Controlled radical polymerization block copolymers

Controlled expansion alloys, 13 520-522 Controlled flavor release systems, 11 528, 543-553, 554-555 characteristics of, ll 544t demand for, 11 555 developments in, 11 558 elements of, 11 555-557 extrusion encapsulation for, 11 550 key aspects of, 11 556t morphologies of, 11 545 Controlled free-radical polymerization, block copolymers, 7 646 Controlled humidity drying, ceramics processing, 5 655-656 Controlled indexing, 18 241 Controlled initiation, 14 268-269 Controlled laboratory studies, in... 

A number of techniques for the preparation of block copolymers have been developed. Living polymerization is an elegant method for the controlled synthesis of block copolymers. However, this technique requires extraordinarily high purity and is limited to ionically polymerizable monomers. The synthesis of block copolymers by a radical reaction is less sensitive toward impurities present in the reaction mixture and is applicable to a great number of monomers. 

Synthesis of Block Copolymers by Controlled Radical Polymerization... 

The living radical polymerization of some derivatives of St was carried out. The polymerizations of 4-bromostyrene [254], 4-chloromethylstyrene [255, 256], and other derivatives [257] proceed by a living radical polymerization mechanism to give polymers with well-controlled structures and block copolymers with poly(St). The random copolymerization of St with other vinyl... 

Wu T, Mei Y, Xu C, Byrd HCM, Beers KL (2005) Block copolymer PEO-b-PHPMA synthesis using controlled radical polymerization on a chip. Macromol Rapid Commun 26 1037... 

Recently, two groups reported controlled radical polymerizations starting from maltooligosaccharides (ATRP [182] and TEMPO-mediated radical polymerization [183]), which will certainly lead to new synthetic routes towards amylose-containing block copolymers. 

Enzymatic polymerizations have been established as a promising and versatile technique in the synthetic toolbox of polymer chemists. The applicability of this technique for homo- and copolymerizations has been known for some time. With the increasing number of reports on the synthesis of more complex structures like block copolymers, graft copolymers, chiral (co)polymers, and chiral crosslinked nanoparticles, its potential further increases. Although not a controlled polymerization technique itself, clever reaction design and integration with other polymerization techniques like controlled radical polymerization allows the procurement of well-defined polymer structures. Specific unique attributes of the enzyme can be applied... 

Controlled radical polymerization (CRP) is an attractive tool, because of the resultant controllability of polymerization, and because of it being a versatile method to synthesize of well-defined polymer hybrids. The three main radical polymerization techniques, ATRP, NMP, and RAFT polymerization, have thus been employed. Other techniques, such as the oxidation of borane groups, have also been studied. In general, using CRP techniques, block copolymers can be synthesized from terminally functionalized PO as PO macroinitiator, and block copolymers can be prepared from functionalized PO produced by the copolymerization of olefins with functional monomers. 

Recent investigations in our laboratory involve the controlled radical polymerization of styrene, initiated by dicumyl peroxide 8 in the presence of Tempo [71,72]. Molecular weights are obtained in the range 2500-300000 with narrow polydispersity (Mw/Mn = 1.5). From such capped Tempo polystyrene 9, polysty-rene-6-chloromethylstyrene (PS-6-PCMSty) [171], PS-h-PBd and PS-h-PBd- -PS block copolymers are prepared with Mw = 50000 and Mw/Mn = 1.5 [72] ... 

Over the past 10 years the advent of controlled radical polymerization has resulted in an explosion of interest in the synthesis of block copolymer systems that were hitherto inaccessible [54]. The most commonly used methods of controlled radical... 

TEMPO, />substituted TEMPO based alkoxyamines 3, and compounds such as 4, 5, and 7 have been applied successfully for polymerizations of styrene, substituted styrenes, and 4-vinylpyridine, and some copolymerizations and block copolymerizations were reported. However, living and controlled radical polymerization of other monomers, especially acrylates, require the use of the more recently developed structures 6, 8, or 9. These also yield well-controlled and living block copolymers, but methacrylates have so far resisted all efforts to obtain large conversions. Undoubtedly, many failures are due to unfavorable rate constants or side reactions. 

Metal-catalyzed living radical polymerizations of vinylpyridines were investigated with the copper-based systems. One of the difficulties in the polymerization is a decrease of catalytic activity imposed by the coordination of the monomers by the metal complex. Controlled radical polymerization of 4-vi-nylpyridine (M-33) was achieved by an initiating system consisting of a strong binding ligand such as L-32 and a chloride-based system [1-13 (X = Cl)/ CuCl] in 2-propanol at 40 °C.214 The Mn increased in direct proportion to monomer conversion, and the MWDs were narrow (MJMn = 1.1 —1.2). In contrast, 2-vinylpyridine (M-34) can be polymerized in a controlled way with chlorine-capped polystyrene as an initiator and the CuCl/L-1 pair in / -xylene at 140 °C.215 Block copolymers with narrow MWDs (Mw/Mn = 1.1 —1.2) were obtained therein. 

Such a controlled radical polymerization can be performed even in the absence of free initiators, where larger amounts of Cu(II) species are added in the system.369 The polystyrene layer obtained from S-3 in the presence of 5 mol % Cu(II) relative to Cu-(I) increased up to 20 nm in thickness, in direct proportion to the Mn of the polymers prepared in the other experiments with ethyl 2-bromopropionate but without surface-confined initiator under similar conditions. For MA, the layer thickness increases up to 60 nm. Block copolymer layers were also prepared by block copolymerization of MA or tBA from the polystyrene. Modification of the hydrophilicity of a surface layer was achieved by the hydrolysis of the poly (styrene-A/oc7c-tB A) to poly (styrene- block-acry lie acid) and confirmed by a decrease in water contact angle from 86° to 18°. 

Becker et al. [64] functionalized a peptide, based on the protein transduction domain of the HIV protein TAT-1, with an NMP initiator while on the resin. They then used this to polymerize f-butyl acrylate, followed by methyl acrylate, to create a peptide-functionahzed block copolymer. Traditional characterization of this triblock copolymer by gel permeation chromatography and MALDI-TOF mass spectroscopy was, however, comphcated partly due to solubility problems. Therefore, characterization of this block copolymer was mainly hmited to ll and F NMR and no conclusive evidence on molecular weight distribution and homopolymer contaminants was obtained. Difficulties in control over polymer properties are to be expected, since polymerization off a microgel particle leads to a high concentration of reactive chains and a diffusion-limited access of the deactivator species. The traditional level of control of nitroxide-mediated radical polymerization, or any other type of controlled radical polymerization, will therefore not be straightforward to achieve. 

Keywords Review, Copolymer, Controlled/living radical polymerization, Block, Graft, Gradient, Statistical... 

Burguiere C, Pascual S, Coutin B, Polton A, Tardi M, Charleux B, Matyjaszewski K, Vairon JP. Amphiphilic block copolymers prepared via controlled radical polymerization as surfactants for emulsion polymerization. Macromol Symp 2000 150 (39). 

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