An investigation of the condensation kinetics in poly(ester-amide) and poly(ester-sulphide) preparation

Synthetic processes leading to hydrophilic biodegradable polymers for bio-inspired applications were investigated from a kinetic point of view. In accordance with the reported mechanism of ester aminolysis, polycondensation reactions of α-amino-ω-esters, diesters, and diamines resulted markedly dependent on the basicity of the alkoxide leaving-group, being relatively fast for penthachlorophenate monomers. Furthermore, experimental data concerning the homopolycondensation of penthachlorophenyl α-amino-ω-oligo(ethyleneglycol) succinates of different degree of oligomerization clearly showed the existence of concurrent first and second-order processes, which were attributed to the intramolecular cyclization and intermolecular polycondensation reaction, respectively. In contrast to theoretical predictions based on the collision theory, however, minor incidence of the cyclization reaction was shown by the shortest monomers, thus suggesting a significant kinetic effect due to steric hindrance and solvent-reagent interactions. Analysis of the base-catalyzed Michael-type addition of α,ω-oligo(oxyethylene)dithiols to methyl (meth)acrylate allowed for the optimization of the relevant polymerization process involving hydrophilic diacrylates. Interestingly, very low reaction rates were determined for methacrylic components, supposedly because of steric and electronic factors connected to the presence of the α-methyl group. Minor effects on the reaction rate were also induced by solvent polarity and catalyst nature.