Pressure-Volume-Temperature Behavior of Two Polycyanurate Networks

The pressure-volume-temperature (PVT) behavior was studied for two polycyanurate networks having different crosslink densities using a pressurizable dilatometer. The sam- ples were studied at temperatures ranging from 60 to 180 � C and at pressures up to 170 MPa to yield PVT data in both rub- bery and glassy states. The Tait equation is found to well describe the isobaric temperature scan and isothermal pres- sure scan data. The thermal expansion coefficients, instantane- ous bulk moduli, and thermal pressure coefficients are extracted from the data and their dependence on crosslink den- sity is examined. The time-dependent viscoelastic bulk modu- lus (K(t)) is also calculated in the vicinity of the a-relaxation from previously published pressure relaxation experimental data, and the strength and shape of the dispersion are found to be independent of crosslink density. The limiting bulk moduli depend strongly on temperature with those of the more loosely crosslinked sample being lower at a given temperature and pressure, although at Tg(P), the limiting mod- uli of the more loosely crosslinked sample are slightly higher than those of the more highly crosslinked sample. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2509-2517, 2010