Surface grafts

The chemical modification techniques refer to the treatments used to modify the chemical compositions of polymer surfaces. Those can also be divided into two categories modification by direct chemical reaction with a given solution (wet treatment) and modification by covalent bonding of suitable macromolecular chains to the polymer surface (grafting). Among these techniques, surface grafting has been widely used to modify the surface of PDMS. 

Witte P, Menzel H (2004) Nickel-mediated surface grafting from polymerization of alpha-amino acid-N-carhoxyanhydrides. Macromol Chem Phys 205 1735-1743... 

Fig. 14. Surface-grafted hyperbranched, branched, and linear polymers from ID to 3D...

The chain architecture and chemical structure could be modified by SCVCP leading to a facile, one-pot synthesis of surface-grafted branched polymers. The copolymerization gave an intermediate surface topography and film thickness between the polymer protrusions obtained from SCVP of an AB inimer and the polymer brushes obtained by ATRP of a conventional monomer. The difference in the Br content at the surface between hyperbranched, branched, and linear polymers was confirmed by XPS, suggesting the feasibility to control the surface chemical functionality. The principal result of the works is a demonstration of utility of the surface-initiated SCVP via ATRP to prepare surface-grafted hyperbranched and branched polymers with characteristic architecture and topography. 

Fig. 15. Schematic representation of the synthesis of hyperbranched, branched, and linear polymers grafted from functionalized silicon wafers SFM images and XPS spectra of the surface-grafted polymers. (Reproduced with permission from [48],Copyright 2001 American Chemical Society.)...

During the last few years, new developments in polymer photochemistry have made it possible to graft various functional monomers onto surfaces of inert polymers like polyethylene, polypropylene and polyethyleneterephthalate. In the first attempts, initiator and monomer were transferred in vapor phase into a "UV Cure" irradiator containing the polymer sheet to be surface grafted. 

UV light in a second step. In later work reported by Tazuke, Kimura et al. (6-8) successful photograftings on the polymer surface of thin films (polyethylene, polypropylene and polystyrene) were achieved with various monomers. In this work, grafting was induced by UV irradiation through the film which was in contact with a solution containing initiator and monomer. The method is slow and - in addition to surface grafting - large amounts of homopolymer are formed. 

UV-induced surface grafting of a polymer sheet using vapor phase transfer of sensitizer and monomer from a volatile solution (9). 

UV-induced surface grafting of a polymer tape or a fiber bundle as substrate in a continuous operation with pretreatment of the substrate (presoaking) in a solution of sensitizer and monomer (10). The grafting takes place in a thin layer of solution on the surface of the moving substrate. 

Figure 1. Surface grafting by vapor phase process.

The results of the surface grafting reactions are analyzed with several different methods. 

Figure 3. Reflection infrared spectra (ATR-IR) of a polypropylene-j surface before (A) and after (B) grafting with acrylamide (AM) by the vapor phase process (above). ESCA spectra of the same surface before (dotted lines) and after (full lines) the surface grafting (below).

Figure 4. Kinetics of surface grafting of polyethylene (PE) and polypropylene (PP) films with acrylamide (AM) by the vapor phase method measured as light absorption at 600 nm after dipping in an aqueous solution of crystal violet (CV).

Table 1. Monomers Used for Surface Graft Copolymerization onto Polyolefin Surfaces...

The surface grafting of a commercial sheet of poly(ethylene tere-phtalate) was analyzed by ESCA spectra and dye adsorption. The sheets were washed with acetone to remove impurities and then grafted by irradiation for 2 and 20 min. (Figure 9). The blank sample showed no Nls peak in the ESCA spectrum. After grafting the Nls peak increased with increasing grafting time. 

Figure 16. Surface grafting of polypropylene film strips after 10 sec. irradiation measured as light absorption after dipping in aqueous crystal violet solution. The presoaking solutions contain 0.2 M benzophenone (all) and 1.3 M acrylamide (1), 0.8 M (2),...

Method (2) is a fast and efficient process which requires only 5 to 10 sec. UV-irradiation for surface grafting of the polymer substrate. About 2/3 of the polymer formed is grafted (about 1/3 is homopolymer). 

Polyester film surface detailed ESC A spectrum, 181/ kinetics of surface grafting, 182 wide-scan ESC A spectra, 179/ Polyethylene... 

Polyethylene film kinetics of surface grafting, 174/ surface grafting, 178/... 

Polyethylene split film ESCA spectra, 183/ kinetics of surface grafting with acrylonitrile, 184/... 

Styrenic-siloxane block and graft copolymers, Tg dependence on architecture and molecular weight, 95,95/ Styrenic-siloxane block copolymers, 86 Substrate catalyst ratio, chloromethylation, 18 Sulfonation, instability of sulfonated PPO, improvement, 6 Surface grafting... 

Transparency is often required. This is achieved by arranging that the particle size of the modifier to be below that of the wavelength of visible light (0.4-0.8 pm). This can normally be achieved by emulsion polymerisation, e.g., polybutadiene, polystyrene. Adhesion and surface compatibility between the polymer and modifier can be achieved by surface grafting of polar groups, e.g., acrylonitrile, various acrylates, onto the impact modifier surface before blending. 

Fig. 4.7 Modification of the pore openings of SBA-15 through surface grafting of the poly(methacrylate)-type polymerto prevent the leaching of proteins.

Moro T, Takatori Y, Ishihara K et al (2004) Surface grafting of artihcial joints with a biocompatible polymer for preventing periprosthetic osteolysis. Nat Mater 3 829-836... 

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