Structure-Property Relationships in Bio-Based Polyhydroxyurethanes

Abstract

This study explores the structure-property relationships of polyhydroxyurethanes (PHUs), sometimes called non-isocyanate polyurethanes (NIPUs), produced from the polymerization of 1,5-pentanediamine, a bio-sourced diamine, with biosourcable cyclic carbonates of diverse structures, such as aromatic and aliphatic backbones with ether and ester linkages. Comprehensive structural, thermal and mechanical characterizations were performed to evaluate polymer thermal stability and mechanical properties. Importantly, all polymers adsorbed moisture under common conditions (50% relative humidity, 22 °C) and this significantly impacts the thermal and mechanical properties. Results of dried samples revealed that aromatic homopolymers exhibited higher thermal stability and glass transition temperatures (Tg) compared to their aliphatic counterparts as measured by differential scanning calorimetry (DSC). The Tg values correlated with polymer backbone structures, decreasing in the order: aromatic ester-ether > aromatic diether ≈ aromatic diester > aliphatic diether (short chain) > aliphatic diester > aliphatic diether (long chain). Dynamic mechanical analysis (DMA) confirmed that aromatic polymers demonstrated glassy behavior with higher storage modulus values, while aliphatic homopolymers exhibited rubbery properties with lower storage modulus values. Furthermore, variations in cyclic carbonate structure significantly influenced polymer mechanical performance, with shorter aliphatic chains showing sharp tan δ transitions, whereas longer chains displayed broader tan δ peaks. This study provides valuable insights into the structure-property relationships of bio-based PHUs, highlighting their potential as sustainable thermoplastic alternatives.