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

The monomeric A 2 plus monomeric B 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 −1 . Through controlling the concentration and stoichiometric ratio of monomers, gel was successfully prevented in the monomeric A 2 plus monomeric B 3 system. The structures of HBPUs were characterized by 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 2 to B 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 2 plus monomeric B 3 system. This novel isocyanate terminated HBPUs are expected to be capable of modifying the curing performance of benzoxazine resin. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013