Tetrafluoro-p-xylene

Fuqua and co-workers17 tried to develop a much shorter route from a,a,a, a -tetrafluoro-p-xylene to poly(tetrafluoro-/ -xylylene) but were unsuccessful in generating a polymer because they conducted their pyrolyses at 820-925°C/3-5 Torr, and under those conditions instead of losing H2 to form a,a,a, a -tetrafluoro-j9-xylylene, a,a,a, a -tetrafluoro-/ -xylene lost HF and underwent rearrangement to form P,p,j9-trifluorostyrene [Eq. (1)]. 

Chow and co-workers 18 developed a multistep synthesis for the commercial production of a,a,a, a -tetrafluoro- p -xylene that uses octafluoro[2.2]paracyclo-phane (PA-F dimer) as the precursor to polymer. PA-F dimer was cracked at 720-730°C and polymer was deposited on a substrate at -25 to -35°C [(Gorham method) Eq. (2)]. Chow19 also attempted to pyrolyze Br2F4C8H4 at very high temperatures. The film that was deposited was of poor quality compared to that prepared from dimer. 

To simplify the synthetic effort required to deposit such films, attempts were made to deposit films by pyrolyzing tetrafluoro-p-xylene (F4C8H6). Under similar reaction conditions, a polymer film was deposited that was different from poly(tetrafluoro-p-xylylene) as the FTIR spectrum indicates that it contains more hydrogen and less fluorine. Presumably HF is preferentially eliminated rather than H2. 

Notably, l,4-bis(trifluoromethyl)benzene is commercially available. It is synthesized from terephthalaldehyde, in a two step reaction. In the first step, terephthalaldehyde is reacted with sulfur tetrafluoride at 150 C under pressure to give tetrafluoro-p-xylene. In the second step, this compound is brominated by a photolysis reaction in the presence of fV-bromo succinimide. 

C Tetrafluoro-p-xylene Bis-quaternary ammonium salt Europe 200... 

Hertler16 was the first to report the preparation ofpoly(tetrafluoro-p-xylylene) by a multistep synthesis as shown in Scheme 2. Pyrolysis (330°C, 0.025 Torr) of dibromotetrafluoro-p-xylene (B CgFL,) over zinc led to deposition of the polymer film in a cold trap. 

Attempts were made not only to find an alternative way to replace dimer and to deposit high-quality poly(tetrafluoro-p-xylylene) film, but also to eliminate the dibromide as the precursor because of the difficulty of synthesis. Therefore, the deposition of poly(tetrafluoro-p-xylylene) film by using hexafluoro-p-xylene as the precursor instead of dibromotetrafluoro-p-xylene was tried. However, no polymer film was deposited on the wafer. Effort was expanded and other metal reagents such as nickel or copper were used to react with l,4-bis(trifluoromethyl)-benzene to generate a,a,a, a -tetrafluoro-p-xylylene to deposit poly(tetrafluoro-p-xylylene) film. However, the result showed that no film was deposited, which was not unexpected, because a C—X bond that is weaker than C—F bonding might be necessary to initiate the formation of the desired intermediate. 

Accidently, using hexafluoro-p-xylene with the contaminated copper wire obtained from the precursor method experiments, a polymer film was deposited on the silicon substrates. Obviously, some dibromotetrafluoro-p-xylene from the precursor method that adhered to, or reacted with, the metal could somehow initiate this VDP process. However, a complete explanation of these results is not yet available. As an extension of this discovery, commercially available 1,4-bis(trifluoromethyl)benzene in conjunction with a catalyst/initiator has proved to be a potential alternative by which to deposit poly(tetrafluoro-p-xylylene) film successfully.23... 

The copyrolysis of 1 wt% dibromotetrafluoro-p-xylylene with commercially available hexafluoro-p-xylene (Aldrich) with metals was examined and it was found that it was indeed possible to prepare films that were spectroscopically indistinguishable from those deposited from dimer. The PA-F films obtained are of excellent quality, having dielectric constants of2.2-2.3 at 1 MHz and dissociation temperatures up to 530°C in N2. A uniformity of better than 10% can be routinely achieved with a 0.5-gm-thick film on a 5-in. silicon wafer with no measurable impurities as determined by XPS. During a typical deposition, the precursor was maintained at 50°C, the reaction zone (a ceramic tube packed with Cu or Ni) was kept at 375-550°C, and the substrate was cooled to -10 to -20°C. The deposited film had an atomic composition, C F 0 = 66 33 1 3 as determined by XPS. Except for 0, no impurities were detected. Within instrumental error, the film is stoichiometric. Poly(tetrafluoro-p-xylylene) has a theoretical composition ofC F = 2 1. Figure 18.2 illustrates the XPS ofthe binding energy... 

The reaction of pentafluorotoluene, tetrafluoro-m- and -p-xylenes with CHjF and SbFj in SO2CIF yielded mixtures of benzenium ions corresponding to the attachment of in the positions substituted by fluorine or a CH3 group... 

Methyl vinyl ketone Propylene 2,2,3,3-Tetrafluoro-1-propanol p-Tolyl diethanolamine p-Xylene intermediate, plastics additives C20-24 aicohols intermediate, p-nitraniline red p-Nitroaniiine intermediate, PC... 

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