Surface-Grafted Polymer Brushes

Fig. 3 Preparation of surface-grafted polymer brush composition gradient. Reprinted with fter-mission from [15]. (Copyright 2006 Wiley-VCH Verlag GmbH Co)...

In the case of dense, surface-grafted polymer brush thin hlms, cross-links are introduced by the simple addition of solutions containing bis(Pd -pincer) compounds 4a or 4b to grafted PVP brushes (Loveless et al. 2006). Because the association constants for pyridine coordination are similar, the uptake of 4a and 4b from equimolar solutions into the PVP brushes (at constant grafting density and molecular weight) is effectively equivalent, producing samples with comparable structure (number and placement of cross-links). 

Loveless DM, Abu-Lail NI, Kaholek M, Zauscher S, Craig SL. Molecular contributions to the mechanical properties of reversibly cross-linked surface grafted polymer brushes. Angew Chem Int Ed 2006 45 7812-7814. 

Zhou F, Huck WTS. Surface grafted polymer brushes as ideal building blocks for smart surfaces. Phys Chem Chem Phys 2006 8(33) 3815—23. 

Gutowski, W. V. 2003. Interface/interphase engineering of polymers for adhesion enhancement Review of micromechanical aspects of polymer interface reinforcement through surface grafted molecular brushes. Journal of Adhesion 79 445-82. 

A. Good Solvents. When two surfaces with grafted polymer brushes approach each other, the overlap of the neutral brushes generates an interaction between surfaces. In good solvents, the Flory—Huggins mixing free energy density (eq 3c) increases with the monomer concentration therefore, one expects that the overlap of the brushes would lead always to repulsion. In the present... 

In Figure 4a, the force per unit area between two identical surfaces with grafted polymer brushes immersed in good solvents, with the parameters selected as above... 

The shape of the experimental isotherm (Fig. 3.38) is qualitatively similar to that found by van Vliet [226] with foam films from aqueous solutions of polyvinyl alcohol. It is also characteristic of the interaction energy as a function of the distance between two mica surfaces bearing grafted polymer brushes in good solvent as determined with Surface Force Apparatus (SFA) [e.g. 242],... 

The previously discussed principles of grafting-to and grafting-from can also be applied for the modification of polymer surfaces with polymer brushes. However, the binding of linkers and polymerization initiators to polymer surfaces is not as straightforward as it is for oxidic inorganic materials. Thus, dedicated pretreatments are usually necessary. These may include rather harsh reaction conditions due to the chemical inertness of many polymers (see Chapter 3). Alternatively, radiation treatment of polymers (to form radicals) followed by exposure to air may be used to form peroxides and hydroperoxides, which can be directly used as initiators for thermally or ultraviolet-induced graft polymerizations [16,17] (see Chapter 2). 

The impact of the chemical functionality of grafted polymer brushes on the wettability of the substrate was investigated for a number of neutral polymers as well as for weak and strong polyelectrolytes (Figure 4.2) [2]. It is evident that the wettability of the hydrophobic ETFE substrate can be tailored over a wide range with polymer brushes. As a general trend, surfaces with more hydrophilic brushes... 

Duebner M, Spencer ND, Padeste C. Light-responsive polymer surfaces via postpolymerization modification of grafted polymer-brush structures. Langmuir 2014 30(49) ... 

Coad, B.R., Styan, K.E., Meagher, L., 2014. One step ATRP initiator immobihzation on surfaces leading to gradient-grafted polymer brushes. ACS Appl. Mafer. Interfaces 6, 7782-7789. 

In summary, different mechanisms are possible and have been successfiilly demonstrated for grafting polymer brushes. Comparison can be made to their solution or bulk pol5unerization coimterparts. These systems differ in (7) rate of pol3unerization, (2) mechanisms and methods of termination, (3) consideration of interfacial properties and reaction conditions, and (4) methods of analysis and correlation with theoretical trends. Again, different polymerization mechanisms can also be foimd with polymer brushes on flat surfaces. 

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