Impurity carbonyl groups

T uminescence studies of commercial polymers have provided valuable -L information on the nature of some of the light absorbing chromophoric impurities believed to be responsible for sunlight-induced oxidation (1-13). The luminescence (fluorescence and phosphorescence) from commercial polyolefins has been attributed to the presence of impurity carbonyl groups (1,2,5,6,8), and recent work on polypropylene has indicated that these groups are conjugated with ethylenic unsaturations... 

The final variable to be mentioned here is the presence of impurities. These may be metallic fragments residual from Ziegler-type processes or they can be trace materials incorporated into the polymer chain. Such impurities as catalyst fragments and carbonyl groups incorporated into the chain can have a serious adverse influence on the power factor of the polymer, whilst in other instances impurities can have an effect on aging behaviour. 

Other products commonly isolated from reactions of DMAD with heterocycles include dimethyl fumarate (17), the acetylene presumably acting as a dehydrogenating agent, and dimethyl methoxyfumarate (18).22 The latter could arise from the addition of methanol, present as an impurity, to the acetylene, or by nucleophilic attack on the carbonyl group of the acetylenic ester followed by expulsion of methoxide ion, which then undergoes a normal nucleophilic addition to the activated triple bond. It can be obtained, among other products, from the reaction of pyridine with DMAD in methanol.23... 

Some polymers show discoloration as well as reduction of the mechanical properties (e.g. aromatic polyesters, aromatic polyamides, polycarbonate, polyurethanes, poly (phenylene oxide, polysulphone), others show only a deterioration of the mechanical properties (polypropylene, cotton) or mainly yellowing (wool, poly(vinyl chloride)). This degradation may be less pronounced when an ultraviolet absorber is incorporated into the polymer. The role of the UV-absorbers (usually o-hydroxybenzophenones or o-hydroxyphenylbenzotriazoles) is to absorb the radiation in the 300-400 nm region and dissipate the energy in a manner harmless to the material to be protected. UV-protection of polymers can be well achieved by the use of additives (e.g. nickel chelates) that, by a transfer of excitation energy, are capable of quenching electronically excited states of impurities (e.g. carbonyl groups) present in the polymer (e.g. polypropylene). 

At the First International Bleaching Conference at Appleton, Wisconsin, in 1955, in the final panel discussion on bleaching problems, fourteen theories were put forward to account for brightness reversion. They are listed here for reference purposes (a) residual lignin (b) furfural (c) reductone formation from carbohydrates (d) residue resin (e) poor washing (f) pH (g) metallic catalysts (h) metallic resinates (i) diffusion (j) carbonyl groups (k) water impurities (1) microorganisms (m) low bleach residual and (n) UV radiation. 

Impurities containing the carbonyl group, e.g. phosgene in chloroform, plasticisers Bound or unbound water can give rise to sharp or broad bands Alkali salts (which also have a weaker band at 1425 cm" 9 can be produced from alkali halides Lens tissues... 

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