Interfacial polycondensation. XII. Variables affecting stirred polycondensation reactions

Abstract

AbstractPreceding papers have described the preparation of many polymers in high molecular weight by interfacial polycondensation under a wide variety of conditions. This paper reports an extended study of the optimum conditions for the stirred preparation of poly (hexamethylene sebacamide) and poly(sebacyl piperazine). The first is a polymer which precipitates from the reaction mixture while the latter may be retained in solution in the organic solvent. For each polymer‐solvent system there are selected conditions which produce a maximum in the viscosity number of the product. The peaks arise from varying the reactant concentrations and the ratio of the water to organic solvent. Their position is influenced by such factors as the polymer‐solvent interaction, the quality of the stirring, the presence of detergents, and the solubility characteristics of the diamine. The optimum conditions results from a balance of these various factors. Maximum molecular weight is achieved when equivalents of the two reactants are brought together in a narrow reaction zone near the interface and within the limited time in which the growing polymer is mobile. The high points in molecular weight often coincide with the highest yield of polymer. For 6‐10 polyamide it was shown further that the number of acid and amine chain ends per unit weight of polymer are nearly equivalent and at a minimum. At the same time the moleculare weight‐viscosity relation deviates least from that derived for polyamide made by melt polycondensation. Reaction rates are preferable high but successful polycondensations will result with slower reactions as long as there are no strongly competing side reactions and the growing polymer is kept mobile. The hydrolysis rates of short chain aliphatic diacid chlorides was found to be very high and yet this did not prevent the preparation of polyamides with hexamethylenediamine with ηinh above 0.5. Monofunctional impurities in the intermediates and solvents may limit molecular weight. Such materials were purposely tested with polyamides, polyesters, and polyurethanes. Their effectiveness depends not only on their relative reactivity and concentration but also on their distribution between the phases. Interfacial polycondensation is conveniently done in two phase liquid systems of which one phase is water. The use of other liquids as a replacement for water was demonstrated.