Study of thin films made from aromatic polyamides with silicon and phenylquinoxaline rings in the main chain

Aromatic polyamides containing silicon and phenylquinoxaline rings in the m ain chain have been prepared by polycondensation reaction of a silicon-cont aining diacid chloride, namely bis(p-chlorocarbonylphenyl)-diphenylsilane, with various aromatic diamines having preformed phenylquinoxaline units. Th ese polymers were easily soluble in polar aprotic solvents, such as N-methy lpyrrolidinone (NMP) and dimethylformamide (DMF), and in tetrahydrofurane. They showed high thermal stability with decomposition temperature being abo ve 450 degrees C and glass transition temperature in the range of 253-304 d egrees C. Polymer solutions in NMP were processed into thin films having th e thickness of tens of nanometer to 10 mu m, by spin-coating onto glass pla tes or silicon wafers. The films had strong adhesion to substrates and exhi bited very smooth surfaces, free of pinholes, in atomic force microscopy (A FM) studies. The free-standing films had dielectric constant in the range o f 3.48-3.69. Thermal treatment of the films up to 350 degrees C rendered th em completely insoluble in organic solvents, while maintaining their smooth ness and strong adhesion to the silicon substrate, and with no T-g in DSC e xperiments. Their FTIR spectra did not show any changes compared to the unt reated films, meaning that polymers maintain their structural integrity at high temperature. (C) 1999 Elsevier Science S.A. All rights reserved.