ISSN:
0887-6266
Keywords:
bulk modulus
;
equation of state
;
heat capacity
;
high-pressure
;
poly(isobutylene)
;
thermal conductivity
;
transient hot-wire method
;
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The thermal conductivity λ and heat capacity per unit volume ρcp of poly(isobutylene)s, one 2.8 in weight average molecular weight and one 85 kg mol-1 in viscosity average molecular weight (PIB-2800 and PIB-85000), have been measured in the temperature range 170-450 K at pressures up to 2 GPa using the transient hot-wire method. At 297 K and atmospheric pressure, λ = 0.115 W m-1 K-1 for PIB-2800 and λ = 0.120 W m-1 K-1 for PIB-85000. The bulk modulus BT has been measured in the temperature range 170-297 K up to 1 GPa. At atmospheric pressure, the room temperature bulk moduli BT are 2.0 GPa for PIB-2800 and 2.5 GPa for PIB-85000 with dBT/dp = 10 for both. These data were used to calculate the volume dependence of λ, \documentclass{article}\pagestyle{empty}\begin{document}$$ g = - \left({{\partial\lambda/\lambda}}\over{{\partial V/V}}\right)_{T}. $$\end{document} At room temperature and atmospheric pressure (liquid phase) we find g = 3.4 for PIB-2800 and g = 3.9 for PIB-85000, but g depends strongly on temperature for both molecular weights. The difference in g between the glassy state and liquid phase is small and just outside the inaccuracy of g of about 8%. The best predictions for g are given by the theoretical model of Horrocks and McLaughlin. We have found that PIB exhibits two relaxations, where one is associated with the glass transition. The value for dTg/dp at atmospheric pressure (for the main glass transition) is about 0.21 K MPa-1 for both molecular weights. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1781-1792, 1998
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
