Surface graft polymerization principle

The creation of active sites as well as the graft polymerization of monomers may be carried out by using radiation procedures or free-radical initiators. This review is not devoted to the consideration of polymerization mechanisms on the surfaces of porous solids. Such information is presented in a number of excellent reviews [66-68]. However, it is necessary to focus attention on those peculiarities of polymerization that result in the formation of chromatographic sorbents. In spite of numerous publications devoted to problems of composite materials produced by means of polymerization techniques, articles concerning chromatographic sorbents are scarce. As mentioned above, there are two principle processes of sorbent preparation by graft polymerization radiation-induced polymerization or polymerization by radical initiators. We will also pay attention to advantages and deficiencies of the methods. 

Most of published results deal with very high graft yield and consequently the bulk properties of the base polymer are altered by grafting. In principle, graft polymerization is an attractive method to impart a variety of surface properties on the condition... 

There are in principle two methods for producing grafted surfaces, as schematically illustrated in Fig. 1 direct coupling reaction of existing polymer molecules to the surface and graft polymerization of monomers to the surface. Each has its own advantages and disadvantages, as demonstrated below. 

The previously discussed principles of grafting-to and grafting-from can also be applied for the modification of polymer surfaces with polymer brushes. However, the binding of linkers and polymerization initiators to polymer surfaces is not as straightforward as it is for oxidic inorganic materials. Thus, dedicated pretreatments are usually necessary. These may include rather harsh reaction conditions due to the chemical inertness of many polymers (see Chapter 3). Alternatively, radiation treatment of polymers (to form radicals) followed by exposure to air may be used to form peroxides and hydroperoxides, which can be directly used as initiators for thermally or ultraviolet-induced graft polymerizations [16,17] (see Chapter 2). 

The fundamental task, in our opinion, is to correlate the principles and methods of the proposed synthesis with those of mechanochemical synthesis. Thus, besides the destruction processes and mechanochemical synthesis discussed in the literature, other lands of transformations sometimes occur as side reactions, or even as major processes. These include chemical fixation of small molecules (methyl chloride or butyl alcohol) on mechanically activated macromolecular backbones grafting of inorganic surfaces (quartz, metals, metallic oxides, inorganic salts, etc.) dispersed by vibratory milling on polymerized fragments synthesized from monomers present in the reaction medium, and activated by centers on the inorganic surface (14) and the possibility of some reactions (such as nitration), achieved so far on macromolecular supports and only as side reactions. 

In this approach, a controlled polymerization reaction is used to amplify chemical defects on a surface, and therefore to access indirectly the chemical reactivity of a functional surface. This strategy has been used to interrogate the reactivity of thin assembled layers of different ATRP polymerization initiators. The principle relies on the ability of the selected experimental conditions of ATRP polymerization, to grow polymer brushes of thicknesses proportional to the polymer molecular mass, M . Then, for surfaces presenting different densities of polymerization initiator, the growth of polymer brushes of similar mass, M, yields polymer thickness, e, proportional to the polymer brush grafting density, Op, according to Equation 8.8 ... 

---