Viscosity of fractions from end-linked polystyrene star macromolecules

A number of OH-terminated three-arm star molecules were prepared by anionic polymerization with a specially functionalized initiator. The stars were crosslinked over the OH groups with varying amounts of toluene-2,4-diisocyanate. The samples were fractionated by size exclusion chromatography (SEC) on-line with a low angle laser light scattering (LALLS) and a viscosity (VISC) detector. The Kuhn—Mark—Houwink—Sakurada (KMHS) relationships from the various samples resulted in a common relationship. Shrinking parameters g′_j≡[η]_j,b/[η]_j,lin were determined for each slice and could satisfactorily be interpreted on the basis of the Zimm—Stockmayer theory in connection with a suggestion by Kurata et al. The Kurata suggestion was checked with data from star molecules. The examination revealed that randomly branched and star-branched macromolecules exhibit significantly different hydrodynamic behavior. The ratio of the Fox—Flory coefficients Φ_b/Φ_lin in the relationship [η] = Φ(R/M) increases in both cases with branching. This is a consequence of the enhanced segment density and the resulting increase in the hydrodynamic interaction.