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New contributions from thermal and dielectric techniques to the understanding of the dynamic properties of medium to long chain poly (propylene glycols)
Author(s) -
Diogo Hermínio P.,
Moura Ramos Joaquim J.
Publication year - 2021
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.25687
Subject(s) - differential scanning calorimetry , glass transition , materials science , fragility , amorphous solid , relaxation (psychology) , polymer , dielectric , atmospheric temperature range , activation energy , thermodynamics , analytical chemistry (journal) , polymer chemistry , chemistry , composite material , crystallography , organic chemistry , physics , optoelectronics , psychology , social psychology
The molecular mobility of poly (propylene glycols) with molecular weights between 2000 and 18,200 g mol −1 was studied in the amorphous solid state, in the region of the glass transition and in the rubbery state; the experimental techniques used were differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). It was found that the glass transition temperature increases slightly with MW and tends to a limit value: T gDSC = −67°C, T gTSDC = −73°C. The different types of molecular mobility were analyzed: below T g the secondary relaxations, and above this temperature the normal mode, were characterized in detail using TSDC; in the glassy transformation region, around T g , the main relaxation was analyzed by both DSC and TSDC. It was found the dynamic fragility, m , behaves as independent of the molecular weight in the studied range: m DSC = 74 and m TSDC = 92. The TSDC results also show that, without influencing the kinetics of the segmental relaxation, the increase in molecular weight slows down the chain relaxation.