Aliphatic-aromatic hyperbranched polyesters by polycondensation of potassium 3,5-bis(bromomethyl)benzoate: Formation of cyclic structures

Aliphatic-aromatic hyperbranched polyesters of reasonable degrees of branching (DB's) but of relatively low molar masses were prepared from 3,5-bis(bromo-methyl)benzoic acid (2a). 2a was synthesized by radical bromination of 3,5-dimethylbenzoic acid. The polymerization of 2a and that of the potassium salt of 2a (2K), both carried out in the presence of a potassium monocarboxylate (RCOOK), led to directly derivatized polyesters. Polyesters bearing free -CH2Br groups were obtained by polymerization of 2K alone or in the presence of 2,4,6-tris(bromo-methyl)mesitylene (TBMM) or by polymerization of 2a in the presence of RCOOK provided that 1 less than or equal to [RCOOK]/[2a] < 2. These polyesters were later derivatized by reaction with RCOOK. In all cases, RCOOK can be chosen in order to introduce, in the polyesters, reactive functional groups such as unsaturated (double or triple bond) and hydroxy ones. The NMR analysis of polymers has shown that a cyclic dimer (C-2) was formed in most cases. Its amount depends on the process of polymerization and on the experimental conditions. The <(M)over bar>(n) of polyesters was found to be correlated with the amount of C-2. The MALDI-TOF analysis of polymers confirmed the formation of cycles and showed that both the polymerization of 2K in the presence of TBMM and that of 2a in the presence of some particular RCOOK's led to the formation of acyclic macromolecules.