Kinetic behavior in free-radical polymerization of isomer methacrylic monomers with active functional groups as side substituents

The kinetic behavior of the free-radical polymerization of 2-hydroxy-4-N-me thacrylamidobenzoic acid (4-HMA) and 2-hydroxy-5-N-methacrylamidobenzoic ac id (5-HMA) in a solution of N,N-dimethylformamide is described. The methacr ylic monomers 4-HMA and 5-HMA were isomers in which the phenolic and carbox ylic functional groups were in different positions on the side aromatic rin g with respect to the methacrylamide group. Semiempirical (AM1 and PM3 trea tments) and ab initio (6-31G**) quantum mechanical calculations indicated t he existence of intramolecular H-bonding between the phenolic and carboxyli c groups. These calculations also indicated a slightly higher reactivity of 4-HMA with respect to 5-HMA under the same experimental conditions as obta ined from the frontier orbital interactions between the highest molecular o rbital of the monomers and the singly occupied molecular orbital of the rad ical obtained by the reaction of a methyl radical with the corresponding mo nomer. Gravimetric study of the free-radical polymerization of 4-HMA and 5- HMA at several temperatures ranging from 50 to 150 degrees C demonstrated t his behavior. The kinetic results obtained and the average molecular weight s of the polymers prepared at different temperatures indicated that the mon omer 4-HMA had a slightly higher reactivity at low temperatures (50-90 degr ees C), whereas at higher temperatures (120-150 degrees C), the reactivity of both monomers became similar as a consequence of the "dead-end" radical polymerization. (C) 1999 John Wiley & Sons, Inc.