Xylene polymers

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). 

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]... 

When the benzyl and xylyl bromides were brought in contact with indium tubes for sampling, the indium was quickly discolored and pitted. The spectra of the material so taken up were recorded despite the clear evidence of reaction between the indium and the bromide. Relative intensities in the low voltage spectra and suggested identities of the compounds responsible for the peaks are shown in Table II. The chief result of indium attack on a-bromo-o-xylene was expected to be removal of a bromine atom to produce a xylyl radical. If this were the case, the major stable products should be xylene polymers of molecular weight 210, 314,... 

The xylenes are very high-lonnage industrial chemicals and are raw materials or intermediate materials for numerous synthetic fibers, resins, and plastics. See also Xylene Polymers. A large amount of p-xylene goes into polyester fiber production, while substantial quantities of d-xylene are consumed by the manufacture of phthalic anhydride. The prime source of xylenes are petroleum refinery reformate streams in conjunction with benzene and toluene extraction. The xylenes occur mixed in these streams. 

William Bauer, Jr.. Rohm and Haas Company, Spring House, PA, hllp //www.rohmhaas.com/. Acrylic Acid and Derivatives W. F. Beach, Alpha Metals. Bridgewater. NJ, Xylene Polymers James Bellows, Wesringhottse Electric Corporation. Orhmdo. FL http // www.westinghouse.com/. Steam... 

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. 

Deberdt, F., Berghmans, H. Phase behavior of syndiotactic polystyrene-o-xylene. Polymer, 35,1688-1693 (1994). 

When -xylene is used as the monomer feed in a plasma polymer process, PX may play an important role in the formation of the plasma polymer. The plasma polymer from -xylene closely resembles the Gorham process polymer in the infrared, although its spectmm contains evidence for minor amounts of nonlinear, branched, and cross-linked chains as well. Furthermore, its solubiUty and low softening temperature suggest a material of very low molecular weight (15). 

Manufacture. For the commercial production of DPXN (di-/)-xylylene) (3), two principal synthetic routes have been used the direct pyrolysis of -xylene (4, X = Y = H) and the 1,6-Hofmaim elimination of ammonium (HNR3 ) from a quaternary ammonium hydroxide (4, X = H, Y = NR3 ). Most of the routes to DPX share a common strategy PX is generated at a controlled rate in a dilute medium, so that its conversion to dimer is favored over the conversion to polymer. The polymer by-product is of no value because it can neither be recycled nor processed into a commercially useful form. Its formation is minimised by careful attention to process engineering. The chemistry of the direct pyrolysis route is shown in equation 1 ... 

Purification. Unsubstituted di- -xylylene (DPXN) is readily purified by recrystaUization from xylene. It is a colorless, highly crystalline soHd. The principal impurity is polymer, which fortunately is iasoluble ia the recrystaUization solvent and easily removed by hot filtration. 

Solvent Resistance. At temperatures below the melting of the crystallites, the parylenes resist all attempts to dissolve them. Although the solvents permeate the continuous amorphous phase, they are virtually excluded from the crystalline domains. Consequently, when a parylene film is exposed to a solvent a slight swelling is observed as the solvent invades the amorphous phase. In the thin films commonly encountered, equilibrium is reached fairly quickly, within minutes to hours. The change in thickness is conveniently and precisely measured by an interference technique. As indicated in Table 6, the best solvents, specifically those chemically most like the polymer (eg, aromatics such as xylene), cause a swelling of no more than 3%. 

For small-scale preparation of samples for scientific studies, the precursor polymer may be dissolved in xylene at 80°C, followed by addition of the cation source. A gelled fluid is normally obtained immediately, and the ionomer is recovered as a powder by chopping the gel in a large excess of acetone using a laboratory blender. 

Surfactants evaluated in surfactant-enhanced alkaline flooding include internal olefin sulfonates (259,261), linear alkyl xylene sulfonates (262), petroleum sulfonates (262), alcohol ethoxysulfates (258,261,263), and alcohol ethoxylates/anionic surfactants (257). Water-thickening polymers, either xanthan or polyacrylamide, can reduce injected fluid mobiHty in alkaline flooding (264) and surfactant-enhanced alkaline flooding (259,263). The combined use of alkah, surfactant, and water-thickening polymer has been termed the alkaH—surfactant—polymer (ASP) process. Cross-linked polymers have been used to increase volumetric sweep efficiency of surfactant—polymer—alkaline agent formulations (265). 

The syndiotactic polymer configuration is not obtained in pure form from polymerizations carried out above 20°C and, thus has not been a serious concern to most propylene polymerization catalyst designers. Eor most commercial appHcations of polypropylene, a resin with 96+% isotacticity is desired. Carbon-13 nmr can be used to estimate the isotactic fraction in a polypropylene sample. Another common analytical method is to dissolve the sample in boiling xylene and measure the amount of isotactic polymer that precipitates on cooling. 

Monomer conversion (79) is followed by measuring the specific gravity of the emulsion. The polymerization is stopped at 91% conversion (sp gr 1.069) by adding a xylene solution of tetraethylthiuram disulfide. The emulsion is cooled to 20°C and aged at this temperature for about 8 hours to peptize the polymer. During this process, the disulfide reacts with and cleaves polysulfide chain segments. Thiuram disulfide also serves to retard formation of gel polymer in the finished dry product. After aging, the alkaline latex is acidified to pH 5.5—5.8 with 10% acetic acid. This effectively stops the peptization reaction and neutralizes the rosin soap (80). 

Aromatic solvents or polycyclic aromatic hydrocarbons (PAFI) in water, e.g. can be detected by QCM coated with bulk-imprinted polymer layers. Flere, the interaction sites are not confined to the surface of the sensitive material but are distributed within the entire bulk leading to very appreciable sensor responses. Additionally, these materials show high selectivity aromatic solvents e.g. can be distinguished both by the number of methyl groups on the ring (toluene vs. xylene, etc.) and by their respective position. Selectivity factors in this case reach values of up to 100. 

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. 

Xylenes (di methyl benzene) QH4(CH3)2 Plasticizers, polymer fibres and resins, solvents... 

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