Showing papers on "Divinylbenzene published in 1995"

Cyclization and Reduced Pendant Vinyl Group Reactivity during the Free-Radical Crosslinking Polymerization of 1,4-Divinylbenzene

Abstract: Free-radical cross-linking polymerization of 1,4-divinylbenzene (1,4-DVB) has been investigated in toluene. The monomer concentration was less than 5 w/v%. Conversion of monomer and pendant vinyl groups, weight-average molecular weight M w , and intrinsic viscosity [η] of the polymers were measured as a function of the reaction time up to the onset of macrogelation. A kinetic model was used to calculate the extent of cyclization and reduced pendant reactivity from the experimental data. Fraction of pendant vinyls in cycles, number of multiple cross-linkages, and the reactivity ratio of pendant to monomeric vinyl were evaluated as a function of the polymerization temperature, initial concentrations of 1,4-DVB and the initiator as well as the amount of styrene as a comonomer. The results indicate that 30-60% of pendant vinyls are used by cyclization reactions and, on average, 100-800 multiple cross-linkages occur per one intermolecular cross-link formed. The average pendant reactivity for intermolecular links is 2-3 orders of magnitude lower than the monomeric vinyl reactivity. These results were found to be in accord with the observed weak M w dependence of [η] of the polymers and their stability against degradation by ultrasonic waves. The critical exponent γ suggests non-mean-field behavior in the vicinity of the gel point

Performance of Differently Cross‐Linked, Partially Fluorinated Proton Exchange Membranes in Polymer Electrolyte Fuel Cells

Abstract: A series of differently cross-linked FEP-g-polystyrene proton exchange membranes has been synthesized by the preirradiation grafting method [FEP: poly(tetrafluoroethylene-co-hexafluoropropylene)]. Divinylbenzene (DVB) and/or triallyl cyanurate (TAC) were used as cross-linkers in the membranes. It was found that the physical properties of the membranes, such as water-uptake and specific resistance, are strongly influenced by the nature of the cross-linker. Generally it can be stated that DVB decreases water-uptake and increases specific resistance; on the other hand TAC increases swelling and decreases specific resistance to values as low as 5.0 {Omega} cm at 60 C. The membranes were tested in H{sub 2}/O{sub 2} fuel cells for stability and performance. It was found that thick (170 {micro}m) DVB cross-linked membranes showed stable operation for 1,400 h at temperatures up to 80 C. The highest power density in the fuel cell was found for the DVB and TAC double-cross-linked membrane; it exceeded the value of a cell with a Nafion{reg_sign} 117 membrane by more than 60%.

Dispersion copolymerization of styrene and divinylbenzene: Synthesis of monodisperse, uniformly crosslinked particles

Abstract: Monodisperse, crosslinked polystyrene latexes were prepared by the dispersion technique. Some general observations regarding the effect of initial reagent concentrations on final particle size and size distribution are offered, in addition to a detailed discussion concerning the problems encountered with the use of the crosslinker divinylbenzene (DVB) in latex preparation. Particles synthesized in very polar media were found to reach their growth plateau sooner than those made in less polar surroundings. This trend was proposed to be the result of more effective nucleation in polar environments, which increases available surface area, thereby allowing the rapid replacement of monomer consumed within the particle phase during the polymerization. Attempts to favorably influence the growth rate and size distribution of particles during the reaction were unsuccessful, underlining the importance of the nucleation period in defining particle size characteristics. Up to 1% DVB was successfully incorporated in the synthesis of coagulum-free, monodisperse, 5 μm beads, by controlling the entry of the crosslinker into the particle phase during the major particle growth period. Latex stability is proposed to be largely dependent on the mobility of the adsorbed steric stabilizer. © 1995 John Wiley & Sons, Inc.

Synthesis of polymer-supported chiral N-sulfonylamino acids and their use in asymmetric diels-alder reaction of cyclopentadiene with methacrolein

Abstract: Crosslinked polymer-supported chiral N -sulfonylamino acids have been synthesized by two methods; namely the chemical modification method and the copolymerization method. In the chemical modification method, the chlorosulfonyl group was introduced into styrenedivinylbenzene copolymers 1 by sulfonation with chlorosulfonic acid followed by chlorination with thionyl chloride. The degree of functionalization could be well controlled by the feed ratio of chlorosulfonic acid to aromatic rings of the polymer. Treatment of l -valine with the polymer having the chlorosulfonyl group 4 gave polymer-supported N -sulfonylated l -valine 5 . An alternative approach to the synthesis of chiral polymers involves the copolymerization of monomers containing the desired chiral groups with styrene and divinylbenzene (DVB). Suspension copolymerization of chiral monomers 6 , styrene, and DVB afforded the chiral polymers 7 in good yield. The N -sulfonylamino acid group in the polymer reacted with borane or monobromoborane to form chiral oxazaborolidinone 8 , which catalyzed the Diels-Alder reaction of cyclopentadiene with methacrolein, leading to optically active cycloadduct having enantiomeric purity of 65% ee.

Coupling to produce inside-out star polymers with expanded cores

Abstract: In the production of "inside-out" star polymers where a first polymer lithium chain is formed, coupled and thereafter additional monomer is introduced to produce the "out" polymer chains, improved control over the second polymerization is obtained by coupling with a mixture of a monoalkenyl-substituted aromatic compound and a polyalkenyl-substituted aromatic compound. For example, a mixture of divinylbenzene and styrene can be used. In another embodiment, an ether is introduced after completion of the first polymer chain formation. The presence of the ether also improves the second stage chain formation. Utilization of both the mixed coupling agents and the ether, preferably a diether such as 1,2-diethoxyethane gives the greatest control over the uniformity of the second stage polymerization, making possible the production of narrower molecular weight distribution polymer having no indication of bimodal distribution. The narrow molecular weight distribution is advantageous in many applications.

Solid-liquid distribution studies of divalent metals from nitrate media using impregnated resins containing a bifunctional organophosphorous extractant (O-methyl-dihexyl-phosphine-oxide O′-hexyl-2-ethyl phosphoric acid)

Abstract: The present paper presents the results of the extraction of Zn(II), Cu(II) and Cd(II) from 0.1 M NaN0 3 at 25°C by impregnated resins containing a bifunctional extractant, incorporating phosphine oxide and phosphoric acid diester funcionalities, O -methyl-dihexyI-phosphine-oxide O′ -hexyl-2-ethyl phosphoric acid (HL). Solvent impregnated resins have been prepared by direct adsorption of HL into the styrene/divinylbenzene macroporous support, Amberlite XAD2, by using the dry impregnation method. The adsorption of HL, on the styrene/divinylbenzene macroporous support is shown by FTIR spectroscopy to be the result of only weak extractant-support interactions. The distribution coefficient of Zn(II), Cu(II) and Cd(II) was determined as a function of pH and extractant (HL) concentration in the resin phase and the data were analyzed graphically using the slope analysis method and numerically using the program LETAGROP-DISTR. The composition of the extracted species in the resin phase has been determined. Analysis of the results showed that the extraction of these metal ions can be explained assuming the formation of metal complexes in the resin phase with a general composition ML, (N0 3 ) t (HL) q where p, t, q take different values depending on the metal. An extraction reaction is proposed and the extraction constants of these species are given.

Emulsifier‐free synthesis of monodisperse core–shell polymer colloids containing chloromethyl groups

Abstract: Both the synthesis of m,p-trimethyl(vinylbenzyl) ammonium chloride (TMVBAC) and the synthesis of polymer colloids consisting of a shell of poly(vinylbenzyl chloride) grafted onto a well-defined, monodisperse poly(styrene–divinylbenzene) core are described. The preparation of the polymer latices consists of a sequence of different emulsifier-free emulsion polymerizations. First, monodisperse poly(styrene–divinylbenzene) seed latices, with 2,2′-azobis(2-amidinopropane) hydrochloride (AIBA·2HCl) as cationic initiator, are prepared under batch conditions. These latices are used for the seeded polymerization of divinylbenzene (DVB), in order to synthesize monodisperse particles, with a well-defined spherical shape, which contain a sufficient amount of pendant vinyl groups for grafting of the vinylbenzyl chloride (VBC) monomer. After the graft polymerization, the chloromethyl groups can easily be modified with a postpolymerization reaction. As an example, the amination with trimethylamine (TMA) is described. © 1995 John Wiley & Sons, Inc.

Preparation of GPC packed polymer beads by a SPG membrane emulsifier

Abstract: Monodispersed porous polystyrene beads crosslinked with divinylbenzene were prepared by in situ polymerization. For this objective, the preparation of uniform oil microdroplets in water was successfully achieved by using a Shirasu Porous Glass (SPG) membrane emulsifier (POEM® from Reika Kogyo Co. Ltd.). Separation abilities for a gel permeation chromatograph (GPC) column were discussed with polymer microbeads obtained by changing key experimental factors such as the pore sizes of the SPG membrane and diluents. Consequently, it was evident from gel permeation chromatography that the porous beads prepared by SPG emulsification can be used for the effective separation of a molecular weight range of 102 to 106.

Preparation of Divinylbenzene Homopolymeric Microcapsules with Highly Porous Membranes by in situ Polymerization with Solvent Evaporation

Abstract: Divinylbenzene homopolyineric microcapsules with porous membranes, where pores act as channels for extraction, were prepared using various solvents in the dispersed phase such as toluene, benzene, 4-methyl-2-pentanone and Exxsol D-80. Experimental evidence suggested that addition of volatile solvents resulted in the formation of divinylbenzene homopolymeric microcapsules with highly porous membranes by in situ polymerization accompanied by a solvent evaporation process. Solvent type was found to be a significant factor to change the surface morphology of the microcapsules. A membrane structure with macropores could be prepared by using volatile solvents. However, for a system of microcapsules with non-volatile solvents or without any solvent, only mesopores were formed in the microcapsule membrane. Using microcapsules with macroporous membranes, hydrochloric acid can be sufficiently extracted from aqueous solution. This infers that macropores formed by solvent evaporation function as efficient channels for extraction. The influence of preparation conditions such as solvent type and monomer concentration on extraction properties was also discussed.

Structure of some styrene–divinylbenzene copolymers

Abstract: Structures of copolymers of styrene and divinylbenzene (50% crosslinking degree) prepared in suspension polymerization in the presence of mixtures of nonsol (heptane or decane) and sol (toluene or tetralin) diluents were investigated. The studies showed that the diluents enriched with nonsol solvents resulted in an increase of pore volumes and posities for the prepared copolymers. The sol diluents affected mainly the gel regions of the polymer matrices. Isotropic swelling of the matrices prepared in the presence of toluene is the opposite of the effect observed for tetralin family copolymers. The virtual difference of both kind of matrices was demonstrated in the sorption of phenol. The tetralin family copolymers were characterized by a prolonged time for column breakthrough. © 1995 John Wiley & Sons, Inc.

Monodisperse polymer beads as packing material for high‐performance liquid chromatography. Preparation of macroporous poly(2,3‐epoxypropyl vinylbenzyl ether‐co‐divinylbenzene) beads, their properties, and application to HPLC separations

Abstract: In search for HPLC separation media with new surface chemistries, a styrene-based monomer, 2,3-epoxypropyl vinylbenzyl ether, containing reactive epoxide groups has been syn-thesized and copolymerized with divinylbenzene in a suspension polymerization. The process involves the use of size monodisperse particles that are swollen with monomer and then polymerized in the presence of a porogenic diluent consisting of a mixture of 4-methyl-2-pentanol and octane. The effect of concentration of divinylbenzene on the pore size dis-tribution and the specific surface area of the resulting uniformly sized porous poly(2,3-epoxypropyl vinylbenzyl ether-co-divinylbenzene) beads has been studied. The epoxide groups of the copolymer have been hydrolyzed and the beads used for reversed-phase chro-matography of both small molecules and proteins to show the effect of hydrophobicity of the matrix on the separation properties. Reversed-phase chromatography of alkylbenzenes follows the expected pattern while for proteins the hydrolyzed beads with the highest content of the crosslinking monomer exhibit a remarkable deviation from the predicted retention characteristics. © 1995 John Wiley & Sons, Inc.

Water sorption and water binding properties of crosslinked polyacrylamides : effect of macromolecular structure and crosslinking

Abstract: The water binding properties of crosslinked copolymers of acrylamide with tetraethyleneglycol diacrylate triethyleneglycol dimethacrylate, N,N'-methylene bisacrylamide and divinylbenzene were investigated. It was observed that the freezing water contents of these copolymers depend on the nature of the monomers and crosslinkers, as well as on the extent of crosslinking

Characterization of crosslinked polystyrene beads and their composite in SBR matrix

Abstract: Monodisperse crosslinked polystyrene (PS) beads were prepared by a reaction of semibatch emulsion polymerization with styrene monomer, divinylbenzene (DVB) crosslinking agent, and potassium persulfate (K2S2O8) initiator in the absence of emulsifier. The glass transition temperature (Tg) and the mean diameter of the beads were increased from 100 to 135°C and from 402 to 532 nm, respectively, for an incorporation of 2–10 mol % DVB. Crosslinking density was also linearly increased with DVB content. Scanning electron microscopy (SEM) photographs of styrene–butadiene rubber (SBR) composite filled with various contents of PS beads revealed that PS beads are relatively well dispersed without changing the spherical shape of the beads in all ranges of compositions. In stress–strain analysis, elongation at break and tensile strength of SBR composite were increased with the bead content. Applicability of the PS beads as a filler in SBR matrix is tested by plotting Mooney–Rivlin or Guth–Smallwood equations. However, mechanical properties of the composite with the beads were not so excellent as those of the composite with carbon black. Crosslinked PS beads are still tentative as a white color reinforcing filler on the SBR matrix. © 1995 John Wiley & Sons, Inc.

Poly(p-acetoxystyrene) resin: a prospective new support for combinatorial synthesis

Abstract: A range of spherical particulate resins have been prepared in high yield by suspension polymerisation of mixtures of p-acetoxystyrene (AS), styrene (S) and divinylbenzene. The particle size is typically 100–400 µm. The functional group content has been varied from ca. 15–60% and the degree of cross-linking from ca. 2–20%. Macroporous and gel-type species have been identified. Hydrazinolysis offers a facile and high conversion hydrolysis route to the free phenolic function independently of overall functional group loading, with the phenol content of resins being quantified by two independent methods. Further chemical modification of the phenol functions has been examined. Reaction with bromine is essentially quantitative, and attachment of dichlorotriazine residues occurs specifically by a single linkage even for heavily loaded resins. Subsequent displacement of chloride from the triazine residues by 2-aminomethylpyridine is again essentially quantitative.These transformations suggest that p-acetoxystyrene-based resins offer an attractive complementary support to chloromethylated resins for exploitation in, e.g., the combinatorial synthesis of libraries of organic compounds.

Process for producing modified cross-linked polymer particles

Abstract: A process for producing modified cross-linked polymer particles which comprises polymerizing 0.01 to 900 parts by weight of (B) a monomer component containing 50% by weight or more of at least one member selected from the group consisting of aromatic monoalkenyl compounds, acrylic acid esters, methacrylic acid esters, fluoroalkyl acrylates, fluoroalkyl methacrylates, unsaturated carboxylic acids, conjugated diene compounds, vinyl esters and organosilane compounds in the presence of 100 parts by weight of (A) cross-linked polymer particles obtained by polymerizing a monomer mixture comprising 50% by weight or more of at least one cross-linking monomer selected from the group consisting of divinylbenzene, ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate.

Interpenetrating Polymer Networks (IPNs) from Poly(metal acrylates): Synthesis and Properties

Abstract: A series of semi-interpenetrating polymer networks (semi-IPNs) based on acrylonitrile and poly(metal acrylates) of chromium, zinc, and copper were prepared. They are formed by cross-linking the acrylonitrile (monomer II) with divinylbenzene in the presence of linear poly(metal acrylate) (Polymer I). Investigations were carried out by swelling measurements, IR spectroscopy, differential scanning calorimetry, thermal analysis, and scanning electron microscopy. It was concluded that the swelling and, therefore, M c follow the order Zn-IPN > Cr-IPN > Cu-IPN. The thermal stability of the various IPNs at 200, 300, and 400 °C have the following order : Cu-IPN > Cr-IPN > Zn-IPN. The T g values have also been determined for the IPN samples.

Aminated polystyrene membranes for a fiber optic pH sensor based on reflectance changes accompanying polymer swelling

Abstract: We have prepared toughened, porous, aminated polystyrene membranes that undergo an increase in reflectance as the pH increases from 6.8 to 8.0. Vinylbenzyl chloride (VBC) is copolymerized with divinylbenzene (DVB) in the presence of a toughening agent, Kraton G1652, a styrene-ethylene, butylene-styrene triblock copolymer, and a porogenic solvent, xylene/ dodecane. The optimum formulation for sensing is 2% DVB (mol DVB/mol VBC), 2% Kraton (g Kraton/g VBC) and 40% (v/v) 2∶1 xylene: dodecane. Benzoyl peroxide is used as the initiator. The components are partially polymerized at 85 °C to a viscosity of 600–800 centipoise. The polymerization is then stopped by reducing the temperature. A drop of the partially polymerized solution is confined between two microscope slides and the polymerization reaction is completed. The resulting membrane is then swollen in 1,4-dioxan and reacted with diethanolamine. These membranes have been incorporated into a pH sensor based on changes in reflected intensity measured through a bifurcated bundle of twenty unbuffered 50/55 core/cladding glass-on-glass optical fibers with numerical apertures of 0.57. The resulting sensor is stable and requires inexpensive optical components, a red-emitting LED as the source and a silicon photodiode as the detector.

Linear Polystyrene-Grafted Silica Gels for High-Performance Liquid Chromatography

Abstract: Linear polystyrene, having a trimethoxysilyl group at one side of the terminal group, was newly synthesized and readily grafted onto porous silica gels using the terminal reactive group. Its packed column showed good selectivity based on the π-π interaction for polyaromatics as well as the usual reversed-phase mode separation for alkyl compounds. The elution behavior (including the elution order) agreed with those that were observed in non-silica-supported poly(styrene- divinylbenzene) spherical particles. However, the asymmetric factor (As) of the elution peaks for polyaromatics was much better in silica-supported polystyrene than in non-supported polystyrene; for example, the values of As for triphenylene were 1.4 and 4.7, respectively. This difference is attributable to the flexibility of the polystyrene chain.

Synthesis and metal binding behavior of hydroxamic acid resins from poly(ethyl acrylate) crosslinked with divinylbenzene and hydrophilic crosslinking agent

Abstract: Porous poly(hydroxamic acid) chelating resin was prepared by the reaction with poly(ethyl acrylate) crosslinked with divinylbenzene and hydrophilic crosslinking agent, and hydroxylamine. The hydrophilic crosslinking agents and diluent used in this article were ethylene glycol dimethacrylate or butanediol dimethacrylate, and 2,2,4-trimethyl pentane, respectively. The characterization of this type chelating resin was carried out by IR spectroscopy, density measurement, and scanning electron microscopy. Various metal binding properties such as extraction, kinetics, and selectivity were investigated with atomic absorption spectrometer and inductively coupled plasma spectrometer. Poly(hydroxamic acid) resins crosslinked with mixed crosslinking agents showed better metal extraction properties and faster adsorption rate than those crosslinked with divinylbenzene alone. And alkali treatment enhances the binding rate for metal ions because of the formation of other chelating ligands or micropores. © 1995 John Wiley & Sons, Inc.