Copolymerization Behavior of 7-Methylene-2-methyl-1,5-dithiacyclooctane: Reversible Cross-Propagation

The copolymerization behavior of 7-methylene-2-methyl-1,5-dithiacyclooctane (MDTO) with a range of common comonomers has been investigated and found to be highly unusual. The resulting copolymers contained blocks of homo-poly(MDTO), even at low MDTO feed ratios. Changes in temperature and monomer concentration have a significant effect on the copolymer composition of methyl methacrylate−MDTO and styrene−MDTO mixtures and therefore on the apparent reactivity ratios. The magnitude of the concentration effect is independent of the solvent. A new copolymerization mechanism is proposed in which the addition of an MDTO radical to the comonomer is reversible while all other propagation reactions are effectively irreversible. To our knowledge, this is the first observation of such a mechanism. Parameters for MDTO−M 2 (M 2 = STY, MMA) according to this model are reported as ( r MDTO, r 2, k - 12 / k 22 ) = (0.06, 7, 17; M 2 = STY) and (0.38, 3.2, 2.5; M 2 = MMA) at 60 °C.