Preparation and properties of novel poly(urethane-imide)s

A series of poly(urethane-imide)s were prepared by a novel approach. Polyurethane (PU) prepolymer was prepared by the reaction of polyester polyol and 2,4-tolylenediisocyanate (2,4-TDI), and then end-capped with phenol. The PU prepolymer was blended with poly(amide acid) or oligo(amide acid) prepared from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and oxydianiline (ODA) at room temperature in various weight ratios. The blend films obtained by casting and then drying were not transparent, suggesting that phase separation occurred between the polyimide (PI) and PU components. The films became transparent, however, after thermal treatment at 100°C and then 200°C for 1 h each, irrespective of the ratio of the two components. The poly(urethane-imide) films showed good solvent-resistance. Dynamic mechanical analysis of the films showed that glass transition temperatures (T_g) shifted depending on the ratio of PI and PU components. This shift of T_g, along with the transparency of the films, suggests that the PU and PI components employed here are miscible to some extent and that domains of each phase by microphase separation are small. Tensile measurement of the blend films from poly(amide acid) showed that the films are plastic or elastic, depending on the ratio of the components. Thermal stability of the PU was found to increase by the incorporation of polyimide component.