Fluoride-vinyl polymers, degradation

A combination of gas chromatography and either electron-impact or chemical ionization mass spectrometry has been used to analyse the products of thermal degradation of poly(vinyl fluoride) and of a number of other polymers [poly(vinyl chloride), aromatic polyimides, polyurethane]. The degradation of poly(vinyl-idene fluoride) has been related to its crystalline form. It is claimed that dehydrofluorination may take place preferentially in crystalline segments containing trans sequences. Thermo-oxidative breakdown is modified if vinylidene fluoride is copolymerized with tetrafluoroethylene or hexafluoroacetone. Dehydrofluorination occurred in both copolymers, but in the latter it was preceded by cleavage of the H from the CHj group in the alpha position to the ether bond followed by scission of the C-0 bond. ... 

In the absence of molecular oxygen, thermal degradation occurs only at 450°C. Poly(vinyl fluoride) is used to manufacture biaxially stretched films and coatings, which exhibit a strong chemical inertia and an excellent resistance to aging. Films are prepared by extrusion of a polymer swollen by polar solvents followed by then-... 

Stability and performance of AEM prepared using poly(4-vinyl pyridine-costyrene), quaternized with 1-bromooctane, and deposited on fibrous woven paper was unsatisfactory [189]. Sanchez and coauthors [190] discussed problems related to the use of certain AEMs. They pointed out that the so-called Hoffman degradation that involves attack of a hydroxyl on a-hydrogen in p-position to a quaternary ammonium attached to an aliphatic chain may cause its removal, followed by release of a tertiary amine and formation of a double bond at the end of a broken chain. Attachment of DABCO on short leash prevented chain break due to Hoffman degradation, but release of DABCO and generation of a double bond attached to the chain could take place. Perhaps thermal cross-linking by DABCO of poly(vinyl benzyl chloride) may solve this problem. Sulfonated polymers prepared by polymerization or copolymerization of phosphazene, siloxans, styrene, vinylidene fluoride, and various monomers with aromatic backbones, and possibly with aliphatic spacers, have been used. Various imides as well as PPS, PEK, PEEK, PSU, PEEKK, and PPSU can also be used [190,191]. 

The characteristic features of the degradation of alkyl methacrylate polymers are considered elsewhere (see Section 15.3.2). In contrast to PEMA, PFEMA gives no monomer. In addition to the ester decomposition products vinyl fluoride and CO2, acetaldehyde and fluoroacetaldehyde are produced. Explanations have been proposed for the latter products on the basis of meth-acrylic acid/FEMA and FEMA/radical end FEMA adjacent unit interactions. It is argued that the ester decomposition route is favoured by F atom activation of the hydrogens, so suppressing depolymerization. 

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