Preparation of Polypropylene/Polystyrene Composite Particles with Multilayered Inner Morphology by Seeded Emulsion Polymerization

Submicron-sized polypropylene (PP)/polystyrene (PS) composite particles were successfully prepared by seeded emulsion polymerization of styrene with a water-soluble cationic initiator. From the observation of the resulting composite particles through scanning and transmission electron microscopies, it was revealed that the particles were surrounded by many patches composed of PS. Surprisingly, the PP/PS composite particles showed an interesting internal morphology in which the PP and PS phases form multilayered structures. It is proposed that this interesting internal morphology was derived from the multi-hollow structure of seed PP particles. The results of the microscopy analysis revealed that the morphology of the composite particles was obtained by infiltration of PS into the voids in seed PP particles. Moreover, the PS phase that could not be extracted using hot tetrahydrofuran was detected by proton nuclear magnetic resonance; therefore, some parts of the PS chain should have been covalently bonded to PP. We also clarified that adhesive performance was superior to the PP/PS emulsion blend system, which indicated that the obtained composite particles would be useful for an application as an adhesive.