Viscosity–molecular weight relationship for polyvinyl acetate

Abstract

AbstractThe relationship between limiting viscosity number and molecular weight of PVAc was determined and compared with the results by several authors. Samples of lowconversion PVAc were used. The weight‐average molecular weights were determined by a light‐scattering method and the number‐average molecular weights by endgroup determinations and the osmotic pressure method. From those experiments, it was proved that the ratio M̄w/M̄n for low conversion PVAc is equal to 2, as expected by theory. The relationships obtained are the following: [η] = 1.02 × 10−2 Mw0.72 (in acetone); [η] = 1.07 × 10−2 Mw0.71 (in MEK); [η] = 3.14 × 10−2 Mw0.6 (in methanol); and [η] = 9.20 × 10−2Mw0.5 (in a ⊖ solvent)where [η] is expressed in milliliters per gram and a mixture of methyl isopropyl ketone (72.7 vol‐%)and n‐heptane (27.3 vol.‐%)was chosen as the ⊖ solvent. These relationships were converted to relationships for perfectly homogeneous fractions. The relationship in acetone, [η] = 1.08 × 10−2 M0.72, was compared with literature data after the latter were converted to data corresponding to perfectly homogeneous fractions in acetone at 30°C., and was found to be in good agreement. Mean‐square radii of gyration, 〈S2〉, and second virial coefficients, A2, of PVAc were also determined in the acetone and methyl ethyl ketone solutions and the results compared with literature values.