Effect of Molecular Weight on the Crystallization and Melt Memory of Poly(ε-caprolactone) (PCL)

作者：Ainhoa Fernández‐Tena, Ricardo A. Pérez‐Camargo, Olivier Coulembier, Leire Sangroniz, Nora Aranburu, Gonzalo Guerrica‐Echevarría, Guoming Liu, Dujin Wang, Dario Cavallo, Alejandro J. Müller · 发表于：Macromolecules · 年份：2023 · DOI：10.1021/acs.macromol.3c00234 · 被引用次数：188 · 研究领域：biodegradable polymer synthesis and properties、Polymer crystallization and properties、Microplastics and Plastic Pollution

High Resolution Image Download MS PowerPoint Slide The role of the molecular weight in the crystallization and melt memory of poly(ε-caprolactone) (PCL) was investigated. To this end, 10 PCL samples of synthetic and commercial origin and different chain ends, covering a number-average molecular weight ( M n ) range between 0.48 and 70.5 kg/mol, were analyzed. Polarized light optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering (SAXS) were employed for in-depth characterization. The thermal transitions, morphology, crystallization kinetics, structural parameters, and memory effects were evaluated as a function of M n . The melting temperature and the equilibrium melting temperature saturate at a particular M n . Instead, the crystallization temperature and the degree of crystallinity display an optimum M n at which the parameters reach a maximum, describing a bell-shaped behavior as a function of M n . Similarly, the primary nucleation rate, spherulitic growth rate, and overall crystallization rate exhibit a bell-shaped behavior as a function of M n, attributed to a competition between nucleation and diffusion. SAXS analysis, which includes the long period and lamellar thickness determination, revealed that at M n < 2.0 kg/mol, PCL crystallizes in an extended-chain conformation, while at M n ≥ 2.0 kg/mol, folded chains are already present. In line with these results, the morphological study showed that the PCL crystallizes as axialites at M n...