Xylylene coatings

Table I. Effect of Weight Percent Poly ( chloro-J-xylylene) Coating on Percent of Pinhole-Free LAH Pellets...

Much better stability was reported for AsFg-doped polyacetylene coated with poly(p-xylylene) (26), which is an excellent barrier toward oxygen and water. Samples having conductivities of 260 S/cm were coated by vacuum deposition thus, the initial concentration of oxygen in the sample was low. After 24 h in air, a conductivity loss of 10% was observed for treated films, whereas the conductivity of uncoated control samples decreased by a factor of 3. After 1 month, the coated samples had a conductivity of 150 S/cm, whereas that of the control was only 11 S/cm. From isothermal aging studies, the poly(p-xylylene) coating was found to increase the first-order activation energy for conductivity loss by 2.4 Kcal/mol, from 17.2 to 14.8. These data... 

One of the earliest methods for the preparation of polymeric p-xylylene coatings is a high-temperature pyrolysis of p-xylene at 800-1,000°C and subatmospheric pressures, followed by cooling the pyrolysis vapors to a polymerization temperature by condensing the vapors on a cold surface. During pyrolysis, reactive radicals are formed that polymerize when cooled down again. 

A poly(amino-p-xylylene) coated functional surface was used to immobilize a polymeric drug release system consisting of poly(A-isopropylacryl-amide)-co-poly(acrylic acid). Into the drug release system, the thrombin inhibitor R-hirudin was incorporated. ... 

T. E. Baker, G. L. Eix, and J. S. Judge. Process for forming polymeric para-xylylene coatings and films possessing improved oxidation resistance. US Patent 4 176209, assigned to Raytheon Corporation (Ixxington, MA), November 27, 1979. 

Para-xylylene coatings are nniqne, since they are applied by vapor deposition (see Sec. 41.4.6) rather than as a Uqnid. They are applied. 0005 to. 002 in. thick. Para-xylylene coatings are often used in biomedical devices dne to the inert character of the coating. 

Water (10 wt%) Poly(p-xylylene) coated polymer/ Zeng et al. (2005a) BSA nanofibers prepared by cbemical vapor deposition on electrospun fiber surface. The altered diffusion kinetics of bovine serum albumin from the nanofibers into buffer studied. 

The linear polymer of PX, poly(p-xylylene) (PPX) (2), is formed as a VDP coating in the parylene process. The energetics of the polymerization set it apart from all other known polymerizations and enable it to proceed as a vapor deposition polymerization. 

The generation of PPV and corresponding derivatives via the dihalide approach is possible not only in solution reaction, but also - via the gas phase -in a so-called chemical vapor deposition (CVD) process. In this process, the vapor of a dichlorinated para-xylene (a,a or a,a) is pyrolyzed at moderately low pressures (0,1-0,2 torr) to form a chlorinated para-xylylene intermediate, which then condenses and polymerizes on a suitable, cooled substrate. The coating of the chlorinated precursor polymer can be heated to eliminate HCl, to form PPV 60 (or a PPV derivative) [88]... 

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. 

Hybrid circuit coating -parylenes as [XYLYLENE POLYMERS] (Supplement)... 

In the commercial Gorham process. PX is generated by the thermal cleavage of its stable dimer, cyc/o-di-p-xylylene (DPX). a [2.2]paracyclo-phane (3). In many instances, substituents attached to the paracyclophane framework are carried through the process unchanged, ultimately becoming substituents of the polymer in the coating. 

The p-xylylene species plays a central role in the coating process itself as well as in the making of the dimers which are used as feed-stocks for the coating process. Polymers and dimers have both been made from precursor p-xylene compounds (4) featuring a variety of X and Y leaving groups. 

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