The polyamidation process in the solid state

Abstract

AbstractPolyamidation is an example of rather rare reactions that can take place in the solid phase. These reactions are of considerable theoretical and practical interest. In a study of the general laws of polycondensation in the solid phase an investigation was undertaken of the polycondensation kinetics of three aliphatic ω‐amino acids, aminoenanthoic, aminopelargonic, and aminoundecanoic, and three hexamethylenediamine salts of adipic, thiodivaleric, and terephthalic acids with respect to temperature. In preliminary runs the kinetics were followed by continuous weighing of a test tube with the monomer and in this way, by measurement of the quantity of water liberated. At present a detailed calorimetric study of the reactions is being carried out, using a differential calorimeter of high sensitivity. The rate of reaction at a given moment is determined by the intensity of the absorbed heat influx (the reactions are endothermal at 170–190°). The work is at present finished with regards to aminoenanthoic and aminopelargonic acids and in general has confirmed the results of the preliminary experiments. As a result of the work carried out one may consider the following to be established. (1) Polycondensation of the amino acids in the solid phase proceeds at a noticeable rate over a rather short temperature range lying close to the melting point of the acids. (2) The rate of the polycondensation reaction in the solid phase has a very high temperature coefficient. (3) With respect to the effective activation energy of the process the amino acids arrange themselves in the series: aminoundecanoic acid < aminoenanthoic acid < aminopelargonic acid. Common to all the amino acids is the high value for activation energies of solid phase polycondensation. In the presence of a liquid phase the activation energy falls sharply. (4) The higher the melting temperature of the hexamethylene diamine salt of the dicarboxylic acid, the larger the temperature range of polycondensation in the solid phase and the lower the temperature coefficient of the rate of polycondensation. A study has been made of the catalytic action of various substances of acidic, basic and neutral nature on the process. Many substances have been found to accelerate solid phase polycondensation. A kinetic series has been established with respect to the efficiency of the various catalytic additions.