Film Properties of Polyazomethines (1). Effect of Incorporation of Intramolecular Cyclodehydrating Units

Abstract

Polyazomethines (PAzMs) were polycondensed from terephthalaldehyde (TPAL) with 2,2′bis(trifluoromethyl)benzidine (TFMB) and 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoropropane (HFBAPP). The PAzMs showed high solubility in N -methyl-2-pyrrolidone (NMP) ( > 15 wt.%) at room temperature and good film-formability. The film properties of the TPAL/TFMB-based PAzM copolymers were evaluated in the present study. In spite of their rod-like backbone structures, the PAzM films showed much higher coefficients of thermal expansion (CTE) in comparison with initial expectation. The results suggest that the simple casting process from the NMP solutions can not be a trigger for inducing pronounced chain orientation toward the direction parallel to the film plane (in-plane orientation). On the other hand, the incorporation of intramolecular cyclodehydrating (thermally imidizable) sites into the rigid TPAL/TFMB-based PAzM backbone by using pyromellitic dianhydride (PMDA) or 4,4′ -oxydiphthalic anhydride (ODPA) allowed the formation of low-CTE films upon imidization even for rather low reactive site contents. A possible mechanism to explain the present results is proposed. The TPAL/TFMB-based poly(imide-azomethine)s (PIAzMs) achieved excellent combined film properties in addition to low CTE (= 6.7-25.5 ppm K-1); namely, they have relatively high Tg values exceeding 300 °C, very low water absorption ( < 0.17%), sufficient toughness, high tensile modulus, and good thermal stability. Accordingly, the PIAzM systems investigated in the present study could be promising candidates for a new type of heat-resistant dielectric material for use in microelectronic applications.