Graft copolymer, properties

In line with the above discussion, the properties of grafts must also depend on the location of the graft copolymer. Properties such as abrasion, enhanced adhesion, wetting and so on only need surface modification. Flame retardancy, water sorbency, and certain other properties, on the other hand, need essentially bulk grafting. These differences can be achieved rather easily in practice and the differences have been clearly demonstrated in a number of cases. 

Polypropylene block and graft copolymers are efficient blend compatibilizers. These materials allow the formation of alloys, for example, isotactic polypropylene with styrene-acrylonitrile polymer or polyamides, by enhancing the dispersion of incompatible polymers and improving their interfacial adhesion. Polyolefinic materials of such types afford property synergisms such as improved stiffness combined with greater toughness. 

The low quantum yield of the photografting process (0 = 2 X 10 ) provides a good opportunity to control the network formation (curing time control), and accordingly, the desirable properties of the crosslinked or grafted copolymer might be obtained. 

Grafting provides a convenient means for modifying the properties of numerous polymers. It is often required that a polymer possess a number of properties. Such diverse properties may not be easily achieved by the synthesis of homopolymers alone but can be achieved through the formation of copolymers or even terpoly-mers. The formation of graft copolymer with sufficiently long polymeric sequences of diverse chemical composition opens the way to afford speciality polymeric materials. 

Chitosan, having a similar chemical backbone as cellulose, is a linear polymer composed of a partially deacety-lated material of chitin [(l-4)-2-acetamide-2-deoxy-/3-D-glucan]. Grafting copolymer chains onto chitosan can improve some properties of the resulting copolymers [48-50]. Yang et al. [16] reported the grafting reaction of chitosan using the Ce(IV) ion as an initiator, but no detailed mechanism of this initiation has been published so far. 

The structure-property relationship of graft copolymers based on an elastomeric backbone poly(ethyl acry-late)-g-polystyrene was studied by Peiffer and Rabeony [321. The copolymer was prepared by the free radical polymerization technique and, it was found that the improvement in properties depends upon factors such as the number of grafts/chain, graft molecular weight, etc. It was shown that mutually grafted copolymers produce a variety of compatibilized ternary component blends. 

Compatibility and various other properties such as morphology, crystalline behavior, structure, mechanical properties of natural rubber-polyethylene blends were investigated by Qin et al. [39]. Polyethylene-b-polyiso-prene acts as a successful compatibilizer here. Mechanical properties of the blends were improved upon the addition of the block copolymer (Table 12). The copolymer locates at the interface, and, thus, reduces the interfacial tension that is reflected in the mechanical properties. As the amount of graft copolymer increases, tensile strength and elongation at break increase and reach a leveling off. 

Intentional hranching may improve the properties of the product polymer through grafting. A graft copolymer can he obtained by creating active sites on the polymer backbone. The addition of a different monomer then reacts at the active site and forms a branch. For example, polyethylene irradiated with gamma rays and then exposed to a reactive monomer, such as acrylonitrile, produces a polyethylene-polymer with acrylonitrile branches ... 

Copolymerization of two monomers gives a product with properties different from those of either homopolymer. Graft copolymers and block copolymers are two examples. 

Systematic studies67) to determine the properties of solutions of the obtained graft copolymers showed that graft copolymers containing stiff main chains (PAA,... 

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