Synthesis and characterization of hyperbranched polyurethanes via monomeric A sub(2) plus monomeric B sub(3) approach

The monomeric A sub(2) plus monomeric B sub(3) approach was employed to prepare hyperbranched polyurethanes (HBPUs) based on 4,4'-methylenediphenyl diisocyanate and trimethylolpropane with the molecular weights ranging from 20,000 to 59,800 g mol super(-1). Through controlling the concentration and stoichiometric ratio of monomers, gel was successfully prevented in the monomeric A sub(2) plus monomeric B sub(3) system. The structures of HBPUs were characterized by super(13)C NMR. Molecular weights of HBPUs were characterized by gel permeation chromatography. A gradual increase in HBPU molecular weight as well as degree of branching was observed when the stoichiometric ratio of A sub(2) to B sub(3) increased. It was exhibited that the solution concentration of the reaction had great effect on the gel point and cyclization of the monomeric A sub(2) plus monomeric B sub(3) system. This novel isocyanate terminated HBPUs are expected to be capable of modifying the curing performance of benzoxazine resin. [copy 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013