Pressure and volume dependence of thermal conductivity and isothermal bulk modulus up to 1 GPa for poly(isobutylene)

✍ Scribed by S. Peter Andersson

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 217 KB
• Volume: 36
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(19980730)36:10<1781::aid-polb19>3.0.co;2-5

✦ Synopsis

The thermal conductivity l and heat capacity per unit volume rc p of poly-(isobutylene)s, one 2.8 in weight average molecular weight and one 85 kg mol 01 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 hotwire method. At 297 K and atmospheric pressure, l Å 0.115 W m 01 K 01 for PIB-2800 and l Å 0.120 W m 01 K 01 for PIB-85000. The bulk modulus B T has been measured in the temperature range 170-297 K up to 1 GPa. At atmospheric pressure, the room temperature bulk moduli B T are 2.0 GPa for PIB-2800 and 2.5 GPa for PIB-85000 with dB T /dp Å 10 for both. These data were used to calculate the volume dependence of l,

At room temperature and atmospheric pressure (liquid phase) we find g Å 3.4 for PIB-2800 and g Å 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 dT g /dp at atmospheric pressure (for the main glass transition) is about 0.21 K MPa 01 for both molecular weights.