Crystal structures, crystallization and II–I transition behaviors of iPB-1 in iPB-1/UHMWPE blends. Part 1. Crystal structures and crystallization behaviors

Abstract

Isotactic polybutene-1 (iPB-1) is of particular commercial interest due to its excellent mechanical performances. The form I polymorph is preferred in most industrial applications, while the form II is kinetically favored while melt processing. The slow II–I transition after melt processing dramatically hinders the iPB-1 applications. With new observations arising, the traditional solid–solid nucleation-controlled II–I transition mechanism encounters challenges. The role of the iPB-1 amorphous phase attracted many researchers' interests. In this work, an ultra-high molecular weight polyethylene (UHMWPE, labeled as PE4012) was melt-blended with iPB-1. The melt crystallization behaviors and the crystal structures of iPB-1 in the blends were investigated. It reveals that PE4012 addition inhibits the overall melt crystallization kinetics of iPB-1 in the blend due to the decreasing the spherulite nucleation density despite the observed radius spherulite growth being enhanced. The melting points, lamella thickness, the degree of crystallinity of forms I and II, the excess free energy of the fold surface σ_e, and the glass transition temperature T_g of form II iPB-1 all decrease with PE4012 weight proportion. The PE4012 component, mainly acting as an “obstacle” dispersed in the blend, disturbs the iPB-1 melt crystallization process with its initial start hindered, and interactions exist between the two components iPB-1 and PE4012 in the immiscible but to some extent compatible blend. Therefore, PE4012 is suitable for blending with iPB-1 and it may provide a good model system to look into the II–I transition process and its mechanism (will be discussed in the future as part 2).