W-Xylylene

A w-xylylene bridge connecting the oxygens in 1,3-position completely hinders the ring inversion. This was shown by Shinkai et al. for compound 83, which is chiral due to the methoxy group at the bridge.156 The racemate could be resolved by enantioselective HPLC (Chiralpak AD). No racemization was observed when a single enantiomer was heated to 100 °C (12 h, different solvents). 

In Japan, a polyamide that is very suitable for tire cord is made from adipic acid and w-xylylene diamine, VI, but this is sensitive to heat and humidity. 

Vigalok, A. Shimon, L. J. W. Milstein, D. Methylene arenium cations via quinone methides and xylylenes stabilized by metal complexation. J. Am. Chem. Soc. 1998, 120, 477 183. 

Paralene [para-xylene] Also called Gorham and also spelled parylene. A process for coating articles with poly-p-xylene. The vapor of di-p-xylylene is pyrolyzed at 550°C, yielding p-xylyl free radicals, -CHj-CgH CH, which deposit and polymerize on cooled surfaces. Developed by W. F. Gorham at Union Carbide Corporation. 

The formation of the heterocycle 1 from the xylylene-bis-phosphonium salt 2 and PCI3 proceeds via a detectable intermediate 3 in a cascade of condensation reactions that is terminated by spontaneous heterolysis of the last remaining P-Cl bond in a cyclic bis-ylide-substituted chlorophosphine formed (Scheme 1) [15]. The reaction scheme is applicable to an arsenic analogue of 1 [15] and to bis-phosphonio-benzophospholides with different triaryl-, aryl-alkyl- and aryl-vinyl-phosphonio groups [16, 18, 19], but failed for trialkylphosphonio-substituted cations here, insufficient acidity prohibited obviously quantitative deprotonation of the phosphonium salts, and only mixtures of products with unreacted starting materials were obtained [19]. The cations were isolated as chloride or bromide salts, but conversion of the anions by complexation with Lewis-acids or metathesis was easily feasible [16, 18, 19] and even salts with organometallic anions ([Co(CO)4] , [CpM(CO)3] (M=Mo, W) were accessible [20]. 

Y. S. Yeh, W. James, H. Yasuda, Polymerization of para-xylylene derivatives, VI. morphology of parylene N an parylene C films investigated by gas transport characteristics, /. Polym. Sci. Part B 1990, 28, 545. 

Recent encouraging results have been reported by Carter et al., who have obtained room temperature lifetimes in excess of 7000 h for encapsulated ITO/PPV/Ca devices at current densities of 60 mA/cm2.37 The polymer used was the PPV copolymer shown in Fig. 5.23, where the conjugation is interrupted by nonconjugated a -acetyloxy-/ -xylylene units. The efficiency of these devices was typically 0.02 lm/W. Devices operating at 80° C had lifetimes in excess of 1100 h. Carter et al., also reported devices based on the same emissive polymer giving efficiencies between 0.5 and 2 lm/W. These devices used a layer of conducting polymer (polyethylenedioxythiophene/polystyrene sulfonate) between the ITO and the PPV, and a sputtered aluminum/lithium alloy as the cathode. The devices... 

The enthalpy of formation of gaseous p-xylylene of 210 20 kJ mol-1 was obtained from the energetics of gas-phase ion-molecule reactions from S. K. Pollack, B. C. Raine and W. J. Hehre, J. Am. Chem Soc., 103, 6308 (1981). Since gaseous p-xylylene polymerizes... 

In another approach to the preparation of communesins, AdUngton and George [26] also utilized what is believed to be an intramolecular IDA cycloadditiOTi reaction of an aza-orf/io-xylylene with an W-methyl-indole (compound 40) as a key synthetic step, this time producing a pentacyclic structure 43 which contains both of the vicinal quaternary centers present in the communesin scaffold, albeit in modest yield (Scheme 12). Two additional side products 41 and 42 (possibly resulting from an electrocyclic reaction involving the vinyl group, or attack by imidazole on the terminal alkene) were also isolated. It should be noted that an alternative mechanism for the formation of the three products, which involves an allylic carbocation species (39), can also be postulated. 

W. F. Gorham. Alkylated di-p-xylylenes. US Patent 3 117 168, assigned to Union Carbide Corp., January 07,1964. 

P. Hanefeld, F. Sittner, W. Ensinger, and A. Greiner. Investigation of the ion permeability of poly(p-xylylene) films, e-polymers 026/2006 [electronic] http //www.e-polymers.org/, 2006. 

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