Monte Carlo modelling of living branching copolymerisation of monovinyl and divinyl monomers: comparison of simulated and experimental data for ATRP copolymerisation of methacrylic monomers

Branching copolymerisation of a monovinyl monomer with a small amount of a divinyl monomer under pseudo-living conditions has been modelled using a Monte Carlo program written in C# code. Molecular weights, polydispersities and the distribution of primary linear chains amongst the branched copolymer molecules can be modelled as a function of conversion. The effect of varying reactivities can be modelled by assigning different probabilities for the reaction of the double bonds of the monovinyl monomer, the unreacted divinyl monomer and the half-reacted divinyl monomer. The predictions of this Monte Carlo model have been compared with experimental data previously obtained for the ATRP of 2-hydroxypropyl methacrylate with ethylene glycol dimethacrylate (I. Bannister et al., Macromolecules, 2006, 39, 7483-7492). The model predicts higher molecular weights and polydispersities than are actually observed experimentally, probably because branching becomes diffusion controlled in real reactions at high conversion and because the model allows couplings between chains which would be spatially constrained in the real system. The model predicts (i) formation of a proportion of residual linear primary chains if the proportion of divinyl monomer is low and (ii) only very low levels of intramolecular (primary) cyclisation to form loops. Comparison of experimental and predicted molecular weight vs. conversion data confirms that the experimentally determined onset of rapid molecular weight rise can be modelled assuming random addition of double bonds of equal reactivity, leading to statistical branching and more homogeneous structures than are obtained by conventional free-radical polymerisation.