Preparation of isotactic polypropylene/polystyrene blends by diffusion and subsequent polymerization of styrene in isotactic polypropylene pellets

Isotactic polypropylene (iPP) pellets were used to prepare isotactic polypropylene/polystyrene (iPP/PS) blends by diffusion and subsequent polymerization of styrene in water medium, with initiator benzoyl peroxide (BPO) added after diffusion of styrene. Two methods, differencing in whether the excess monomer was removed after diffusion, were used and parameters influencing PS contents were investigated. Diffusion kinetic study showed that the diffusion coefficient at 90 °C is 2.8 times that at 80 °C due to the α relaxation of iPP segments. Investigation on the distribution state of styrene in the mixture before diffusion revealed that most styrene adsorbed on the surface of iPP pellets, and thus the diffusion behavior of styrene into iPP pellets in water medium is similar to that in bulk styrene. Phase morphology of a typical iPP/PS blend showed an average particle size of about 90 nm in the inner part of the iPP pellets. The diametrical distributions of PS showed that styrene can diffuse up to the center of the pellets at 90 °C. It is important to note that the depth of styrene is limited when the initiator BPO is added along with styrene, providing a good explanation for the previously reported ineffective solid-state modification of melt-extruded iPP pellets.