Viscosities of dilute solutions of polymethyl methacrylate

Abstract

Abstract Viscosities of dilute solutions of six fractions of polymethyl methacrylate in the molecular weight range of 48,000–400,000 have been obtained with benzene, toluene, chloroform, tetrachloroethane, and n ‐amyl methyl ketone as solvents at different temperatures in the range 25–60°C. There is evidence for association of polymer in amyl methyl ketone, and degradation in tetrachloroethane is possible at higher temperatures. Variations of [η] and of k ′ with solvent agree generally with those observed by other workers. Where comparison is possible, values of K and a in the expression [η] = KM a are also in general agreement with other values. Values of K ′ in the Flory equation [η] = K ′ M 1/2/ α 3 may possibly vary with solvent, and it is suggested that in cases where solvation of polymer occurs, the chains may be prevented from adopting the unperturbed configuration adopted in less polar solvents. [η] increases with increase of temperature in all cases but that of tetrachloroethane, but there appears to be a maximum value near 53°C. with both benzene and amyl methyl ketone. The variation of the exponent a with temperature is similar to that of [η]. In the cases of benzene and chloroform, the temperature coefficient of [η] seems to be primarily due to changes in the value of the swelling factor α, but in other cases changes in the value of (r̄ 0 2 / M ) are important, r̄ 0 2 being the mean square unperturbed end‐to‐end distance of the polymer chains.