High molecular weight acrylonitrile-butadiene architectures via a combination of RAFT polymerization and orthogonal copper mediated azide-alkyne cycloaddition

alpha-Functional nitrile butadiene rubber (NBR) building blocks were employed in the copper mediated 1,3-dipolar Huisgen coupling upon addition of 1,4-bis(azidomethyl) benzene (4). Polymer-polymer coupling afforded linear polymers with molecular weights ranging from 2500 g mol(-1) to 97 000 g mol(-1) and polydispersities from 1.1 to 1.6. The alpha-functional NBR building blocks were obtained via the reversible addition-fragmentation chain transfer (RAFT) copolymerization of acrylonitrile (AN) and 1,3-butadiene (BD) at 100 degrees C, utilizing the high temperature azo initiator 1,10-azobis(cyclohexane-1carbonitrile) and chlorobenzene or acetone as solvents. A novel alkyne-functional trithiocarbonate 2 was synthesized in 64% yield via the N, N0-dicyclohexylcarbodiimide mediated coupling of 2-(( dodecylsulfanyl) carbono-thioyl) sulfanyl propanoic acid (DoPAT, 1) and propargyl alcohol. 2 was shown to be an efficient controlling agent for the controlled/living radical copolymerization of acrylonitrile and 1,3-butadiene. The use of copper mediated azide-alkyne cycloaddition was extended towards the side-chain modification of acrylonitrile-butadiene rubbers as well as applied in the synthesis of branched and cross-linked NBR structures. For this purpose an acrylonitrile-1,3butadiene-propargyl methacrylate (PMA) terpolymer of 3900 g mol(-1) with a PDI of 1.3 was synthesized by a DoPAT-mediated RAFT polymerization. Herein, monomers were employed in the ratio of 56 : 35 : 9 (BD : AN : PMA). The ability of the terpolymer to undergo side-chain modification was demonstrated upon addition of 1-undecane azide. Cross-links were established via addition of 1,4bis( azidomethyl) benzene. The current study provides the first successful approach to employ an orthogonal conjugation technique on this technically important class of synthetic rubbers.