From multi-functional siloxane-based cyclic carbonates to hybrid polyhydroxyurethane thermosets

In this study, various novel cyclic carbonate-siloxane monomers were synthesized by hydrosilylation and CO2 carbonation of allyl glycidyl ether and epoxy-eugenol functions. Different structures were obtained from cyclic siloxane (D4) or linear PMHS-PDMS polymers with dangling cyclic carbonate functions. This hybrid route gives access to highly functional and low viscous cyclic carbonate monomers. Cyclic siloxane-carbonate monomers were reacted with 1,5-diamino-2-methylpentane (DYTEK-A) and 1,3-cyclohexanebis(methylamine) (CBMA) to afford polyhydroxyurethane (PHUs) thermosets as non-isocyanate polyurethanes (NIPUs) with high conversions and good reactivity. PHU thermosets were characterized to compare the thermal and mechanical properties of those different structures. The impact of the functionality was highlighted with different functional oligomers playing on cross-linking density of materials. D4 structure led to short and functional star shape monomers and afforded polymers with the highest mechanical properties. Eugenol, with an aromatic moiety, increased the stiffness and the thermal stability of PHU thermosets. Such hybrid PHU-siloxanes polymers combined flexibility of siloxanes with high mechanical performances of urethane groups.