Regioselective crosslinking

The examples discussed above illustrate the importance of block copolymer chain segment incompatibilities for the phase separation of bulk materials, combined with the ability to perform chemistry within specific nanoscale domains to impose permanence upon those self-assembled nanostructured morphologies. Each is limited, however, to crosslinking of internal domains within the solid-state assemblies in order to create discrete nanoscale objects. To advance the level of control over regioselective crosslinking and offer methodologies that allow for the production of additional unique nanostructured materials, the pre-assembled structures can be produced in solution (Figure 6.4), as isolated islands with reactivity allowed either internally or on the external... 

Regioselective crosslinking of the core domain of cylindrically shaped, wormlike micelles composed of poly[(butadiene)45-b-(ethylene oxide)55] and assembled in aqueous solution at < 5% block copolymer concentrations, was performed using radical coupling of the double bonds throughout the poly(butadiene) phase [27] (Figure 6.3b). This resulted in a 13% reduction in the core diameter, from 14.2 to 12.4 nm, as measured by small-angle neutron scatter-... 

Advanced characterization of the structure, properties and function of the self-assembled precursor can be extrapolated from studies on the more robust crosslinked material, especially in changing or challenging environments, in which the assemblies would not remain intact. The introduction of crosslinks has aided in the maintenance of native conformations as a powerful technique during studies to determine the order and structure of biological assemblies [61, 62], Moreover, the robust characteristics that the crosslinks provide, combined with the ability to define their regioselectivity, are expected to expand the realm of possible applications for nanoscale materials. 

Oxovanadium(V) and oxomolybdenum(VI) were incorporated into crosslinked polystyrene resins functionalized with iminodiacetic acid or diethylenetriamine derivatives 921 The polymer complexes were used as catalysts in the oxidation of olefins with f-butylhydroperoxide. Vanadium(V) complexes promote the epoxidation of allylic alcohols in a highly regioselective manner, e.g., 2,3-epoxide was obtained in 98 % selectivity from e-geraniol at 80 °C. The catalytic activity of the vanadium(V) complexes is generally higher than that of the molybdenium(VI) complexes in the oxidation of allylic alcohols, whereas an opposed trend holds for the epoxidation of cyclohexene. 

Takaya and Nozaki invented an unsymmetrical phosphin-phosphite ligand, (R,S)-BINAPHOS, which was used in the Rh(l)-catalyzed asymmetric hydroformylation of a wide range of prochiral olefins, with excellent enantioselectivities [120, 155]. A highly crosslinked PS-supported fR,S)-BINAPHOS(257)-Rh(I) complex was prepared and applied to the same reaction (Scheme 3.83) [156]. Using the polymeric catalyst, the asymmetric hydroformylation of olefins was performed in the absence of organic solvents. The reaction of cis-2-butene, a gaseous substrate, provided (S -methylbutanal with 100% regioselectivity and 82% ee upon treatment with II, and CO in a batchwise reactor equipped with a fixed bed. 

Non-crosslinked polystyrene with salen ligand Non-crosslinked polystyrene with onium salt residues Non-crosslinked polystyrene copolymerised with a chiral phosphine ligand 14,765 0.5-3.8" 0.7-2.3 CH2Cl2,THF, EtOAc, DMF DMF,DMSO,DMA, toluene, anisole, MeOH,MeCN, diglyme Asymmetric epoxidation Regioselective addition reaction of phenyl glycidyl ether with S-phenyl thioacetate Pt-catalysed asymmetric hydroformylation of olefins Precipitation (methanol) (r) Precipitation (diethyl ether) (r) [68] [142] [143]... 

Treatment of MBH addcut 1 with carboxylic adds under Mitsunobu conditions gave almost exclusively the S 2 products 4, rather than S 2 product 5. Weak and bulky carboxylic acids and low temperatiues favor S 2 addition. Although the reaction conditions were effective for alkyl substituted derivatives, the addition of EtsN to the Mitsunobu conditions was necessary to improve the 5n2 S 2 ratios for the vinyl and phenyl derivatives (Scheme 3.3). " More recently, it was found that the nucleophilic substitution reaction mediated by triphenylphosphine linked to non-crosslinked polystyrene 6 led to a significantly more regioselective transformation. Tri-substituted alkenes 4 were obtained almost quantitatively via a highly regioselective 5n2 Mitsunobu reaction (Scheme 3.3). ... 

The reaction of an alcohol with a vinyl ester proceeds much faster than with an alkyl ester or a haloalkyl ester to form the desired product in higher yields Kobayashi and co-workers [36-41] studied the polymerisation of the divinyl esters of dicarboxylic acids with diols, triols and sorbitol. The polymerisation behaviour was strongly dependent on the monomer structure, enzyme origin and reaction conditions. Under appropriate conditions, an aliphatic polyester with a MW higher than 2 x lO Da was obtained. The polymerisation of divinyl adipate with 1,4-BDO by PFL, in isopropyl ether at 45 °C for 48 h, produced a polyester with a MW of 6,700 Da and a yield of 50% (Scheme 12.8, [1]), whereas the use of CAL was also employed to produce crosslinkable polyesters [40]. Divinyl sebacate and glycerol were polymerised in the presence of the unsaturated fatty acids, oleic acid, linoleic acid and linoleinic acid. NMR analysis revealed that the reaction proceeded with regioselectivity during the... 

Reaction or the procyanidins with formaldehyde proceeds so rapidly that these products are usually not useful as wood adhesives. Herrick and Bock (153) advocate crosslinking these compounds with methylol-phenols rather than aldehydes. To gain further information about these reactions, both catechin and tetra-O-methyl catechin have been reacted with p- and o-hydroxybenzyl alcohol (142, 247). Reactions of catechin with /7-hydroxybenzyl alcohol gave the C-6, C-8, and C-6 + C-8 disubstituted products in approximately equal mole ratios. With o-hydroxybenzyl alcohol, substitution at C-8 was favored, with approximate yield ratios of 1 2.5 1.7, respectively. Foo and Hemingway (105) have also examined the regioselectivity of reactions of catechin with furfuryl alcohol and have obtained 2-furyl-(6-catechinyl)-methane and 2-furyl-(8-catechinyl)-methane in approximate relative yields of 1 2.7. 

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