Poly-p-xylene

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. 

As expected, the 1H—NMR spectrum shows only one absorption in the aromatic region (r=2.7). This is shifted considerably compared with that of unsubstituted [2.2]paracyclophane (t=3.7). In the IR spectrum an intense band occurs at 718 cm-1, as is characteristic for other [2.2]paracyclophanes, e. g. methoxycarbonyl[2.2]paracyclophanes 8 and 9 35>, though it is absent in the spectrum of the linear poly-p-xylene (10). The parent hydrocarbon 2 shows this absorption, ascribed to the distorted aromatic rings, at 725 cm-1 36>. 

These polymers do not contain a functional group within the polymer chain but are classified as condensation polymers, since water is split out during the polymerization process. Another example is poly(p-xylene). which is produced by the oxidative coupling (dehydrogenation) of p-xylene ... 

Figure 3. Electron mean free path as a function of electron kinetic energy through organic materials. Key V, PMMA , poly(p-xylene) O, plasma polymerized fluorocarbon , barium stearate 0, cadmium arachidate and A, carbon. (Reproduced, with permission from Ref. 35.)...

Similar to the synthesis of a germanium-containing poly(p-xylene) (PPX), the tin-containing block copolymer of unsubstituted PPX and a diorganotin bridged PPX were prepared134 (Scheme 29). 

The luminescence spectra of various polymers and solid model compounds induced by 1 MeV have been compared [200]. An enhanced triplet emission and the absence of fluorescence have been observed for poly(p-xylene) and poly(monochloro-p-xylene). A longer wavelength emission assigned to triplet excimer is reported. Poly(ethylenetereph-thalate) and polysulphone emit primarily from singlet and singlet excimer states. Comparison of electron and UV induced luminescence in these polymers would be very useful for the interpretation of the spectra reported. 

Another example of aromatic polymer is poly (p-xylene), which is usually vacuum deposited as thin films on substrates. In one application the monomer is di-p-xylylene formed by the pyrolysis of p-xylylene at 950°C in the presence of steam. When this monomer is heated at about 550°C at a reduced pressure, a diradical results in the vapor phase, which, when deposited on a surface below 70°C, polymerizes instantaneously and forms a thin, adherent coating. 

Poly(p-xylene tetrahydrothiophenium chloride) solution Sigma-Aldrich... 

Poly(p-xylene). A linear polymer consisting of directly linked / -xylene units in the macromolecular chain. Applications high-temperature dielectric films or coatings for special purpuses. Trade name Parylene (USA). 

The methylene bonds are the weakest in the poly(p-xylene) macrochain. The cleavage of such bonds causes the formation of two macroradicals, which should decompose via a chain mechanism to yield monomer ... 

In the oxidative pyrolysis of poly-p-xylene, the oxygen attacks methylene groups first to form hydroperoxides [536]. This is followed by chain cleavage ... 

Bier, A. K. Bognitzki, M. Schmidt, A. Greiner, A. Gallo, E. Klack, P. Schar-tel, B., Synthesis, Properties and Processing of New SHoxane-Substituted Poly(p-xylene) via CVD. Macromolecules 2012,45,633-639. 

Thus poly(p-xylene carbonate) has been synthesized from potassium carbonate and p-xylene dibromide under the influence of 18-crown-6-ether. The crown ether formed a complex with the metal cation, thereby providing highly reactive unsolvated anions. Aromatic polycarbonates have been prepared and subjected to studies of their heat stability, mechanical strength, transparency, and electrical properties. Spiro o-carbonates have been synthesized and their poly-racrizability, by cationic initiation, has been assessed. 

Hydrocarbon polymers with aromatic rings in the backbone have high melting temperatures due to the extended chain conformations that approach those of liquid crystals. For example, poly(p-xylene) based on the repeat unit... 

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