Coupled stochastic simulation of the chain length and particle size distribution in miniemulsion radical copolymerization of styrene and N-vinylcaprolactam

Abstract

Kinetic Monte Carlo modeling is applied for the coupled simulation of the chain length and particle size distribution (CLD and PSD) in isothermal batch miniemulsion copolymerization of styrene and N-vinylcaprolactam (VCL), which are an interesting comonomer pair in view of thermoresponsive polymer nanoparticle applications. Considering a polymerization temperature of 333 K and the oil soluble initiator azobisisobutyronitrile (AIBN), it is shown that disparate terminal monomer reactivity ratios induce consecutive dominant incorporation of styrene and VCL, ultimately leading to a bimodal CLD with relevance of diffusional limitations on termination. Moreover, the initial comonomer fractions are shown to affect the ability of growing oligomers to exit the particle in which they have been generated, thereby affecting the CLD evolution. A strong effect of the initial (Gaussian) PSD is also highlighted, with much higher polymerization rates if this PSD shifts to lower particle sizes. Overall, a very dynamic PSD evolution is simulated, with negative skewing at low monomer conversions and uniformization of the PSD as the monomer conversion increases. The current modeling platform can be further extended with additional reactions such as crosslinking on a longer term.