Mediated radical polymerization

Figure 1.1 Publication rate of journal papers on radical polymerization and on living, controlled or mediated radical polymerization for period 1975-2002 based on SeiFinder search (as of Mar 2005).

Chung and coworkers have reported on the use of stable borinale or boroxyl radicals (e.g. 114) to mediate radical polymerization." Methacrylates (MMA) and acrylates (trifluoroelhyl acrylate) have been polymerized at ambient temperature to yield polymers with relatively narrow molecular weight distributions.231233 The method has been used to prepare block copolymers and polyolefin graft copolymers.2 4 37... 

ORl OX w di-Miutyl peroxyoxalalc deactivation by reversible chain transfer and bioinolecular aclivaiion 456 atom transfer radical polymerization 7, 250, 456,457, 458,461.486-98 deactivation by reversible coupling and untmolecular activation 455-6, 457-86 carbon-centered radical-mediated poly nierizaiion 467-70 initiators, inferlers and iriiters 457-8 metal complex-mediated radical polymerization 484... 

Lewis acids 436 metal complex-mediated radical polymerization 484-6 molecular weight distributions 251,453-4, 458-60,490-1.499-501 molecular weight conversion dependence 452-3,455... 

Synthesis of Block Copolymers by Nitroxide-Mediated Radical Polymerization, NMP... 

There are a number of other reactions that can be used cycloaddition of an azide group allowed binding of polystyrene [43], while a radical coupling was exploited to graft polymers prepared by a nitroxide-mediated radical polymerization [121]. Other end groups could be used it was shown above how amide bonds were utilized to attach water-soluble polymers amino or hydroxyl moieties are other conventional groups. 

In this review, synthesis of block copolymer brushes will be Hmited to the grafting-from method. Hussemann and coworkers [35] were one of the first groups to report copolymer brushes. They prepared the brushes on siUcate substrates using surface-initiated TEMPO-mediated radical polymerization. However, the copolymer brushes were not diblock copolymer brushes in a strict definition. The first block was PS, while the second block was a 1 1 random copolymer of styrene/MMA. Another early report was that of Maty-jaszewski and coworkers [36] who reported the synthesis of poly(styrene-h-ferf-butyl acrylate) brushes by atom transfer radical polymerization (ATRP). 

Sciannamea, V. Jerome, R. Detrembleur, C. In-situ nitroxide-mediated radical polymerization (NMP) processes Their understanding and optimization. Chem. Rev. 2008,108, 1104-1126. 

New seven-membered diazepinone alkoxyamines 394 for nitroxide-mediated radical polymerization were prepared through the Beckmann rearrangement (equation 159). 

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. 

Recently, living radical polymerizations have been well developed, and various methods such as (1) iniferter mediated radical polymerization [31], (2) transition metal-mediated radical polymerization or atom transfer radical polymerization (ATRP) [32-34] (3) nitroxide-mediated free-radical poly-... 

Cunningham and coworkers [65-68] have completed detailed modeling of nitroxide mediated radical polymerization in miniemulsion. They found that issues of distribution of the control agent between the aqueous and organic phases can be critical to maintaining livingness. 

Nitroxide mediated radical polymerization (NMRP) was pioneered by Riz-zardo and Solomon in the mid-1980s [1]. Their work went unnoticed for almost a decade until Georges et al. reported the preparation of narrow polydispersity (PD) (<1.2) polystyrene using NMRP [2]. This report initiated an explosion of research aimed at both understanding the mechanism of NMRP and also utilizing it to prepare block copolymers. This chapter describes the application and limitations of NMRP for making styrene-containing block copolymers. 

MALDI spectrum of a hydroxyl functional polymer prepared by GTP the level of the impurity is easily seen and the success of this reaction clearly observed. However, this is not a universally applicable technique. Perhaps the most topical living polymerisation at present is transition metal mediated radical polymerization. This typically gives a polymer with a tertiary halide terminal group. This group, as has nitroxide, has been found to be very labile in the mass spectrometer leading to fragmentation. 

Wu et al. reported on a rod—coil diblock copolymers based on mesogen-jacketed liquid crystalline polymer as the rod block and polystyrene as the coil block (Scheme 6).82 Styrene was polymerized by TEMPO mediated radical polymerization, followed by sequential polymerization of 2,5-bis[4-methoxyphenyl]oxy-carbonylstyrene (MPCS) to produce the rod—coil diblock copolymer (20) containing 520 styrene and 119 MPCS repeating units. The rod—coil copolymer was observed to self-assemble into a core—shell nanostructure in a selective solvent for polystyrene... 

Hybrid graft copolymers having silicon-based polymer backbones were also prepared by the metal-mediated radical polymerizations of styrene. The phenyl groups of poly[(methylphenyl)silylene] were bromomethylated and then employed as the grafting points of polystyrene (G-16).294,441 Polysiloxane can be employed also as a backbone (G-17) by introduction of benzyl chloride units into the pendant vinyl-functionalized poly(dimethylsiloxane).409... 

Spherical silica nanoparticles, with an average diameter of 70 nm, modified with the initiator moiety (S-8) were employed for the copper-mediated radical polymerization of styrene.457 The diameter of the particles and the molecular weights of the obtained polymers increased with conversion. For example, the average diameter of the particles obtained at 58.8% monomer conversion was increased to 188 nm, where the Mn and MWDs of the arm polymers were 26500 and 1.33, respectively. Given a narrow size distribution (<10%), the nanoparticles within the film domains were observed to pack into hexagonal arrays. A smaller silica nanoparticle with 14 nm was employed also for the copper-catalyzed radical polymerization of styrene initiated with S-9.458... 

Alternative total solid phase-based strategies for the preparation of polymer-peptide block copolymers were based on the polymerization of the synthetic polymer block from the supported peptide segment using either nitroxide-mediated radical polymerization (NMP) or ATRP (Fig. 15) [64,65]. 

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. 

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