The effect of primary cyclization on free radical polymerization kinetics: experimental characterization

Free radical polymerization kinetics are influenced by many factors including solvent concentration during polymerization, monomer structure, and comonomer composition. This study isolates the effects of the balance between primary cyclization and crosslinking on the polymerization kinetics. Isomeric crosslinking agents, 1,2-cyclohexanediol dimethacrylate (1,2-CHDDMA), 1,3-cyclohexanediol dimethacrylate (1,3-CHDDMA), and 1,4-cyclohexanediol dimethacrylate (1,4-CHDDMA), were utilized for the study because they have differing cyclization rates due to the conformation of the two methacrylate groups in the monomer, but they are otherwise similar. In copolymerizations of 1, 2, 5, and 10% crosslinking agents with 2-methoxyethyl methacrylate (MEMA), the 1,4-CHDDMA samples were always found to have an earlier onset of autoacceleration than 1,2-CHHDMA samples. 1,3-CHDDMA copolymerized with MEMA had a polymerization rate between the 1,2-CHDDMA and 1,4-CHDDMA, as expected. Mechanical property data showed that copolymer samples made with the 1,4-CHDDMA crosslinking agent exhibited a lower Mc and higher Tg than the analogous 1,2-CHDDMA copolymers. It is concluded that reduced mobility from greater crosslinking than cyclization causes the earlier onset of autoacceleration in the 1,4-CHDDMA copolymers.