Synthesis and characterization of thermally stable poly(urethane–imide)s based on novel diols-containing imide and alkynyl groups

Two novel diols having both imide and aromatic groups in main chains, including N, N-(pyromellitoyl)-bis-l-phenylalanine diacid ester glycol (PBDCG) and N, N-(pyromellitoyl)-bis-l-phenylalanine diacid ester butynediol (PBDCB), were synthesized. Then, the novel thermoplastic-segmented poly(urethane–imide)s (PUIs), in which 4,4′-diphenylmethane diisocyanate and the diols as the hard segments and poly(tetrahydrofuran) as the soft segments, were prepared via two-step polymerization. The prepared polymers were characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), gel permeation chromatography, tensile tests and UL 94 vertical burn test. TGA result indicates that the novel PUIs with the rigid hard segments have slower degradation rates than the conventional polyurethanes, and PBDCB-based PUIs are more thermally stable than PBDCG-based PUIs. DSC and x-ray diffraction results confirm that they are amorphous structures. Moreover, DSC analysis indicates that the glass transition temperature of PUIs increases by increasing the contents of hard segments. The weight-average molecular weights of PUIs are in the range of 1.12–4.19 × 104. The UL 94 vertical burn test according to the ASTDM D3801 test method indicates that the PUIs are classified under vertical ranking V-2.