Chloro-p-xylylene

Parylene-C, the trade name of the film formed from the Union Carbide Corp. brand of dichloro-p-xylylene, is a vapor deposited film formed by the reaction shown in Figure 1. The solid dimer(I) is vaporized and pyrolyzed at 650° C to 750 C to the reactive olefinic monomer, chloro-p-xylylene(II), which polymerizes on cool surfaces in the low pressure deposition chamber to form the crystalline linear polymer poly(chloro-p-xylylene) (III) (5). 

Copolymerization of Chloro- and Butyl- -xylylene. Mixtures of dichloro-di-p-xylylene (XIII) and butyl-di-p-xylylene (XIV) were pyro-lyzed to form chloro-p-xylylene (XV), butyl-p-xylylene (XVI), and p-xylylene (VII). In the initial polymerization zone (ca. 90°C.) chloro-p-xylylene (XV) and butyl-p-xylylene (XVI) condensed and polymerized. Since this temperature is above the Tc of p-xylylene at 0.3 mm., p-xylylene molecules passed through and condensed and polymerized in the final, air-cooled zone. In this way it was possible to study the copolymerization of chloro- and butyl-p-xylylenes starting from the mixtures of the three monomers XV, XVI, and VII. 

Poly(chloro-p-xylylenes) containing (in theory) about 5, 10, and 20% butyl-p-xylylene were prepared in this way (see illustration on p. 650). The crystalline melting points of the products (XVII) were in the range 220°-250°C. compared with 290°C. for pure poly (chloro-p-xylylene). Solubility characteristics of the products and a sample of poly (chloro-p-xylylene) were studied by heating in a-chloronaphthalene. The solution temperature is the minimum temperature required to dissolve the product with slow heating. The gel temperature is that at which the solution of the product in a-chloronaphthalene sets to a gel on gradual cooling. Results were as follows ... 

Copolymers of ethyl- and chloro-p-xylylene were also prepared by pyrolytic polymerization of mixtures of dichloro-di-p-xylylene and diethyl-di-p-xylylene at 50°C. This is an example of preparation of a copolymer by pyrolysis of a mixture of two disubstituted di-p-xylylenes. 

Figure 2. Mesh coated with poly(chloro-p-xylylene). Polymer is transparent inner rings. 16.5 X...

For these reasons uniform thickness films are deposited on all surfaces. Unique features which result are the deposition of uniform thickness coatings on sharp edges, in crevices, and around the inside of holes. A metallizing mask was coated with 1.5 mils of poly(chloro-p-xylylene). Figures 2 and 3 are magnifications of the coated saw tooth and coated... 

In a further elaboration of this feature the ability of the monomer to penetrate between closely positioned glass slides and into deep crevices was investigated. In the initial experiment, several pairs of 3 inch X 3 inch glass slides were placed in a polymerization zone, the distance between the parallel surfaces of the plates varied from 0.017 to 0.125 inch, and sufficient chloro-p-xylylene was introduced to deposit 1.0 mil poly(chloro-p-xylylene) on the walls of the chamber and exposed surfaces. The plates were placed perpendicular to the flow of the gaseous monomer. At the end of the experiment the samples were removed, and the thickness of the coating at the center point on the inside surface of the plates was examined with the following results ... 

In a second series of experiments, 3 inch X 3 inch glass slides were joined at one end, the side openings were closed with tape, and the angle of the open end (0) varied from 90° to 1°. This experiment was designed to investigate the degree of penetration of the monomer-polymer into a crevice. The polymerization was conducted to deposit 1.0 mil polv-(chloro-p-xylylene) on the walls of the chamber. The samples were removed at the end of the run, and the thickness of the film at the bottom point of the 3-inch crevice was measured. 

Example 1 Encapsulation of Lithium Aluminum Hydride with Poly(chloro-p-xylylene). In the distillation zone were placed 5.0 grams of dichloro-di-p-xylylene. In a 4-oz. polyethylene bottle were placed 10.0 grams (400 pellets) of lithium aluminum hydride (LAH). LAH was obtained from Metal Hydrides, Inc., as 1/8-inch diameter pellets. The bottle was positioned in the coating chamber, the system was... 

Example 2 Encapsulation of 3/16-inch Sodium Hydroxide Pellets with Poly( chloro-p-xylylene ). Fifty grams of sodium hydroxide pellets were encapsulated with polymerizing chloro-p-xylylene generated by pyrolysis of 5.0 grams of dichloro-di-p-xylylene over a 15-minute period. The bottle was rotated at 60 r.p.m. during the run. A pyrolysis temperature of 660°C. and system pressure of 50 //, were employed. A total of 51.97 grams of encapsulated pellets was recovered at the end of the run. 

Surprisingly high levels of protection were achieved in the encapsulated products when poly (chloro-p-xylylene) was used as the encapsulant. 

Attention was then turned to encapsulation of a more reactive species, lithium aluminum hydride (Example 1). Several batches were encapsulated readily with poly (chloro-p-xylylene) utilizing the standard tumbling process. Products with from 1-20 wt. % coating were prepared. 

The correction for the contribution of a substituent on a single aromatic backbone ring to NYd differs depending upon whether or not the substituent contains hydrogen atoms. For example, the chlorine substituent in poly(chloro-p-xylylene) (Figure 5.2) contributes +10 to NYd, while the methyl (-CH3) substituent at the same location in poly(methyl-p-xylylene) contributes only +5. 

Another possibility is that, as in polycondensation, the formation of per-chloro-p-methylbenzyl radical is also brought about by iodide ion, but its subsequent reaction with iodide ion occurs so fast that its dimerization to perchloro-p,/7 -dimethylbibenzyl or subsequent vicinal chlorine elimination is prevented. Accordingly, when the reaction is carried out in the presence of toluene as hydrogen-atom donor (see preceding section) the yield of per-chloro-p-xylylene diminishes (72%), the rest being a, a //-octachloro-p-xylene, benzyl acetate, and, according to H-nmr spectroscopy, a mixture of cis- and tra 5-a/7,a //-tetradecachlorostilbene (46) (Diaz-Alzamora, 1968). 

It has been indicated before that its perchlorinated counterpart, per-chloro-p-xylylene (p. 304) withstands, surprisingly enough, even aggressive reagents and moderately high temperatures (Ballester and Castaner, 1960a Ballester et al, 1966). 

Figure 2.7. X-ray diffractograms of Ag-poly(chloro-p-xylylene) systems (a) cocondensate Ag-CIPX polymerized at 80 K and annealed at 293 K (b) layer-by-layer deposition of CIPX and Ag followed by polymerization and annealing at 293K. X-ray diffractogram peaks of Cu foil are used as a standard.

The properties of Parylenes can be tailored by forming copolymers. The fabrication consists of the simultaneous co-evaporation of two precursors with subsequent vapor deposition. Suitable comonomers are p-xylyl-ene, chloro-p-xylylene, perfluorooctyl methacrylate, and 4-vinylbiphenyl, and in general [2.2]paracyclophanes functionahzed with hydroxy, meth-oxy, amino, triflate, or trifluoroacetyl groups. ... 

Various t) es of Parylenes are sold. There are four forms of Parylene. Parylene N is the polymer of p-xylylene. Parylene C or Galaxyl Parylene C is poly(chloro-p-xylylene). Parylene D is poly(dichloro-p-xyl-ylene). Parylene HT is poly[(2,3,5,6-tetrafluoro-l,4-phenylene)(l,1,2,2-tetrafluoro-l,2-ethanediyl)]. Suppliers and commercial grades are shown in Table 2.6. Tradenames appearing in the references are shown in Table 2.7. 

H. Maruyama. Dichloro tetraflouro-(2,2 -paracyclopane, aprocess for manufacturing thereof and poly-a, a-difluoro-chloro-p-xylylene film prepared therefrom. US Patent 6 194620, assigned to Daisan Kasei Kabushiki Kaisha (Tokyo, JP), February 27,2001. 

Huang, H. L. Xu, Y. G. Low, H. Y. Effects of film thickness on moisture sorption, glass transition temperature and morphology of poly(chloro-p-xylylene) film. Polymer, 2005, 46(16), 5949 5955. 

Poly(chloro-p-xylylene) is suitable for its use in implantable, microfabricated devices [83]. It is hydro-phobic, with a low dielectric constant, and a good biocompatibility. However, for many bioelectrical applications, its poor wet adhesion may be a drawback. 

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