Synthesis of polyurethane-imide (PU-imide) copolymers with different dianhydrides and their properties

This study reports the synthesis of polyurethane-imide (PU-imide) copolymer s using 4,4'-diphenylmethane diisocyanate (MDI) polytetramethylene glycols (PTMGs) and different aromatic dianhydrides. Differential scanning calorime try (DSC) results indicate that PU-imide copolymers had two phase structure s containing four transition temperatures (T-gs, T-ms, T-gh and T-mh). Howe ver, only PU-imide copolymers were formed by soft PTMG(2000) segments posse ssing a T-ms (melting point of soft segment). When different aromatic dianh ydrides were introduced into the backbone chain of the polyurethane, althou gh the T-gs (glass transition temperature of the soft segment) of some of P U-imide copolymers did not change, the copolymers with long soft segments h ad low T-gs values. The T-gh (glass transition temperature of hard segment) values of PU-imide copolymers were higher than that of polyurethane (PU). In addition, the high hard segment content of PU-imide copolymer series als o had an obvious T-mh (melting point of hard segment). According to thermog ravimetric analysis (TGA) and differential thermogravimetric analysis (DTGA ), the PU-imide copolymers had at least two stages of degradation. Although the T-di (initial temperature of degradation) depended on the hard segment content and the composition of hard segment, the different soft segment le ngths did not obviously influence the T-di However, PU-imide copolymers wit h a longer soft segment had a higher thermal stability in the degradation t emperature range of middle weight loss (about T-d 5%-50%). However, beyond T-d 50% (50% weight loss at temperature of degradation), the temperature of degradation of PU-imide copolymers increased with increasing hard segment content. Mechanical properties revealed that the modulus and tensile streng th of PU-imide copolymers surpassed those of PU. Wide angle X-ray diffracti on patterns demonstrated that PU-imide copolymers are crystallizable. (C) 1 999 Society of Chemical Industry.