Tacticity as a Factor Contributing to the Thermal Stability of Polystyrene

Abstract

TGA has been used to study the thermal degradation of PS in atactic (aPS), syndiotactic (sPS), and isotactic (iPS) forms. Thermal stability of sPS is similar to that of aPS, whereas iPS degrades at a notably higher temperature. TGA‐FT‐IR data do not show any obvious difference in the degradation products of the three materials. Isoconversional kinetic analysis of non‐isothermal TGA data yields somewhat higher activation energy for degradation of iPS than for aPS that is found to result in a smaller rate constant for iPS. Another important factor contributing to slower degradation rate of iPS is found to be the reaction model that has been experimentally determined from isothermal TGA measurements. The enhanced thermal stability of iPS correlates with its hindered molecular mobility that appears to originate from intramolecular confinement. The hindered mobility has been detected by comparing the glass transition dynamics in amorphous iPS and aPS samples. By using multi‐frequency temperature modulated DSC (TOPEM®) it has been demonstrated that the activation energy of the glass transition is noticeably larger for iPS than for aPS that supports the hypothesis of the slowed down molecular mobility.

Limitations of model-fitting methods for kinetic analysis: Polystyrene thermal degradation

“…Other works employing similar single-curve model-fitting kinetic procedures reached analogous conclusions (Ahmad et al , 2010, Ahmed and Gupta, 2009, Krishna and Pugazhenthi, 2011. However, some other works, employing isoconversional and non-linear model fitting methods, have revealed the unsuitability of nth order reaction models and suggest an acceleratory model instead (Chen et al , 2007, Sanchez-Jimenez et al , 2010, Snegirev et al , 2012, Vyazovkin et al , 2004. Such was confirmed by Sanchez-Jimenez et al, proposing a random chain scission model (Sanchez-Jimenez et al , 2010, Sanchez-Jimenez et al , 2012.…”

“…An important volume of work has been devoted to the determination of the activation energy and kinetic model describing the thermal degradation of polystyrene (Brems et al , 2011, Chen et al , 2007, Chen and Vyazovkin, 2006, Faravelli et al , 2001, Peterson et al , 2001, Sanchez-Jimenez et al , 2012, Snegirev et al , 2012, Sterling et al , 2001, Westerhout et al , 1997. However, results show a wide divergence in the activation energy values and the kinetic models proposed.…”

Vitrification and Devitrification during the Non‐Isothermal Cure of a Thermoset. Theoretical Model and Comparison with Calorimetric Experiments

“…TOPEM is based on the application of stochastic temperature pulses superimposed on the underlying constant heating rate, which allows the evaluation of the response over a wide range of frequencies in a single experiment, [9] e.g., for the study of the kinetics of the glass transition. [10,11] In the second part of this work, we make use of a theoretical simulation to obtain the vitrification and devitrification times as a function of frequency in order to compare them with the experimental results.…”

Vitrification during the Isothermal Cure of Thermosets: Comparison of Theoretical Simulations with Temperature‐Modulated DSC and Dielectric Analysis

“…TOPEM is based on the application of stochastic temperature pulses superimposed on the underlying constant heating rate, which allows the evaluation of the response over a wide range of frequencies in a single experiment, [9] for example for the study of the kinetics of the glass transition. [10,11] In the second part of this work, we make use of a theoretical simulation to obtain the vitrification and devitrification times as a function of frequency in order to compare them with the experimental results.…”