Radical Graft Polymerization

Such correlation may be derived from the assumption that the termination is caused by oxidation of Ce " or mutual collision of the graft polymeric radical. With the sample of D3, the plot of ln(l00-ij ) versus In t yieled the straight... 

Above equation was derived assuming that the termination is caused by bimolecular collision between the graft polymeric radical and homopolymeric radical. ... 

In all manufacturing processes, grafting is achieved by the free-radical copolymerization of styrene and acrylonitrile monomers in the presence of an elastomer. Ungrafted styrene—acrylonitrile copolymer is formed during graft polymerization and/or added afterward. 

Etherification and esterification of hydroxyl groups produce derivatives, some of which are produced commercially. Derivatives may also be obtained by graft polymerization wherein free radicals, initiated on the starch backbone by ceric ion or irradiation, react with monomers such as vinyl or acrylyl derivatives. A number of such copolymers have been prepared and evaluated in extmsion processing (49). A starch—acrylonitrile graft copolymer has been patented (50) which rapidly absorbs many hundred times its weight in water and has potential appHcations in disposable diapers and medical suppHes. 

Yu et al. [31] pointed out that hydroxymethene radical will react with Ce(lV) ion to form a carbonyl group very quickly, and then it can further oxidize to form carbonyl radical. Therefore, the grafting polymerization would take place on the carbonyl radical as the following ... 

A large number of SAHs described in the literature combine synthetic and natural macromolecules in the network structure. The natural components are usually starch, cellulose, and their derivatives. It is assumed that introduction of rigid chains can improve mechanical properties (strength, elasticity) of SAH in the swollen state. Radical graft polymerization is one of the ways to obtain such SAH. 

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. 

The theory of radiation-induced grafting has received extensive treatment [21,131,132]. The typical steps involved in free-radical polymerization are also applicable to graft polymerization including initiation, propagation, and chain transfer [133]. However, the complicating role of diffusion prevents any simple correlation of individual rate constants to the overall reaction rates. Changes in temperamre, for example, increase the rate of monomer diffusion and monomer... 

Ejaz, M., Yamamoto, S., Ohno, K., Tsujii, Y. and Fukuda, T. (1998) Controlled graft polymerization of methyl methacrylate on silicon substrate by the combined use of the Langmuir-Blodgett and atom transfer radical polymerization techniques. Macromolecules, 31, 5934-5936. 

Photoinduced free radical graft copolymerization onto a polymer surface can be accomplished by several different techniques. The simplest method is to expose the polymer surface (P-RH) to UV light in the presence of a vinyl monomer (M). Alkyl radicals formed, e.g. due to main chain scission or other reactions at the polymer surface can then initiate graft polymerization by addition of monomer (Scheme 1). Homopolymer is also initiated (HRM-). 

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

For internal graft polymerization or grafting on to polymers reactive to radical attack, inhibition by oxygen is not a serious problem. However, surface photografting of polyolefins in an open system is very inefficient. The results in Figure 13 indicate that oxygen diffused through or in OPP film is an efficient retarder. 

The possibility of using graft polymerization of styrene on to allylated wood to provide covalent bonding between surfaces was also investigated (Ohkoshi, 1991). In this case, a free-radical initiator (BPO) was present in the styrene monomer that was used to impregnate the allylated wood, prior to hot-pressing. Bond strength was determined by... 

In the presence of a dissolved polymer, the radical polymerization of a monomer by thermal decomposition of an initiator results in a mixture of homopolymerization and graft polymerization [Brydon et al., 1973, 1974 Ludwico and Rosen, 1975, 1976 Pham et al., 2000 Russell, 2002], Polymer radicals (XXX), formed by chain transfer between the propagating radical and polymer, initiate graft polymerization of styrene. The product (XXXI) consists of polystyrene grafts on the 1,4-poly-1,3-butadiene backbone. Polymer radicals are also formed... 

Polymer radicals can also be produced by the irradiation of a polymer-monomer mixture with ionizing radiation. Thus, the interaction of ionizing radiation with polyethylene-styrene produces radical centers on polyethylene, and these initiate graft polymerization of styrene to produce poly(ethylene-gra/i-styrene) [Rabie and Odian, 1977]. 

Redox initiation is often an efficient method for graft polymerization. Hydroxyl-containing polymers such as cellulose and poly(vinyl alcohol) undergo redox reaction with ceric ion or other oxidizing agents to form polymer radicals capable of initiating polymerization... 

Block copolymers have been obtained from polymeric radicals, which—unlike those employed for graft polymerization—have the radical centers at the ends of the polymer chains. This can be achieved by breaking chemical bonds in the polymer backbone by mastication (mixing) of the polymer [Ceresa, 1973, 1976, 1978 Sakaguchi and Sohma, 1978]. If... 

Methods for detecting whether peroxy compound have been used for cross-linking elastomers have been reviewed. An important application of dialkyl peroxides is as initiators of cross-linking and graft polymerization processes. The success of both processes depends on the ability of the peroxide to produce free radicals and the ability of the free radicals for H-abstraction from a relevant donor substrate. A method for evaluating this ability consists of inducing thermal decomposition of the peroxide dissolved in a mixture of cyclohexane and MSD (225). The free radical X" derived from the... 

Keywords Graft polymerization Living radical polymerization Polymer brush ... 

The introduction of the functional group, being capable to initiate the radical graft-polymerization, has been sometimes carried out by two- or three-step reactions using reactive reagents, such as butyllithium or thionylchloride. Therefore, some... 

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