Free-radical ring-opening polymerization of cyclic allylic sulfides. 2. Effect of substituents on seven- and eight-membered ring low shrink monomers

The effect of substituents on the free-radical ring-opening polymerization behavior and polymerization volume shrinkage of the cyclic allylic sulfides 6-methylene-1,4-dithiacycloheptane (2a) and 3-methylene-1,5-dithiacyclooctane (2b) has been investigated. The monomers were 2-(hydroxymethyl)-6-methylene-1,4-dithiacycloheptane (3a), 6-methylene-1,4-dithiacycloheptan-2-ylmethyl acetate (3b), 6-methylene-1,4-dithiacycloheptan-2-ylmethyl methacrylate (3c), 7-methylene-1,5-dithiacyclooctan-3-ol (4a), 7-methylene-1,5-dithiacyclooctan-3-yl acetate (4b), 7-methylene-1,5-dithiacyclooctan-3-yl benzoate (4c), and the bicyclic monomer bis(6-methylene-1,4-dithiacycloheptan-2-ylmethyl) diglycolate (5). The monomers were polymerized in bulk with thermal (AIBN, VAZO88) and photochemical initiators (Darocur 1173) with selected solution polymerizations also performed. The presence of a substituent on the monomers gave dear amorphous polymers unlike the crystalline polymers obtained from the unsubstituted parent monomers (2) previously reported. The substituted, monofunctional seven-membered ring monomers (3a,b) polymerize to moderate conversions (ca. 60%) and gave amorphous, soluble sticky gumlike polymers. The difunctional monomer 3c in contrast gave an insoluble rigid material. Eight-membered ring monomers 4a, 4b, and 4c were made to undergo complete conversions. The dual cyclic monomer 5 was polymerized to give an insoluble material containing only traces of extractable monomer. Those liquid monomers 3c, 4b, and 5 that polymerized to complete conversion (3c, 4b) or near complete (5) were further examined and gave polymerization shrinkages of 7.3, 2.0, and 2.1% (respectively) and glass transition points of 78, -0.2, and 28 degrees C, respectively.