Shear-Induced Crystallization in Novel Long Chain Branched Polypropylenes by in Situ Rheo-SAXS and -WAXD

• DOI: 10.1021/ma034154l
• Publication Date: 2003-07-08T05:13:43Z
• Authors: Pawan K. Agarwal; Rajesh H. Somani; Weiqing Weng; Aspy Mehta; Ling Yang; Shaofeng Ran; Lizhi Liu; Benjamin S. Hsiao
• Keywords: Branching (polymer chemistry); Small-angle X-ray scattering; Tacticity; Molar mass distribution

The characteristic properties of a new class long chain branched isotactic polypropylene (LCB-iPP) polymers and the effects its molecular architecture on nature orientation-induced crystallization precursor structures kinetics in flow were investigated. In these polymers, branching (LCB) was introduced via situ polymerization propylene diene monomer using metallocene catalyst technology. LCB-iPP exhibited improved melt strength mechanical properties, such as flexural modulus tensile yield strength. As determined by gel permeation chromatography coupled with multiangle laser light-scattering (GPC−MALLS) analysis, it noted that had significant population highly chains high weight component distribution. Dynamic viscoelastic obtained small-amplitude oscillatory shear technique showed increase degree LCB caused broadening relaxation spectrum, especially longest time regime. unique shear-induced development investigated rheo-SAXS (small-angle X-ray scattering) -WAXD (wide-angle diffraction) techniques. results upon application step (rate = 60 s-1, ts 0.25 s, T 140 °C), oriented crystals fraction substantially higher than linear iPP polymer. rate analyzed an Avrami model; value exponent, n, ranged from 1.8 to 2.8 indicating rod or disklike crystal growth geometry. addition, enhanced more order magnitude when compared polymer under shear. details crystalline phases WAXD data that, addition monoclinic α-form crystals, they triclinic γ-form crystals. contribution total phase independent level attributed regio defects chain. Enhancements various well their strong orientation flow, are due which turn strongly broadened complex behavior.