Synthesis of uniform polyurethane particles by step growth polymerization in a dispersed medium

Polyurethane microspheres were prepared by polyaddition of ethylene glycol (EG) and tolylene-2,4-diisocyanate (TDI) at 60 degreesC in cyclohexane as the organic dispersion medium, in the presence of dibutyl tin dilaurate (DBTDL) as catalyst and poly(styrene)-b-poly(ethylene oxide) block copolymers or omega-hydroxypolystyrenes as the steric stabilizers. Different parameters such as the manner of addition of the reactants, the concentration, and length of the stabilizer were varied to tune the polyurethane particle size. When omega-OH polystyrenes of low molar mass ((M) over bar (n) = 2000-3000 g mol(-1)) were used as the reactive stabilizers of dispersion, polyurethane particles in a tunable size range of 0.2-5 mum with a narrow size distribution (span = 0.7) could be prepared.