Correlation between Grafting Density and Confined Crystallization Behavior of Poly(ethylene glycol) Grafted to Silica

作者：Xiangning Wen, Yunlan Su, Yudan Shui, Weiwei Zhao, Alejandro J. Müller, Dujin Wang · 发表于：Macromolecules · 年份：2019 · DOI：10.1021/acs.macromol.8b02007 · 被引用次数：57 · 研究领域：biodegradable polymer synthesis and properties、Polymer crystallization and properties、Polymer Nanocomposites and Properties

The interfacial interactions of polymer–nanoparticles have dramatical effects on the crystallization behavior of grafted polymers. In this study, methoxypolyethylene glycol (MPEG) (molecular weights 750, 2000, and 4000 g mol –1 ) was grafted onto amino-modified nanosized silica (SiO 2 -NH 2 ) by the “grafting to” method. The effects of the grafting density and molecular weight on the confined crystallization of grafted MPEG (MPEG- g -SiO 2 ) were systematically investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and wide-angle X-ray scattering (WAXS). It was found that confinement effects are stronger when lower molecular weights of grafted MPEG are employed. These grafted MPEG chains are more difficult to stretch out on SiO 2 -NH 2 surfaces than when they are free in the bulk polymer. Both crystallization temperature ( T c ) and crystallinity of grafted MPEG chains decrease with reductions of grafting density. Additionally, covalent bonding effects and interfacial interaction confinement effects are strengthened by the decrease in grafting density, leading to an increase in decomposition temperature and to the disappearance of the self-nucleation Domain (i.e., Domain II), when self-nucleation experiments are performed by DSC. Overall isothermal crystallization kinetics was studied by DSC, and the results were analyzed with the Avrami equation. An Avrami index of n ≈ 3 was obtained for neat MPEG (indicating that instantaneous spherulites...