Non-isocyanate poly(amide-hydroxyurethane)s from sustainable resources

Abstract

A two-step synthesis of epoxidation and carbonation afforded a hetero-functional AB monomer with cyclic carbonate and methyl ester (CC-ME) using plant oil-based methyl 9-decenoate and CO₂. A unprecedented one-pot synthetic platform of CC-ME with 1,12-diaminododecane and poly(tetramethylene oxide) (PTMO)-based polyether diamine allowed synthesis of both nonsegmented poly(amide-hydroxyurethane) (PA₁₂HU) and segmented PA₁₂HU-PTMOs with varying polyether contents. ¹H NMR spectroscopy confirmed complete conversion of cyclic carbonates and methyl esters to hydroxyurethanes and amides, respectively. Thermal analysis revealed distinctive thermal stability and transitions of PA₁₂HU and PA₁₂HU-PTMOs compared to their precursors and model oligomers. PA₁₂HU and PA₁₂HU-PTMOs were melt compression molded into semicrystalline, free-standing films, except for PA₁₂HU-PTMO100 with 100% polyether diamine. PA₁₂HU-PTMO100 was a viscous liquid with a glass transition temperature (T_g) of −64 °C and zero-shear melt viscosity of 449 Pa s. PA₁₂HU formed a semicrystalline, rigid film with T_g of 11 °C. Polyether incorporation afforded creasable PA₁₂HU-PTMO films with broad glass transitions near −50 °C. Thermal and thermomechanical analysis revealed significant phase-mixing of the hard and soft segments from annealed PA₁₂HU-PTMO films. Polyether soft segments mixed with the amorphous hard segments, forming a miscible soft phase; crystallizable hard segments with ordered hydrogen bonding formed a hard phase. Surface morphological analysis of each PA₁₂HU-PTMO film displayed ribbon-like, hard domains with composition-dependent aspect ratios. PA₁₂HU-PTMOs exhibited higher moisture uptake than traditional thermoplastic polyurethane (TPU) due to resultant hydroxyls. Variable temperature FTIR spectroscopy demonstrated that ordered hydrogen bonding in the crystalline domains was disrupted or dissociated as the crystallites melted. Although tensile strength of segmented PA₁₂HU-PTMOs proved lower than traditional polyurethanes due to phase-mixing, these compositions represent the first examples of film-forming, linear isocyanate-free polyurethanes with mechanical integrity and processability.