Synthesis and characterization of poly(isobenzofuran) films by chemical vapor deposition

This paper describes the synthesis and properties of poly( isobenzofuran) ( PIBF) films prepared by a thermal chemical vapor deposition (CVD) process. The synthesized precursor monomer, 1,2,3,4-tetrahydro-1,4- epoxynaphthalene, is pyrolyzed by flowing it through a tube furnace at temperatures of 600-750 degrees C. A reactive intermediate, isobenzofuran (IBF) monomer, is produced by this pyrolysis and deposited onto a silicon substrate where it polymerizes to form a thin coating of poly( isobenzofuran) ( PIBF) on the surface. The chemical structure and composition of the PIBF films are supported by nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The weight-average molecular weight of the PIBF films range from 5500 to 9400 by varying the deposition ( stage), pyrolysis ( furnace), and vaporization ( source) temperatures. With the variation of deposition temperature ( 5, 10, 15, 20, 25 degrees C) and pyrolysis temperature (600, 650, 700, 750 degrees C), significant changes are observed in deposition ( growth) rate, molecular weight, and morphology while the chemical structure of the PIBF films remain the same as probed by FT-IR and XPS analysis. On the other hand, variation of the vaporization temperature ( 40, 45, 50, 55, 60 degrees C) leads to significant changes in the chemical structure as well as in the deposition rate, molecular weight, film uniformity, and morphology. By exploring several operating conditions, we have obtained optimal conditions for deposition temperature (10 degrees C), pyrolysis temperature (750 degrees C), and vaporization temperature (60 degrees C) that provide good film properties as well as fast film growth. To investigate the possible role of cationic initiation in IBF polymerization, PIBF films were deposited on several surfaces tailored with self-assembled monolayers (SAMs) of thiols that have functional groups of different acidities, including a carboxylic acid (-COOH), a phenol (-PhOH), an alcohol (-OH), an amine (-NH2), and a methyl group (-CH3). We observed the fastest growth of PIBF (k = 2.5 angstrom/s) on the carboxylic acid-terminated surfaces whereas the slowest growth was on the methyl-terminated surfaces (k = 0.02 angstrom/s). On the basis of the experimental observations, we proposed a growth mechanism for the PIBF films by the CVD process.