P-xylene polymer

JJC. Hubbard, Nitrated p-Xylene Polymers , USP 2726217 (1955) CA50, 5292 (1956) [The inventor claims an expl compd which has a partial decompn temp of 220°, and an expl ign pt of 282°. It is sol in cyclohexanone. Prepn is affected by the portion-wise addn of 5g of 20 mesh p-xylene polymer to 200cc of 90% fuming nitric add so that the temp does not exceed 45-50°. Soln is said to occur in one hr, with stirring required for an addnl three hrs. The soln is then filtered and the filtrate drowned in ice-w. The resulting ppt is then w-washed and vac-dried at 70° to give the dinitrate. It is claimed to be a HE comparable to TNT with a friction sensy similar to that of RDX. It forms a brittle film from a 10% cyclohexanone soln]... 

Isomerization [17] H-ZSM-5 zeolites xylenes, toluene p-xylene polymers, bulk chemicals... 

L. A. R. Hall. Production of p-xylene polymers. US Patent 2719131, assigned to Du Pont, September 27, 1955. 

PX forms j xylylene when heated above 1200°C. The stmctuie of J-xylylene is represented by a i)-quinoid stmcture or as a i)-ben2enoid brtadical. Condensation yields poly(p-xylylene) (19—22) (see Xylene polymers). 

This polymer first appeared commercially in 1965 (Parylene N Union Carbide). It is prepared by a sequence of reactions initiated by the pyrolysis of p-xylene at 950°C in the presence of steam to give the cyclic dimer. This, when pyrolysed at 550°C, yields monomeric p-xylylene. When the vapour of the monomer condenses on a cool surface it polymerises and the polymer may be stripped off as a free film. This is claimed to have a service life of 10 years at 220°C, and the main interest in it is as a dielectric film. A monochloro-substituted polymer (Parylene C) is also available. With both Parylene materials the polymers have molecular weights of the order of 500 000. 

Physico-chemical standards benzoic acid with a stated melting point, p-xylene with a stated flash point, sand with a quoted particle size distribution and polymers with quoted molecular weight distributions. 

W.J. Swatos and B. Gordon, III, Polymerization of 2,2-di- -hexyloxy-a,a -dichloro-p-xylene with potassium tert-butoxide a novel route to poly(2,5-di- -hexyloxy-p-phenylene vinylene), Polym. Prepr., 31(1) 505-506, 1990. 

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. 

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. 

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... 

First of all p-xylene is dehydrogenated to obtain its dimer (i.e., di-/ -xylene). This is done by using superheated steam at 950°C. The dimer formed is a crystalline solid at room temperature and it is heated to 600°C at 1 mm pressure when it sublimes and forms and equilibrium mixture of diradical and a quinonoid. This equilibrium mixture when quenched to 50°C over metal surface results in the formation of a linear polymer known as... 

The color of the final product primarily depends on the qualification of the raw materials, TPA, DMT and EG. The content of heavy metals in TPA, residues of catalysts employed during oxidation of p-xylene, and polymer processing affect the final color of the polymer. The tendency of certain catalysts, such as titanium or tin derivatives, to make the polyester yellowish in color is well established. The conversion during esterification is prolonged due to larger TPA particles or their hardness. Color can be influenced by these factors, as well as by chemical impurities in the raw materials, such as water, aldehydes or the quality of insufficiently recovered EG. Similar effects on color can be observed as a result of impurities caused by additives, particularly from less purified Sb2C>3. The quality of the latter can be assessed simply by the color of its solution in EG. 

The polyethylene film thus obtained was packed in a 100 mesh stainless steel basket, extracted with hot p-xylene in a Soxhlet extractor for 48 hours, washed with acetone for 4 hours in the same type extractor, dried in vacuum for 20 hours at 40°C and weighed. The gel fraction (Gf) of the polymer was detrmined by the equation (2) from the weight change by the extraction. 

NaOH solution of the diol and an organic solution of the dihalide in the presence of a phase-transfer catalyst (31). The best results were obtained with dichloro-p-xylene as comonomer and gave polymers with the furanic-aromatic structure 26 ... 

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