Direct graft polymerization

S.W. Hu, X.Q. Ren, M. Bachman, et al.. Surface-directed, graft polymerization within microfluidic channels, Anal. Chem., 2004, 76, 1865-1870. 

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. 

In its simplest form the direct grafting method involves the irradiation of polymeric substrate in the absence or presence of oxygen. Graft copolymerization of the monomer to the polymer is then initiated through the free radicals generated in the latter. The reaction can be schematically written as ... 

Direct Radiation Grafting of Polymer in the Presence of Vinyl Monomer. This leads to the formation of free radicals on both polymer and monomer, resulting in graft polymerization and homopolymerization. The extent of homopolymerization depends on the sensitivity of the monomer used. 

With adequate swelling vinyl monomers can be satisfactorily grafted to cellulose and its derivatives by the three main methods developed for other polymers (98). These are (1) the mutual or direct method where the polymer is irradiated in the presence of the monomer or monomer vapor, (2) the pre-irradiation (sometimes called post-irradiation grafting) method where the polymer is first irradiated and then brought into contact with the monomer, and (3) the peroxide method in which the polymer is irradiated in air and the resulting polymeric peroxide used to initiate graft polymerization. 

The polyisoprenyl radicals (R ) initiate graft polymerization, while the hydrogen atoms do not lead to free polymethyl methacrylate but react more easily with rubber to form grafting sites, instead of initiating free chains. Evidently, if radicals directly derived from the monomer behaved in the same way, then almost quantitative graft copolymerization would be expected in the case of rubber (12, 221). 

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. 

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

The hydroxyl radicals can react with cellulose, initiating graft copolymerization, or react with monomer, resulting in homopolymerization. A similar redox system is based on the use of ceric ions, which produce radicals by direct oxidation of the cellulose chains and thus initiate graft polymerization ... 

Many electroluminescent materials have poor charge transport properties. The present invention is directed to polymeric agents containing grafted naphthalene or pyrene, which makes then effective as both hole transport and electroluminescent agents. 

The initiation efficiency depends on the relationship between the rate of macroradical formation and that of initiation. In Table 1 are compiled results on certain redox systems employed for the initiation of cellulose grafting either by direct oxidation of cellulose (or its derivative) or chain transfer from active low molecular weight radicals. Table 1 indicates that in systems where the matrix acts as a reducing agent (1st group), the initiation efficiency does not exceed 15%, i.e. only a minor portion of macroradicals formed at the first stage of oxidation initiates graft polymerization while the rest is oxidized to stable... 

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