Kinetics of grafted chains in polymer

GAO AND OU-YANG Kinetics of Grafted Chains in Polymer Brushes... 

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. 

Concentration profiles of PS graft chains were studied by a neutron reflection method [101]. Graft chains consisted of end-functionalized deuterated polystyrene. Although the measurement was not performed under the true equilibrium conformation, the observed metastable state was in good agreement with that predicted from the SCF theory. The kinetics of the penetration of graft chains into the polymer matrix was also investigated. 

We now consider a system that involves bare clay sheets and a polymer mixture that contains both functionalized and nonfunctionalized species. In particular, some fraction of the polymers contain "stickers" that are highly attracted to the surface. Aside from the sticker sites, the functionalized and nonfunctionalized chains are chemically identical. The functionalized polymers will bind to the clay and form a grafted layer. The remainder of the polymers will interact witii the anchored species. Since the free and grafted chains are comparable in length, the free polymer can readily penetrate the grafted layer and form a broad interphase, which promotes the formation of exfoliated hybrids While the experimental result will depend on the kinetics of the process, the SCF calculations can indicate, for example, how the fraction of functionalized chains in the mixture affects the thermodynamic stability of the product To test the feasibility of this approach, we varied the fraction of functionalized polymers within a melt of chains of comparable length. 

The preparation of polymer brushes by controlled radical polymerization from appropriately functionalized polymer chains, surfaces or particles by a grafting from approach has recently attracted a lot of attention.742 743 The advantages of growing a polymer brush directly on a surface include well-defined grafts, when the polymerization kinetics exhibit living character, and stability due to covalent attachment of the polymer chains to the surface. Most work has used ATRP or NMP, though papers on the use of RAFT polymerization in this context also have begun to appear. 

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