Effect of low‐temperature physical aging on the dynamic transitions of atactic polystyrene in the glassy state

Abstract

The 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

Structural Transitions in Glassy Atactic Polystyrene Using Transition-State Theory

“…Dashed lines in the main figure correspond to macroscopic relaxation rates of the four relaxation processes, namely α, β*, γ, and δ (from left to right, respectively) obtained by dielectric relaxation experiments. 100 , 101 …”

“…The time scales of those maxima appear close to the dashed lines that mark macroscopic relaxation time scales, probed by Dielectric Spectroscopy (DS). Grigoriadi et al 100 have succeeded in measuring the dielectric response of freshly quenched aPS. Their experiments identified three distinct relaxation processes, namely the α-relaxation of the glass transition, a β*-relaxation that was present only in the case of freshly quenched glasses and disappeared after aging of the samples, and a γ-relaxation that was always measured irrespectively of the thermal history of the sample.…”

“…In the inset to the figure, a power-law fit (with the exponent a defined in the text) to the lower half (10 –15 ≤ k A → B ≤ 10 5 ) of the distribution is presented in double-log representation. Dashed lines in the main figure correspond to macroscopic relaxation rates of the four relaxation processes, namely α, β*, γ, and δ (from left to right, respectively) obtained by dielectric relaxation experiments. , …”

Physical aging of PC:PS blends: Dynamic mechanical analysis and nuclear magnetic resonance studies

“…[1] This phenomenon, which is thermo-reversible, affects several physical properties such as density, impact strength, permeability, modulus, specific enthalpy, and so forth. [1][2][3][4][5] This is valid for polymers, [6][7][8][9][10][11][12][13][14] polymer blends, [15][16][17][18][19][20] and polymer nanocomposites. [21][22][23] It is thus highly important to study the physical aging of polymer systems to determine their long-term evolution.…”

“…[31][32][33][34] But more recently, efforts to better understand the aging of polymers focused on a wide range of various techniques including positron annihilation lifetime spectroscopy, spectroscopic ellipsometry, and fluorescence spectroscopy. [11,13,14,19,20,[35][36][37] Among all the commercial polymers available today, polycarbonate (PC) and polystyrene (PS) have been widely used because of their good properties including thermal stability, transparency, and their similar mechanical and dielectric properties, which allow them to be used as a blend pair in the preparation of nanocomposites and modified blends. Furthermore, PC:PS blends have been highly studied to account for the advantages of each polymer.…”