Understanding the structure development in hyperbranched polymers prepared by oligomeric A2+B3 approach: comparison of experimental results and simulations

Structure development in highly branched segmented polyurethaneureas based on oligomeric A2+B3 approach was investigated by experimental studies and kinetic Monte-Carlo simulations. In both simulations and experiments, hyperbranched polymers were produced by the slow addition of A2 onto B3. Experimental studies showed strong influence of solution concentration on the gel point and the extent of cyclization in the polymers formed. In polymerizations conducted at a solution concentration of 25% by weight gelation took place at the stoichiometric ratio [A2]/[B3]=0.886. This is somewhat higher than the theoretical ratio of 0.75. In very dilute solutions, such as 5% solids by weight, no gelation was observed although the stoichiometric amount of A2 added well exceeded the theoretical amount for gelation. Both experimental studies by size exclusion chromatography (SEC) and kinetic Monte-Carlo simulations demonstrated a gradual increase in polymer molecular weights as more A2 is added onto B3. This was followed by a sharp increase in the polymer molecular weight as the gel point is approached. A very similar behavior was observed for the polydispersity values of the polymers formed. Kinetic Monte-Carlo simulations performed at different cyclization ratios showed very good agreement with experimental results.