Kinetic investigation of the condensation reaction of activated ester-amides containing oligo(oxyethylene) segments

The kinetics of polycondensation of activated ester-amides, namely pentachlorophenyl alpha-amino-omega-oligo(ethyleneglycol)succinate hydrochlorides (PSPnNH)having a degree of oligomerization n = 1-3, were investigated in solution in dichloromethane in the presence of excess triethylamine. The large extinction coefficient of,the pentachlorophenate formed during the reaction allowed the use of the, stopped flow technique. Experimental, data resulted in agreement with the existence of concurrent first- and second-order processes, attributable to the intramolecular cyclization and intermolecular polycondensation reactions, respectively. The relative incidence of the cyclization reaction decreased on increasing the monomer concentration and on decreasing the number of oxyethylene units in the monomer. These hypotheses were confirmed by SEC, TLC, FT-IR, and NMR characterization. of the reaction products. The kinetics of PSP3NH are in very good agreement with the predictions of both the collision theory and the condensation theory of linear systems at equilibrium. However, the behavior of shorter chain monomers was opposite to that of the theoretical, one, demonstrating that other parameters, such as steric hindrance and solvent interactions; must be taken into proper account. The reported findings clearly evidenced that polymerization of the investigated ester-amides must be performed in bulk in order to suppress the cyclization reaction and to obtain high-molecular-weight polymers