A Study On The Mechanism Of Free Radical Polymerization Of Multivinyl Monomers:Monte Carlo Simulations

The free radical polymerization of multivinyl monomers(MVMs)inevitably leads to gelation even at low monomer conversion.Flory and Stockmayer(F-S theory)studied it based on two fundamental assumptions:(1)independent and equivalent vinyl groups,(2)no intramolecular cyclization.This theory has been experimentally proven in conventional free radical polymerization(FRP/FRcP)of several MVMs(e.g.divinyl benzene,DVB).However,until now its applicability to FRP and reversible deactivation radical polymerization(RDRP)(such as atom transfer radical polymerization(ATRP))of MVMs is still controversial,especially regarding the prediction of the gel point and the extent of intramolecular cyclization.In this paper,Monte Carlo simulations were used to study FRP and ATRP of divinyl monomers using two kinetic models: with cyclization(w.c.)and without cyclization(wo.c.– corresponding to F-S theory)models.In terms of the applicability of F-S theory to FRP of MVMs,the results of the Monte Carlo simulations of FRP/FRcP of divinyl monomers were compared with the calculated gel points based on F-S theory and the experimental data.It is found that the F-S theory can successfully predict the gel points of FRP of MVMs,moreover,the intramolecular cyclization has a negligible impact on the polymerization process and the gel point before gelation.Thus F-S theory is suitable for the prediction of FRP of MVMs.Regarding its applicability to ATRP of divinyl monomers,the simulated gel points of ATRP of divinyl monomers using w.c./wo.c.model were compared with those obtained from simulations using dynamic lattice liquid(DLL)model,from ATRP experiments and from calculation using F-S theory.The results show that the gel points obtained from both models are lower than the values from DLL model and experiments.This indicates that F-S theory is not sufficient for predicting polymerization of MVMs via ATRP.And this inapplicability is not only due to neglecting intramolecular cyclization,but also due to spatial restrictions which cause the reactivity and accessibility of vinyl groups becoming non-equivalent in ATRP of MVMs.