Polymer resin halogenation methods

Another traditional method used for polymer support characterization is elemental analysis. Its use as an accurate quantitative technique for monitoring solid-phase reactions has also been demonstrated [146]. Microanalysis can be extremely valuable if a solid-phase reaction results in the loss or introduction of a heteroatom (usually N, S, P or halogen). In addition, this method can be used for determination of the loading level of a functional group (e. g. usually calculated directly from the observed microanalytical data). For example, in many cases, the displacement of chloride from Merrifield resin has been used as a guide to determine the yield of the solid-phase reaction. 

Polymer-supported catalysts, especially those based on polystyrene resins, have been used on many occasions but they also suffer from low thermal stability as well as high cost and a tendency to swell in solvent.147,148 Simple physisorbed supported PTCs can be prepared by the incipient wetting method. In this way, alumina-supported phosphonium compounds have been prepared and used to catalyse various halogen exchange reactions in the gas phase along with various other nucleophilic substitutions (Figure 4.24). 

Significant effort has recently been put in for the elimination of polymer wastes from electric and electronic equipment (WEEE) by pyrolysis. WEEE includes mainly epoxy resins and styrene polymers. They often contain brominated aromatics, which are highly contaminant. However, their elimination by simple thermal treatments is no longer possible as one of the most important drawbacks in dealing with thermal treatment of WEEE is the likely production of supertoxic halogenated dibenzodiox-ins and dibenzofurans. A pyrolysis method at low temperature range was developed, which limited the formation of such toxic by-products and reduced pyrolysis costs, even at relatively long residence times in the reactor. 

For other polymers alternative methods must be used. For example, for butyl rubber (HR) it has been found that treatment of the textile with a resorcinol/formaldehyde resin solution will give significant improvement to the adhesion levels. This is often increased still further by the use of an interply of a halogenated butyl polymer (particularly chlorobutyl). 

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