Abstract
As part of our continuing studies concerned with the free-radical crosslinking polymerization of multivinyl compounds, this article deals with the preparation of crosslinked polymer microspheres by the emulsion polymerization of allyl methacrylate (AMA); the resulting microspheres as pseudo-microgels were characterized and post-polymerized. Firstly, the solution polymerization behavior of AMA was pursued by light scattering in comparison with the polymerization of ethylene dimethacrylate in which microgelation occurs easily ; thus no microgelation was observed up to the gel-point conversion as a reflection of the low reactivity of growing methacrylyl radical toward the pendant allyl groups of prepolymer resulting in the suppressed occurrence of intramolecular crosslinking. Secondly, the emulsion polymerization of AMA was compared with the bulk polymerization ; no gelation was observed even above 90% conversion, while in the bulk polymerization the gel point was determined as 4%. The resulting polymers were then characterized by examining the conversion dependences of weight-average molecular weight and molecular-weight distribution, the correlations of molecular weight vs elution volume and r. m. s. radius of gyration vs molecular weight, the intrinsic viscosity, 1H-NMR spectrum, and the conversion dependence of residual allyl group, thus suggesting that the microgel-like polymers of low crosslinking density could be obtained by the emulsion polymerization. Finally, these reactive crosslinked polymer microspheres of abundant pendant allyl groups were post-polymerized as comared with the post-polymerization of an ordinary prepolymer : The rates of polymerization and gel formation were low in the post-polymerization of microsphere and they became remarkable with increasing microshere size. The swelling ratio of resulting gel was quite small even at an early stage of polymerization and its conversion dependence showed a minimum point. In addition, the post-polymerization behavior of microsphere depended markedly on concentration. These are discussed, considering the concurrent occurrence of intramolecular and intermolecular crosslinking, and the entanglement of polymer chains.
