Graft polymerization procedure

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. 

Radiation-induced graft polymerization may be carried out by the following procedures [69] ... 

An alternate approach was the synthesis [85,86] of PBZT copolymers (XIX) containing pendent 2,6-dimethylphenoxy graft sites. Such copolymers do not lead to any breaks within the rigid-rod backbone thereby, they have no adverse effects upon rod reinforcement efficiency. Using the conventional PBZT polymerization procedure, 2-(2,6-dimethylphenoxy)terephthaloyl chloride was substituted for terephthaloyl chloride up to 30 mol %. The pendent dimethylphenoxy copolymers were then reacted with m-phenoxybenzoic acid in PPMA. 

The selective oxidation of cellulose to dialdehyde by sodium periodate is well known. It has been postulated by Criegee (74) and by Waters (73) that this reaction proceeds by a free radical mechanism. Toda (76) and Morimoto, Okada, Okada, and Nakagawa (77) have concluded that sodium periodate oxidation should initiate graft polymerization. They succeeded in grafting methyl methacrylate and acrylonitrile onto cellulose substrates, such as rayon and paper. A similar procedure is recommended in a patent of Chemische Werke Huels (78) to graft vinyl monomers onto cotton, polyethylene oxide, copolymers of vinyl chloride-vinyl acetate, and others. 

Anionic graft-polymerization of paraformaldehyde onto starch and dextrin has been effected in methyl sulfoxide solution, polymerization being initiated by the carbohydrate potassium alcoholate formed from the reaction of the carbohydrate with naphthalene potassium, a metallation procedure not previously described for carbohydrates.220... 

Persulfate-bisulfite-initiated graft polymerization was accomplished (Table I) using the procedure of Feairheller et al (11). Lyophilized rat skins were soaked in 100 ml of a 0.4% aqueous solution of an octyl-phenyl ether of polyethylene glycol containing 9-10 ethylene oxide groups. After 1 hr, 0.4 g potassium persulfate and 0.135 g sodium bisulfite were added, and CO2 was passed through the solution before 5 ml of monomer were added. 

The same protocol was used for the grafting from procedure to graft mixed brushes on to polymeric substrate. Plasma treatment was used to introduce hydroxyl (oxygen plasma) and amino (NH3 plasma) functional groups on to the polymeric surfaces and then Cl-ABCPA and two different homopolymers were grafted by polymerization from the functionalized surface. 

Below are provided some examples of photoinduced graft polymerizations in solution, chiefly to elucidate the synthetic approach employing type I and type II initiation. Subsequent pages are devoted to a number of selected surface grafting procedures. 

The grafting from procedure requires the generation of active sites on the main polymer chain which are capable of initiating the polymerization of a second monomer. Free radicals can be created by several methods such as irradiation of a polymer in the presence of oxygen [31,32], chain transfer to the backbone [33,34] or redox reaction [35]. Several commercial products have been produced by these methods because they are simple and rather easy to perform. Nevertheless, significant amounts of homopolymers are produced, and, in combination with the poor control of radical polymerization, the final products are characterized by chemical heterogeneity. 

One interesting aspect of this method of producing a suspension polymer is the fact that this method produces beads of poly(vinyl acetate) which may be loosely coated with poly(vinyl alcohol). This coating may be removed much more readily than the poly(vinyl alcohol) used in a conventional polymerization procedure. In the conventional process, a fair amoimt of the suspending agent probably forms a graft copolymer with vinyl acetate and is, therefore, permanently bound to the polymer bead. The properties of the two types of bead polymers are expected to be somewhat different since the graft copolymer with poly(vinyl alcohol) is present only in one and not the other polymer. 

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