Copolymers Prepared by ATRP

Macroinitiator1 Monomer 2a Catalyst /Ligand Solvent Temp. °C 

Commercial end functional polymers have been converted to alkoxyamines and used to prepare PEO-Woci-PS. The hydroxyl group of alkoxyamine 284 was used to initiate ring-opening polymerization of caprolactonc catalyzed by aluminum Iris(isopropoxide) and the product subsequently was used to initiate S polymerization by NMP thus forming polycaprolactone-Woc/r-PS. The alternate strategy of forming PS by NMP and using the hydroxy] chain end of the product to initiate polymerization of caprolactonc was also used. 

Other block copolymers prepared using similar strategies include PEO (anionic) with second block poly(4-vinylpyridine).  

Many examples exist where a polymerization has been continued by ATRP. Often the procedure involves functionalization of a hydroxy-terminated polymer with bromoisobutyroyl (BriBBr, 314) or bromoisopropionoyl (BriPBr, 315) bromide. Examples include poly(ethylene oxide) and poly(propylene 

Ring-opening metathesis polymerization (ROMP) of 1,4-cycloocladiene was used to prepare poly(l,4-B) terminated with halo end groups.This was then used as a macroinitiator of ATRP with heterogeneous Cu bpy catalysts to fonn PS-block- o y 1,4-B)-b/oc A-PS and PMMA-Woc/ -poly( 1,4-B)-6/ot A-PMMA, 

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Living Radical Polymerization Table 9.27 Diblock Copolymers Prepared by ATRP... 

After the development of catalyst-transfer condensation polymerization of polythiophene, the block copolymer of polythiophene and poly(alkyl acrylate) was prepared more easily. Vinyl-terminated polythiophene was first prepared. The vinyl group was converted to the 2-hydroxyethyl group by hydroboration, followed by esterification with 2-bromopropionyl bromide to give a macroinitiator for ATRP (Scheme 50) [142]. The allyl-terminated polythiophene was also converted to a macroinitiator for ATRP, which led to block copolymers of polythiophene and poly (aUcyl methacrylate) [143] or poly(acrylic acid) [144]. This allyl-terminated polythiophene has a bromine atom at the other end, which has an adverse effect on the purity of block copolymers prepared by ATRP. Hawker, Kim, and coworkers reported that replacement of the bromine with a phenyl group, followed by functionalization of the allyl group for the ATRP initiator unit, allowed access to narrower molecular weight distribution diblock copolymers of polythiophene and ATRP-derived vinyl block [145]. 

Zhang Y et al. Structure and properties of poly(bntyl acrylate-block-snlfone-block-butyl acrylate) triblock copolymers prepared by ATRP. Macromol Chem Phys 2005 206(l) 33-42. 

ATRP has emerged as one of the most powerful synthetic techniques for the preparation of functional materials in polymer science since it allows the synthesis of polymers with predetermined MW, narrow molecular weight distribution (MWD), as well as desired composition and molecular archi-tecture. " Copolymers prepared by ATRP retain high chain end functionality, which allows them to serve as macroinitiators in the synthesis of block copolymers or participate in various postpolymerization modifications to prepare tele-chelic copolymers with functionality selected for specific end use applications. " A variety of organic/inorganic nano-composites, bioconjugates, " and other complex nanostractured materials have also been sjmthesized by this technique. 

Polystyrene/polyethylene oxide dendrimers were prepared by ATRP using tri- and tetra (bromomethyl) benzene as the initiators [207]. Each bromine end-group of the resulting stars was transformed first to two - OH groups and subsequently to potassium alcholate, as shown in Scheme 114. These - OK sites served to initiate the anionic polymerization of EO. The synthesized dendritic copolymers were found to display monomodal and narrow molecular weight distribution. 

The properties of the hybrid diblock structures can be altered drastically by simply taking advantage of the high terminal functionality of the dendritic block. For example unusual diblock structures useful for the modification of surfaces have been prepared by ATRP of polystyrene (PS) initiated from the benzylic halide focal point of Frechet-type dendrons with terminal isophthalate ester groups [9b], Well-defined copolymers with narrow molecular weight distributions were obtained and excellent agreement was observed between calculated... 

Scheme 8.12 Preparation of the diblock copolymer 57 by random copolymerization of PMMA block prepared by ATRP, methacrylic esters containing alkoxyamine nnits 55 and 56 [44],...

The PMMA-fc-PMPS-fe-PMMA triblock copolymers prepared by the macroinitiator approach using ATRP [60] were only characterized using differential scanning calorimetry. The glass transition temperature (T of PMPS is usually difficult to observe but within the copolymers it was clearly evident at 125-130°C. The T s of the PMMA blocks increased with block length in a manner consistent with the variation with chain length for homopolymers of PMMA and were also clearly visible by DSC. The presence of two T s provides strong evidence for microphase separation of the blocks. 

Scheme 10. Alternating copolymers of St with maleimide monomers prepared by ATRP [132]...

ATRP is a useful tool for preparing statistical copolymers with various monomer combinations. Unlike the TEMPO systems detailed above, the ATRP systems can be used to copolymerize styrene, acrylate, or methacrylate based combinations, potentially leading to materials with better and/or different physical and mechanical properties than the corresponding homopolymers or block copolymers. This may also include monomers which cannot yet be homopolymer-ized by ATRP such as isobutene or vinyl acetate [86,130]. Table 2 summarizes statistical copolymers prepared using ATRP systems. 

AB and ABA type acrylate/methacrylate block copolymers can also be prepared by ATRP using a sequential addition of monomers technique, resulting in a well-defined central block and an outer block composed of a mixture of the... 

The use and limitations of Atom Transfer Radical Coupling (ATRC) reactions including polyrecombination reactions for the preparation of telechelic polymers, segmented block copolymers, and polycondensates are presented. Specifically, the preparation of telechelic polymers with hydroxyl, aldehyde, amino and carboxylic functionalities, poly(/i-xylylene) and its block copolymers, and polyesters via ATRC process is described. The method pertains to the generation of biradicals at high concentration from polymers prepared by ATRP or specially designed brfunctional ATRP initiators. The possibility of using silane radical atom abstraction (SRAA) reactions, that can be performed photochemically in the absence of metal catalysts, as an alternative process to ATRC is also discussed. 

Figure 3. GPC traces of PSt and resulting PSt-b-PtBA block copolymers prepared by ARGET ATRP. General experimental conditions tBA/PSt/CuBr2/TPMA/Sn(EH)2 = 150/1/0.0075/0.05/0.05, in anisole (1.0vA>vs.

In the area of novel materials CMU protected (co)polymers prepared by ATRP except with CCI4 initiator and telechelic polymers prepared by CRP with MW > 20,000 (49) copolymers with a tme gradient segment (30) polar ABA block copolymers, (30) and well defined graft copolymers and segmented copolymers with one or more CRP blocks where the macroinitiator had been prepared by another polymerization process. (36) In addition, the use of tethered initiators allowed synthesis of hybrid core/shell copolymers. Pending applications disclose other novel polymeric materials. 

Figure 11 Facing page) (a) Structural formula of pH-responsive triblock copol3uner consisting of poly[(diisopropylamino)ethyl methaciylate]-6-pol3Kmethacryloyloxyethyl phosphorylcholine)-6-poly[(diisopropylammo)ethyl methacrylate] prepared by ATRP technique, (b) Formation of macroscopic gels of concentrated solution of triblock copolymer, (c) Drug release behavior from triblock copolymer gels at 37°C and at pH 7.4. (From Ref. 72.)...

Meng T, Gao X, Zhang J, Yuan JY, Zhang YZ, He JS (2009) Graft copolymers prepared by atom transfer radical polymerization (ATRP) from cellulose. Polymer 50 447-454... 

Singha et al. reported DA cross-linked products [158] using furan-modified polymethacrylate (PFMA) as the polymeric precursor, which was prepared through atom transfer radical polymerization (ATRP) and free-radical polymerization (FRP). Furthermore, the self-healing behavior of a triblock copolymer (PFMA-co-MMA) prepared by ATRP was demonstrated by means of scanning electron microscopy (SEM). With the modification, an almost fully recovered surface from knife-cut samples has been observed [159]. Chen et al. also reported the DA polymer product of PFMA-BM possessing thermal reversibility, whereas the homopolymer was prepared from anionic polymerization [160]. 

Degradable brush PHEMA-PDMAEMA-based copolymers were prepared by a combination of ATRP and click chemistty. Click chemistry introduced by Sharpless et al. is one of the most widely used approaches to prepare well-controlled macromolecules and biomolecules. " An azido-modified ATRP initiator was used to prepare PDMAEMA. PHEMA prepared by ATRP was modified with carbonyldiimidazole (CDI)-activated PDMAEMA. The click reaction between two polymers yielded brush polymers of varying molecular weights (Scheme 3.11). A brush copolymer of PDMAEMA of 50 kDa showed high p-galactosidase expression in Cos-7 cells, compared to analogues of other molecular weights. ... 

Double hydrophilic and amphiphilic AB2 miktoarm star copolymers were prepared by ATRP techniques and their micellar stmctures were studied in aqueous solutions showing pH and thermal sensitivity. For example, the PPO(PDMAEMA)2... 

Figure 9 Homo- and copolymer molecular brushes prepared by ATRP of PEOMA and OPOPhN macromonomers. Reprinted from Neugebauer, D. Thels, M. Pakula, T. etal. Macromolecules 2006, 39(2), 584-593, with permission from ACS. ...

Table 3 Block copolymers prepared by anionic-to-ATRP transformation ...

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