Gel-type Resin Research Articles

Chiral Monomers with MinimalFunctional Group Linkages for Suspension Co-polymerization: A SuzukiCoupling Approach

A new strategy for the synthesis of chiral monomers for co-polymerization with styrene is described. Suzuki coupling of 4-vinylphenylboronic acid with chiral aryl triflates 5 and 13, and subsequent elaboration has resulted in chiral monomers 9 and 10. One of these monomers 10 has subsequently been incorporated into a polystyrene gel-type resin 16 with a functional group loading of 0.48 mmolg-1.

Metal catalysis inside polymer frameworks: evaluation of catalyst stability and reusability.

The polymer framework of a resin-based catalyst built up with Pd nanoclusters (ca. 3 nm) dispersed inside the nanoporous domains of a thermally stable gel-type polyacrylic resin exhibits a good chemical stability under 5 bar H(2) at 40 degrees C for reasonable contact times. Chemical and physico-chemical integrity of the polymer framework are checked with a variety of instrumental analytical methods. Catalyst reusability turns out to be quite good.

Nanostructure and molecular accessibility of gel-type resins for supported bio-catalysis: Part I. Poly-hydroxyethylmethacrylate-hydroxypropylmethacrylate-trimethylolpropanetrimethacrylate

Hydroxyethylmethacrylate (HEMA), hydroxypropylmethacrylate (HPMA) and trimethylolpropanetrymethacrylate (TMPTM) are copolymerised by γ-irradiation to give five potentially amphiphilic gel-type resins. The molar fraction of TMPTM (the cross-linker) is constant (4 mol%) while the five resins are featured by different HEMA/HPMA molar ratios (96/0, 68/28, 48/48, 28/68 and 0/96, respectively). The swollen state morphology of the five materials is investigated by means of inverse steric exclusion chromatography (ISEC) and electron spin resonance (ESR) spectroscopy based on the spin-probe TEMPONE (2,2,6,6-tetramethyl-4-oxo-1-oxyl-piperidine) both in water and tetrahydrofuran (THF). In THF, swelling and accessibility of the polymer network increase with the increase in HPMA content. In contrast, the five materials are poorly swollen by water and no apparent dependence of swelling on HPMA/HEMA ratio is detected.

Stainless steel microbeads coated with sulfonated polystyrene-co-divinylbenzene

A new kind of gel-type magnetic cation-exchange resin based on stainless steel microspheres coated with sulfonated polystyrene-co-divinylbenzene has been synthesized in a two-step process. First, magnetic polymeric beads were prepared by radical suspension polymerization, after which these particles were functionalized by a post-polymerization sulfonation process. The effects of slight modifications in the synthesis process (metal surface modification, initial contact between metal and catalyst, and the use of double polymerization) on the thickness of the polymeric layer were evaluated. Both the precursor magnetic polymeric beads and the final cation exchange resins were studied by scanning electron microscopy and X-ray energy dispersive (EDX) analysis. Finally, the cation exchange capacity of the resins was determined.

Generating palladium nanoclusters inside very lipophilic gel-type functional resins: preliminary catalytic tests in the hydrogenation of 2-ethyl-anthraquinone to 2-ethylanthrahydroquinone

Four lipophilic polystyrene–methacryloylethylensulfonic acid–divinylbenzene gel-type resins, with 2 and 4% cross-linking degree, are synthesized and used as supports for “atomic” dispersion of Pd(II) finalized to the preparation of resins-supported palladium metal catalysts. Properly performed reduction of Pd(II) to Pd(0) achieves homogeneous dispersion of ca. 3 nm metal nanoclusters inside the supports particles in the more cross-linked resin. Resulting resin-supported palladium catalysts are efficient and moderately chemoselective in the hydrogenation of 2-ethylanthraquinone to 2-ethylanthrahydroquinone.

Gram-scale synthesis of suspension-polymerized styrene-divinylbenzene-based resins using an oscillatory baffled reactor.

Both macroporous and gel-type high-quality spherical particulate styrene-divinylbenzene resins (see representative optical micrograph) can be synthesized in good yield on a small scale by using an oscillatory baffled reactor. The methodology is tolerant to the use of functional co-monomers.

The preparation of polymer beads by photocationic suspension co-polymerisation of 2-(arylsilyl)ethyl vinyl ethers

Polymer beads have been prepared by photocationic suspension polymerisation of 2-(aryldimethyl)silyl ethers in perfluorooctane in the course of our studies on polymer-supported desymmetrisation of 1-silacyclohexa-2,5-dienes. Good yields of 100–200 μm beads of satisfactory shape have been obtained using a perfluorinated co-polymer as stabilising agent. These beads have no permanent porosity although they have a high nominal cross-linking level. Their swelling in common organic solvents is comparable with those of Merrifield or TentaGel gel-type resins.

Preparation of soluble and insoluble polymer supported IBX reagents

A series of soluble and insoluble polymer supported versions of the versatile oxidizing reagent IBX has been prepared. Each of the reagents were evaluated for their efficiency in the conversion of benzyl alcohol to benzaldehyde. Results from this study were that the soluble, non-crosslinked polystyrene supported IBX reagent gave the best rate of conversion to benzaldehyde, while the macroporous polymer supported IBX resin provided a superior rate of conversion to benzaldehyde when compared with a gel type resin. The macroporous IBX reagent was also shown to convert a series of alcohols to the corresponding aldehydes and ketones.

Molecularly imprinted composite materials via iniferter-modified supports

Wide pore silica (DP = 100 nm) and gel-type or macroporous (12% nominal crosslinking density) Merrifield resins were modified with iniferter groups for grafting of crosslinked molecularly imprinted or non-imprinted polymer layers through quasi-living polymerisation. Prior to iniferter coupling, the silica supports were premodified by silanisation with p-(chloromethyl)phenyl trimethoxysilane. The iniferter groups were then introduced by reacting the resin-bound chloromethyl groups with sodium N,N-diethyldithiocarbamate. It was shown that the coupling yield, measured as the conversion of the chloromethyl groups, could be varied between 5 and 85% through kinetic control, with the fastest conversions observed for the macroporous resins. This allows the density of radical generating groups to be finely adjusted. Ultraviolet light-initiated copolymerisations of ethyleneglycol dimethacrylate and methacrylic acid in toluene resulted in grafting of 0.2–1.9 g of polymer per gram of support, where the grafted amount increased with reaction time, iniferter content and monomer concentration. The dry-state texture of the composite beads prepared from the gel-type resin depended strongly on the amount of grafted polymer. According to the scanning electron micrographs, the beads with the lower grafted amounts (0.4 g polymer per g support) were deformed exhibiting a peculiar folded structure, whereas the beads containing more grafted polymer (1.6 g polymer per g support) were spherical, with an appearance similar to the precursor particles. None of these materials exhibited permanent porosity. Only the composites obtained from the porous precursor particles also exhibited porosity after grafting. Among these, the silica-based composites also showed recognition for their templates when assessed in the chromatographic mode, whereas no imprinting effects could be demonstrated for the polystyrene-supported materials.

Dehydration of 1-pentanol to di- n-pentyl ether over ion-exchange resin catalysts

The dehydration reaction of 1-pentanol to di- n-pentyl ether (DNPE) and water in the liquid phase was studied at 110–180 °C and 1 MPa on sulfonic styrene–divinylbenzene (S/DVB) copolymers and the perfluoroalkanesulfonic resin NR50. S/DVB-based catalysts were macroreticular and gel-type resins both sulfonated conventionally and oversulfonated. Macroreticular resins tested include resins whose working phase in catalysis is gel phase (i.e. Amberlyst-15 and Amberlyst-35) and XN1010 whose working phase in catalysis is macropores surface. By comparing 1-pentanol conversion, selectivity to DNPE and initial reaction rates at 150 °C it is concluded that gel-type S/DVB resins that swell moderately in the reaction medium, as CT-224, are the more suitable catalysts for the reaction. NR50, which is thermally stable up to 200 °C, is the most selective catalyst tested but it is too much expensive for industrial use. Selectivity to DNPE decreases as temperature increases showing that side reaction of dehydration to 1-pentene is more sensitive to temperature. Apparent activation energies for the dehydration reaction of 1-pentanol to DNPE were found to be about 100 kJ/mol.

Generating palladium nanoclusters inside functional cross-linked polymer frameworks

The use of functional resins as designable supports for palladium nanoclusters is reviewed. Data are related to the generation of Pd nanoparticles under various conditions and inside gel-type or macroporous frameworks. The combination of different physico-chemical techniques (ISEC, ESR and PGSE NMR) is illustrated as a powerful tool for evaluating nanomorphology and molecular accessibility, mainly of gel-type resins. A few examples of catalytic applications are presented and discussed and prospects for wider utilizations are evaluated.

Regio-reactive resin: A platform for orthogonal loading using the polymer backbone and cross-linker

A new support for solid-phase combinatorial organic synthesis has been developed, which we term a regio-reactive resin (R 3-resin). The resin is based on a unique hydroxyl-functionalized cross-linker readily synthesized in two steps starting from 4-hydroxybenzaldehyde. The cross-linker's ease of synthesis and high purity enables the preparation of gel-type resins with regio-reactive orthogonal loading sites. The resin's swelling properties were investigated, and its potential utility was demonstrated via orthogonal reactivity of the pendant and cross-linker sites.

Comparison of Activity and Selectivity of Weakly Basic Anion-Exchange Catalysts for the Aldolization of Butyraldehyde with Formaldehyde

Aldols are important intermediates in the production of polyols, which are raw material for lubricants, surface coatings, and synthetic resins. The activities and selectivities of gel-type and macroporous anion-exchange resin catalysts in the aldolization of butyraldehyde with formaldehyde in an aqueous environment were investigated at 60 °C. The experiments were carried out batchwise in a stirred glass reactor, and the reaction products were analyzed with high performance liquid chromatography. Two main products were observed, 2-ethyl-3-hydroxy-2-hydroxy-methylpropanal (trimethylolpropane aldol) and 2-ethylpropenal (ethylacrolein). The product ratio was strongly dependent on the catalyst. The selectivity with respect to trimethylolpropane aldol varied within the range 2.7−7.3 for the catalysts investigated. Systematic kinetic experiments were carried out at 50−70 °C with the gel-type resin catalyst displaying the highest aldol selectivity. A kinetic model based on molecular mechanisms was able to describe the product distribution.

Dynamics of Sodium and Lithium Counter-Ions and Water Molecules in Cation-Exchange Resins as Shown by NMR Spectroscopy

The dynamics of water molecules and cations (lithium and sodium counter-ions) in cation-exchange resins were investigated by measuring relaxation time and self-diffusion coefficients of 1H, 7Li, and 23Na NMR. Five gel-type cation-exchange resins with different by the crosslinked poly(styrene sulfonic acid) copolymer swollen in water and salt aqueous solution were studied. A macroporous-type resin was studied for comparison. Activation energy for the lithium and sodium ions obtained from the Arrhenius plots of spin-lattice relaxation times T1 correlated well with the cross-linking of resins. Since T1 of the cations in every resin are shorter than in corresponding aqueous solution, the correlation time of the rotational motion of cations is longer in the resins. With higher cross-linking of the resin, the rotational motion of the cations becomes slower and more restricted. Self-diffusion coefficients of water molecules and lithium and sodium counter-ions in the gel-type resin were directly measured by pulsed field-gradient NMR methods. Translational diffusion of these species was closely related to the cross-linking of resin similar to T1. The diffusion of water molecules and cations becomes slower in higher cross-linked resin. Apparent diffusion coefficients of Li+ ions and water molecules were dependent on diffusion time. This may be explained by restricted diffusion in a three dimensional network structure of gel-heteroporous type ion-exchange resins.

Reasons for deactivation of unpromoted polymeric catalysts in bisphenol A synthesis

Quantitative speciation of sulfonic groups and compositional analysis of gel-type cation-exchange resins used as unpromoted catalysts in bisphenol A synthesis, deactivated at the commercial plant, were carried out. It was proved that building-in the polyphenol-type high-molecular-weight compounds, formed inside the catalyst grains, into the catalyst polymeric matrix is the basic reason for deactivation of the catalyst. It was found that the rate of formation of these polyphenols is only to a small degree dependent on the concentration of bisphenol A synthesis by-products in the reaction mixture circulated through the fixed catalyst bed.

Intraparticle diffusion during selective ion exchange with a macroporous exchanger

Chlorophenols, quaternary ammonium compounds, benzene and naphthalene sulfonates and benzene carboxylates are examples of environmentally significant synthetic organic compounds which exist as ions in water over a wide range of pH values. This study discusses the sorption kinetics, and more specifically, intraparticle diffusion behaviors of trace concentrations of pentachlorophenate (PCP −) and other chlorophenates onto a commercially available macroporous polymeric anion exchanger (IRA-900). The anion exchanger is essentially biphasic, i.e. every single exchanger particle contains an enormous number of tiny microgels and an interconnected network of pores. Ion exchange functional groups reside solely within the microgels. For comparison, a gel or microporous anion exchanger is also included in the study. Experimental results reveal a distinctly different type of effect of competing chloride ion concentration on gel and macroporous ion exchangers pertaining to sorption of pentachlorophenate (PCP −). While the effective intraparticle diffusivity of PCP − for gel-type resin remained unaltered with a change in competing chloride concentration, the same increased significantly for the macroporous exchanger with an increase in chloride concentration. Pore diffusion is considered to be the predominant intraparticle transport mechanism for highly preferred PCP − inside the macroporous exchanger. Under the normal hydrodynamic conditions of a fixed bed column run, intraparticle diffusion was found to be the rate-limiting step. For various chlorophenates, the effective intraparticle diffusivities were inversely correlated to the octanol–water partition coefficients of their parent chlorophenols.

Reversibly collapsible macroporous poly(styrene-divinylbenzene) resins

A series of poly(styrene–divinylbenzene) (poly(PS–DVB)) resins have been prepared by suspension polymerisation of styrene–DVB mixtures with DVB contents of 1–12 mol%. In each case 2-ethyl-hexan-1-ol was used as a porogen. Those resins prepared with <10 mol% DVB collapsed to clear glassy particles on drying from dichloromethane or toluene. However, on drying these resins from acetone, methanol and scCO 2 some opacity was retained. The surface area of each dried species was measured by applying the BET theory to N 2 sorption isotherms. Those resins containing ≤6 mol% DVB and dried from the former two solvents indeed have negligible surface area and superficially are very like gel-type resins. All the resins dried from the latter group of solvents have significant surface area which decreases systematically with fall in DVB mol%. The resin with 6 mol% DVB and negligible surface area dried from toluene was re-swollen in acetone and re-dried. This process re-established the pore structure and surface area. Using inverse size exclusion chromatography the porosity of all the resins was investigated when swollen in tetrahydrofuran. In all cases significant surface area (110–250 m 2 g −1) was detected. This group of resins are therefore macroporous but, depending on the solvent and drying procedure, the porous morphology can be collapsed reversibly to form dry resins superficially similar to gel-type species. However, in practice these novel resins retain a latent pore structure which is readily re-established on treatment with suitable solvents.

Metal ion implantation onto acidic resins upon reaction of metal acetates and carbamates: Part I. Synthetic results

Moderately cross-linked gel-type resins bearing –SO 3H, –COOH and –OH groups undergo facile metallation with Pd II, Cu II and Ni II acetates with concomitant release of acetic acid. Successful and facile metallation is also observed upon reaction with Pd II, Cu II and Ni II carbamates.

Polymer Supports with Novel Physical Morphologies and Macroscopic Formats

P olymer supports in the form of suspension polymerised styrene-divinylbenzene (DVB), beads have been the centre-piece of solid phase peptide synthesis ever since they were introduced by Merrifield in 1963. Not surprisingly they have also become a key component in the more recent developments involving solid phase combinatorial and parallel synthesis. Usually lightly crosslinked swellable gel-type resins are the species of choice in the latter methodology, although the rigid more highly crosslinked macroporous morphological variants are preferred for large packed-bed column operations, and for the heterogenisation of transition metal complex catalysts. Both gel-type and macroporous resins have their advantages and disadvantages and, these together with a mechanistic explanation of how the morphologies are generated, have been reviewed recently. Interestingly the interface region between these two morphologies has not been well investigated, and certainly not well documented.

Metal palladium dispersed inside macroporous ion-exchange resins: the issue of the accessibility to gaseous reactants

Commercial macroporous ion-exchange resins (Lewatit SPC 118 and UCP 118) were used to support Pd metal by a two step ion-exchange and reduction procedure. The textural features of the resins were determined by Inverse Steric Exclusion Chromatography (ISEC) measurements. TEM characterization of the obtained Pd/resin composite showed the presence of uniformly sized Pd crystallites located at the macropore “surface”. Pulse chemisorption analysis gave evidence for the lack of accessibility of the crystallites when the resin composite is in the dry state. This suggests that the metal particles are in fact embedded in a gel-type resin layer at the “surface” of the macropores and therefore practically unaccessible to the molecules of a gaseous phase unless the support is in the swollen state.