Heterogeneities at the Onset of Reaction Acceleration during Bulk Polymerization of Methyl Methacrylate Investigated by Small-Angle Neutron Scattering

Abstract

During bulk free-radical polymerization of methyl methacrylate below the glass-transition temperature of poly(methyl methacrylate), the relative fraction of monomer and polymer changes as the reaction proceeds. The liquid monomer is eventually converted to a solid glassy polymer. In other words, polymerization-induced vitrification or glass transition occurs. This process was traced by small-angle neutron scattering (SANS). The scattering profile discontinuously changes at the vicinity of vitrification. This discontinuous change was correlated with a sudden reaction acceleration known as the Trommsdorff effect. Ornstein–Zernike analysis revealed that the intensity at q = 0 (I(0)) and the correlation length of concentration fluctuation (ξ) suddenly increase at the discontinuous change of the scattering profile. The obtained data implies that the increased heterogeneity (i.e., microscopic concentration fluctuation) is intimately related to the Trommsdorff effect.