Impact of Long-Chain Branching on Polypropylene Nucleation and Crystallization over a Wide Temperature Range without the Influence of Shear

作者：Xinyan Chen, Ricardo A. Pérez‐Camargo, Pan Ma, Yilong Liao, Ying Zhao, Jin‐Yong Dong, Xia Dong, Alejandro J. Müller, Dujin Wang · 发表于：Macromolecules · 年份：2024 · DOI：10.1021/acs.macromol.4c02256 · 被引用次数：15 · 研究领域：Polymer crystallization and properties、biodegradable polymer synthesis and properties、Polymer Nanocomposites and Properties

Even though the crystallization of long-chain branched polypropylene (LCB-PP) has been widely studied, the role of long-chain branches within isotactic polypropylene ( i PP) under shear-free conditions and a comprehensive understanding of its isothermal crystallization kinetics over a wide crystallization temperature ( T c ) range are still lacking. The samples in this work were prepared by solution casting to eliminate any possible shear effects. Then, the impact of LCB on the crystallization behavior of i PP with varying content of long-chain branches (LCB) was investigated in the entire crystallization window range. Polarized light optical microscopy (PLOM) and scanning electron microscopy (SEM) revealed that the i PP nucleation density increased with branching content. Standard differential scanning calorimetry (DSC) and ultrafast scanning chip calorimetry (or FSC, fast scanning calorimetry) showed that the overall crystallization rates had different dependence on the branching content across a wide temperature range (5–136 °C). Above 95 °C, only the α-phase of i PP formed, with an increasing crystallization rate with branching content. In addition to the typical heterogeneous nucleation, the LCBs provoke a significant increase in the nucleation density through a homogeneous nucleation process triggered by the topological constraints of the segments linked to the branch point. These constraints stabilize the PP chain’s helical structure and facilitate the self-assembly of...