Modification direct graft polymerization

Surface graft modification includes direct graft polymerization modification and surface-initiated grafting polymerization modification. The former requires the particle surface to have active groups to copolymerize with other monomers, whereas the latter require that active groups to copolymerize with other monomers are generated from the grain surface by chemical or physical methods. 

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). 

This entry has revealed that a grafting method is useful to direct a polymeric effect in HPLC. The advantage of this method is quite clear. Firstly, grafted polymers are not appreciably influenced by carrier particles. This feature is very important to maintain the original functions of polymers. For example, ODA can undergo a phase transition, even after immobilization on silica. The other advantage is based on the fact that the functions of polymers are absolutely mnable by judicious selection of the monomer. Copolymerization would expand their versatility remarkably. Also, potential applicability of a polymer grafting method for surface modification must be limited to use in HPLC. 

As far as enzyme immobilization is concerned, the biocompatibility of support is another important requirement [120-123], as the biocompatible surface can reduce some non-biospecific enzyme-support interactions, create a specific microenvironment for the enzymes and thus provide substantial benefits to the enzyme activity [124], To increase the biocompatibility of the support, various surface modification protocols have often been used to introduce a biofriendly interface on the support surface, such as coating, adsorption, self-assembly and graft polymerization. Among these methods, it is relatively easy and effective to directly tether natural macromolecules on the support surface to form a biomimetic layer for enzyme immobilization. In fact, this protocol has been used in tissue engineering recently [125-127]. 

Earner et al. [174] recently reported the synthesis of core-shell poly(divinylbenzene) (PDVB) microspheres via the RAFT graft polymerization of styrene. Cross-linked PDVB core microspheres containing double bonds on the particle surface were used directly to attach polymers from the surface by RAFT without prior modification of the core microspheres. The RAFT agent 1-phenyl-ethyl dithiobenzoate (PEDB) was used. PEDB controlled the particle weight gain, the particle volume, and the molecular weight of the soluble polymer. 

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