Surface modification initiated grafting polymerization

Batich, C. and Yahiaoui, A. (1987) Surface modification. I. Graft polymerization of acrylamide onto low-density polyethylene by Ce +-induced initiation, J. Polym. Sci., Polym. Chem. Ed., 25, 3479-3488. 

In recent years, many kinds of temperature-responsive PNIPAAm and its copolymer hydrogels with other acrylic monomers have been synthesized [142]. Besides being used for hydrogels, NIPAAm monomer can be grafted on to polymer substrates by electron beam, irradiation or UV-initiated graft polymerization to achieve special modification of polymer surfaces. Thus NIPAAm has been grafted on porous polymer films such as LDPE, PP, or polyamide films in order to prepare novel films for pervaporation of liquid mixtures or separation membranes [150,151]. 

Currently, UV-initiated graft polymerization has been widely used for the surface modification of polymer manbranes in attempts to develop composite manbranes with enhanced resistance toward organic fouling and biofouling. As can be seen in Table 3.1, different hydrophilic monomers, such as Af-vinyl-2-pyrrolidone (NVP), A-vinylformamide (NVF), A-vinyl-caprolactam (NVC), 2-hydroxyethyl methacrylate (HEMA), acrylic acid (AA), acrylamide (AAm), 2-acrylamidoglycolic acid (AAG),... 

UV-initiated graft polymerization of AA on the surface of a PES manbrane via the immersion method using a 365 nm wavelength UV lamp was studied (Abu Seman et al. 2010). It was shown that irreversible manbrane fouling with humic acids (HA) was reduced after modification due to the increase in the hydrophilicity and the negative surface charge of the modified manbranes. 

Based on the membrane surface properties and the HA properties, various researchers have attempted to change the membrane surface characteristics by surface modification. Different techniques have been performed, such as ion beam irradiation, plasma treatment, redox-initiated graft polymerization, photochemical grafting, and interfacial polymerization (IP). In this chapter, two surface modification techniques, IP and photochemical grafting, are discussed by means of experimental examples. The surface characteristics of the unmodified membrane and the modified membranes are studied and their relationships with irreversible fouling and NF performance are reported. 

Surface graft modification includes direct graft polymerization modification and surface-initiated grafting polymerization modification. The former requires the particle surface to have active groups to copolymerize with other monomers, whereas the latter require that active groups to copolymerize with other monomers are generated from the grain surface by chemical or physical methods. 

In general, the modification of the membrane surface by UV graft polymerization may be realized with or without using an appropriate photoinitiator. Formation of starter radicals for graft polymerization may be promoted by the addition of photoinitiators into a modification solution or on a membrane surface. On the other hand, when a chromophore on a polymer backbone absorbs UV light, it goes to an exited state that may dissociate into reactive free radicals, which initiate the grafting process. 

In contrast to UV-initiated graft polymerization, the redox-initiated grafting allows the modification of the polymer membranes in situ, even inside commercial wound membrane elements [71]. Redox system most often used consists of potassium persulfate (K2S2O8) and potassium metabisulfite (K2S2O3) [71,72]. Redox reaction that occurs generates radicals on the membrane surface, upon which monomers can be attached ... 

Surfaces play crucial roles in many important properties, including optical, mechanical, thermodynamic, and chemical properties, and thus surface modification is an important issue. One of the effective surface modification methods is surface-initiated graft polymerization. Fukuda et used LRP... 

In general, in the field of materials or condensed matter, the preparation of polymer brushes on solid surfaces is of great interest for surface modification and composite material preparation [4-6]. A number of model surface grafting techniques have been used on planar surfaces and particles and have been the subject of previous reviews. While a munber of polymer brush preparation methods have been reported using physisorption or chemisorption or so-called grafting onto methods, the emphasis of this review is on surface-initiated polymerization (SIP) methods or grafting from methods. 

Modern electron processors offer high speed (high dose-rate) curing of low viscosity liquid coatings so that surface modification of films becomes practicable. A process has been developed for grafting vinyl monomers to polyolefin film surfaces with the aid of functional silane primers using electron initiated polymerization. 

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). 

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