Shear‐induced β‐form polypropylene in long chain branching isotactic polypropylene

Long chain branching polypropylene (LCBPP) with different long chain branching (LCB) contents were prepared by reactive extrusion in the presence of styrene and benzoyl peroxide, and their shear‐induced crystallization behaviors were investigated. The results indicated that the LCB structure extended the relaxation time of LCBPP in the molten state, which led to the formation of β‐form polypropylene under shear and high cooling rate. The content of β‐form (Kβ) increased with the increase of LCB content, shearing rate and cooling rate. The Kβ value of LCBPP3 whose weight average molecular weight was 920,000 g mol−1 could be up to 52.0% with a shear rate of 60 s−1 associated with a cooling rate of 280°C min−1. This study is expected not only to have a deeper understanding of the shear‐induced crystallization behavior of LCBPP, but also provide a new strategy to obtain high level β‐form polypropylene. POLYM. ENG. SCI., 56:240–247, 2016.