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

Abstract

This study reports the synthesis of polyurethane–imide (PU–imide) copolymers using 4,4′-diphenylmethane diisocyanate (MDI) polytetramethylene glycols (PTMGs) and different aromatic dianhydrides. Differential scanning calorimetry (DSC) results indicate that PU–imide copolymers had two phase structures containing four transition temperatures (Tgs, Tms, Tgh and Tmh). However, only PU–imide copolymers were formed by soft PTMG(2000) segments possessing a Tms (melting point of soft segment). When different aromatic dianhydrides were introduced into the backbone chain of the polyurethane, although the Tgs (glass transition temperature of the soft segment) of some of PU–imide copolymers did not change, the copolymers with long soft segments had low Tgs values. The Tgh (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 also had an obvious Tmh (melting point of hard segment). According to thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTGA), the PU–imide copolymers had at least two stages of degradation. Although the Tdi (initial temperature of degradation) depended on the hard segment content and the composition of hard segment, the different soft segment lengths did not obviously influence the Tdi. However, PU–imide copolymers with a longer soft segment had a higher thermal stability in the degradation temperature range of middle weight loss (about Td 5%–50%). However, beyond Td 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 strength of PU–imide copolymers surpassed those of PU. Wide angle X-ray diffraction patterns demonstrated that PU–imide copolymers are crystallizable. © 1999 Society of Chemical Industry