubber (NBR) is reported, providing nitrile rubbers with molar masses of up to 48 000 g·mol–1. NBR was obtained via the reversible addition–fragmentation chain transfer (RAFT) mediated copolymerization of acrylonitrile and 1,3-butadiene employing a novel photoreactive tetrazole-functionalized trithiocarbonate. The herein reported tetrazole-functionalized trithiocarbonate representsto the best of our knowledgethe first ever reported photoreactive RAFT agent capable of undergoing light-induced ligations with enes. Molar masses of the tetrazole-functionalized NBRs were in the range of 1000 to 38 000 g·mol–1 with dispersities between 1.1 to 1.6. By an appropriate choice of the tetrazole substituents, a reaction of the in situ formed enophile with the double bonds or the nitrile moieties of the incorporated monomer units within the polymer backbonepresent in high excess relative to the dipolarophile linker moleculewas not observed. Underpinned by DFT calculations, the selectivity was identified to originate from a reduced LUMO energy level of the maleimide linker compared to the nonactivated backbone olefins when employing a nitrile–imine of moderate reactivity.