Chromophores polymer impurities

Water-soluble polymeric dyes have been prepared from water-insoluble chromophores, viz., anthraquinone derivatives. Unreacted chromophore and its simple derivatives, which are all water-insoluble, remain in solution due to solubilization by the polymeric dye. A method has been developed to separate and quantitate the polymeric dye and these hydrophobic impurities using Sephadex column packing. The solvent developed has the property of debinding the impiirities from the polymer, and further allows a separation of the imp irities into discrete species. This latter separation is based on the functional groups on the impurity molecules, having a different interaction with the Sephadex surface in the presence of this solvent. The polymer elutes at the void volume... 

The ordinary monomer units of PVC are not expected to absorb any terrestrial solar radiation (1>.2>.3 A) Thus, under the usual ambient conditions, photodegradation of the polymer must be initiated by chromophoric impurities. These impurities may simply be structural defects in the PVC itself, or they may be extraneous substances that have been incorporated into the polymer. Several of these potential photosensitizers are discussed in the following sections. 

If any ground-state interactions occur among the chromophores of the polymer, the UV absorbance will be altered. However, such alterations are more likely to be caused by impurity chromophores on the polymer chain. Since it is extremely difficult to obtain high polymer which is free from defects and impurities, another standard for the polymer UV absorbance is desired. 

Nearly all polymers are susceptible to degradation by the action of heat and light, especially in the presence of oxygen (B-75MI11500, B-78MI11500). This is in part due to the structures of the polymers themselves and in part due to the presence of impurities, such as traces of transition metal ions and various chromophores. Free radical processes are... 

These molecules have no absorption in the near UV, so they cannot act as internal filters. There is no evidence that they could act as quenchers of the excited impurity chromophores in common polymers, and it has been mentioned already that such quenching action would be, in any case, unlikely to be important in relatively rigid systems such as polymers. This remark does not apply to free radical scavengers, because a free radical has an unlimited lifetime since it can disappear only through a chemical reaction with another open-shell molecule. 

In contrast, diallylamino-substituted dyes copolymerized poorly with MMA, despite the reported polymerizability of other aliphatic (24-25) and aromatic (26) diallylamines. The concentration of dye-bearing repeat units m the polymer was far below the monomer feed concentrations. The possibility that these diallyl dye-monomers (or some unidentified impurity in them) acted as inhibitors of polymerization can be ruled out because the dye was found to be present uniformly in all molecular weight fractions and the molecular weights of the copolymers were again nearly identical to control samples of PMMA. Therefore, only a small amount of the diallyl amino substituted chromophores can be covalently incorporated into the crosslinked matrix because of the apparently unfavorable reactivity ratio. The balance of the chromophore remains simply dissolved in the mixture. 

Acrylic Crosslinkers. Butanediol diacrylate (IV) (BDDA) is a popular crosslinker used in the preparation of many polymers used for inks, paints, and plastics. Low-levels of impurities can adversely affect product properties. As previously discussed, K+IDS provides a powerful qualitative technique, but yields poor quantitative data when analyzing volatile chemicals. BDDA is amenable to analysis by GC, unfortunately any higher-molecular-weight adducts exceed the volatility range amenable to GC. Moreover, BDDA is not chromophoric thereby HPLC characterization is also difficult. 

The photodegradation of PS is induced by chromophoric impurities. Once a radical has been formed, it produces macroradicals by abstraction of a hydrogen atom from the polymer structure. The mechanism of PS photooxydation is presented in Scheme 30.1. 

None of these products contribute towards the initiation of photooxidation of the polymer other than having some u.v. antioxidant action. On long-wavelength irradiation (365 nm) photoinitiation occurs via impurity chromophore whereas with light of wavelengths shorter than 300 nm direct excitation of the diphenylcarbonate unit occurs. 

Aliphatic polyamides (PA) and products on their base are polymers with low stability to ultra-violet irradiation and under the effect of solar radiation they destruct less than in a year [1]. In natural conditions ultra-violet part of solar spectrum with wave-length 290-350 nm is more dangerous for these polymers, though aliphatic PAs in this field have very weak absorption of chromophore amide group [2, 3], That is why while examining the problem of PA phototransformations, unlike other polymers, both possibility of light absorption by impurities and self-absorption should be taken into consideration [4],... 

Since pure PP does not incorporate chromophoric groups, it is clear that photoinitiation of radical degradation processes must involve chromophoric impurities. There has been a great deal of discussion of this in the past and hydroperoxides or carbonyl structures formed by oxidation of the parent polymer and transition metal residues from the polymerization catalyst seem to be the most likely candidates. It is not appropriate to discuss this aspect in the present paper, suffice it to say that the association of methane with photoinitiation, but not thermal initiation, suggests that photoinitiation involves C-CH3 bond scission to form chain side radicals in contrast to thermal initiation which involves scission of the C-C bond in the main chains. 

The fluorescence and phosphorescence excitation and emission spectra of commercial polypropylene and poly(4-methylpent-l-ene) are examined using a fully compensated spectrofluorimeter. The excitation spectra of the polymers are compared with the absorption spectra of model chromo-phores of those believed to be present in the polymers. The fluorescence emission is associated primarily with the presence of enone and the phosphorescence is associated with dienone impurity chromophoric units. Bromination of cold hexane extracts of the polymers reduces significantly the intensity of the fluorescence confirming the presence of ethylenic unsaturation. The behavior of the luminescent enone and dienone groups during irradiation under sunlight-simulated conditions is examined also. Possible mechanisms for the participation of these chromophoric units in the photooxidation of the polymers are discussed. 

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... 

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