Abstract
ABSTRACTThe local and cooperative dynamics of atactic PS (a‐PS) were studied by broadband dielectric relaxation spectroscopy (BDRS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR). The a‐PS has been subjected to thermal rejuvenation and subsequent quenching, short‐term aging (6 weeks), and long‐term aging (1 year) at ambient conditions. Where for the rejuvenated sample only an α‐ and a γ‐relaxation is observed, short‐term aging results in an additional β*‐relaxation that merges with the α‐relaxation at longer aging times. The γ‐relaxation is increasing in intensity and activation energy during aging. The α‐process shows no spectral changes and shift in the relaxation time upon aging. This may be attributed to a possible erasure of history of the material during the temperature‐sweep mode measurement. Fourier transform infrared spectroscopy (FTIR) results suggest that the energetically favorable trans‐trans (tt) conformers are increased in population with aging. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1394–1401
Highlights
The glass-transition temperature Tg, glasses are known to be in a nonequilibrium state and their relaxation toward equilibrium is called physical aging.[1]
We study rejuvenated and fast cooled atactic polystyrene (a-PS) using dielectric and ATR-Fourier transform infrared spectroscopy (FTIR)
Dielectric Relaxations The molecular dynamics of thermally rejuvenated, short- and long-term aged a-PS were studied by broadband dielectric relaxation spectroscopy (BDRS)
Summary
The glass-transition temperature Tg, glasses are known to be in a nonequilibrium state and their relaxation toward equilibrium is called physical aging.[1] Physical aging causes a slow alteration of the physical structure of the material. A gradual increase of the yield stress of the material is observed, which causes embrittlement,[2] resulting in a gradual loss of the design function and ultimate failure. These macroscopic changes make physical aging of enormous importance, both on a technical and research level. Numerous studies have been done to examine the effect of physical aging on the macroscopic mechanical behavior of glassy polymers[3,4,5,6,7,8] and for the enthalpy changes upon aging.[8,9,10,11,12,13,14] Most of the studies are trying to explain their results based on the free-volume theory,[1] in which the changes of the properties of the material are interpreted solely by the changes in free volume.[15,16,17,18,19] Other studies try to explain their results from the standpoint of segmental/chain mobility.[20,21] the link between the molecular structure and intrinsic properties is still lacking
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