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Molecular dynamics, crystallization and hydration study of Poly(Propylene succinate) based Poly(Ester amide)s

: Klonos, P.A.; Kluge, M.; Robert, T.; Kyritsis, A.; Bikiaris, D.N.


Polymer 186 (2020), Art. 122056, 13 S.
ISSN: 0032-3861
Fraunhofer WKI ()
poly(propylene succinate); poly(ester amide)s; polymer crystallization; glass transition; dielectric spectroscopy; local dynamics

Poly(ester amide)s, PEA, based on poly(propylene succinate), PPS, improved by the addition of a new symmetrical amido diol, AD, at various molar fractions are investigated in this article. The emphasis is given on the effect of AD (hard segment) on crystallization and molecular mobility of the polymer. To that aim, we employed differential scanning calorimetry, DSC, and broadband dielectric spectroscopy, BDS. AD was found to systematically facilitate crystallization, both with respect to the rate and the fraction (CF increases from 0 up to ~50 wt%), which is desirable for industrial processing and applications. In agreement with previous findings on the same systems, our results suggest that the crystallites consist mainly of the hard AD segments, whereas soft segments (PPS-related) are the main contributors to the glass transition. AD was found to increase the glass transition temperature, Tg, of the soft segments both calorimetric and dielectric, indirectly via the increase in the CF. The rigid amorphous fraction, RAF, of the polymer existing in the vicinity of the formed crystals was estimated and is proposed to consist mainly of soft segments without, however, excluding a minor contribution of non-crystallized AD. RAF exhibits non-systematic alternations with CF, most probably due to the expected variations in the semicrystalline morphology. BDS allowed the full-temperature range dynamics mapping and, subsequently, revealing of effects of the polymer composition in combination with CF and the involved traces of water on the local (β and βw relaxations) and segmental (α relaxation) dynamics. Upon addition of AD, the ester bond-related local β relaxation of PPS accelerates, exhibiting, however, unchanged activation energy (Eact~39 kJ/mol). Simultaneously, α relaxation, related to the glass transition, slows down (in agreement with calorimetry) and exhibits a worth noting decrease in cooperativity. These results indicate severe effects on molecular dynamics and suggest possible changes in the polymer free volume/density in the PEAs. βw relaxation with Eact~58 kJ/mol is recorded for the first time in PPS and is related with the same ester group as β, moreover, with water molecule(s) attached.