Synthesis and Structural NMR Characterization of Novel PPG/PCL Conetworks Based upon Heterocomplementary Coupling Reactions

摘要

A new approach to hybrid model network formation based upon heterocomplementary end-linking of four-arm star poly-ε-caprolactone (PCL) and linear polypropylene glycol (PPG) precursors is demonstrated. Specifically, hydroxyterminated PCL(-OH)_4 and an amino-terminated linear PPG(-NH_2)_2 are reacted with a bifunctional coupling agent containing one carboxylic acid chloride group and one oxazinone group. PCL(-OH)_4 is first reacted with the former in a solution, and the so-obtained oxazinone-terminated intermediate is then reacted with PPG(-NH_2)_2 to form a network both in the solution and in the melt. A strong effect of electron-withdrawing groups on the reactivity of the oxazinone group, and thus on the network formation, is evidenced. Network structure and properties are studied by swelling experiments and lowfield multiple-quantum (MQ) NMR, which confirm the successful formation of hybrid networks and provide information on the significant network inhomogeneities. On the methodological side, a reliable approach to MQ NMR data analysis for networks of variable degree of inhomogeneity is discussed.