Synthesis of a new thermally‐curable elastomer via regioselective chlorination of a polyimidosulfide

Abstract

Recently, we exploited the well established nucleophilic addition of dithiols to bismaleimides' to prepare a sena of high molecular-weight, elastomeric polyimidosullides (Tg = 6.5-13"C), such as 1, via polymerizations of various alkanedithiols with N,N'-bismaleimido-1,8-octane [eq. (1)12 1An an ap roach to the rational introduction of unsaturated curin sites in polymers like 1 under mild conflitions, we studied oxidative conversions of 3-thi~l-~~~y1-2,5-pyrrolidinediones (21, prepared from N-phenylmaleimide (3) via eq. 2), to the corresponding 3-thio-1-phenyl-1H-pyrrole-2,5-diones (4) through chlorination of 2 w i 6 N-chlorosuccinimide (NCS):c, R = 4-ClPhCH2-Extrapolating from the known regioselective chlorination of unsymmetrical benzylic sulfides with NCS? one can view analogous reactions of 2 as initial formation of chlorosulfonium salts 6 [eq. (3)] with subsequent abstraction, by succinimidyl anion (from NCS), of the acidic ring methine proton a to sulfur.