Microwaves; a very promising solution for the in-melt elaboration of innovative materials. Kedafi Belkhir, Fréderic Becquart Université de Lyon, Ingénierie des Matériaux Polymères, UMR CNRS 5223, Université de Saint-Etienne, Jean Monnet, F-42023 Saint-Etienne, France Microwaves have gained a growing interest these last decades due to their ability to interact directly with materials having “good” dielectric properties i.e. polar or ionic systems. Then, microwave technology found major and very efficient applications in ceramics elaboration, drying and cooking in food industry. In chemistry and polymer chemistry, microwaves find more and more applications thanks to their direct wave-matter interaction leading to rapid heating and faster reactions. Their higher selectivity also favors reactions without solvent, with higher yields and limited side reactions. These promising advantages explain the dramatic growth of academic scientific production in chemistry and polymer chemistry under microwaves. [1] In polymer chemistry, microwaves are used for polymerization, chemical modification, grafting, depolymerization, pyrolysis and other processes. Both synthetic polymers, biosourced ones like polyesters and a majority of natural polymers from biomass are involved. This potential of application is very high and real with the additional possibilities to achieve reactions with less amounts of, or without, catalysts (atom economy) and lower energy consumption than the conventional conductive heating. Thus, microwaves are naturally an attractive way to face the current societal challenges. [2] However, one major counterpart exists, due to its selective interaction with the most polar bonds at the molecular scale in a reactive system, some heterogeneous heating with hot spots, may appear (Figure 1) [3]. So, we propose to present conceptually how it could be possible to take advantage from both this selectivity and this heterogeneity in the specific polymer reactive systems which could be biphasic. Biphasic polymer systems are very common in polymer blends or filled polymers, especially reactive systems are performed without solvent, at high temperature in the molten state and ideally under shear. In this way, microwaves offer the exclusive possibility to innovate in polymer science. Some concrete examples will illustrate the presented concepts. Figure 1. Microwave-generated hot spots in dispersed Pd/AC catalyst during Suzuki-Myaura reaction with different stirring rates. [1] A. Loupy; Microwave in Organic Synthesis; 2008;2nd Ed;WILEY-VCH [2] L. Zong et al. J. Microw. Power. Electromagn. Energy. 2003, 38, 49-74. [3] S. Horikoshi et al. Ind. Eng. Chem. Res. 2014, 53, 14941-14947.