Grafted chains

The first case concerns particles with polymer chains attached to their surfaces. This can be done using chemically (end-)grafted chains, as is often done in the study of model colloids. Alternatively, a block copolymer can be used, of which one of the blocks (the anchor group) adsorbs strongly to the particles. The polymer chains may vary from short alkane chains to high molecular weight polymers (see also section C2.6.2). The interactions between such... 

Monomer compositional drifts may also occur due to preferential solution of the styrene in the mbber phase or solution of the acrylonitrile in the aqueous phase (72). In emulsion systems, mbber particle size may also influence graft stmcture so that the number of graft chains per unit of mbber particle surface area tends to remain constant (73). Factors affecting the distribution (eg, core-sheU vs "wart-like" morphologies) of the grafted copolymer on the mbber particle surface have been studied in emulsion systems (74). Effects due to preferential solvation of the initiator by the polybutadiene have been described (75,76). 

K. O Connor, T. McLeish. Entangled dynamics of heahng end-grafted chains at sohd/polymer interface. Faraday Discuss Chem Sci 95 67-78, 1994. 

Copolymer macromolecules are composed of a single backbone having simple grafts attached to it, i.e., the macromolecules are of the comb-like type. No further grafting of grafted chains is contemplated (4). 

It was found that acid enhances grafting and homopolymer formation. Analysis of homopolymers shows that acid reduces the chain length but increases the number of grafted chains. 

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. 

The possibility of producing graft polymers with the same pre-assigned length of grafted chains ... 

The deformation of densely grafted chains reflects a balance between interaction and elastic free energies. In this discussion of structure, we assume that a dense... 

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. 

FIG. 15 Free energy per unit area as a function of surface separation for five different values of x-The parameters are Ng = 25, p = 0.04, N = 100, and Xsurf = 0. The cartoon on the left shows the reference state, where the grafted chains form a melt between the surfaces. In the cartoon on the right, the surfaces are separated by polymers that have localized between the interfaces. (From Ref. 100.)... 

Kato, K., Uchida, E., Kang, E. T, Uyama, Y. and Ikada, Y. (2003) Polymer surface with graft chains. Prog, Polym. Sci., 28, 209-259. 

The steric stabilization of dispersed particles by both grafted chains and by physically adsorbed polymers has been much studied in recent years. In the present paper we extend earlier work on... 

With respect to SCF models that focus on the tail properties only (typically densely packed layers of end-grafted chains), the molecularly realistic SCF model exemplified in this review needs many interaction parameters. These parameters are necessary to obtain colloid-chemically stable free-floating bilayers. A historical note of interest is that it was only after the first SCF results [92] showed that it was not necessary to graft the lipid tails to a plane, that MD simulations with head-and-tail properties were performed. In the early MD simulations (i.e. before 1983) the chains were grafted (by a spring) to a plane it was believed that without the grafting constraints the molecules would diffuse away and the membrane would disintegrate. Of course, the MD simulations that include the full head-and-tails problem feature many more interactions than the early ones. 

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