Ring‐chain competition in a branched polycondensate system

In this paper, the kinetics of copolyesterification of the well studied branching system formed by the reaction of 1,3,5‐tri(carboxymethyl)benzene, (BTA), and decane‐1, 10‐diol, (DMG) are described with special reference to the relative rates of inter‐ and intramolecular reactions (ring‐chain competition). The conversion β at time t , and the gel point β c were measured by continuously monitoring the pressure of steam evolved in a closed system at 175°C. during the course of polycondensation, using a pressure transducer. Experiments were carried out using 1,3,5‐tri(diphenylmethylcarboxymethyl)benzene as a diluent to further encourage intramolecular reaction. The experimental ratecurves passed smoothly through the gel point, and agreed well with those rate curves calculated using the “spanning tree” model of cascade theory, until substantially after the gel point. The overall reaction order was very close to the third order (acid self‐catalyzed) kinetics expected from studies of simple esterification. The amount of cyclization in the BTA/DMG system was confirmed to be small. Less than 1.2% of links are formed intramolecularly, at the gel point, β c β c was found to be 0.718 ± 0.006, compared to 0.707 i.e., 2 −1/2 for a random 2:3 functional alternating copolycondensation. The small difference indicates that the BTA/DMG system is the closest approach yet to a random tree‐like network.