Synthesis and Characterization of Poly(isobenzofuran) Films by Chemical Vapor Deposition

Abstract

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 °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 weightaverage 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 °C) and pyrolysis temperature (600, 650, 700, 750 °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 °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 °C), pyrolysis temperature (750 °C), and vaporization temperature (60 °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 (-NH 2 ), and a methyl group (-CH 3 ). We observed the fastest growth of PIBF (k ) 2.5 Å/s) on the carboxylic acid-terminated surfaces whereas the slowest growth was on the methylterminated surfaces (k ) 0.02 Å/s). On the basis of the experimental observations, we proposed a growth mechanism for the PIBF films by the CVD process.

Chemical Vapor Deposition of Conformal, Functional, and Responsive Polymer Films

“…In the absence of a plasma, the large energetic barrier to creating charged species in the gas phase guarantees that heterogeneous processes will be the dominant pathways for reactions of ions. Explicit reports of ionic chain polymerization in CVD are limited but include the cationic polymerization of isobenzofuran 29–31…”

Structure and Morphology of Poly(isobenzofuran) Films Grown by Hot-Filament Chemical Vapor Deposition

“…The furanoid C−O stretch absorptions are detected in a pair at 1285 and 1038 cm -1 . Other absorptions, such as weak combination/overtone bands for the ortho -substituted benzene (1690−1900 cm -1 ) and an out-of-plane bending vibration for the ortho -substituted benzene (755 cm -1 ), support the chemical structure of the PIBF polymer. , The PIBF films prepared at T f = 680 and 738 °C show nearly identical IR spectra, whereas reductions in peak intensities and shifts in peak positions are observed from the film prepared at T f = 800 °C (Figure c). The reduction in the peak intensities of the sp 2 C−H stretch from the aromatic ring (3040 cm -1 ) and the sp 3 C−H stretch from the polymer backbone (2874 cm -1 ) suggests a decrease in the degree of polymerization, which is supported by the decrease in the weight-average molecular weight of the films from 10000 ( T f = 680 °C) to 1000 ( T f = 800 °C) as determined by GPC.…”

Polymer-Based Gate Dielectrics for Organic Field-Effect Transistors

“…Various examples of CVD-processed polymer thin films have been reported, including conjugated polymers (e.g., poly(pyrrole) and poly(thiophene)), 93 poly(ethylene glycol) (PEG) for biological application, 94 poly(isobenzofuran) and polymers of other kinds. 95 Initiated chemical vapor deposition (iCVD) technique is a technique particularly applied to the polymers that can be synthesized by free radical polymerization. It is beneficial to low-k dielectrics (detailed discussion of low-k polymers is provided in Section 4.1.2), with which a thin film (e.g., a few tens of nanometers thick) is normally needed for high capacitance.…”

“…This process included the vaporization and pyrolysis of the di- p -xylylene (parylene dimer) in a single compact nozzle, producing a jet of monomer that polymerized into a film toward the substrate in contact. Various examples of CVD-processed polymer thin films have been reported, including conjugated polymers (e.g., poly­(pyrrole) and poly­(thiophene)), poly­(ethylene glycol) (PEG) for biological application, poly­(isobenzofuran) and polymers of other kinds …”