Copolymers Prepared by RAFT Polymerization

Commercial end functional polymers have been converted to alkoxyamincs and used to prepare PKO-Worri-PS.040 The hydroxyl group of alkoxyamine 284 was used to initiate ring-opening polymerization of caprolactonc catalyzed by aluminum tris(isopropoxide) and the product subsequently was used to initiate S polymerization by NMP thus forming polycaprolactone-Wodr- P8.641 The alternate strategy of forming PS by NMP and using the hydroxyl chain end of the product to initiate polymerization of caprolactonc was also used. 

Kobetaki et a/. 89 642 have examined the combination of conventional free radical and NMP to prepare PBMA-Woci-PS and the combination of anionic and NMP to prepare PB-6/oc -PS. 

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

Many examples exist where a polymerization has been continued by ATRP. V Often the procedure involves functionalization of a hydroxy-terminated polymer with bromoisobutyroyl (BriBBr, 314) or bromoisopropionoyl (BriPBr, 315) bromide. Examples include polyethylene oxide)044,646 and polypropylene 

Ring-opening metathesis polymerization (ROMP) of 1,4-cyelooctadiene was used to prepare poly(l,4-B) terminated with halo end groups.647 This was then used as a macroinitiator of ATRP with heterogeneous Cu bpy catalysts to form PS- /ti /r-poly(l,4-B)-WoeA -PS and PMMA-Moc.T-poly(l,4-B)-Wof A-PMMA. 

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Table 9.28 Diblock Copolymers Prepared by RAFT Polymerization ...

Vogt, A.P. and Sumerlin, B.S. (2009) Temperature and redox responsive hydrogels from ABA triblock copolymers prepared by RAFT polymerization. Soft Matter, 5, 2347—2351. 

Scheme 10 Polysulfobetaines prepared by RAFT polymerization as homopolymers and part of block copolymers...

Architecture. The advent of LRP has allowed the synthesis of cationic copolymers of well-defined architectures, hence allowing a careful analysis of the structure-activity relationship of these polymers. Synthetic linear cationic glycopolymers of statistical, block and block-statistical architectures were prepared by RAFT polymerization and studied for their gene expression profiles, as a function of molecular weight, carbohydrate content as well as architecture. The copolymers of 30-40 kDa and of... 

Dynamic covalent chemistry has in recent years complemented tmly noncovalent and metal-bgand chemistries. Jackson and Fulton expanded this concept to block copolymer synthesis. Aldehyde and alkoxyamine functional polymeis prepared by RAFT polymerization react to form oxime bonds, a dynamic link that can be reversed tbrougb equUibriinn perturbations. The block copolymers formed were capable of furtber self-assembly into micellar sttuctures. 

Since the number of monomers, and thus the resulting polymer structures, are limited by any of the specific living polymerization techniques, appropriate combination of different polymerization mechanisms can lead to a variety of new and useful polymeric materials. Therefore combinations of controlled radical polymerizations and other polymerizations applied to synthesize block copolymers have been developed. Generally, polymers with active sites, such as carbon-halogen or nitroxide or dithioester terminal groups, are synthesized by other living polymerizations, and the product is further used to initiate the controlled radical polymerization. In many cases, this method is essentially a variant of the macroinitiator method discussed above. However, in some cases, these kinds of macromolecules do not act as initiators, and may act as transfer agents. For example, an AB-type amphiphilic block copolymer, CLB-2 was prepared by RAFT polymerization of 2-(N-dimethylamino)ethyl methacrylate... 

Table 9.9 Block Copolymers Prepared by Macromonomer RAFT Polymerization under Starved-Feed Conditions.380"595...

Prepared by bulk polymerization, an MIP for the detection of dicrotophos based on the Eu3+ complex has recently been presented [58]. The authors used reversible addition fragmentation chain transfer (RAFT) polymerization followed by ring closing methathesis (RCM) to obtain the star MIP with arms made out of block copolymer. The star MIP containing Eu3+ exhibited strong fluorescence when excited at 338 nm with a very narrow emission peak (half width -10 nm) at 614 nm. This MIP was sensitive to dicrotophos in the range of 0-200 ppb, but showed saturation above this limit. Cross-reactivity of this MIP was evaluated with respect to structurally similar compounds dichlorvos, diazinon and dimethyl methylphosphonate. In these tests no optical response of the polymer was detected even at concentrations much higher than the initial concentration of dicrotophos (>1000 ppb). 

Chen, Z. Wang, X.L. Su, J.S. Zhuo, D. Ran, R. Branched methyl methacrylate copolymer particles prepared by RAFT dispersion polymerization. Polym. Bull. 2010,64 (4), 327-339. 

In the case of AB diblock copolymers prepared by the RAFT technique, the order of monomer addition must be taken into account. A characteristic example of such a block copolymer synthesis is demonstrated in Scheme 19. Initially, a poly(N, N-dimethylacrylamide) (PDMA) macro-CTA was prepared, followed by the use of PDMA-CTA as an initiator to polymerize successfully the second monomer N,N-dimethyl vinyl benzy-lamide (DMVBA). The final diblock copolymer is not contaminated with homopolymer. It has been discovered that the reverse approach is impossible, probably due to the slow fragmentation of the intermediate radical or due to the slow initiation efficiency of the intermediate radical (styrenic macroradical). 

Guan, C.-M. Luo, Z.-H. Qiu, J.-J. Tang, P.-P., Novel Fluorosilicone Triblock Copolymers Prepared by Two-Step RAFT Polymerization Synthesis, Characterization, and Surface Properties. Eur. Polym. J. 2010, 46,1582-1593. 

C. W. Scales et ah. Corona-stabilized interpolyelectrolyte complexes of SiRNA with nonimmunogenic, hydrophilic/cationic block copolymers prepared by aqueous RAFT polymerization. Macromolecules, 39(20), 6871-6881 (2006). 

The two sequential steps for the preparation of PSt-b-PnBA- -PSt triblock copolymer by RAFT polymerization using DPET as the chain transfer agent are shown in Scheme PI 1.23.1. 

Block copolymer coatings for tuning the interfacial properties of PDMS surfaces also play an important role in biomaterials science because PDMS surfaces are often employed in biomedical devices [126]. Iwasaki et al. reported the functionalization of pretreated PDMS films with well-defined triblock copolymers by spin coating [127]. The polymers were prepared using RAFT polymerization. Hydrophobic PDMS-based polymers were copolymerized with 2-methacryloyloxyethyl phospho-rylcholine (MPC). The polymeric coating material was spin-coated on thin PDMS films and chemically immobilized via hydrosilylation. The block copolymers were very effective in reducing the surface friction coefficient and improving wettability. 

Cloud point temperature of HEA-MEA and HEA-HPA copolymers prepared by NMP or RAFT polymerization as function of HEA fraction (Fhea) (Hoogenboom etai, 2012). (Source-. Reprinted with permission from the RSC.)... 

Several characteristic random copolymers were also prepared, as shown in Fig. 6 [125-127]. Matyjaszewski et al. have reported the development of an injectable thermoresponsive hydrogel [poly(NIPAM-co-BMDO)] (31) consisting of PNIPAM with degradable units as an injectable scaffold to enhance fracture repair. Poly(NIPAM-co-BMDO) was prepared by ATRP and RAFT [125]. Temperature- and pH-sensitive random copolymers of NIPAM and propylacrylic acid (32) were prepared using RAFT polymerization by Stayton and Hoffman et al. The dual temperature and pH responses were characterized, and their sharp and tunable phase transitions were demonstrated around neutral pH [126]. 

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