Monomer stabilization polymeric peroxides

This group covers polymeric peroxides of indeterminate stmcture rather than polyfunctional macromolecules of known stmcture. These usually arise from autoxidation of susceptible monomers and are of very limited stability or... 

This group covers polymeric peroxides of indeterminate structure rather than polyfunctional macromolecules of known structure. These usually arise from autoxidation of susceptible monomers and are of very limited stability or explosive. Polymeric peroxide species described as hazardous include those derived from butadiene (highly explosive) isoprene, dimethylbutadiene (both strongly explosive) 1,5-p-menthadiene, 1,3-cyclohexadiene (both explode at 110°C) methyl methacrylate, vinyl acetate, styrene (all explode above 40°C) diethyl ether (extremely explosive even below 100°C ) and 1,1-diphenylethylene, cyclo-pentadiene (both explode on heating). 

Inhibition of spontaneous polymerization of (meth) acrylates is necessary not only at their storage but also in the conditions of their synthesis proceeding in the presence of sulfuric acid. In this case, monomer stabilization is more urgent, since sulfuric acid not only deactivates mat r inhibitors but also is capable of intensifying polymer formation. The concentration dependence of induction periods in these conditions has a brightly expressed nonlinear character. And, unlike polymerization in bulk, decomposition of polymeric peroxides is observed at relatively low temperatures in the presence of sulfuric acid, and the values [X] of the amines studied are by ca. 10 times lower than [HQ]. ... 

Finally, NMRP has been used for the preparation of ABA triblocks through sequential monomer addition. Benzoyl peroxide (BPO) as the initiator, 2,2,6,6-tetramethylpiperidinoxy (TEMPO) as the nitroxide stabilizer, and camphorsulfonic acid as the accelerator were used to polymerize sequentially AcOSt, St, and again AcOSt. The obtained PAcOSt-PSt-PAcOSt can be... 

The practieal importanee of inhibitors is often associated with their usage for monomer stabilization and preventing various spontaneous and undesirable polymerization proeesses. In industrial eonditions, polymerization may proeeed in the presenee of air oxygen and, henee, peroxide radicals MOO serve aetive centers of this ehain reaetion. In sueh eases, eompounds with mobile hydrogen... 

Suspension polymerization is carried out using a single reactor or two parallel reactors. A mixture of monomers, monomer-soluble initiator (peroxides and azo compounds), and any additives (e.g., chain transfer agents) is dispersed in water by mechanical agitation in the presence of a suspension stabilizer. The suspension polymerization temperatures ranges from 70°C to 125 C. The reactor temperature is increased gradually during the batch. SAN copolymer particles of 10-3(K)0 p,m are obtained. To keep the copolymer composition constant, a mixture of monomers is added into the reactor as in emulsion processes. 

The aqueous phase into which the monomer mix is dispersed is also prepared in a separate tank before transferring to the copolymerization ketde. It contains a catalyst, such as benzoyl peroxide [94-36-0], to initiate and sustain the polymerization reaction, and chemicals that aid in stabilizing the emulsion after the desired degree of dispersion is achieved. Careful adherence to predeterrnined reaction time and temperature profiles for each copolymer formulation is necessary to assure good physical durabiHty of the final ion-exchange product. 

However, the initial absence of unstable groups is no guarantee for long-term stability of the compound. For example, some aldehydes and ethers are easily converted to peroxides by reaction with oxygen from air [35,37,38]. Organic peroxides represent a class of unstable materials while monomers represent a class of substances that can self-react by polymerization if not properly inhibited and if the temperature is not properly maintained. Runaway reactions can result in both of these examples. 

The monomer addition scheme, shown at the top, requires an initiator which is capable of removing a hydrogen atom from the allylic position of the butadiene, resonance stabilization of the radical from AIBN does not permit this initiator to effect this reaction while benzoyl peroxide is capable of reaction to remove a hydrogen atom and initiate the reaction. On the other hand the polymeric radical addition scheme requires that homopolymerization of the monomer be initiated and this macroradical then attack the polymer and lead to the formation of the graft copolymer. Huang and Sundberg explain that the reactivity of the monomer... 

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