DSC analysis was performed on uniaxially oriented and unoriented atactic polystyrene samples prior to and after annealing at 80 °C. With increasing annealing times, an endothermic peak appeared, whose area increased with the duration of the annealing period. No difference was found between the endotherm areas for the oriented and the unoriented polymer.
Authors:T. Watanabe, G. Zhang, H. Yoshida, and T. Kawai
The miscibility of crystalline syndiotactic polystyrene (SPS)/non-crystalline atactic polystyrene (APS) blend was estimated
by the crystallization dynamics method, which evaluated the nucleation rate, the crystal growth rate and the surface free
energy parameter. The melting temperature depression suggested that SPS/APS blends were the miscible system but not in molecular
level. The relationship between the blend content and the chemical potential difference evaluated at a constant crystal growth
rate showed a good linear relationship. These facts suggested that SPS/APS blends contained the concentration fluctuation
with the size between few nm to less than 80 nm.
Authors:E. Marti, E. Kaisersberger, and E. Moukhina
heat capacity or the specific heat is for any crystalline, partially amorphous
or completely amorphous substance or material a significant thermodynamic
property. The glass transition may be regarded as the melting point of amorphous
substances and materials, a transition property of an outstanding technical
importance. A crucial point is the fact that the presence of a glass transition
is an unequivocal proof of an amorphous content of a material. Furthermore,
the change of the specific heat at the glass transition temperature enables
the quantitative determination of the amorphicity on a relative or absolute
level of any substance or material. The absolute determination of the amorphicity
affords a calibration with a reference corresponding to the material under
investigation. The crystallinity for this reference substance must be known
from the preparation and or by any independent analytical method.
literature data for the specific heat and the glass transition of polystyrene
were collected and evaluated. Data were found for the specific heat in literature
from 10 to 470 K. The data were unified for each of the reported temperature
in a mean value and the corresponding standard deviation was determined. An
excellent conformity was found in the glassy state of polystyrene with standard
deviations lower than 0.7%. The standard deviations above the glass transition
were considerably higher.
All these literature data were transferred
for each of the literature sets separately into linear specific heat functions
in the vicinity of the glass transition. One set of our measurements performed
with the DSC 204 and with polystyrene SRM 705a as sample material was additionally
integrated in the mean of these functions for the glassy state and the liquid
amorphous state respectively. The addition of our results gave practically
no change of the mean coefficients and only a decrease of the standard deviations.
In such a way, the data with the best statistical base for the specific heat
of polystyrene are listed in this paper ( ‘Conclusions’).
The glass transition as a transition in and out of a non-equilibrium
state, the glassy state, is sensitive to all kind of influences such as thermal
and mechanical treatments as well as to the selected experimental conditions.
Therefore, certain standardized conditions procedures must be fulfilled to
get reproducible data. The literature data for the glass transition temperature
were also used to get a mean value. However, two values were omitted for the
formation of the mean, because the authors reported values, which were too
low on the base of impurities present. The mean value of the glass transition
for polystyrene is according to the literature 3692 K. A mean value
of 3702 K was extrapolated for an infinite molecular mass.
The DSC and TMDSC measurements for the three thermodynamic properties
reported in this paper, namely the specific heat, the glass transition temperature
and the corresponding change of the specific heat gave results without significant
differences compared with the literature values.
is a rather ideal polymer together with sapphire as calibration substance
to elucidate and validate the DSC and TMDSC procedures for the determination
of the specific heat and the glass transition.