Polymerization of 5-aza-1-oxa-cycloundecan-4,11-dione; a mechanistic study

N-(3-Hydroxypropionyl)-epsilon-aminocaproic acid lactone [c(3HP-epsilon AC) , 1] was polymerized in dimethylformamide solution with dibutyldimethoxytin as initiator at 100 degrees C. A strictly alternating poly(amide-ester), p oly(3-hydroxypropionate-alt-epsilon-aminocaproate), was obtained, a semicry stalline polymer with a melting point of 145.9 degrees C. The polymerizatio n was found to proceed via a tin alcoholate active species as was deduced f rom H-1 NMR endgroup analysis of the polymer quenched with water. In additi on, the active chain ends were quenched with diphenyl chlorophosphate and a nalyzed by means of P-31 NMR spectroscopy; a diphenylalkyl phosphate was id entified, proving the alcoholate active site. The polymerization follows a pseudo-first order rate law only at low conversions. However, a linear depe ndence of the number-average molecular weight on conversion was found, prov ing that transfer reactions play a minor part throughout the polymerization process. A mechanism for the initiation and propagation is proposed.