Effects of chain ends and molecular weight on specific volumes of anionic polystyrene melts

Abstract

Specific volumes of anionic polystyrenes prepared by butyl lithium initiation have been measured at temperatures between 110° and 237°C. Molecular weights of the fractions studied ranged from 2500 to 700 000. Plots of isothermal specific volume against reciprocal molecular weight ( M −1) are fitted by two straight lines intersecting at a molecular weight near 10 000. This parallels the behaviour of thermally initiated polystyrene fractions, which have different end-groups. Volumes attributable to end-groups are greater for the anionic polymers. The specific volume-molecular weight-temperature relations in the M ≤ 10 000 region are explained quite well by the equation of Francois and coworkers, in terms of end-group volumes and a uniform volume contribution from internal repeating units. Restraints on the motion of the butyl end-groups in these polymers by the attached polystyrene chain appear to be temperature dependent in terms of this model. Specific volumes of polymers with M ≥ 10 000 are affected by chain ends and by variation of the volumes of non-end repeating units with molecular weight. The present results parallel those which have been reported for partial specific volumes of polystyrenes in dilute solution and suggest that the same factors operate in both cases.