The preparation of cyclic macromolecules has always represented a challenging task in polymer science mainly due to difficulties in connecting chain extremities together. Initiated with the pioneering works of Jacobson and Stockmayer, preparative pathways to cyclic polymers have been considerably improved within the last two decades thanks to the advent of both controlled polymerization mechanisms and efficient coupling reactions in organic chemistry. In the frame of this presentation, a special attention on both application and development of the Ring-Closure (RC) technique to the controlled preparation of low molecular weight cyclic aliphatic polyesters has been brought. In a first approach, cyclo-poly(lactide) (PLA) was obtained in high yields using the usual copper-catalyzed alkyne azide cycloaddition (CuAAC) of the corresponding linear PLA. Suffering from time-consuming and incomplete purification procedures combined with complex experimental setup, we further looked for simpler experimental conditions. In this context, we developed a catalyst-free RC method, based on a UV-induced Diels-Alder (DA)\click" coupling of O-quinodimethane and acrylate moieties. Initially, the method lies on the use of UV-emission device to promote the RC reaction, affording the rapid preparation of cyclic aliphatic polyesters in high purity and yields in an ambient temperature, catalyst- and purification-free approach. In the current context of sustainable development, we then successfully applied this protocol to the use of natural ultraviolet sunlight. In both summer and winter conditions, the reactions induced by solar radiation showed impressive robustness and versatility, allowing the synthesis of cyclic aliphatic polyesters in an energy-friendly approach. In the second part of the talk, an alternative characterization method for topological polymer isomers based on MS techniques will be presented. The developed method relies on the fact that linear and cyclic isomers, having different connectivities of the atoms, will present different fragmentation behaviors in double-stage mass spectrometry (MSMS) experiments. Cyclo-PLA obtained by the CuAAC was selected as a model. Combined with the use of the survival yield technique, MS identification and quantification of the isomers in a mixture was achieved with high sensitivity and accuracy, even at the trace level.

Towards quantitative macrocyclizations by original synthetic approach and characterization methods

255th National Meeting (2018)

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