Creation of Grafted Surfaces

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. 

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Fig. 1a,b. Creation of grafted surfaces by a direct polymer coupling reaction b graft polymerization... 

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. 

A heterogeneous olefin epoxidation catalyst containing both V and Ti in the active site was prepared by sequential non-hydrolytic grafting. The silica was exposed first to VO(OiPr)3 vapor followed by Ti(0 Pr)4 vapor. Formation of propene is evidence for the creation of Ti-O-V linkages on the surface. Upon metathesis of the 2-propoxide ligands with BuOOH, the catalyst becomes active for the gas phase epoxidation of cyclohexene. The kinetics of epoxidation are biphasic, indicating the presence of two reactive sites whose activity differs by approximately one order of magnitude. 

Another deposition method is that involving the creation of a strong bond, for example, a covalent bond, between the support and the active element [7,8], This process is typically called grafting or anchoring. This procedure is carried out by a chemical reaction between functional hydroxyl groups on the surface of the support and a properly chosen inorganic or organometallic compound of the active element. 

The creation of a positive charge to the membrane surface by for example grafting of polycations or adsorption of chitosan, introduces antibacterial properties [28-30]. 

Chemical modification is generally taken to mean a process involving the creation of a chemical bond (usually covalent) between a surface cell wall polymer and an introduced reagent to form a novel adduct. This can be done through several approaches, including plasma activation and graft polymerization with vinyl monomers, which are very well described in literature. The primary... 

The graft modifications by y-irradiation, electron beams, or plasma are some of such methods that provide covalent modification of materials with the creation of interesting architecture. These three methods provide materials with a high level of purity they are surface-selective or may lead to the bulk modification of the matrix, although y-rays are preferred for their high... 

It is allowed to form on PETP surface of given number of polar groups and to decrease electron affinity of surface. The mentioned above ways of obtaining of function groups are used in a method of active points for creation of reactive centers for a grafting [81], Surface treatment by hot air [82] or ozone [83,84] can be applied for... 

As it is clear from Fig. 8, plasma treatment leads to increase of zeta potential due to creation of more polar groups on surface and this effect depends on exposure time positively. Subsequent grafting of PEG influences surface chemistry dependently on its molecular weight. While PEG 300 and PEG 20000 in most cases causes a slight decrease of zeta potential, PEG 6000 for shorter exposure time causes increase of zeta potential. It indicates quite different surface chemistry and nevertheless these changes are quiet slight, they play important role in process of adhesion and proliferation of living cells (see Fig. 9). 

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