Abstract

Abstract

Abstract

Abstract

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Abstract

Abstract

Liquid/liquid separations using gravity and two phases of different density are a practical and viable way to recover, separate and reuse soluble polymer-supported catalysts. Such separations are facilitated by using polymers that have phase-selective solubility under biphasic conditions. Such polymers can be designed to be soluble either in a non-polar or a polar phase. Since catalyst and ligand loading can be at a low mole percent level on the polymer, the polymer’s intrinsic solubility can be maintained with a variety of ligands and catalysts making such separation strategies general. Catalysis with such soluble polymer-supported species can either be carried out under biphasic or monophasic conditions. In the former case, aqueous/organic, fluorous/organic or other biphasic regimes can be used. In the later case, thermomorphic or latent biphasic conditions can be employed. In either case, catalyst separation and recovery can be accomplished simply without using significant quantities of additional solvent.

The lower critical solution temperatures (LCSTs) for mass fractionated samples of poly(N-isopropylacrylamide) (PNIPAM) were studied to determine the effect of polymer molecular weight on the LCST using a high throughput temperature gradient apparatus. PNIPAM fractions prepared by a conventional radical polymerization using azoisobutyronitrile (AIBN) as the initiator had LCSTs that were largely invariant with molecular weight or dispersity. Only slight deviations were noted with lower molecular weight samples. An 18-kDa sample had a 0.6 °C higher LCST. A 56-kDa sample had a 0.2 °C higher LCST. PNIPAM derivatives prepared with a triphenylmethyl (trityl) functionalized azo initiator were also prepared and mass fractionated. These samples' LCSTs were identical to those of PNIPAM samples prepared using AIBN initiation when higher molecular weight samples were compared. The trityl-containing PNIPAM fractions' LCSTs varied when the molecular weight decreased below 100 kDa. Acidolysis of the trityl end groups provided a third set of PNIPAM derivatives whose LCST differed only with samples with M_w values < 60 kDa. These results show there is no effect of molecular weight on LCST until the degree of polymerization is such that end group structure becomes significant. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1492–1501, 2006

A practical synthetic route to polybasic, polyamine, hyperbranched grafts using commercially available polyethyleneimine (PEI) and cyanuric chloride as a coupling agent is described. The grafting process was followed by XPS spectroscopy, TGA analysis, ATR-IR spectroscopy, acid–base titration, and by ¹³C CP-MAS NMR spectroscopy. In the case of silica gel, thermal gravimetric analyses showed that a 35 wt % loading of graft could be obtained. Acid–base titration of hyperbranched PEI grafts on silica gel and oxidized polyethylene powder showed the ion-exchange capacities of these PEI-grafted substrates were 1.00 and 0.17 mmol of base/g of solid, respectively. Although the focus of the paper is on grafting on silica gel, the influence of the kind of support and solvent on the grafting process and the ion-exchange capacity was examined. Water was a good solvent for PEI grafting onto silica gel, but a more hydrophobic polyethylene support required the use of dichloromethane as a solvent for PEI graft synthesis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4654–4665. 2005

The use of soluble thermoresponsive polymers to sequester or scavenge hydrophobic guest molecules from dilute aqueous solutions on heating is described. In these studies, a homopolymer of N-isopropylacrylamide was shown to sequester 46–83% of a soluble monochlorotriazine from 0.1–10 ppm aqueous solutions when heating above this polymer's lower critical solution temperature (LCST). Substitution of the reactive piperidine-containing 20:1 copolymer poly(N-isopropylacrylamide)-c-poly[N-4-(acrylamidomethyl)piperidine] for this unreactive polymer led to >98% scavenging of these same triazines when heating above this reactive polymer's LCST. The monochlorotriazine guests studied included the herbicide atrazine and two dye-labeled analogues of this herbicide. In one case, an atrazine analogue was designed so as to contain a dansyl group for fluorescence analysis. In the second case, an atrazine analogue was labeled with a methyl red group to facilitate visual and spectrophotometric analysis. Atrazine concentrations were measured with liquid chromatography–mass spectrometry. The enhanced efficiency of the reactive piperidine-containing copolymer scavenger in removing triazines from solution is attributed to covalent bond formation by nucleophilic aromatic substitution of the chlorine of the monochlorotriazines by the piperidine nucleophile on the copolymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6309–6317, 2004

Soluble polymers that bind metals and that in turn can be separated from other components of a reaction mixture are described. The polymers used include derivatives of acrylamides, acrylates, polystyrene and other polymers. Both sequestration of trace metals and recovery of homogeneous catalysts is discussed. Separation methods using liquid/liquid mixtures that are monophasic during a reaction but biphasic during a separation are emphasized.

Several enzymes immobilized on thermo-responsive polyacrylamide polymers are nearly as active as their soluble forms, and can be recovered for reuse after gentle heating and precipitation. Carbohydrates attached to these polymers have been used for enzymatic glycosylation, and the products have been isolated by thermal precipitation followed by release from the polymer, thus greatly simplifying product purification in water.

The attributes and design of soluble polymer supports for catalysis and synthesis are discussed. By manipulating polymer structure, polymer supports can be prepared so that the solubility of an attached reagent, substrate, or ligand is affected by heating, cooling, pH, or solvent identity. Supports with such engineered solubility are useful both in organic synthesis and catalysis. They can be used as purification handles in organic synthesis as a way to recover catalysts, as a way to turn reactions on or off, and more generally, as a handle for separations. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2351–2363, 2001

Interphase oligomerization of thiophene within a supported thin film is described. Polyethylene (PE) surfaces containing an irregularly hyperbranched poly(acrylic acid) (PAA) graft were first prepared by multistep grafting of poly(tert-butylacrylate) onto oxidized PE. The product ultrathin PAA grafts were then further modified by amidation or esterification with thiophenes containing amino or hydroxyl groups to form new interfaces containing thiophene monomers. These thiophene-modified grafts were characterized by attenuated total reflectance infrared spectroscopy and were shown to be suitable as substrates in an oxidative polymerization method with FeCl₃ as an oxidant. The product 2,5-coupled thiophene oligomers (3-PAA/PE–oligomerized thiophene ester, OTE) emitted a yellow-green light under UV irradiation, indicating that a conjugated fluorescence oligothiophene had been prepared within these hyperbranched films. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4119–4128, 2001

Synthetic methods for modifying the carboxylic acid groups of hyperbranched thin film grafts were studied. Amidation, esterification, reduction, and alkylation reactions of carboxylic acid derivatives that proceed in high conversion (>90%) are described. The stability of ultrathin, hyperbranched film grafts attached to self-assembled monolayers on gold to conditions of strong base, strong acid, heat, and organic solvents is detailed. Practical procedures that can be used to prepare and modify poly(acrylic acid) hyperbranched grafts on gold, polyethylene film, and powder for use in the synthesis of cationic polyelectrolyte grafts, for use in the synthesis of poly(allyl alcohol) grafts, for use in the synthesis of poly(allyl ester) grafts, and for use as substrates for organometallic chemistry and further graft chemistry are discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3944–3953, 2000

Semipermeable nanoskopische Hohlkugeln oder Käfige mit Durchmessern vom Sub-Mikrometerbereich bis in den 100-nm-Bereich lassen sich durch Selbstorganisation von Polymeren auf sub-Mikrometer-großen Partikeln (Möhwald et al.) oder Bildung von hüllenverknüpften polymeren Micellen (Wooley et al.) und anschließenden chemischen Abbau des Teilchen- bzw. Micellenkerns herstellen (siehe Schema).

Semipermeablenanoscopichollowspheresorcages with diameters in the sub-micrometer to the 100 nm range are accessible by the self-assembly of polymers onto sub-micrometer sized particles (Möhwald et al.) or by the formation of shell-cross-linked polymeric micelles (Wooley et al.) followed by chemical degradation of the underlying particle or micelle core (see scheme).