Living cationic polymerization combination

Much research has already been devoted in the past couple of years to (i) the immobilization of ATRP active metal catalysts on various supports to allow for catalyst separation and reycycling and (ii) ATRP experiments in pure water as the solvent of choice [62]. A strategy to combine these two demands with an amphiphilic block polymer has recently been presented. Two types of polymeric macroligands where the ligand was covalently linked to the amphiphilic poly(2-oxazo-line)s were prepared. In the case of ruthenium, the triphenylphosphine-functiona-lized poly(2-oxazoline)s described in section 6.2.3.2 were used, whereas in the case of copper as metal, 2,2 -bipyridine functionalized block copolymers were prepared via living cationic polymerization [63] of 2-methyl-2-oxazoline and a bipyridine-functionalized monomer as shown in Scheme 6.8. 

Keywords Living cationic polymerization Polyisobutylene Block copolymers Macromolecular architecture Combination of polymerization mechanism... 

As the range of styrene derivatives for living cationic polymerization expands (Chapter 4, Section V.C), a variety of block copolymers with sty-renic segments have been synthesized. Most of the reported examples involve combinations of styrene derivatives with vinyl ethers or isobutene. Some examples of styrene derivative-vinyl ether block copolymers are listed in Fig. 6 [16,87-89]. Monomers that can form similar block copolymers with isobutylene are listed in Fig. 7 (Section III.B.3). 

Common for these three approaches is that living cationic polymerization permits the introduction of a variety of interesting functional groups at specific positions (outer arm layer, arm ends, central core, etc.) of the multiarmed polymer architectures. The combinations of these functional groups and the unique molecular topology would lead to physical properties and functions that cannot be found in the conventional linear counterparts. 

Both methods spread the charge on the growing macrocation and render the /9-proton less likely to transfer to monomer (as in reaction 9-41). The first method is typified by initiation with HI/I2 in which the nucleophilic counterion is the Ie//2 anion. The second primarily involves combinations of a cation-generator, like a tertiary alkyl halide, with a Lewis acid, such as EtAlCl2- A number of initiator combinations of the latter type have been reported for living cationic polymerization of isobutene [S). 

Combination of a living ionic polymerization and a metal-catalyzed radical polymerization also leads to comb polymers, where both the molecular weights of the arm and main-chain polymers are well controlled. PMMA with poly(vinyl ether) arm polymers of controlled molecular weights (C-l) were prepared by the copper-catalyzed radical polymerization of methacrylate-capped macromonomers carrying a poly-(isobutyl vinyl ether), which were obtained by living cationic polymerization with a methacryloxy-capped end-functionalized initiator.428 Comb polymers with... 

S. Kwon, H. Chun, and S. Mah, Photo-induced living cationic polymerization of isobutyl vinyl ether in the presence of various combinations of halides of diphenyliodonium and zinc salts in methylene chloride. Fibers Polymers, 2004, 5(4), 253-258. 

Scheme 11.20 Synthesis of block copolymers by combination of living cationic polymerization and ATRP using macroinitiator technique.

Lu J., Liang H., Zhang W., Cheng Q., Synthesis of poly(beta-pinene)-g-poly(meth)acrylate by the combination of living cationic polymerization and atom transfer radical polymerization, J. Polym. Sci. A Polym. Chem., 41(9), 2003,1237-1242. 

LRP is a powerful tool for the synthesis of complex polymer architectures as was shown above. However, in some cases it is desirable to combine structures that are hardly or not at all accessible via radical polymerization techniques. In such cases it may be beneficial to combine LRP with another polymerization mechanism. Many examples have been reported so far. A few examples will be listed here. Polystyrene-6-pol3risobutylene-6-polystyrene was synthesized via a combination of living cationic polymerization and ATRP (98). Polyolefin Graft Copolymers (qv) were synthesized by first polymerizing alkoxyamine-substituted olefins via metallocene catalysis, and subsequent polymerization of vinyl monomers via... 

The combination of living cationic polymerization and NCA polymerization has also been reported. Schlaad synthesized poly(2-isopropyl-2-oxazoline)-h-PBLG (16) based on an ammonium-mediated polymerization system. By adding an acid in the NCA polymerization, a primary amino (NH2)-propagating chain end could be transformed into an ammonium (NH3 ) chain end via equilibrium and this system suppresses the generation of the aminyl anion of an NCA monomer that causes byproducts via activated monomer mechanism (Scheme 13.2) (Dimitrov and Schlaad, 2003). 

Similar results have been obtained by combining the living cationic polymerization of vinyl ethers and the ROP of thietane. In this case, the thietane acts as growing species stabilizer for the vinyl ether polymerization by reversible formation of an a-alkoxy-thietanium ion. This ion can, however, also be attacked at an endocyclic methylene by another thietane molecule leading to an alkyl-thietanium ion. This ion is incapable of reacting with a vinyl ether but is the active species for the thietane polymerization. Also in this case the end product is a star-shaped segmented polymer. 

Scheme 21 Synthesis of cyclic poly(THF) by the combination of living cationic polymerization...

Schappacher and Deffieux [93] first reported the cyclization from heterodifunctional linear polymers. The linear precursor was made from 2-chloroethyl vinyl ether (CEVE) by living cationic polymerization from a styryl vinyl ether with hydroiodic acid and ZnCl2 as catalyst combination. By treating with SnCLi, the iodo endgroup was converted to carbocation and coupled to the styrene chain end to form the cyclic polymer (Scheme 24). With the same strategy, they successfully synthesized a series of cyclic polymer derivatives based on the monomer CEVE. 

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