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Characterization of the Slow Molecular Dynamics of Poly( l ‐Lactic Acid) in α and α′ Phases, in a Glassy State, and in a Complex with Poly( d ‐Lactic Acid) by Solid‐State NMR
Author(s) -
Chen Wei,
Zhou Wenxuan,
Makita Yuta,
Wang Shijun,
Yuan Shichen,
Konishi Takashi,
Miyoshi Toshikazu
Publication year - 2018
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.201700451
Subject(s) - lactic acid , arrhenius equation , molecular dynamics , activation energy , amorphous solid , kinetics , glass transition , chemistry , temperature jump , arrhenius plot , proton nmr , materials science , crystallography , polymer chemistry , polymer , stereochemistry , computational chemistry , organic chemistry , physics , genetics , quantum mechanics , bacteria , biology
Recently, slow molecular dynamics of poly( l ‐lactic acid) (PLLA) by using 1D and 2D exchange NMR are investigated. In this work, slow molecular dynamics of PLLA chains in the α′, a stereocomplex (SC) with poly( d ‐lactic acid), and glassy states are investigated in terms of centerband‐only detection of exchange (CODEX) NMR. The mixing‐time dependence of the CODEX data demonstrates that the molecular dynamics of stems become slower in the order of α′, α, and SC. The temperature dependence of the correlation time 〈τ c 〉 of the helical jump motions in the α and SC phases simply exhibits Arrhenius behaviors, with activation energy, E a , values of 91 ± 1 and 97 ± 1 kJ mol −1 , respectively. In contrast, the temperature dependence of 〈τ c 〉 in the α′ sample exhibits two Arrhenius lines with substantially different E a values of 273 ± 12 and 16 ± 14 kJ mol −1 at temperatures below and above 84 °C. The obtained kinetics of molecular dynamics not only establish the relationship between packing structure and dynamics in PLLA polymorphs and in the SC, but also allow for an understanding of the coupled dynamics between the crystalline and amorphous regions at approximately T g .