CHAIN EXTENSION AND CROSS-LINKING OF TELECHELIC OLIGOMERS .2. MICHAELADDITIONS OF BISTHIOLS TO BISMALEIMIDES, BISMALEATES AND BIS(ACETYLENE KETONE)S TO GIVE LINEAR AND CROSS-LINKED POLYMERS

Thiol-terminated oligosulfides undergo crosslinking under mild conditi ons with bismaleimides in the presence of catalytic amounts of triethy lamine in polar solvents. The mechanism of crosslinking is thought to be the formation of the thiolate anion which adds to the olefinic grou p on the maleimide to give a carbanion species which then undergoes fu rther addition reactions. To illustrate this possibility, an ABA block copolymer consisting of oligosulfide (B) and maleimide (A) blocks was prepared by reaction between the oligosulfide and a maleimide in the presence of triethylamine. Reaction between dithiothreitol and a bisma leimide under similar conditions does not result in a crosslinked prod uct and this is attributed to the interaction of hydroxyl groups with any carbanion species formed. Crosslinking was observed in the reactio n between an oligosulfide and hexane bismaleate although much more slo wly than for bismaleimide. Reactions between dithiothreitol and a bis( acetylene ketone), and an oligosulfide and a bis(acetylene ketone), bo th resulted in linear polymers of moderate molar mass.