High-temperature quasi-hexagonal phase in the simplest model of a polymer crystal (original) (raw)
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Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services or for technical support, please contact our Customer Care Department within the 2 Packing of Macromolecules in Polymer Crystals 88 2.1 General Principles, 88 2.2 The Principle of Density (Entropy)-Driven Phase Formation in Polymers, 92 CONTENTS vi CONTENTS 2.3 Symmetry Breaking, 96 2.4 Impact of Chain Folding on Crystal Structure Symmetry, 103 2.5 Frustrated Polymer Crystal Structures, 107 2.6 Chiral Crystallization of Polymers with Helical Chain Conformations, 110 2.7 Packing Effects on the Conformation of Polymer Chains in Crystals: The Case of Aliphatic Polyamides, 113 References, 118 3 Methods in Crystal Structure Determination from X-Ray Diffraction 123
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Three-Dimensional Conformation of Folded Polymers in Single Crystals
Physical Review Letters, 2015
The chain-folding mechanism and structure of semicrystalline polymers have long been controversial. Solid-state (SS) NMR was applied to determine the chain trajectory of 13 C CH 3-labeled isotactic poly(1butene) (iPB1) in form III chiral single crystals blended with nonlabeled iPB1 crystallized in dilute solutions under low supercooling. An advanced 13 C-13 C double-quantum NMR technique probing the spatial proximity pattern of labeled 13 C nuclei revealed that the chains adopt a three-dimensional (3D) conformation in single crystals. The determined results indicate a two-step crystallization process of i) cluster formation via self-folding in the precrystallization stage and ii) deposition of the nanoclusters as a building block at the growth front in single crystals.
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A mean-field lattice theory is developed to describe the configurations of long-chain molecules at the crystal/amorphous interface in semicrystalline polymers. Chains are assumed to satisfy continuity and space-filing requirements. The theory permits systematic levels of approximation for correlations among neighboring bonds along the chains subject to the interfacial constraints. We consider the two lowest levels of approximation here: (i) single bonds (two segments) or (ii) bond pairs (three segments). Both models predict that approximately 73% of the chains which emerge from the crystal reenter at sites which are immediately adjacent and that the interfacial region should therefore be small, provided the chains are freely flexible. The models predict that the ratio of chain loop8 to ties in the amorphous region is smaller, and the mean lengths are greater, than predicted by random walk models.