Polymerization and copolymerization of cyclic unsaturated sulfides

Abstract

AbstractThe polymerization and copolymerization behaviour of the unsaturated cyclic sulfides 2,3‐dihydrothiophene (1), 2,3‐dihydrothiopyran (2) and p‐Dithiene (3) was studied. With cationic initiators such as borontrifluoride etherate, all three monomers were transformed into polymers. The five‐membered ring compound 1 gave quantitative yields, the two six‐membered ring compounds 2 and 3 gave limited conversions. This was attributed to the advantageous geometrical position of the pen‐penultimate sulfide function toward the growing chain‐end to form a sulfonium ion. Radical homopolymerization was impossible for all three monomers but copolymerization with different vinyl monomers yielded copolymers with various sulfide unit contents. From the copolymerization reactivity parameters of the copolymerization with methyl acrylate, the reactivity of the different monomers towards a growing polymer chain ending with a methyl acrylate radical could be compared. The sequence was 1≥vinyl sulfides ≫2>3. Copolymerization with maleic anhydride yielded alternating copolymers independent of the monomer feed composition. This copolymerization is believed to occur via the formation of a charge‐transfer complex between the two comonomers. The association constants of complex formation in chloroform were measured.