Grafting From Technique

This technique is based on the use of a linear polymer with pendant functional groups that can be activated to initiate the polymerization of a second monomer. Based on this definition, the linear precursor polymer can be considered as a multifunctional macromolecular initiator. The importance of the grafting from technique by cationic polymerization of the second monomer increased considerably with the advent of living cationic polymerization. The advantage is the virtual absence of homopolymer formation via chain transfer to monomer. 

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In a similar way, the grafting-from technique has been applied to the synthesis of poly(chloroethylvinylether) chains by grafted PCL segments, i.e., po-ly(CEVE-g-CL) graft copolymers. Purposely cationically prepared PCEVE were partially modified by the introduction of 5-10% hydroxyl groups [79]. An equimolar reaction of the pendant hydroxyl functions with HAI/BU2 provided diisobutyl aluminum monoalkoxides dispersed along the polyether backbone. 

A dense polymer brush is obtained using the grafting from techniques. Surface-initiated polymerization in conjunction with a living polymerization technique is one of the most useful synthetic routes for the precise design and functionalization of the surfaces of various solid materials with well-defined polymers and copolymers. Above all, surface-initiated living radical polymerization (LRP) is particularly promising due to its simplicity and versatility and it has been applied for the synthesis of Au NPs. 

The chief objective of all research in the field of macromonomers is to get an easy access to a wide choice of graft copolymers. The main limitation of the earlier procedures to synthesize graft copolymers is the small number of systems to which grafting onto or grafting from techniques could be efficiently applied. The random copolymerization of a macromonomer with another monomer offers a much broader choice, and it is also much easier to carry out, in most cases by means of free-radical initiators. 

Fig. 14 Schematic representation of a spherical polyelectrolyte brush prepared by the photoemulsion grafting from technique (details see text). The brush consists of a solid polystyrene core and surface-attached strong (PSS) or weak (PAA) polyelectrolyte brush shell (Reprinted from Ref. [71] with permission from the American Physical Society)...

In another approach, PMMA- g-poly(/j-butyrolac-tone) copolymers were synthesized using the grafting from technique.149 Anionically polymerized PMMA was treated with the 18-crown-6 complex of potassium hydroxide in toluene, resulting in an macro-molecular initiator (Scheme 67). The average number... 

The grafting from technique can also provide a route to graft copolymers via ATRP. Matyjaszewski et al. used a poly [(vinyl chloride)-co-(vinyl chloroace-tate)] copolymer, containing about 1% of the chloroacetate groups, to initiate the ATRP of St, MA, nBA, and MMA, resulting in graft copolymers with well-defined graft units(Scheme 43) [297]. 

There have been many examples in the literature of using a grafting from technique to obtain novel polymers and this method has proven to be robust and useful under a variety of reaction conditions. Table 10 summarizes the examples discussed in the above section. Table 10. Examples of grafting from using CRP methods ... 

Zhao and Brittain also used the grafting from technique to grow polymers off silicon surfaces [329]. In their example, however, they first prepared tethered pSt cationically, which was terminated with a chlorine chain end, then used it as the initiator for the ATRP of MMA using the CuBr/PMDETA catalyst system. Use of a chlorine-terminated pSt chain in conjunction with a CuBr catalyst, however, produces a mismatch between the rates of cross-propagation and the rate of po-... 

Graft Copolymers. As in the case of ring-opening polymerization, labile halides can be used in conjunction with a Lewis acid in this case to produce carbeniura species. If the initiation takes place by addition, graft copolymers can be obtained by the grafting from technique when the labile halide is part of a polymer chain (10, 163-165). 

Heterogeneous Graft Copolymerization. Poly(vinyl chloride) films and powders (183) and chlorinated polypropylene (184) fibers were grafted with styrene, isobutylene, and styrene, respectively. Grafting from techniques were used. By using the same technique a silica surface first treated with chlorosilyl functional groups was grafted with polyIsobutylene and butyl rubber (185. 186) ... 

The emulsion polymerization in the third step is carried out in the presence of a water soluble monomer, such as acrylic acid. The radicals formed by the photolysis of HMEM (Fig. 6.18b) on the surface start radical chain polymerization by a grafting-from technique (see Section 6.13.3) thus generating chains of poly(acrylic acid). The polymer chains remain bound to the surface by an ester bond which can be cleaved by hydrolysis to obtain the polymer for analysis. Thus the molecular weight of the bound polymer chains can be determined which gives their contour length Lc. The thiclcness L of the brush (Fig. 6.17) attached to the surface of the particles can be deduced from the hydrodynamic radius as measured by dynamic light scattering. 

Figure 6.19 Schematic representation of the grafting-from technique for the preparation of terminally attached polymer monolayers by radical chain polymerization. (After Pmcker and Riihe, 1998.)...

Grafting from technique was widely used for the preparation poly(methyl methacrylate) (PMMA) and related polymer-grafted nanotubes. For example, Qin et al. reported the preparation of poly(/j-butyl methacrylate)-grafted SWNTs by... 

Figure 1.1. (a) Stmeture of the spherical polyelectrolyte brushes having cationic polyelectrolyte chains on their surface. The core consists of poly(styrene) and has diameters of approximately 100 nm. The chains are densely grafted to the surface of these cores by a grafting-from technique ( photoemulsion polymerization, cf. Ref. 24). (b) The core-shell microgel particles shown in a schematic fashion The core consists of poly(styrene) (PS) whereas the network consists of poly(iV-isopropylacrylamide) (PNIPA) crosslinked by JVdV -methylenebisacrylamide (BIS). 

Similar to PANI, the carbon-related materials, activated carbon, carbon nanotube, and GO, were also doped with PPy to fabricate PPy/carbon-related material composites for wastewater treatment. PPy/impregnated porous carbon was prepared by vapor infiltration polymerization technique to obtain a mesoporous structure [72], The as-prepared composite exhibited an improved adsorption ability to remove heavy metal ions, such as Hg(II), Pb(II), and Ag(I) due to amino groups of PPy. PPy/carbon nanotube composites can be prepared by grafting from technique either chemically or electrochemically. The chemical fabricated PPy/carbon nanotube composite can effectively remove heavy metals, anions and chemical oxygen demand from paper mill waste [73]. The electrochemical synthesized PPy/carbon nanotube provided a simple and highly effective method for ClO removal via electrically switched ion exchange technique (Figure 11.15) [74]. 

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