Modification of the Crystallization Behavior of Isotactic Polypropylene by Grafting Styrene Segments

As a typically semicrystalline polymer, the physical properties of isotactic polypropylene (iPP) are directly related to its crystallization. In this work, styrene (St) is grafted onto iPP chains by reactive processing to modify its crystallization behavior. The St grafting segments disrupt the stereoregularity of the iPP chain, leading to the appearance of a γ-crystal. More interestingly, the presence of St grafting segments can remarkably increase the crystallization temperature and crystallization rate of iPP and reduce the size of crystals. On the one hand, the rigid structure of benzene rings in St grafting segments can squeeze easily iPP chains to form the relatively ordered structure, which can be further stabilized by the mutual π–π conjugation between the benzene rings and the helix chains of iPP. On the other hand, the St grafting segments locating in the amorphous phase can hinder the growth of crystals, which leads to finer and more crystals.