Effect of chain conformations on the crystallization behavior of thermoplastic copolyester

Abstract

The nonisothermal and isothermal crystallization behavior of the thermoplastic copolyester based on 1-4 cyclohexane dimethanol, ethylene glycol, and terephthalic acid was investigated by differential scanning calorimetry. The copolyester is normally an amorphous polymer with the cyclic moiety in the main chain suppressing crystallization. However, the amorphous pellets crystallize during the heating mode. The crystallization behavior from the glassy solid state was found to be influenced by the melt temperature and the dwell time at the melt temperature. The onset of crystallization shifts progressively to lower temperatures, and the peak becomes narrower with increasing melt temperature and dwell time. The isothermal crystallization time at a given temperature of crystallization was also found to decrease significantly with increasing melt temperature. Thus, the crystallizing ability of the polymer and the rate of crystallization were found to be influenced by the melt temperature and the dwell time. The results are interpreted in terms of the temperature-dependent equilibrium ratio between the two possible chain conformations corresponding to the "Trans" and "gauche" forms of the cyclohexane moiety in the chain.