Polyurethane macroiniferter/poly(methyl methacrylate) block copolymer dispersions with inverse core-shell morphologies were obtained from 1,1,2,2,-tetraphenylethane-1,2-diol, dimethylol propionic acid, 4,4'-diphenylmethane diisocyanate, and poly(propylene glycol) via a living radical mechanism. Molecular weight, particle size and dispersion viscosity, and thermal, mechanical, and dynamic mechanical properties of the dispersion cast films are reported as a function of copolymerization time. (C) 2003 Wiley Periodicals, Inc.