Preparation and characterization of aromatic polyimides derived from 4,4′-oxydiphthalic anhydride and 4,4′-diaminodiphenylmethane with different alkyl substituents

New soluble polyimides were synthesized from different 4,4′-diaminodiphenylmethane monomers with different alkyl substituents [4′4′-diamino-3,3′-dimethyl-diphenyl-methane, DDMDPM; 4,4′-methylene -bis(2-ethyl-6-methylaniline), MBEMA; and 4,4′-methylene-bis(2,6-diethylaniline), MBDEA] in one-step with the poly(amic acid)s prepared from the polyaddition of 4,4′-oxydiphthalic anhydride (ODPA). The structures of the synthesized polyimides were confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy measurements. The sizes and numbers of alkyl substituents affected the thermal properties, dielectric constants, and solubilities of the polyimides. The obtained polyimides were soluble in various solvents, such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), tetrahydrofuran (THF), dichloromethane (DCM), and chloroform (CClH₃). These polyimides exhibited excellent thermal stability with a decomposition temperature (T_d) greater than 500 °C and relatively low coefficients of thermal expansion and dielectric constants. The resulting properties make these new polyimides attractive for practical applications.