Polymer supported concentrated solutions

Comparing the results from radical release in solution and on solid support, it was determined that the amounts of recombined product were reduced significantly in the matrix-supported reaction even at higher concentrations (0.1 M solution 2.6%, 0.16 M polymer support 0.4%). On the other hand, in both solution and polymer gel experiments, the... 

We will begin with a brief survey of linear viscoelasticity (section 2.1) we will define the various material functions and the mathematical theory of linear viscoelasticity will give us the mathematical bridges which relate these functions. We will then describe the main features of the linear viscoelastic behaviour of polymer melts and concentrated solutions in a purely rational and phenomenological way (section 2.2) the simple and important conclusions drawn from this analysis will give us the support for the molecular models described below (sections 3 to 6). 

An analysis of computer simulations of water at different pressures by Hummer et al. (110) suggested that hydrophobic contact pairs become increasingly destabilized with increasing pressure. The proposed scenario could explain the pressure denaturation of proteins as a swelling in terms of water molecules that enter the hydrophobic core by creating water-separated hydrophobic contacts. Additional support for the validity of Hummer s IT-model analysis has been achieved by pressure-dependent computer simulation studies of isolated pairs of hydrophobic particles, as well as rather concentrated solutions of hydrophobic particles (111, 112). Recently, the pressure-induced swelling of a polymer composed of apolar particles at low temperatures can be observed (113). 

Preparation of 52 [50] A solution of polymer-supported morpholine 47 (170 mg), l-phenyl-l,3-butanedione 50 (0.5 mmol), and (4-carboxyphenyl)hy-drazine hydrochloride (0.6 mmol) in methanol was shaken for 2.5 h. The methanol was then removed under a stream of nitrogen, dichloromethane (4 mL) and polymer-supported isocyanate 48 (350 mg) were added, and the reaction mixture was shaken for a further 16 h. An additional portion of polymer-supported isocyanate 48 (120 mg) was then added. After 4h, the resin was filtered off and washed with dichloromethane (2 x 1.5 mL). The combined organic phases were concentrated in vacuo to give the desired product, 4-(3-methyl-5-phenylpyrazol-l-yl)benzoic acid 51. 20 mg (70 umol) of this benzoic acid was dissolved in dichloromethane and the solution was treated with polymer-supported morpholine 47 (100 mg) and 0.1 m isobutyl chloroformate in dichloromethane (0.75 mL, 75 pmol). The resulting slurry was shaken under nitrogen at rt for 30 min and then treated with a solution of (3-isopropoxypropyl)amine (100 mg, 85 pmol) in dichloromethane... 

Preparation of the reagent [70] A solution of PEG monomethyl ether 89 (MW = 750 5.88 g, 7.8 mmol) in benzene (20 mL) was dried azeotropically for 24 h in an apparatus fitted with a Dean-Stark trap and subsequently added dropwise to a solution of chlorosulfonyl isocyanate (88) (1.10 g, 7.8 mmol) in dry benzene (20 mL). The mixture was stirred at room temperature for 1 h, then concentrated to dryness. A solution of this residue in benzene (35 mL) was added dropwise to a solution of triethylamine (2.5 mL, 17.3 mmol) in benzene (15 mL). The mixture was stirred for 30 min at room temperature, then filtered, and the solid was dried to yield polymer-supported Burgess reagent 91 (6.2 g, 82%). 

The results show clearly that, in the presence of water, the acid catalytic activity of supported sulfonic acid groups is essentially the same on polymer and silica supports, except where the level of polymer sulfonation is high, when the sulfonic acid exhibits significantly enhanced activity. The trend in molar enthalpies of neutralisation with aqueous NaOH is similar. On silica supports, and polymer supports with low sulfonic acid concentrations, these enthalpies are very similar to those of strong mineral acid solutions. In contrast, resins with high levels of sulfonation show significantly higher molar enthalpies of neutralisation. 

Some polymers (PEG or PEG-like) have low cloud points (the critical solution temperature) in water. If these polymers support the formation of an ABS, metal ion stripping by temperature programming may be possible. Rogers et al. [35] have found that UCON (a random copolymer of ethylene oxide and propylene oxide) can replace PEG-2000 and give better extraction of TcO in certain ABSs. UCON has a cloud point around 50 C and can form an ABS with salt solutions at lower salt concentrations [68]. TcO " can be extracted into the UCON-rich phase, and the UCON-rich phase can be separated, heated, and the two new phases separated again [35]. Thus, metal ions can be stripped from a polymer-rich phase directly into water. This technique shows promise, but more research is needed to define clearly the conditions necessary for a successful separation. 

Dendrimer-encapstdated catalysts are another area of active research for polymer-supported catalysts. The nanoparticles are stabilized by the dendrimers preventing precipitation and a omeration. Bimetallic nanoparticles with encapsulated metals (dendrimer-encapsulated catalyst DEC) from commercially available fourth-generation PAMAM dendrimers and palladium and platinum metal salts were prepared via reduction by Crooks and co-workers [34], following previous work in this area [35], The simultaneous incorporation of Pt and Pd reflects the concentrations in solution. The bimetallic DECs are more active than the physical mixture of single-metal DEC [35, 36] in the case of the hydrogenahon of allyl alcohol in water, with a maximum TOP of 230 h compared to TOP = 190 h obtained for monometallic palladium nanoparticles (platinum TOP = 50 h ). 

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