Grafted surface layer

Fig.22. Evolution of the critical shear rate y at the onset of the marginal regime as a function of the surface density in the grafted surface layer, o, for mP=970 kg mol-1, and mN= 96 kg mol-1. For 0.003

The detailed chemistry of radiation grafting has, in most cases, not been rigorously established. Process characterization is complicated by the fact that often only surface layers are involved and, in other cases, by the substrates being cross-linked or intractable. 

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],... 

In the continuous process the solution of sensitizer and monomer forms a thin surface layer on the polymer in which the photoinitiated reaction takes place without affecting the bulk phase of the polymer. In the vapor phase process, the grafting reaction starts at the... 

Method (1) is a slow process which requires several minutes of UV-irradiation for grafting a surface layer of an acrylic monomer onto the polymer substrate. 

For the two methods, the resulting grafting of functional monomers, e.g. acrylic acid and acrylamide, has been measured by multiple reflection IR spectra, ESCA spectra, and dye adsorption from an aqueous solution of crystal violet. The measurements indicate that the inert surfaces of the polymer substrates are modified by a complete surface layer of the grafted monomers. 

We could not conclude at the moment whether the solvent dependent surface properties are to be explained only by the difference in the depth of graft layer. Another possibility is the change in polar group orientation in graft layer as suggested by Hoffman(18). This arguement will be settled by direct determination of the thickness of graft layer prepared under various conditions. Clarification of the surface layer thickness - sur-... 

Experimentally, two basic ways of building a grafted polymer layer can be distinguished In the first, the polymerization is started from the surface with some suitably chosen surface-linked initiator. The advantage of this grafting-... 

Fig. 4 A Atomic force microscope (AFM) images, projected at 30° for viewing, of non-treated dithiocarbamated polymer film surface (a) and the PST(polystyrene)-grafted surface by UV irradiation through the lattice-patterned projection mask for 5 (fc), 10 (c), and 20 min (d). B Relationship between the average thickness of the PST-grafted layers and UV irradiation time...

Fig. 17 a Dependence of the repulsive interaction distance between the albumin (Alb)-fixed tip and the photograft-polymerized surface of DMAm on the photoirradiation time. A magnification of the plot within 60 s is shown in the inset, b Dependence of compressive force of the DMAAm graft-polymerized layer on its compression deformation... 

Fig. 28 Cell density versus distance histogram at 3 days after incubation on item a non-grafted photoreactive copolymer surface, and graft-polymer-layer-thickness gradient surfaces of a polyDMAPAAmMel, b polyMA, c polyDMAAm. The number of cells per unit area (0.225 mm ) is plotted against the unit distance (500 jim) from the edge of the photomask...

Okano et al. [51] applied poly(IPAAm) to modifying the surface of commercial polystyrene1 culture dishes for bovine aortic endothelial cells as well as for rat hepatocytes. Graft polymerization of IPAAm onto the polystyrene dishes was carried out by using an electron beam. The thickness of the poly(IPAAm)-grafted layer in aqueous systems was 0.5 pm at 37 °C and 0.6 pm at 15 °C. After endothelial cells were cultured at 37 °C for 2 days, the temperature was decreased to 10 °C and the number of cells that were detached from the surface was counted. Okano et al. observed that 100% of cells were detached from the poly(IPAAm)grafted surface. 

---