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Crystallization of Long-Spaced Precision Polyacetals I : Melting and Recrystallization of Rapidly Formed Crystallites

Crystallization of Long-Spaced Precision Polyacetals I : Melting and Recrystallization of Rapidly Formed Crystallites

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ZHANG, Xiaoshi, Xiaobing ZUO, Patrick ORTMANN, Stefan MECKING, Rufina G. ALAMO, 2019. Crystallization of Long-Spaced Precision Polyacetals I : Melting and Recrystallization of Rapidly Formed Crystallites. In: Macromolecules. 52(13), pp. 4934-4948. ISSN 0024-9297. eISSN 1520-5835. Available under: doi: 10.1021/acs.macromol.9b00922

@article{Zhang2019-07-09Cryst-46572, title={Crystallization of Long-Spaced Precision Polyacetals I : Melting and Recrystallization of Rapidly Formed Crystallites}, year={2019}, doi={10.1021/acs.macromol.9b00922}, number={13}, volume={52}, issn={0024-9297}, journal={Macromolecules}, pages={4934--4948}, author={Zhang, Xiaoshi and Zuo, Xiaobing and Ortmann, Patrick and Mecking, Stefan and Alamo, Rufina G.} }

Ortmann, Patrick Alamo, Rufina G. Alamo, Rufina G. Rapidly melt-crystallized polyethylenes with acetal groups (−O–CH<sub>2</sub>–O−) precisely spaced by 12, 18, 19, or 23 methylene backbone carbons exhibit two reorganizations and three melting endotherms on heating at relatively low heating rates. Real-time wide-angle X-ray diffraction (WAXD) experiments further confirm that these transitions are associated with a reorganization to a different crystalline structure. The differential scanning calorimetry endotherms are associated with melting of the initially formed disordered (or hexagonal) phases, followed by melting of Form I and by melting of Form II crystals with increasing temperature. In parallel with these structural changes, the long spacing undergoes a discrete step increase at the polymorphic transitions. Upon the transition from disordered to Form I crystals, the core crystal thickness increases by one repeating unit, whereas the crystal thickness remains basically unchanged during the transition from Form I to Form II crystallites. The effect of even vs odd CH<sub>2</sub> spacer on the observed melting temperatures is prevalent for spacer <10 CH<sub>2</sub> units. The even or odd number of methylenes between acetals also affects the type and kinetics of packing assembly in layered crystallites. Although a disordered mesomorphic-like structure develops under fast cooling in odd-spaced polyacetals (PA-19, PA-23), the formation of Form I crystals cannot be bypassed in PA-12 and PA-18. Furthermore, some differences are also found in the WAXD patterns of Form II between odd- and even-spaced polyacetals, denoting that staggering of the acetals in the crystallites is affected by the configuration of consecutive acetals with respect to the methylene sequence. Zhang, Xiaoshi 2019-07-31T07:32:20Z Mecking, Stefan Crystallization of Long-Spaced Precision Polyacetals I : Melting and Recrystallization of Rapidly Formed Crystallites Zhang, Xiaoshi 2019-07-31T07:32:20Z Ortmann, Patrick Zuo, Xiaobing Mecking, Stefan eng Zuo, Xiaobing 2019-07-09

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