Free-radical scavengers, polymeric

Here we discuss a new class of polypropylene stabilizers—the polymeric phenolic phosphites. These compounds exhibit unique, broad-spectrum activity which may allow simplification of polypropylene stabilizer systems. The most active species are synergistic with thiodipro-pionate esters, are effective processing stabilizers when used alone or with other compounds, and contribute to photostability. Compounds of this type appear to function as both free radical scavengers and peroxide decomposers, and through a mechanism not yet completely understood, allow significant reductions in the concentration of ultraviolet absorbers required to achieve high levels of photostability. 

Another common additive found in inkjet ink formulas are in-can stabilizers to extend the shelf life of the product. Typically, the shelf life must be at least 9 months although 12 months is preferred. Frequently, radical scavengers are used to prevent polymerization from occurring in the container. Also, it is important to leave adequate headspace in the bottle, as oxygen is also a very effective inhibitor of free radical initiated polymerization. 

To understand this effect requires a discussion of the mechanism of autoinitiation. Of the mechanisms proposed, two receive most of the discussion in the literature. A mechanism proposed by Flory [15] involves a 1,4-cyclobutane diradical intermediate and has been supported experimentally by polymerization in the presence of a free radical scavenger. Several of the dimers found in thermally initiated polystyrene are also attributed to a Flory initiation mechanism. 

Beilstein Handbrjok Reference) AI3-28026 BRN 1731349 CCRIS 964 Diethylhydroxyl-amine N,N-Diethylhydroxyamine EINECS 223-055-4 Ethanamine, N-ethyl-N-hydroxy- Hydroxylamine, N,N-diethyl- N-Hydroxydiethylamine Pennstop 1866. Free radical scavenger used by the rubber industry as an emulsion polymerization inhibitor vapor phase inhibitor for olefin or styrene monomer recovery systems in-process inhibitor for production of styrene, divinyl benzene, butadiene and isoprene. Liquid mp = 10° bp = 133° d = 0.8669. ElfAtochem N. Am. 

Oxygen content is important because this element is a free-radical scavenger that can act as an inhibitor or a retardant in emulsion polymerizations depending on the water solubility of the monomer(s) [75] and stirring [76-78]. 

Fronts of concentrations of 0.03, 0.06, and 0.15% (AIBN to MMA) were run at the temperatures ranges of 42 to 47,47 to 52 and 66 to 68 C. The ranges were a result of temperature fluctuations due to the type of thermostat used. Three samples at each set of conditions were run to determine an average and standard deviation. To ensure that the fronts were initiated by the polymeric seed, controls were run that did not contain seeds. To ensure that the gradient movement detected was not solely seed dissolution, controls using seeds and solutions of 4.0% TEMPO, a free-radical scavenger used as an inhibitor, in... 

Certain polymerizations can be stopped by additives. Diphenyl picryl-hydrazyl, for example, is a free radical scavenger, and stops free radical polymerizations. Ionic mechanisms are not affected. Benzoquinone, on the other hand, is also an inhibitor for free radical polymerizations. Because it is strongly basic, it reacts with cations, however, so that it is impossible to employ this additive to distinguish between free radical and cationic polymerizations. 

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