Heterogeneous styrene–divinylbenzene copolymers in collapsed and reexpanded states

The pore structure of styrene–divinylbenzene (DVB) copolymers formed by phase separation before or after gelation was compared using apparent densities and mercury porosimetry. The copolymers were prepared with di-2-ethylhexyl phthalate (DOP) as diluent. The pore structure of copolymers formed in homogeneous gelation can collapse upon drying in the rubbery state. The collapsed pores have a mean diameter of about 100–200 Å corresponding to the interstices between the microspheres. The collapsed microspheres reexpand again during the sulfonation or chloromethylation reactions, or during the solvent exchange. The pore structure of styrene–DVB networks formed in heterogeneous gelation do not collapse on drying in the swollen state, this being a stable and permanent porosity. The critical crosslink density for transition from homogeneous to the heterogeneous gelation represents a borderline between stable and unstable porosity. The drastical change of swelling and porosity values at the critical crosslink density is due to the collapse of unstable pores.     

Pore memory of macroporous styrene–divinylbenzene copolymers

The variation of the pore structure of styrene–divinylbenzene (S–DVB) copolymer beads with the drying conditions was investigated. Macroporous S–DVB copolymer beads with various DVB contents were prepared in the presence of toluene‐cyclohexanol mixtures as a diluent. It was found that the pores of 10¹‐nm radius, corresponding to the interstices between the microspheres, collapse upon drying of the copolymers from toluene. The collapsed pores reexpand if the copolymers were dried from methanol. The collapse–reexpansion process of the pores was found to be reversible, indicating that the actual pore structure formed during the crosslinking copolymerization is memorized by the copolymer network. The magnitude of the pore structure variation increased on worsening the polymer–diluent interactions during the gel formation process due to the simultaneous increase in crosslink density distribution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1055–1062, 1999     

Styrene–divinylbenzene copolymers. Construction of porosity in styrene divinylbenzene matrices

Experimental data are presented describing the formation of porosity in styrene–divinylbenzene copolymers as a function of the organic components present during the suspension polymerization. The reaction system contains a mixture of diluents such as toluene and hexane, which results in matrices that differ significantly in pore structure from the porous resins so far known. From these data a model of the physical structure is proposed.     

Heterogeneous styrene–divinylbenzene copolymers. Stability conditions of the porous structures

The change in the porosity of styrene–divinylbenzene (S–DVB) copolymers during drying as a function of the quality of the diluent and of the divinylbenzene (DVB) concentration was investigated after drying the networks from water (maximum porosity) and from toluene (stable porosity). Two different diluents, namely toluene and cyclohexanol, were used in the polymerization system at a fixed volume fraction of the organic phase (0.50). The phase separation in toluene is accompanied by a slight deswelling of the network phase, whereas that in cyclohexanol leads to largely unswollen network phase. The stable porosity increases abruptly over a narrow range of the DVB concentration, i.e., between 40 and 50% DVB in toluene and between 15 and 25% DVE in cyclohexanol. The maximum porosity increases almost linearly with increasing DVB concentration up to a certain value, and then remains constant. The results indicate that the two main factors which determine the physical state of the swollen heterogeneous S–DVB copolymers, as well as the stability of the porous structures, are (1) the critical conversion at the incipient phase separation and (2) the degree of the inhomogeneity in crosslink distribution.     

Porous structure and swelling properties of styrene–divinylbenzene copolymers for size exclusion chromatography

Small spherical particles of styrene–divinylbenzene copolymers have been synthesized by modified suspension polymerization. The effects of divinylbenzene (DVB) contents, dilution degree of the monomers and diluent composition on the porous structure and swelling properties of the copolymers were investigated. Toluene uptakes of macroporous copolymers were considered as a result of three contributions: filling of the fixed pores, expansion of the fixed or collapsed pores, and nuclei swelling and heptane uptakes as a result of the two first contributions. The increase of DVB content in the copolymers synthesized in presence of a solvating diluent (toluene) provoked a decrease on the nuclei swelling. The increase of dilution degree with solvating diluents changed the toluene and heptane uptakes, and when the diluent–copolymer affinity was reduced, the fixed pore volume increased. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1257–1262, 1997     

Styrene–divinylbenzene copolymers: Influence of the diluent on network porosity

The formation of the permanent porosity in the classical matrix, styrene–divinylbenzene copolymers, using cyclohexane, cyclohexanol, or cyclohexanone as diluent was studied. The data concerning porous networks were corroborated with the solvent–polymer interaction factor and the cohesive energy density which are important in the prediction of copolymer porosity. Between diluents there are noticeable differences, though the diluent volume and the divinylbenzene percent strongly influence the porous structure of the network. Cyclohexanal was the most efficient diluent for building up the highest porosity even at low percents of divinylbenzene.     

Styrene — divinylbenzene copolymers,IV. Porosity changes during chloromethylation

The change in the porosity of styrene-divinylbenzene (S-DVB) copolymers during the chloromethylation reaction was investigated using apparent densities and equilibrium swelling in toluene. Maximum porosity of S-DVB copolymers does not change appreciably with the chloromethylation reaction. Only a slight decrease in the maximum porosity was observed in rigid networks, probably due to the partial destruction of the pore structure. However, with the substitution by chloromethyl groups, the degree of swelling decreases, which results in an increase in the stability of the porous structure in chloromethylated copolymers.     

Porous poly(2-hydroxyethyl acrylate) hydrogels prepared by radical polymerisation with methanol as diluent

Dynamic-mechanical and water sorption properties of porous and non-porous hydrogels have been studied as a function of their porosity and crosslinking density. Porous hydrogels with different crosslinking densities were prepared by co-polymerisation of 2-hydroxyethyl acrylate and ethyleneglycol dimethacrylate in solution in methanol. Pores were formed due to the segregation of the solvent from the polymer network during the polymerisation process. The porosity of the samples was observed by scanning electron microscopy. The pores collapse during the drying process after polymerisation but they reopen when the xerogel is immersed in liquid water. Bulk polymer networks with varying crosslinking densities were also synthesised and used as a reference in the analysis of the porous hydrogels. Water sorption from the gas phase and from the liquid phase was studied by means of equilibrium sorption isotherms and immersion experiments, respectively. Dynamic-mechanical spectroscopy conducted on the xerogels shows that the elastic modulus in the rubber-like state highly depends on the amount of solvent used in the polymerisation what is attributed to the presence of discontinuity surfaces in the xerogel although the pores are closed.     

Swelling of porous styrene–divinylbenzene copolymers in water

The swelling capacity of porous styrene–divinylbenzene (DVB) copolymers in water was studied by displacing methanol from the swollen polymer. The copolymers with different amounts of DVB were prepared in the presence of solvents with different solvating powers as inert diluents. Using a solvating solvent or its mixture with a nonsolvent as diluent, most of the obtained copolymers increase their volume in water, and the increase in volume becomes more significant with increasing the degree of crosslinking in some range of the DVB contents. The swelling capacity in water for the same copolymers with a high degree of crosslinking is linearly dependent on the dilution degree in the initial reaction mixture, to some extent. The unusual swelling behaviors in water were explained by the inner strain, which existed mainly in the less crosslinked domains between the highly crosslinked microgel particles, which are released in the course of swelling of the copolymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 536–544, 2000     

The effect of corrosion particles present in water solutions on the behavior of strong acid cation-exchange resins during the process of cobalt removal

The effect of the presence of corrosion particles on the behavior of different structure types of cation-exchange resins during the adsorption process of ⁶⁰Co from water solutions was studied. Comparative valuation of sorption behavior and capacity of polyreticular and monoreticular structure type cation-exchangers was carried out. It was found that the ion-exchange filtration efficieny depends upon the presence of corrosion particles on the surface of ion-exchange beads and in their pore structure. The cation-exchange process of ⁶⁰Co is affected differently by different structure type ion-exchange resins. The fouling phenomenon caused by iron-corrosion particles during the water clean-up process at a RWCU system in BWR and by CVSE demineralizers in PWR dose not affect negative phenomenon for ion-exchange behavior of ion-exchange resins to remove polyvalent ions from the water. The polyreticular cation exchanger Amberlite 200C can better remove ⁶⁰Co cations from water solutions than the monoreticular (gel type) cation-exchanger Amberlite IR 120. Evidently this is due to the true porous macroreticular structure of the cation-exchange beads. In parallel with the ion-exchange processes, the sorption process of the corrosion products situated on the larger surface area of the true physical pore structure of Amberlite 200C also plays an important role. The information obtained will be very useful to the technological service of nuclear power stations.     

Macroporous styrene-divinylbenzene copolymers: Formation of stable porous structures during the copolymerization

Summary The variation of the pore structure of styrene-divinylbenzene (S-DVB) copolymer beads depending on the polymerization time was investigated. Macroporous S-DVB copolymer beads with 10 mol % DVB content were prepared in the presence of cyclohexanol as a diluent. It was found that the stable pores in S-DVB copolymers mainly form at an early stage of the copolymerization, i.e., at the gel point. Thus, the early phase separated portions of the network, where the crosslink density is locally high, do not collapse on drying and illustrate the stable part of the porosity of S-DVB copolymers. The number of stable pores does not change much during the whole course of the copolymerization. The maximum porosity first decreases on rising the post-gelation time due to the decreasing degree of dilution of the gel phase. Then, it increases continuously due to the increasing crosslink density of the gel. The pores formed at a later stage of the copolymerization are unstable and they collapse during the drying process. This is due to the lower crosslink density of the network regions forming later. Received: 27 February 1998/Revised version: 18 June 1998/Accepted: 18 June 1998     

Porous maleic anhydride–styrene–divinylbenzene copolymer beads

The formation of the porosity and the pore stability in maleic anhydride–styrene–divinylbenzene (MAn–St–DVB) copolymer beads were investigated using the apparent density measurements of the samples dried from methanol (maximum porosity) and from dioxane (stable porosity). The copolymer beads were prepared by the suspension polymerization method in glycerol instead of water as the dispersing medium. A toluene–dioxane (1:1) mixture was used as the diluent at a fixed volume fraction of the organic phase (0.47). Compared to St–DVB copolymers prepared in the presence of nonsolvating diluents, porous MAn–St–DVB copolymers are obtained at relatively low DVB concentration, i.e., at 1–3% DVB. The porosity of the copolymers increases with decreasing MAn concentration in the feed due to the decrease in the copolymer yield. The results of the elemental analyses and titrimetric methods indicate that approximately only half of the MAn units in the copolymer are able to react with amine or with water. A possible rearrangement of the MAn units into the cyclopentanone structures was suggested.     

On the structure of macroreticular styrene-divinylbenzene copolymers

The influence of the removal of various diluents, pore forming agents from the porous styrene-ethylstyrene-acrylonitrile-divinylbenzene copolymers on the structure of the matrix was investigated by several methods. The most advantageous pathway to preserve the initial structural edifice of the porous networks performed in the presence of solvating diluents consisted in the removal of the inert media with methanol as it was noticed from the experimental data. If the steam treatment is applied, the collapse effect takes place and the anion exchangers prepared from such matrices exchange/adsorb less dye stuff by comparison with ones formed from beads treated with methanol, because the pore size was changed. It was also noticed that the porous copolymers performed in the presence of the solvating diluents (mixtures of solvatings and precipitants) swell very well in methanol though it is a precipitating medium for the polystyrenic macromolecular chains.     

Formation of macroporous styrene–divinylbenzene copolymer networks: Theory vs. experiments

A kinetic–thermodynamic model is presented to predict the total porosities of macroporous copolymer networks formed by free‐radical crosslinking copolymerization of styrene (S) and commercial divinylbenzene (DVB, a mixture of meta and para DVB isomers and ethylstyrene). The kinetic part of the model predicts, based upon the method of moments, the concentration of the reacting species, the gel, and sol properties as a function of the monomer conversion. The thermodynamic part of the model describes the phase equilibria between the gel and separated phases during the S–DVB copolymerization and predicts the volume of the separated phase, which is the pore volume of the crosslinked material, as a function of the monomer conversion. Calculation results show that the porosity of S–DVB networks increases as the polymer–diluent interaction parameter increases, or as the initial monomer concentration decreases. Porosity also increases on increasing the DVB content of the monomer mixture. Both the polymerization temperature and the initiator concentration affect significantly the kinetics of S–DVB copolymerization. However, the final porosity of S–DVB copolymers is largely insensitive to the amount of the initiator and to the polymerization temperature. All calculation results are in accord with the experimental data published previously. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2181–2195, 1999     

Pore collapse during the fabrication process of rubber‐like polymer scaffolds

Rubbery polymer scaffolds for tissue engineering were produced using templates of the pore structure. The last step in the fabrication process consists of dissolving the template using a solvent that, at the same time, swells the scaffolding matrix that was a polymer network. Sometimes the polymer matrix is stretched so strongly that when the solvent is eliminated, i.e., the network is dried, it shrinks and is not able to recover its original shape and, consequently, the porous structure collapses. In this work we prepared, using the same fabrication process (the same template and the same solvent), a series of polymer scaffolds that results in collapsed or noncollapsed porous structures, depending on the polymer network composition. We explain the collapse process as a consequence of the huge volume increase in the swelling process during the template extraction due to the large distance between crosslinking points in the scaffolding matrix. By systematically increasing the crosslinking density the porous structure remains after network drying and the final interconnected pores were observed. It is shown that this problem does not take place when the scaffolding matrix consists of a glassy polymer network. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1475–1481, 2007     

Carbon aerogels, cryogels and xerogels: Influence of the drying method on the textural properties of porous carbon materials

Carbon materials with tailored texture can be obtained from drying and pyrolysis of resorcinol-formaldehyde gels. The pore texture of both dried and pyrolyzed material depends on the drying process. Several more or less expensive methods (supercritical drying, freeze-drying, evaporative drying) were tested in order to determine which process is the most suitable for the synthesis of a porous carbon with a definite texture. Supercritical drying leads to the highest pore volume and the widest texture range, but residual surface tensions and shrinkage are not avoided when the pore size is small or when the material density is low; this hampers to fix both the pore volume and the pore size easily. Monoliths are very difficult to obtain by freeze-drying, and the appearance of huge channels due to ice crystal growth at high dilution ratio hinders the fabrication of low density materials. Moreover, gels with small pores do not remain frozen throughout drying, which leads to surface tensions and shrinkage. Although generally replaced by more complicated techniques, evaporative drying is suitable when dense carbons are needed or when the only selection criterion is the pore size: all pore sizes are reachable, but this parameter is in this case strongly correlated to the pore volume.     

Structure of some styrene–divinylbenzene copolymers

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.     

Water‐swellable hydrophobic porous copolymer resins based on divinylbenzene and acrylonitrile. I. Water‐swelling behavior

Hydrophobic porous copolymer resins based on divinylbenzene (DVB) and acrylonitrile (AN) could be prepared as directly swellable in water by using purified DVB (98.8%) and technical DVB (79.3%) in the presence of 1,2‐dichloroethane as porogen. Compared with the resins based on DVB and methyl acrylate (MA/DVB resins), the AN/DVB resins thus obtained are water‐swellable over a wider range of copolymer compositions, and the swelling ability of the AN/DVB resins in water was further confirmed by investigating the water‐swelling behavior of the AN/DVB resins undergoing solvent treatment. The copolymer composition (AN and DVB contents) of the resins and the property of the porogen affect the water‐swellable behavior of the AN/DVB resins profoundly. The results in this paper provide additional evidence to support the hypothesis that the swelling ability of a hydrophobic porous copolymer in water originates from the existence of the inner stresses in the strained polymer network of the resins and the weak interaction between polymer and water that is negligible in the case of a conventional hydrophobic polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2041–2049, 2004     

Synthesis of strong acid resins from macroporous styrene–divinylbenzene copolymers: Is diluent extraction step necessary?

Strong acidic cation‐exchange resins derived from the same batch of styrene–divinylbenzene copolymers with and without acetone washing are compared with respect to ion‐exchange capacity and leachable organics. The capacity was the same throughout 10 cycles of resin exhaustion and regeneration. Ultraviolet spectra showed the same level of leachable organics in the two cases compared. Fourier transform infrared spectra were also similar. The results are explained on the basis of the fact that n‐heptane and toluene used as diluents were removed through a steam distillation phenomenon during the copolymer curing step. Residual homopolymers were washed away with water after the sulfonation of the copolymers just like acetone washing of them from the copolymer. Acetone washing, which accounts for about 80% of the cost of the chemicals in the copolymer synthesis, can be eliminated in the case of diluents such as n‐heptane and toluene, making the process simple, economical, and environment friendly. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Synthetic resins. XVIII. Chelation ion exchange properties of 2,4-dinitrophenylhydrazone of 4-hydroxy acetophenone–formaldehyde resins

A large number of copolymers were synthesized by condensing 2,4-dinitrophenyl hydrazone of 4-hydroxy acetophenone (4HA 2,4 DNPH) with substituted benzoic acids/phenols and formaldehyde in the presence of NaOH or HCl as catalyst. The resins were characterized by IR spectra. The decomposition temperature, solubility parameter, and viscositv of the polymers have been determined. The ion-exchange properties have been studied using the batch equilibrium method. The measurement of the distribution of a given metal ion between an aqueous solution and the resins has been performed. The investigation was carried out over a wide range of pH and varying the ionic strength of the medium. © 1992 John Wiley & Sons, Inc.