Poly cleavage reactions

The FTIR spectra of the gas mixture evolved in thermal decomposition of Bisphenol AF poly(formal) (7) at various temperatures suggest the existence of benzene rings, C—O—C bonds, and C=C bonds. In a pyrogram of pyrolysis gas chromatography (Py-GC) of Bisphenol A (3), a-methylstyrene, phenol, p-cresol, 4-hydroxy-amethylstyrene, and isopropyl phenol are observed as major peak products. The cleavage reactions shown in Scheme (5) is suggested for the formation of phenol and 4-hydroxy-a-methylstyrene from Bisphenol A (3). 

Most of the polymers are easily depolymerized photochemically and thermally in solution to the corresponding monomers, as is expected from the ring cleavage reaction of a number of cyclobutane derivatives yielding two olefins. For example, poly-DSP in solution is depolymerized to DSP nearly quantitatively upon photoirradiation for a relatively short period36 or by heating at above 200°C70). 

In contrast to peptide synthesis, the application of insoluble supports on the basis of polystyrene has never found broad ajqilication [40,59,131,132]. One of the main reasons for that is probably the steric hindrance by the structure of crosslinked polymers during condensation and cleavage reactions. Also, non-crosslinked, soluble carriers based on polystyrene are not especially appropriate because the solubility of loaded supports decreases with increasing numbers of condensation reactions. However, hydrophilic supports, such as poly(vinyl alcohol), have been used successfully for the synthesis of oligonucleotides. 

Because the chain cleavage reaction is presumably favored by a high electron-density in the lone-pair-electron orbital at skeletal nitrogen, we have assumed that the use of the more electronegative fluorine atoms in poly-(difluorophosphazene) may favor halogen substitution at the expense of chain cleavage. Poly(difluorophosphazene)... 

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