Online monitoring of the final, divergent growth phase in the step-growth polymerization of Polyamines

Using automatic, continuous online monitoring of polymerization reactions (ACOMP) the final, divergent growth phase (FDGP) of the condensation polymerization of dimethylamine, epichlorohydrin, and ethylenediamine was monitored, which produced a highly ramified, polyelectrolytic polyamine. The weight average mass, M-w, increased exponentially during the FDGP, whereas weight averaged intrinsic viscosity [eta](w) increased slowly, reaching a plateau. Multi-detector gel permeation chromatography (GPC) revealed that polymers of mass 20.000 to 10(6) are branched and self-similar, but above this mass, [eta] increases less strongly with M. This appears to be due to higher order ramification, a precursor to gelation. The ACOMP trends in M-w and [eta](w) provide direct online evidence of this process. It is shown computationally that a mere increase in polydispersity cannot explain this behavior. GPC showed the mass distribution becomes highly asymmetric as conversion increases. A plausible kinetic model for the distribution asymmetry is introduced, and a complementary model for the effects of higher order ramification on [eta](w).