Thermal stability resist systems, example

Many fluorinated polymers have been prepared using free-radical processes and the intensity of interest in this field stems from the number of rmique properties that are bestowed on the polymer by the presence of the carbon-fluorine bonds in a system. For example, excellent resistance to chemically aggressive environments, high thermal stability, low dielectric constant, low flammability and very low surface energies are just some of the properties of fluorinated materials that have been exploited. Uses range from... 

Recent studies have shown that incorporation of boron element into sihcon-based ceramics increases their thermal stability and retard crystallization [202-204]. For example, the materials of the binary system Si—N start to crystallize at 7 =1,000 °C forming a-Si3N4, while metastable solid solutions of the ternary and quaternary systems Si—C—N and Si—B—C—N withstand crystallization up to 1,450 and 1,700 °C, respectively [205]. In order to form an amorphous uniform phase in the final multinary ceramics, the ceramic elements are preferably distributed homogeneously in the preceramic polymers. The general consensus in the ceramics community is that the quaternary system Si—B—C—N as well as the ternary systems Si—B—N and Si—B—C would be particularly suitable for producing amorphous ceramics that resist the microstructural changes even at top loads. 

The copolymerization of a,p-unsaturated ketones has been studied extensively in order to improve the poor chemical and thermal stability exhibited by the homopolymers. The vinyl ketones have been copolymerized with most of the common vinyl and diene monomers. The data are given in Ref. [326]. For initiation, the same reagents could be used as for free-radical homopolymerization. Copolymerization was carried out in bulk [371] and in emulsion systems [372]. In copolymerization with methyl methacrylate, vinyl acetate [373], and styrene [371] it was concluded that the relative reactivities of the vinyl ketones increase with the increasing electron-withdrawing nature of the vinyl ketone substituent. Polar and steric effects are not observed. Most of the work has been directed toward the preparation of oil- and solvent-resistant rubbers to replaee styrene-butadiene rubber. Emulsion eopolymerization of butadiene with methyl isopropenyl ketone yielded rubbers with good solvent resistance and low temperature flexibility, but the products tended to harden on storage and were not compatible with natural rubber [374]. The reactive earbonyl function caused sensitivity to alkine reagents. Copolymers of butylacrylate and methyl vinyl ketone, for example, can be erosslinked by treatment with hydrazine [375]. 

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