UV quencher

Uv methods Uv-quenchers Uv radiation uv Radiation Uv Radiation Uv stability Uv stabilizers... 

Plastics Additives. Many claims have been made for the use of nickel chemicals as additives to various resin systems. By far the most important appHcation is as uv-quenchers in polyolefins (173,174). Among the useful nickel complexes in these systems are dibutyldithiocarbamate nickel [13927-77-0], nickel thiobisphenolates, and nickel amide complexes of bisphenol sulfides (175). The nickel complex of... 

In general, the activities of these artifacts can be loosely classified into major categories detergent-like, toxic, polyphenol, antioxidant, and UV quenchers. 

Problem Dusty nickel-based UV quenchers can be hazardous in the workplace. 

UV quenchers also inhibit initiation, although they function later in the degradation sequence than do absorbers. Quenchers are organic nickel compounds. They are typically used in polyolefins. Unlike absorbers, quenchers are effective in thin sections. They are often used along with UV absorbers. Quenchers usually impart color. 

UV quenchers UV quenchers are usually metal complexes, which can decrease the activity of UV light. UV quenchers can take over the energy absorbed by molecules and dissipate it as heat or as fluorescent or phosphorescent radiation. 

The benzoin ethers (75, R-alkyl R H) and the ot-alkyl benzoin derivatives (75, R=H, alkyl R =alkyl) undergo a-scission with sufficient facility that it is not quenched by oxygen or conventional triplet quenchers.276 This means that the initiators might be used for UV-curing in air. Unfortunately, it does not mitigate the usual effects of air as an inhibitor (Section 5.3.2). The products of a-scission (Scheme 3.53) are a benzoyl radical (13) and an ( -substituted benzyl radical (76) both of which may, in principle, initiate polymerization, 76 2"... 

The quinone diazide 2o was investigated using LFP in solution at room temperature.25 As with la, the carbene lo does not show characteristic absorptions in the UV /vis region and therefore could not be directly monitored during the LFP experiments. By extrapolation of quenching plots to zero quencher concentration the life-time of lo in Freon-113 was determined to 2.5 p,s, slightly longer than that of la with 1.65 ps. 

Copper in minerals luminescence is usually considered only as an effective quencher. Nevertheless, it is well known that a bright blue luminescence is emitted from Cu ions in inorganic solids by UV light irradiation. It was found that these materials have potential application to tunable lasers. For example, in Ca0-P20s glasses Cu is characterized by a luminescence band at 440 nm with a half-width of 100 nm and an excitation maximum at 260 nm. The decay time of luminescence is approximately 25 ps (Tanaka et al. 1994). Red fluorescence possibly connected with the Cu" pair is also known (Moine et al. 1991). 

Rate measurements are straightforward if the carbene can be monitored directly. As a rule, the decay of carbene absorption is pseudo-first order due to rearrangement and/or reaction with the solvent. In the presence of a quencher, the decay is accelerated and the rate constant is obtained from a plot of feobs versus the concentration of the quencher (Eq. 7). Carbenes that contain a UV chromophore (e.g., DPC ) are readily observed and their decay kinetics during the reaction can be readily followed by LER... 

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. 

Novel helical polybinaphthyls, including 38, have been synthesized, and their structures were characterized by NMR, UV, FL, and CD. Their optical properties have also been studied, and it was observed that these compounds exhibit a significantly increased fluorescence effect to an amino alcohol quencher over the parent l,l -bi-2-naphthol < 2004MM 2695 >. 

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