Effect of reaction temperature on conversion and thermal properties of polyamide hot-melt adhesives

The work described in this paper aims at exploring the effect of reaction temperature, with and without a catalyst on the conversion and thermal properties of polyamide hot-melt adhesives. The polyamides were synthesized from C₃₆ dimer acid and ethylenediamine; o-phosphoric acid was used as catalyst. The thermal properties investigated were glass transition temperature, melting point, heat of fusion, and molecular weight of the final products. Glass transition temperatures, heat of fusion, and melting point were found to increase with increasing molecular weight. Glass transition temperature was found to be in the range of 62-66°C; however, for noncatalytic reaction at 130°C, the final product was in liquid phase at room temperature and no glass transition temperature was detected. Results show that as the polymerization reaction temperature increases, the number average molecular weight increases. In the reaction, ethylenediamine and dimer acid should be taken in equivalent amounts to produce polyamides with high and desirable molecular weights. Excess of ethylenediamine will lead to low molecular weight products with the free amine group left unreacted. However, an extra amount of the ethylenediamine should be added initially to compensate for the evaporated loss of ethylene diamines. The excess amount should be equivalent to the amount that would evaporate during the preheating process. Parameters of the rate equations and the empirical parameters were determined with nonlinear regression analysis. The kinetic model was used to simulate experiments that were not included in the empirical parameter estimation. The comparison of the model predictions with the experimental data showed good agreement.