The Thermal Properties of Poly(oxy-1,4-benzoyl), Poly(oxy-2,6-Naphthoyl), and its Copolymers

The thermal properties, i.e., heat capacity, enthalpy, entropy, and Gibbs function, and the transition behavior of the copolymer system of 4-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid have been studied based on differential scanning calorimetry. The heat capacities of the glass, crystal, and anisotropic melt are shown to be largely additive on a molar basis. Additivity is lost in the two transition regions, glass transition and disordering transition. Isothermal crystallization experiments on the copolymers revealed the existence of two types of crystals which melt at high temperature (fast-grown crystals) and low temperature (slowly grown crystals). The ATHAS computation method is used to bring heat capacities of the solid state into agreement with approximate frequency spectra. The changes in heat capacity at the glass transitions occur at 434 degrees K for the poly(oxy-l,4-benzoyl) [33.2 J/(K mol)] and at 420 degrees K for poly(oxy-2,6- naphthoyl) [46.5 J/(K mol)]. The copolymers have a transition range of above 100 degrees K. The anisotropic melt is linked to the well-known condis state of poly(oxy-1,4-benzoyl) by a continuous change in disorder and mobility without an additional first-order transition.