Atom block copolymer synthesis

Kunitake and Takarabe" as 2—30 ms. This result seems reasonable since the presence of the methoxy substituent would be anticipated to stabilize a positive charge on the a carbon atom in the case of p-methoxystyrene. Equally interesting is the observation that propagating intermediates are generated most slowly with 12 as catalyst, but once formed these are the longest lived. Perhaps not surprisingly therefore the system displays some of the characteristics of a living system, and allows block copolymer synthesis to be achieved with isobutyl ether. 

Figure 13.3 Overview showing the use of bifunctional initiators for block-copolymer synthesis. Two examples using either reversible addition fragmentation chain transfer polymerization or atom transfer radical polymerization combined with eROP are shown.

Except for ozonides obtained from vinylsiloxanes, the ozonides that result from these reactions are surprisingly stable. Figure 1 shows the C-NMR spectrum of an ozonide that was prepared from DC 7697 (n = 30). It contains resonances at 1, 18, 23, 29, 41, 94 and 104 ppm. Chemical shifts calculated for the carbon atoms in this compound (1.5(3,4), 15.7(1),24(2),26.3(6),30.4(7),97.3(5) and 99.3(6) ppm) correspond reasonably well with those observed. Polysiloxanes containing the ozonide functionality can, in fact, be used as macroinitiators for block copolymer synthesis (13). 

Synthesis of Block Copolymers by Atom Transfer Radical Polymerization, ATRP... 

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). 

Controlled free-radical polymerization methods, like atom-transfer radical polymerization (ATRP), can yield polymer chains that have a very narrow molecular-weight distribution and allow the synthesis of block copolymers. In a collaboration between Matyjaszewski and DeSimone (Xia et al., 1999), ATRP was performed in C02 for the first time. PFOMA-/)-PMMA, PFOMA-fr-PDMAEMA [DMAEMA = 2-(dimethylamino)ethyl methacrylate], and PMMA-/)-PFOA-/)-PM M A copolymers were synthesized in C02 using Cu(0), CuCl, a functionalized bipyridine ligand, and an alkyl halide initiator. The ATRP method was also conducted as a dispersion polymerization of MMA in C02 with PFOA as the stabilizer, generating a kine-... 

Cai, Y Armes, S. P. Synthesis of well-defined Y-shaped zwitterionic block copolymers via atom-transfer radical polymerization. Macromolecules 2005, 38, 271-279. 

Numerous examples of block copolymers formed in supercritical C02 via the bifunctional initiator approach have been reported [54], Perhaps the most common approach is to incorporate eROP with free-radical polymerization-the general scheme for this methodology is shown in Figure 13.3. Howdle et al. [55] was the first to report the synthesis of a block copolymer by the bifunctional initiator approach in supercritical C02 and showed the simultaneous eROP of e-caprolactone with controlled free radical polymerization of methyl methacrylate by atom transfer radical polymerization (ATRP)-at this time simultaneous eROP and ATRP had not been reported in any media. The bifunctional initiator incorporated both a primary hydroxyl group (as an initiation site for eROP of e-caprolactone) and a bromine moiety (for initiation of ATRP). Howdle showed that... 

Recently the synthesis and characterization of a new star-block architecture, the inverse star-block copolymer, was reported [19].These 4-arm star molecules, with poly(styrene-Msoprene) arms, have two of the arms connected to the silicon atom by the polystyrene (PS) end of the diblock arm while the other two are connected to the central point by the polyisoprene (PI) end (Scheme 4). 

Novel rathenium complexes with carborane ligands were employed as efficient catalysts for controlled polymer synthesis via Atom Transfer Radical Polymerization (ATRP) mechanism. The ability of carborane ligands to stabihze high oxidation states of transition metals allows the proposed catalysts to be more active than their cyclopentadienyl counterparts. The proposed catalysts do not reqnire additives such as aluminium alkoxides. It was shown that introdnction of amine additives into the polymerization mixture leads to a dramatic increase of polymerization rate leaving polymerization controlled. The living nature of polymerization was proved via post-polymerization and synthesis of block copolymers. 

Controlled/ Living radical polymerization (CRP) of vinyl acetate (VAc) via nitroxide-mediated polymerization (NMP), organocobalt-mediated polymerization, iodine degenerative transfer polymerization (DT), reversible radical addition-fragmentation chain transfer polymerization (RAFT), and atom transfer radical polymerization (ATRP) is summarized and compared with the ATRP of VAc catalyzed by copper halide/2,2 6 ,2 -terpyridine. The new copper catalyst provides the first example of ATRP of VAc with clear mechanism and the facile synthesis of poly(vinyl acetate) and its block copolymers. 

VAc has been successfully polymerized via controlled/ living radical polymerization techniques including nitroxide-mediated polymerization, organometallic-mediated polymerization, iodine-degenerative transfer polymerization, reversible radical addition-fragmentation chain transfer polymerization, and atom transfer radical polymerization. These methods can be used to prepare well-defined various polymer architectures based on PVAc and poly(vinyl alcohol). The copper halide/t is an active ATRP catalyst for VAc, providing a facile synthesis of PVAc and its block copolymers. Further developments of this catalyst will be the improvements of catalytic efficiency and polymerization control. 

Heise, Palmans, de Geus, Villarroya and their collaborators (17,41,42) have been working on a chemoenzymatic cascade synthesis to prepare block copolymers. They combine enzymatic ring-opening polymerization (eROP) and atom transfer radical polymerization (ATRP). The synthesis of block copolymers was successful in two consecutive steps, i.e., eROP followed by ATRP. In the one-pot approach, block copolymers could be obtained by sequential addition of the ATRP catalyst, but side reactions were observed when all components were present from at the onset of reactions. A successful one-pot synthesis was achieved by conducting the reaction in supercritical carbon dioxide. 

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