Reactivity of secondary amines for the synthesis of non-isocyanate polyurethanes

• We studied reactivity of secondary amines towards cyclic carbonates.
• Reaction between secondary amines and cyclic carbonates was performed.
• Polyhydroxyurethanes PHUs were synthesized from di- and tri-cyclic carbonates and secondary amines.
• Properties of PHUs polymers were characterized.

The role of secondary amine, usually not taken into account in the case of polyhydroxyurethanes (PHUs) synthesis, was inspected. Butanediol bis carbonate BBC, trimethylolpropane tris carbonate TMPTC and resorcinol bis carbonate RBC were synthesized by carbonation of corresponding epoxides. The products, obtained with high yield, were characterized by NMR and mass spectrometry analysis. These carbonates were converted to biobased polyhydroxyurethanes by step growth polymerization with tetraethylene pentamine TEPA. The optimal carbonate–amine ratio was determined from the differential scanning calorimeter results. A maximum Tg value of 16 °C was found for the BBC–TEPA system considering three reactive amine group among five of TEPA hardener. These results were completed by model reactions. Firstly, the reaction between BBC and a secondary diamine (N,N′-dimethyl-1,6-hexanediamine) was hightlighted by differential scanning calorimetry. Moreover, the products of reaction between a monocarbonate (i.e. propylene carbonate) and TEPA or N,N′-dimethyl-1,6-hexanediamine were characterized by FTIR, NMR and mass spectrometry, allowing the demonstration of the formation of hydroxyurethane groups. Contrary to most of the results found in the literature, this work clearly demonstrates that secondary amines can also react with cyclic carbonates. Further details, such as activation energy of 28 kJ mol−1 (BBC–TEPA system), glass transition temperatures (from 16 to 67 °C) and good degradation temperature (Td 5% between 198 and 256 °C) completed this work.

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