Specific solvent interactions in the stereo‐regular polymerization of methacrylic acid

Abstract

AbstractA study has been made of the marked effect of solvent on the stereoregularity of poly (methacrylic acid) prepared by the radical polymerization of methacrylic acid initiated by Co60 gamma radiation. The specific interaction of the solvent with the monomer and the growing polymer chains, leading to particular structures at the growing chain end, leads to the observed effect on the stereoregularity of the polymer. It is apparent that solvents of intermediate hydrogen bonding strength and bulkiness lead to highly syndiotactic polymer. Thus poly (methacrylic acid) prepared at −78°CC in a 20% by volume solution of methacrylic acid in 2‐propanol contains 95% syndiotactic triads. The effect of the steric hindrance of the solvent is amply demonstrated by the fact that polymerization in 2‐methylcyclohexanol results in the highest degree of syndiotacticity at 0°CC (82% syndiotactic triads) but yields polymer having only 69% syndiotactic triads at −78°CC. This is in contrast to the usual effect on stereoregularity upon lowering the temperature of radical polymerization. The detailed mechanism of this polymerization and its relation to the polymerization of other monomers capable of hydrogen bonding to solvents will be discussed with specific reference to the particular structures that may give rise to the observed effects.