Polymer processing free radical generation

If the loss of solubility of these initially linear polymers takes place through a free-radical-chain process in which the cross-linking reaction represents the termination step, one may be hesitant at first to explain the fact that a free radical, generated at one point on a relatively sluggish polymer chain, can find a radical on a neighboring chain with which to terminate. However, perhaps reactions of the type R + R H --- RH + R or R00 + R H-- ... 

The emulsion polymerization process involves the polymerization of liquid monomers that are dispersed in an aqueous surfactant micelle-containing solution. The monomers are solubilized in the surfactant micelles. A water-soluble initiator catalyst, such as sodium persulfate, is added to the aqueous phase. The free radicals generated cause the dispersed monomers to react to produce polymer molecules within the micellar environment. The surfactant plays an additional role in stabilizing dispersion of the produced polymer particles. Thus, the surfactants used both provide micelles to house the monomers and macroradicals, and also stabilize the produced polymer particles [193,790], Anionic surfactants, such as dodecylbenzene sulfonates, are commonly used to provide electrostatic stabilization [193], These tend to cause production of polymer particles having diameters of about 0.1-0.3 pm, whereas when steric stabilization is provided by, for example, graft copolymers, then diameters of about 0.1-10 pm tend to be produced [790,791]. 

Safety requirements must be satisfied before a cobalt-60 source can be installed and licensed. Radiation-trained personnel must be on the staffbefore a license can be issued. At least 500,000-1,000,000 Ci (curies) of cobalt-60 are required in a production source for making wood-polymers, and at 1.00 or more per curie, a considerable investment must be made before production can begin. Besides cost considerations, the cobalt-60 radiation process does have some distinct advantages in making wood-polymer composites. Because the monomer is not catalyzed it can be stored at ambient conditions as long as the proper amount of inhibitor is maintained. The rate of free radical generation is constant for a given amount of cobalt-60 and does not increase with temperature. 

The anhydride units interrupt the unzipping process characteristic for PMMA pyrolysis. A similar effect may have the free radicals generated during the decomposition of one polymer and interacting with the other one in a blend. 

As effective as these surface modification processes might be, they present limitations in terms of the extent to which the surfaces of polymers can be modified. Plasma-induced grafting offers another method by which chemical functional groups can be incorporated. In this process, free radicals are generated on the surface of a polymer through the use of an inert gas plasma. Because of the nonreactive nature of the inert gas plasma, surface chemical modification of the polymer does not occur. If the polymer surface that has been... 

Free radical chain polymerisation is the method used to prepare the most common polymers. A free radical is generated and reacts with one molecule of monomer (initiation). Then monomer molecules react with this first species, leading to formation of a long chain by successive additions of monomer (propagation). Finally, chains are terminated by reaction of two chains bearing radicals (termination). As radicals are very reactive species, side reactions are likely to occur and modify the simple process (transfer). 

Any process by which one polymer chain is terminated (e.g., by a solvent, monomer or additive) and another free radical generated, is known as chain transfer because the new radical can propagate a new chain. Chain transfer cannot start a polymer chain and should not influence the rate of pol5unerization, but can give shorter chains with a consequent reduction in the relative molecular weight. 

The other class of molecules that self-reacts consists of monomers that readily form polymers—often these are alkenes or dienes. The polymerization process is usually free-radical generated and with polymeric products sometimes involving thousands of monomer linkages that produce... 

H. Gisser (Frankford Arsenal) I would like to comment on the polymer formation. The information coming from many sources not only do not contradict but support each other. From chemistry of the system, a free radical generated during the process polymerizes vinyl chloride now we have seen evidence that such a polymer has been formed as demonstrated by Don Buckley with auger spectroscopy. 

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