Grafting sites

The dose and dose rate of irradiation are important factors in any radiation grafting system. In the direct method the total dose determines the number of grafting sites, while the dose rate determines the number of grafting sites, and the dose rate determines the length of the grafted branches. The length of the branches is also con-... 

The structural effect of alkyl groups such as methyl, ethyl, and -butyl on the Rp is small. Alkyl 4-methyl-phenylcarbamate can be chosen as a model compound for the hard segment of poly(ether-urethane) (PEU). This group can initiate grafting reaction with Ce(IV) ion and the grafting site was proposed at the hard segment of PEU [3,15] as shown in Scheme (1). 

For a layer comprised of f grafted chains, the surface area, S, of the shell containing a given sublayer is given by S a fE,2. For a flat layer, all sublayers are of equal area and this translates to the Alexander result, t, (S/f)1/z d. However, for curved surfaces, S, and consequently depend on the distance, r, from the grafting site. Thus, a spherical layer is characterized by S r2, leading to E, a r/f1/2. For a cylindrical layer of length H, we have S rH and E, (rH/f)1/2. Once q(r)... 

Tethering may be a reversible or an irreversible process. Irreversible grafting is typically accomplished by chemical bonding. The number of grafted chains is controlled by the number of grafting sites and their functionality, and then ultimately by the extent of the chemical reaction. The reaction kinetics may reflect the potential barrier confronting reactive chains which try to penetrate the tethered layer. Reversible grafting is accomplished via the self-assembly of polymeric surfactants and end-functionalized polymers [59]. In this case, the surface density and all other characteristic dimensions of the structure are controlled by thermodynamic equilibrium, albeit with possible kinetic effects. In this instance, the equilibrium condition involves the penalties due to the deformation of tethered chains. 

Graft copolymers are usually prepared from copolymers whose backbone attaches functional groups which can be converted into grafting sites. A variety of techniques for synthesizing copolymers with backbone grafts have been investigated294. ... 

The hydroxyl radicals formed may abstract hydrogen from the cellulose fiber substrate which gives grafting sites and subsequently grafted polymer with monomer present. The HO- radicals may also initiate homopolymerization. This means that reaction (17) is not specific for initiation of grafting. Another disadvantage is that the Fe + ions formed - if not carefully removed -may cause discoloration of the resulting product. 

For a series of reactions where the molecular weight of the branches (Mb) and the number of grafting sites per backbone chain (grafting site density,/) remain constant for each generation, the molecular weight of a generation G polymer can be predicted using equation (3). 

The synthesis and characterization of a series of dendrigraft polymers based on polybutadiene segments was reported by Hempenius et al. [15], The synthesis begins with a linear-poly(butadiene) (PB) core obtained by the sec-butyllithium-initiated anionic polymerization of 1,3-butadiene in n-hexane, to give a microstructure containing approximately 6% 1,2-units (Scheme 3). The pendant vinyl moities are converted into electrophilic grafting sites by hydrosilylation with... 

In the present discussions, we neglect the effects of homo-polymer formation. HomopolyAM deposited on OPP surface in the course of grafting may prevent diffusion of AM to the grafting site, which may slow down the rate of grafting. It is however difficult to explain by this reasoning the change in time-conversion profile as a function of [AM]/[BP] ratio. Since our aim is surface modification, the amount of homopolymer was not determined. ... 

Radiolysis Effects. Radicals formed in solvent (SH) and trunk polymers (PH) are important in the grafting of monomers (MH) with gamma radiation. With polymers such as polyethylene, grafting sites are formed by direct bond rupture (Equation 1). Additional sites are also... 

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