Surface-Initiated ATRP

Recently, Kong et al. [159] functionalized MWNT with polyacrylic acid (PAA) and poly(sodium 4-styrenesulfonate) (PSS) by surface-initiating ATRP (atom transfer radical polymerization) following the Schemes 1 and 2 ... 

A Au-coated substrate is another model surface, to which many surface characterization methods can be applied. To achieve surface-initiated ATRP on Au-coated substrates, some haloester compounds with thiol or disulflde group were developed [80-84]. Self-assembled monolayers (SAM) of these compounds were successfully prepared on a Au-coated substrate and used for ATRP graft polymerization. Because of the limited thermal stability of the S - Au bond, the ATRP was carried out at a relatively low temperature, mostly at room temperature, by using a highly active catalyst system and water as a (co)solvent (water-accelerated ATRP). 

Surface-initiated ATRP was applied not only on planer substrates but also on various kinds of flne particles. The latter systems will be reviewed separately in Sect. 5.1. Porous materials are also fascinating targets for chromatographic application making use of the unique structure and properties of high-density polymer brushes. Wirth et al. were the first to report the grafting of poly(acrylamide) (PAAm) on a porous silica gel [109,110]. 

Table 1 Surface-initiated ATRP and RAFT polymerization of MMA... 

To discuss the kinetic aspects of surface-initiated ATRP, the system shoifld be modeled as a confined polymerization, confined in the graft-layer phase. In the system producing free polymers, the polymerization will simultaneously proceed in the solution phase. The unbound reactants such as free polymer radicals, monomer, catalytic species, and other additives will be partitioned between these two phases. The polymerization is usually carried... 

Fig. 10 Plots of Le/f-cw vs. dimensionless graft density a (1) PS brushes prepared by adsorption of PS-polydimethylsiloxane block copolymers (Mw,ps = 60000) and 0 (Mw,ps = 169000) [21,22]. (2) PEO brushes prepared by adsorption of PEO-PS block copolymers A (Mw.peo = 30800) and V (Mw.peo = 19600) [201]. (3) PMMA brushes prepared by surface-initiated ATRP (M = 31 300 267400). Data reprocessed from [116,117]...

Fig. 11 Wet thickness (H) of PAAm in water as a function of the PAAm graft density for samples prepared by surface-initiated ATRP on substrates with gradient of initiator density. The initiator was immobilized by the vapor-diffusion method using mixtures of l-trichlorosilyl-2-(fn/p-chloromethyl phenyl)ethan n-octyl trichlorosilane (w/w) 1 1 (squares), 1 2 (circles), and 1 5 (triangles). The inset shows a cartoon illustrating the polymer behavior. Reproduced with permission from [134] (Copyright 2003 American Chemical Society)...

Fig. 21 Topographic AFM images of PMMA/PS-mixed homopolymer brushes with different ratios of (Tpmma and aps but nearly equal opmma + <7ps 0-5 chains nm ) after treatment with acetone, where

This section reviews studies on the synthesis of fine particles coated with polymer brushes by surface-initiated ATRP. SiP are among the most extensively studied particles for the application of surface-initiated ATRP [85-93]. Patten et al. first succeeded in the surface-initiated ATRP of ST and MMA on two SiPs with average diameters of 75 and 300 nm [85,86]. Several groups investigated the synthesis of hybrid SiP with different monomers. Maty-jaszewski et al. synthesized an initiator-functionalized SiP with a diameter of... 

Owing to the simphcity and versatility of surface-initiated ATRP, the above-mentioned AuNP work may be extended to other particles for their two- or three-dimensionally ordered assemblies with a wide controllabiUty of lattice parameters. In fact, a dispersion of monodisperse SiPs coated with high-density PMMA brushes showed an iridescent color, in organic solvents (e.g., toluene), suggesting the formation of a colloidal crystal [108]. To clarify this phenomenon, the direct observation of the concentrated dispersion of a rhodamine-labeled SiP coated with a high-density polymer brush was carried out by confocal laser scanning microscopy. As shown in Fig. 23, the experiment revealed that the hybrid particles formed a wide range of three-dimensional array with a periodic structure. This will open up a new route to the fabrication of colloidal crystals. 

Kim et al. used the exchange reaction to synthesize cross-linked AuNP-PNIPAM core-shell hybrid structures, as well as a brush-type AuNP/PNIPAM hybrid through surface-initiated ATRP in an aqueous medium. The disulfide initiators, [BrC (CH3)2COO(CH2)iiS]2, were bound to AuNPs synthesized by citrate reduction. They have studied the effect of cross-linking on the thermo-responsiveness of the AuN / PNIPAM hybrids for potential use as a stimuli responsive optical device, such as surface plasmon resonance-based sensing materials [91]. 

Recently, the Klok group also prepared side-chain PEG-coated surfaces for protein immobilization [201], They employed surface-initiated ATRP for the synthesis. Terminal hydroxyl groups of the PEGs were activated with p-nitrophenyl chloroformate, and subsequently 06-benzylguanine was bound. The 06-benzylguanine-functionalized PEG brushes were used to chemoselectively immobilize 06-alkylguanine-DNA-alkyltransferase fusion proteins with a defined orientation and surface density. 

MMA, and St from magnetite nanoparticles functionalized with an organophosphono initiator, was reported by Babu and Dhamodharan [107c]. Mesoporous hybrid materials made of mesoporous silica and a covalently grafted polymer with controlled chain length were successfully synthesized by surface-initiated ATRP of St and MMA [107d]. 

Surface-initiated ATRP either in water or in organic solvent... 

The CNT surface-initiated ATRP technique can be also extended to other carbon surfaces such as carbon fibers,carbon spheres,carbon onions and carbon black to grow various polymers from their surfaces. 

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