Free Radical Ring-Opening Polymerization of Cyclic Allylic Sulfides: Liquid Monomers with Low Polymerization Volume Shrinkage

摘要

The free radical poiymerization of four methylated cyclic allylic sulfides was exaniined with reference to their polymerization volume shrinkage and the effect of ring size on reactivity. The compounds examined were 2-methyl-5-methylene-1,3- dithiane (5) (solid), 2-methyl-6-methylene-1,4-dithiepane (6) (liquid), 6-methyl-3-meth- ylene-1.5-dithiacyclooctane (7) (liquid), and 6,8-dimethyl-3-methylene-1,5-dithiacy- clooctane (8) (liquid). The monomers were stable materialcs not requiring any special handling or storage conditions. They were polymerized in bulk using thermal azobis- isobutyronitrile (AIBN, VAZO88) and photochemical initiators {Ciba DAROCUR 1173) and in benzene solutions (AIBN, 70 °C). The six-membered ring monomer 5 was unreactive whereasseven-membered ring monomer 6 polymerized to high conversion in bulk. In addition, 6 did not polymerize in benzene solution at 70 °C at [6] = 1.25M. Eight-membered ring monomers 7 and 8 polymerized in bulk to complete conversion with thermal and photochemical initiators to give lightly crosslinked materials. Near complete conversion to soluble polymers could be obtained in solution polymerizations in benzene. Soluble polymers were also obtained in photochemical initiated bulk poly- merizations by lowering initiator concentrations or length of irradiation. The methyl substituent had no effect on which allylic carbon-sulfur bond fragmented in the ring- opening step. The polymerization volume shrinkages of monomers 7 and 8 were 1.5 and 2.4% respectively and together with monomer 4 (1.5-2.0% shrinkage) are the best available liquid free radical ring-opening monomers that can be polymerized in bulk at room temperature.