Article Cite This: Macromolecules XXXX, XXX, XXX−XXX
pubs.acs.org/Macromolecules
Intramolecular and Intermolecular Packing in Polymer Crystallization Shijun Wang,† Shichen Yuan,† Kun Wang,† Wei Chen,‡ Koji Yamada,§ Deborah Barkley,∥ Tadanori Koga,∥,⊥ You-lee Hong,# and Toshikazu Miyoshi*,† †
Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909, United States National Synchrotron Radiation Lab, CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, P. R. China § Advanced Processing Technology Unit, Research Center, Toyobo Co., Ltd. 2-1-1 Katata, Otsu, Shiga 520-0292, Japan ∥ Department of Chemistry and ⊥Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, New York 11794, United States # RIKEN CLST-JEOL Collaboration Center, RIKEN, Yokohama, Kanagawa 230-0045, Japan
Downloaded by NEW JERSEY INST OF TECHNOLOGY at 05:52:00:982 on June 10, 2019 from https://pubs.acs.org/doi/10.1021/acs.macromol.9b00702.
‡
S Supporting Information *
ABSTRACT: Recently, the chain-folding structure of 13Clabeled poly(L-lactic acid) (PLLA) with different molecular weights (M) of 46K (small, s), 90K (middle, m), and 320K g/ mol (large, l) in the solution-grown crystals [Macromolecules 2018, 51, 8729−8737] was studied by solid-state nuclear magnetic resonance (ssNMR). In this work, the chain-folding and packing structures, long period, and morphology of 13Clabeled s-, m-, and l-PLLA in the melt-grown crystals crystallized at Tc = 90 and 150 °C are investigated by ssNMR, small-angle X-ray scattering (SAXS), wide-angle Xray diffraction (WAXD), and polarized optical microscopy (POM), respectively. All the s-, m-, and l-PLLA adopt thermodynamically stable α crystals and large spherulites with a diameter of ∼2 mm at Tc = 150 °C. A large supercooling induces kinetically favored disordered α′ crystals and nodular structures for all three samples. By comparing the experimental 13C−13C double quantum (DQ) buildup data with the simulated ones, we found that all three PLLA samples with different Mws adopt adjacent re-entry structure with the same mean value of successive adjacent re-entry number, n, of 1.5−2 in both α and α′ crystals under the assumption of full adjacent reentry, F = 100%. Through systematic studies on the chain-folding structure as functions of Tc and Mw, it is concluded that the chain-folding process is a local event and is independent of the overall crystallization process. On the basis of the chain-folding and packing structures in both solution- and melt-grown crystals, contributions of the intramolecular and intermolecular packing to the order−disorder phenomenon of the overall packing structure will be discussed. to structural studies under a large supercooling.14−19 To avoid this problem, Zheng et al. used monodisperse polyethylene (PE) oligomers only with the chain end labeled by 2H and studied the chain-level structure of PE during isothermal crystallization by in-situ neutron scattering.20 Recently, our group developed a novel experimental strategy to access the detailed chain-folding structures in the melt- and solution-grown crystals21−31 by using selective 13C isotope labeling and 13C−13C double quantum (DQ)32 NMR spectroscopy. The 13C−13C DQ NMR provides a measure of apparent dipolar coupling strengths for a given 13C site, which represent the root-mean-square sum of many 13 C−13C pair couplings which are determined by chain
1. INTRODUCTION Crystallization of long polymer chains induces structural formations at hierarchical length scales, i.e., conformation, packing, crystalline lamellae, and spherulites.1−5 These structures and their time evolutions have been successfully characterized by various experimental techniques in the past decades.6−10 One of the missing structures in polymer crystallization is the chain-level structure.11,12 Because synthetic polymers consist of the same repeating monomer units, it is challenging to distinguish the intramolecular packing structure from the intermolecular one. So far, 2H or 13C isotope labeling combined with characterization techniques has been applied to study the chain-level structure of synthetic polymers (intramolecular structure) in the solution- and melt-grown crystals.13−31 However, 2H/1H polymer systems showed segregations under a low supercooling13 and thus was limited © XXXX American Chemical Society
Received: April 6, 2019 Revised: May 25, 2019
A
DOI: 10.1021/acs.macromol.9b00702 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules trajectory of 13C-labeled polymers.21−31 The dipolar coupling strength is inversely proportional to third power of the internuclear distance. Thereby, this method is particularly sensitive to a short-range structure (120 °C and
