Free-radical polymerization induced macrophase separation in poly(methyl methacrylate)/dimethacrylate blends: Experiment and modeling

• Styrene/dimethacrylate/PMMA mixtures undergo phase separation during reaction.
• A spinodal decomposition mechanism frozen at early stages is evidenced.
• We propose a thermodynamic model to describe the phase separation process.
• The model computes the evolution of the unstable region as a function of conversion.
• The accuracy of the proposed thermodynamic model is verified.

This work presents the analysis of a polymerization-induced macrophase separation taking place during free-radical copolymerization of styrene and dimethacrylate in the presence of poly(methyl methacrylate) (PMMA) as a modifier. The PMMA does not participate in the polymerization but induces phase separation in the course of the reaction. An experimental study based on real-time static light scattering measurements with the aim of monitoring the phase behavior during the isothermal copolymerization is firstly presented. Then, an original and innovative contribution is made by modeling the evolution of the unstable region of the phase diagram as a function of conversion and by predicting phase separation in spinodal condition. The analysis is performed using an expression for the free energy of a reactive network-forming mixture based on the Flory–Rehner lattice model for swollen gels. The accuracy of the proposed model is verified by the good agreement found between its predictions and the experimental results.

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