Unusual Spherulitic Morphology of Poly(propylene fumarate)
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ARTICLE
POLYMER SCIENCE
https://doi.org/10.1007/s10118-021-2518-y Chinese J. Polym. Sci.
Unusual Spherulitic Morphology of Poly(propylene fumarate) Xiao-Yu Meng, Yi Li, Shu-Fang Yao, Xue-Wei Wei, and Hai-Mu Ye* Department of Materials Science and Engineering, College of New Energy and Materials, China University of Petroleum, Beijing 102249, China
Abstract Spherulites are the most common crystalline morphology and thus the visual expression of crystal structures for polymers. The diversified patterns have provided intuitive morphology probes for various crystallization behaviors, while the correlations between them are still needed to be enriched. In this work, the complicated spherulitic morphology of poly(propylene fumarate) (PPF), which is sensitive to crystallization temperature, is investigated. PPF melt, respectively, crystallizes into rough spherulites, regularly banded spherulites, and spherulites containing both two kinds of morphology at low, high, and mediate temperatures. By systematically assaying, it is clear that the growth axis along the radial direction changes from a-axis to b-axis as the crystallization temperature increases, which leads to the formation of unique crystallization-temperature-dependent spherulites. Based on detailed characterization of Fourier transform infrared spectroscopy, the packing state of the specific hydrogen bonds of “C＝C―H···O＝C―C＝C” in PPF crystal lattices is determined, and furthermore, the mechanism for temperature-dependent selection of growth axes for PPF spherulites in melt is reasonably speculated. Keywords Spherulite; Crystallization; Growth axis; Hydrogen bond Citation: Meng, X. Y.; Li, Y.; Yao, S. F.; Wei, X. W.; Ye, H. M. Unusual spherulitic morphology of poly(propylene fumarate). Chinese J. Polym. Sci. https://doi.org/10.1007/s10118-021-2518-y
INTRODUCTION Spherulites can be found in small organic molecules, synthetic ceramics, minerals and nearly all crystallizable polymers.[1−3] The spherical structure, a polycrystalline aggregate composed of fine lamellae, is the most common morphology of semicrystalline polymer,[2] which is often crystallized from viscous melts or solutions at large supercoolings. When detected between orthogonal linear polarizers, the arresting birefringent characteristics originated from anisotropic bodies in quasi-twodimensional spherulites reflect a number of structural informations. Consequently, spherulites have become essentially important morphological probes to unveil crystal structure of polymer, and thus develop crystallization theory.[4−7] Morphology of spherulite has been effectively used to reveal the packing state of polymer lamellae. A positive spherulite has its highest refractive index for the light vibrating along the radius, and a negative spherulite has the highest refractive index for the light vibrating tangentially. For example, poly(L-lactide) (PLLA) formed negative nonbanded spherulites, corresponding to the predominate growing of edge-on lamellae along radial directions.[8,9] The signs of the b
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