The equation of state and heat of fusion of poly(ether ether ketone)

The pressure‐volume‐temperature properties of poly(ether ether ketone) (PEEK) were studied experimentally at temperatures of 400°C and pressures to 200 MPa. Specific volume data were fitted successfully to the empirical Tait equation for T < T_g and T > T_m and to the theoretical Simha‐Somcynsky equation of state for the melt. The pressure dependence of the glass‐transition temperature is about 0.57–0.59°C/MPa and that of the melting point 0.483°C/MPa. The pressure dependence of the melting point, the specific volume of the melt at T_m, and the specific volume of the crystal at T_m determined from x‐ray diffraction data at elevated temperatures were combined in the Clapeyron equation to calculate a heat of fusion of 161 ± 20 J/g for the PEEK crystal. This value is somewhat higher than the previously reported value of 130 J/g.