Preparation and end-linking of hydroxyl-terminated polystyrene star macromolecules

Abstract

An up-scale synthesis of 3-arm hydroxyl-terminated polystyrene (PS) star polymers is reported. Subsequent end-linking of these hydroxyl-terminated star polymers with 2,4-toluene diisocyanate gave branched polymers. The extent of reacted groups was measured by UV spectroscopy. The quenched samples were characterized by static-dynamic light scattering. The experimental gel point (critical hydroxyl conversion, pOH, cr = 0.65) is shifted significantly from the theoretically predicted gel point (pOH,cr = 0.50), indicating extensive ring formation during the end-linking process. Analysis of the shrinking factors (gh, gs) and the molar mass dependencies of the radii of gyration Rg, hydrodynamic radii Rh, and the second osmotic virial coefficient A2 gave qualitative agreement with crosslinking theories. The deviations are discussed to arise from the large non-uniformity in the size distribution and from a cross-over of mean field to percolation behavior, as was previously found from the quantitative analysis of molar mass distributions.