Poly oxidative degradation

Poly(acrylic acid) and Poly(methacrylic acid). Poly(acryHc acid) (8) (PAA) may be prepared by polymerization of the monomer with conventional free-radical initiators using the monomer either undiluted (36) (with cross-linker for superadsorber appHcations) or in aqueous solution. Photochemical polymerization (sensitized by benzoin) of methyl acrylate in ethanol solution at —78° C provides a syndiotactic form (37) that can be hydrolyzed to syndiotactic PAA. From academic studies, alkaline hydrolysis of the methyl ester requires a lower time than acid hydrolysis of the polymeric ester, and can lead to oxidative degradation of the polymer (38). Po1y(meth acrylic acid) (PMAA) (9) is prepared only by the direct polymerization of the acid monomer it is not readily obtained by the hydrolysis of methyl methacrylate. 

Poly(hydrosilane)s have been successfully applied as processing stabilizers for organic polymeric materials subject to oxidative degradation. The degradation of polyolefins during processing takes place by a widely accepted... 

Surprisingly, the fine regulation of the enzymes involved in poly(3HB) degradation has been hardly investigated at all (cf. Chap. 10 of this book). Most of the research on intracellular mobilization of poly(3HB) and oxidation of the monomers was done more than 25 years ago. 

Sealants obtained by curing polysulfide liquid polymers with aryl bis(nitrile oxides) possess stmctural feature of thiohydroximic acid ester. These materials exhibit poor thermal stability when heated at 60°C they soften within days and liquefy in 3 weeks. Products obtained with excess nitrile oxide degrade faster than those produced with equimolar amounts of reagents. Spectroscopic studies demonstrate that, after an initial rapid addition between nitrile oxide and thiol, a second slower reaction occurs which consumes additional nitrile oxide. Thiohydroximic acid derivatives have been shown to react with nitrile oxides at ambient temperature to form 1,2,4-oxadiazole 4-oxides and alkyl thiol. In the case of a polysulfide sealant, the rupture of a C-S bond to form the thiol involves cleavage of the polymer backbone. Continuation of the process leads to degradation of the sealant. These observations have been supported by thermal analysis studies on the poly sulfide sealants and model polymers (511). 

Although Parylene-N possesses an outstanding combination of physical, electrical, and chemical properties, the benzylic C—H bonds present are potential sites for thermal and oxidative degradation. It is well known that replacing a C— bond with a C—F bond not only enhances the thermal stability of the resulting polymer, but also reduces the dielectric constant. Because incorporation of fluorine is known to impart thermal and oxidative stability, it became of interest to prepare poly(a,a,a, a -tetrafluoro- p -xylylene), Parylene-F Joesten reported that the decomposition temperature of poly(tetrafluoro-j9-xylylene) is ca. 530°C. Thus, it seemed that the fluorinated analog would satisfy many of the exacting requirements for utility as an on-chip dielectric medium. 

Oxidative Degradation of Poly(vinyl Alcohol) with Periodic Acid... 

Some of recent papers by Ratner et al. [63, 64] revealed that there are significant differences in the surface chemistry of Biomer lots. The surface of some lots was dominated by poly(diisopropylaminoethyl methacrylate) (DPAEMA or DIPAM), a high molecular weight UV stabilizer, which was absent from some older lots [65]. Ratner et al. carried out comparative studies on in vitro enzymatic and oxidative degradation of two lots of Biomer, BSU 001 and BSP 067. Lot BSU 001 contains both DPAEMA and an antioxidant, Santowhite powder, while BSP 067 contains only the antioxidant. It was found that DPAEMA retarded the enzymatic degradation process, but accelerated oxidative degradation. 

In a series of publications Berlin et al. 87-90) describe block copolymers with poly-azophenylene units which are extremely stable with respect to both thermal and oxidative degradation. From an emulsion polymerization of isoprene initiated by the... 

Sulfonated Fe and Mn phthalocyanines are catalysts for the oxidative degradation of chlorinated phenols such as 2,4,6-trichlorophenol, a contaminant from paper mills that use chlorine for bleaching. Fe-tetrasulfophthalo-cyanine supported on poly(vinyl-4-methylpyridinium) converts 2,4,6-trichlorophenol with the K+ salt of Caro s acid, KHSO5, or H2O2 as the oxidant (112) ... 

Other Polymers. Various other polymers frequently require stabilization against thermal or thermo-oxidative degradation. Poly(vinylidene chloride) is stabilized by epoxides and sodium pyrophosphate. 

Zitting A, Savolainen H. 1980. Effects of single and repeated exposures to thermo-oxidative degradation products of poly(acrylonitrile-butadiene-styrene) on rat lung, liver, kidney and brain. Arch Toxicol 46 295-304. 

Nowadays there are more and more demands to reuse waste materials, especially in the case of polymers. Our research seeks to reveal the oxidative degradation processes of poly(vinyl chloride) (PVC), which may provide new methods for treating and recycling of PVC waste materials. 

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