Abstract

Wide-angle X-ray data point to a three-phase structure in isotropic and drawn specimens of a homogeneous poly(ethylene-co-octene) (7.3 mol % 1-octene). In addition to the amorphous halo, the unoriented polymer exhibits Bragg reflections characteristic of the orthorhombic crystalline phase and an additional reflection that is assigned to the hexagonal mesophase. On stretching 800%, the degree of crystallinity increases from ∼25% to ∼50%, due mainly to the formation of smaller hexagonal crystallites, while the proportions of the orthorhombic and amorphous phases decline. Small-angle X-ray data reveal a distinct long period, pointing to the existence of lamellae that become oriented perpendicular to the draw direction. On releasing the specimen, there is a considerable permanent set (∼350% extension), and the crystallinity declines to ∼30% as the hexagonal crystallites appear to revert to the amorphous structure. The results suggest that the hexagonal mesophase is formed by chain segments that have octene side chains, once these segments become oriented by deformation.

The heat capacity of poly(trimethylene terephthalate) (PTT) has been measured using adiabatic calorimetry, standard differential scanning calorimetry (DSC), and temperature‐modulated differential scanning calorimetry (TMDSC). The heat capacities of the solid and liquid states of semicrystalline PTT are reported from 5 to 570 K. The semicrystalline PTT has a glass transition temperature of 331 K. Between 340 and 480 K, PTT can show exothermic ordering depending on the prior degree of crystallization. The melting endotherm of semicrystalline samples occurs between 480 and 505 K, with a typical onset temperature of 489 K (216°C). The heat of fusion of the semicrystalline samples is about 15 kJ mol−1. For 100% crystalline PTT the heat of fusion is estimated to be 30 ± 2 kJ mol−1. The heat capacity of solid PTT is linked to an approximate group vibrational spectrum and the Tarasov equation is used to estimate the heat capacity contribution due to skeletal vibrations (θ1 = 550.5 K and θ2 = θ3 = 51 K, Nskeletal = 19). The calculated and experimental heat capacities agree to better than ±3% between 5 and 300 K. The experimental heat capacities of liquid PTT can be expressed by: \documentclass{article}\pagestyle{empty}\begin{document}$ C^L_p(exp) $\end{document} = 211.6 + 0.434 T J K−1 mol−1 and compare to ±0.5% with estimates from the ATHAS data bank using contributions of other polymers with the same constituent groups. The glass transition temperature of the completely amorphous polymer is estimated to be 310–315 K with a ΔCp of about 94 J K−1 mol−1. Knowing Cp of the solid, liquid, and the transition parameters, the thermodynamic functions enthalpy, entropy, and Gibbs function were obtained. With these data one can compute for semicrystalline samples crystallinity changes with temperature, mobile amorphous fractions, and resolve the question of rigid‐amorphous fractions.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2499–2511, 1998