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Analogies of the Spatial Proximity of Polymer Racemate Glass and Crystal as Revealed by NMR Crystallography:
Chenxuan Sun1,2, Zheng Huang1, Fan Jin1
1School of Polymer Science and Polymer Engineering, The University of Akron, Akron, Ohio 44325-3909, United States.
Abstract:
The crystallization pathway of long and flexible polymer chains is debatable because of the lack of an initial melt/glass structure. To identify the crystallization pathway, we focus on two binary blends of poly(lactic acid) racemates that form stereocomplex crystals (SCCs). NMR crystallography is used to identify the stereocomplex (SC) structure and SC fraction with or without long-range order. There are significant structural analogies between glass and crystals for both high-molecular-weight (M) and low-M racemates. The observed analogies and kinetics of crystallization indicate that polymer crystallization proceeds via chain segments moving the least possible distance ("freezing in" mechanism) and that topological constraints govern nucleation barriers.
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