Adsorption of end-functionalized polymers

Light Scattering Studies of Adsorption of End-Functionalized Polymers in Colloidal... 

Colloidal solutions, light-scattering studies of adsorption of end-functionalized polymers, 96-109... 

Highly branched polymers, polymer adsorption and the mesophases of block copolymers may seem weakly connected subjects. However, in this review we bring out some important common features related to the tethering experienced by the polymer chains in all of these structures. Tethered polymer chains, in our parlance, are chains attached to a point, a line, a surface or an interface by their ends. In this view, one may think of the arms of a star polymer as chains tethered to a point [1], or of polymerized macromonomers as chains tethered to a line [2-4]. Adsorption or grafting of end-functionalized polymers to a surface exemplifies a tethered surface layer [5] (a polymer brush ), whereas block copolymers straddling phase boundaries give rise to chains tethered to an interface [6],... 

The distinctive properties of densely tethered chains were first noted by Alexander [7] in 1977. His theoretical analysis concerned the end-adsorption of terminally functionalized polymers on a flat surface. Further elaboration by de Gennes [8] and by Cantor [9] stressed the utility of tethered chains to the description of self-assembled block copolymers. The next important step was taken by Daoud and Cotton [10] in 1982 in a model for star polymers. This model generalizes the... 

The introduction of functional groups at the end(s) or along the polymer chain can produce new materials that can be used as models to study and manipulate fundamental phenomena in polymer science, such as association, adsorption, chain dynamics, and block copolymer morphology.61 65 The synthesis of end-functionalized polymers remains a challenging problem in polymer chemistry. Among the different... 

Huang H, Penn LS, Quirk RP, Cheong TH (2004) Effect of segmental adsorption on the tethering of end-functionalized polymer chains. Macromolecules 37 516-523... 

Fig. 9.19 Preparation of polymer brushes on solid surfaces by a) chemical grafting of end-functionalized linear polymers or selective adsorption of asymmetric block copolymers and b) by surface-initiated polymerization (SIP) using initiator functions on the solid surface. The depicted SAM bearing to-functionalities...

In the above discussion we have assumed that the polymer molecules are free in the solution, so that they scatter light individually. When the end-functionalized polymer is added into the colloidal suspension, some of the polymer molecules adsorb on the surface of the colloidal particle, and form colloid-polymer micelles. If all the polymer molecules adsorb on the colloidal surfaces (complete adsorption), the mixture can be viewed as a single-component system consisting of only colloid-polymer micelles. In this case the standard virial expansion for the scattering light intensity is still valid, and Eq. (1) becomes ... 

The upper solid curve in Fig. 3a is a plot of Eq. (4) with /2//1 =0.11. The equation for the non-adsorption mixture fits the data well. Our previous study of the same system also suggests that the PEP polymer does not adsorb onto the colloidal spheres. The two end-functionalized polymers are found to be partially adsorbed onto the colloidal surfaces. The lower solid curve in Fig. 3a is a fit to Eq. (8) with ao = 0.21. In the range 0 < a < 24, ao is found to be independent of the molar ratio u. In this range of a , the overall polymer concentration P2 is below the polymer overlap concentration. The zwitterion-PEP data can also be fitted to Eq. (8) with a constant ao = 0.18. The dashed curve in Fig. 3b is a plot of Eq. (8) with a = 1 (complete adsorption). One can immediately see from Fig. 3 that the measured y(u ,ao) for our end-functionalized polymers lies in-between the non-adsorption and complete adsorption curves. 

Preferential adsorption effects have been found for different end-functionalized polymers and in comparing linear and cyclic polymers of the same monomers. These effects are much stronger than would have been anticipated and may have implications in studies where differently ended polymers are being compared. 

FIG. 3 The different adsorption mechanisms discussed in this chapter, (a) Adsorption of a homopolymer, where each monomer has the same interaction with the substrate the tail, train, and loop sections of the adsorbing chain are shown, (b) Grafting of an end-functionalized polymer via a chemical or a physical bond, (c) Adsorption of a diblock copolymer where one of the two blocks is attached to the substrate surface, while the other is not. 

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