EVALUATION OF SCISSION AND CROSSLINKING YIELDS IN GAMMA-IRRADIATED POLY(ACRYLIC ACID) AND POLY(METHACRYLIC ACID) FROM WEIGHT-AVERAGE AND Z-AVERAGE MOLECULAR-WEIGHTS DETERMINED BY SEDIMENTATION EQUILIBRIUM

Weight- and Z-average molecular weights, M ̄w(D) and M ̄z(D), of poly(methacrylic acid) (PMMA) and poly(acrylic acid) (PAA) have been determined by sedimentation equilibrium in the ultracentrifuge after various doses D of γ-radiation in vacuum. Relationships between [Mi(0)/Mi(D)-1]/D and D (i=w or Z), derived recently by O'Donnell and coworkers, have been used to determine radiation chemical yields for scission and crosslinking of G(S)=6.0, G(X)=0 for PMAA and G(S)=0, G(X)=0.44 for PAA. Allowance was necessary for the effects of COOH decomposition on the average values of the molecular weight and partial specific volume for irradiated PAA. © 1990.