Chemical modification of polymer surface

Feijen J (2001) Microbial adhesion onto superhydrophobic fluorinated low density poly(ethylene) films. In Olde Riekerink MB (ed) Thesis Structural and Chemical Modification of Polymer Surfaces by Gas Plasma Etching. Printpartners Ipskamp, Enschede,... 

L S. Penn, H. Wang, Chemical modification of polymer surfaces A review. Polymers for Advanced Technologies 5... 

The interactions and adhesion involved is basically a surface phenomena, and the nature and characteristics of interfaces and interphases are of prime importance. They can be promoted by use of proper compatibilizing agents (5) or directly, by modifying surface properties (6). Permanent chemical modification of polymer surfaces is a rather difficult task, and for polyolefins, which are poorly reactive this difficulty is even greater. On the other hand, if activated, polyolefins can react with oxygen of the atmosphere easily which is a chain reaction with... 

Plasma techniques are employed for the deposition of thin polymer films on solid substrates, for the chemical modification of polymer surfaces, and for the etching of polymer coatings. These processes are usually performed with the aid of low-pressure, low-temperature continuous plasmas, so-called continuous wave (CW) plasmas. Some typical laboratory-scale set-ups for these plasma processes are shown in Figure 1.6 [45]. 

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. 

Chemical modification of the surface to change the substrate-polymer interactions... 

When any polymer is to be used as film, plate, fiber, or molded material, the surface properties are as important as the bulk properties. In comparison with the large number of works devoted to the development of new polymers, relatively minor efforts have been directed to the modification of polymer surface. In particular, owing to the difficulties of studying chemical and physical properties of polymer surface, few articles have been published on the correlation between the condition of surface treatments and the imparted surface properties. 

Aside from the use of polymers as supports for phase transfer catalyst centers, much excellent work has been reported on the use of PTC in polymer chemistry for pol)rmerization methods (28), for the chemical modification of already formed polymers(29). for the modification of polymer surfaces without change of the bulk polvmerOO). and for the preparation and purification of monomers(31). 

Keller, T.S., Hoffmann. A.S., Ratner, B.D., McElroy, B.J. (1981). Chemical modification of Kevlar surfaces for improved adhesion to epoxy resin matrices I. Surface characterization. In Proc. Intern. Symp. Polymer Surfaces. Voi. 2 (K.L. Mittal ed ). Plenum Press, New York, pp. 861-879. 

In most practical uses of polymeric particles, their surfaces play a very important role by taking part in interfacial interactions such as recognition, adsorption, catalytic reactions, etc. When we want to use polymer particles, we first check whether the chemical and physical structures of the surfaces meet the purpose. If some of them do not satisfy the criteria, we may seek other particles or try to modify the existing particles. This chapter mainly deals with the modification of surface of existing particles. In addition to chemical modification of particle surfaces, modification of the morphology of particles is also described. 

Chemical modification of electrode surfaces by polymer films offers the advantages of inherent chemical and physical stability, incorporation of large numbers of electroactive sites, and relatively facile electron transport across the film. Since th% polymer films usually contain the equivalent of one to more than 10 monolayers of electroactive sites, the resulting electrochemical responses are generally larger and thus more easily observed than those of immobilized monomolecular layers. Also, the concentration of sites in the film can be as high as 5 mol/L and may influence the reactivity of the sites because their solvent and ionic environments differ considerably from dilute homogeneous solutions [9]. 

The modification of the chemical composition of polymer surfaces, and thus their wettability with chemical substances, can be realized in different ways electric discharges more commonly called Corona effect, oxidation by a flame, plasma treatment, UV irradiation and also UV irradiation under ozone atmosphere. Numerous studies have been devoted to the effects of these different treatments. More recently, Strobel et al. [204] compared the effects of these treatments on polypropylene and polyethylene terephthalate using analytical methods such as E.S.C.A., F.T.I.R., and contact angle measurements. They demonstrated that a flame oxidizes polymers only superficially (2-3 nm) whereas treatment realized by plasma effect or Corona effect permits one to work deeply in the polymer (10 nm). The combination of UV irradiation with ozone flux modifies the chemical composition of the polymers to a depth much greater than 10 nm, introducing oxygenated functions into the core of the polymer. 

A pulsed plasma has been used to prepare pinhole-free films from relatively nontoxic N vinylpyrrolidone.323 The pulsing reduced fragmentation of the monomer and cross-linking. This method should be tried with other monomers. Plasmas are often used for the modification of polymer surfaces.324 These methods are relatively rapid and use no solvent. Decorative coatings of TiN and other inorganic compounds can be applied to metals and other inorganic substrates by sputtering, chemical vapor deposition, plasmas, and such, as described in Chap. 4.325... 

Chemical modification of the surface of engineering polymers is an attractive approach to the problem of economically producing a barrier or a permselective structure with tailored properties. The following discussion will focus on applications of this technology... 

One limitation of flame treafmenf as currenfly practiced is fhat it is only capable of oxidation of polymer surfaces. However, there are many instances in which a different type of chemical modification of the surface... 

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). 

Chemical modification of oxide surfaces, immobilization of polymers on them, addition of different surfactants or solvents (e.g., alcohols) to the aqueous suspensions can be responsible for alterations in the hydrogen bond network and the free energy of the interfacial layers, surface charge distribution, and so on, which can affect the dispersion stability and other characteristics of both suspensions and powders prepared from these suspensions [9-15]. The last with adsorbed molecules (e.g., drugs, PVP, proteins, cellulose, etc.) can be of interest for medicine, biotechnology, etc. 

---