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     

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.     

Porous structure of highly crosslinked styrene-divinylbenzene copolymers

Porous structure of two series of styrene (S)-divinylbenzene (DVB) copolymers has been studied. The copolymers were prepared by suspension copolymerization of the monomers (50 wt.-% of DVB) in the presence of heptane-toluene mixtures as inert diluents. The fraction of diluents in the polymerization system or heptane: toluene ratio was changed. Both the pore volume and specific surface area increase as does dilution or the fraction of heptane in diluents, but the measured values change depending on sample pretreatment. A mechanism of structure built up is discussed and the porosity changes explained in terms of a microsyneresis of inhomogeneous S-DVB copolymer gel.     

Heterogeneous Structures in the Synthesis of Hydrophobic Lauryl Acrylate-Styrene-Ethylene Glycol Dimethacrylate Copolymer Particles

Novel crosslinked hydrophobic lauryl acrylate-styrene-ethylene glycol dimethacrylate copolymer particles were synthesized with heterogeneous structures by radical suspension copolymerization with benzoyl peroxide as the initiator. Ethylene glycol dimethacrylate was used as a crosslinking agent; toluene, cyclohexanol, 1-octanol and liquid paraffin were used as porogens. The effects of the crosslinking monomer and porogens on the morphologies of the copolymer microspheres were investigated. The copolymers were characterized by FTIR, SEM and swelling in toluene. Permanent pores remained in the dried polymeric particles prepared with nonsolvating porogens at certain crosslink densities as indicated by SEM pictures. The results of swelling revealed that 1-octanol was the most effective porogen, leading to the LA-S-EGDMA copolymer particles with maximum porosity and optimized spheric morphology. Furthermore, lower crosslink density and higher porogen contents promote the formation of porous morphology.     

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.     

Styrene-divinylbenzene copolymers,V. Inhomogeneity in the structure and the average degree of swelling

The compositional inhomogeneity and the average degree of swelling of heterogeneous styrene-divinylbenzene (S-DVB) copolymers were investigated using two morphological features of porous copolymers. At a fixed volume fraction of a nonsolvating diluent, the extent of inhomogeneous crosslinking increases with increasing DVB concentration. In addition, the crosslinking density of less crosslinked regions of the network decreases as the DVB concentration increases. The experimental results can be explained by the microgel-model of the network formation. The average degree of volume swelling can be predicted from the composition of the starting monomer mixture and from the porosity of the final copolymer dried from water. Depending on these parameters, the changes in the value of v₂, the volume fraction of copolymer in the swollen gel, and the conditions for the pore stability are discussed.     

Inhomogeneity of gel and microsyneresis in porous styrene-divinylbenzene copolymers

The porosity of styrene-divinylbenzene copolymers prepared by suspension copolymerisation of the monomers carried out in the presence of inert diluent changes due to solvent pretreatment is investigated. The changes seem to reflect the inhomogeneity of copolymer gel. Various portions of it are transferred from the rubber-like into the glassy state at different stages of either swelling solvent exchange or the drying process. A microsyneresis, i.e. a local collapse of loosely crosslinked gel portions not followed by a shrinkage of the whole system, leads to the porosity changes.     

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.     

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.     

Characteristics of phosphinated styrene-divinylbenzene copolymer containing RuCl2(PPh3)3 for 1-hexene isomerization

Summary Chloromethylated styrene-divinylbenzene(S-DVB) copolymer beads were prepared in macroporous type via direct copolymerization of chloromethylstyrene and divinylbenzene and then phosphinated. Dichlorotris(triphenylphosphine)ruthenium, RuCl₂(PPh₃)₃, was anchored on the phosphinated S-DVB copolymer, and then applied to the isomerization of 1-hexene. The physical properties of the catalysts varied with degree of crosslinking and type of pore-forming agents. Anchoring the ruthenium complex onto the phosphinated S-DVB resin favored trans-isomer and stabilized the catalyst in the isomerization of 1-hexene comparing with the homogeneous reaction. Solvent effects on catalytic activities of polymer-anchored catalysts were also discussed.     

Styrene–divinylbenzene copolymers. II. The conservation of porosity in styrene–divinylbenzene copolymer matrices and derived ion-exchange resins

The collapse of pores in styrene–divinylbenzene copolymers and corresponding ion-exchange resins was studied during the removal of solvating liquids. The process can be followed in a most simple way by measuring the volume of the bead-shaped copolymers upon drying. Other parameters observed during drying were the apparent density and incidently the internal surface. The collapse of pores is considered to be a result of cohesional forces when solvated polymer chains are approaching each other by loss of solvent. The effect will thus be more pronounced in gel-type networks than in porous ones. In porous networks, the effect will be stronger in smaller pores than in larger ones. It is shown that crosslinks, increasing the rigidity of the structures, will favor the conservation of porosity. In ion-exchange resins the pore stability is best when the material is in its lowest state of hydration. Generally, the collapse of pores is a reversible process. The collapsed material can in most cases be reswollen by the proper choice of solvent.     

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.     

Modification of porous copolymers network based on acrylonitrile

Summary The preparation of a chelating ion-exchange network based on acrylonitrile was carried out by chemical modification with hydroxylamine. The beads of resin were synthesized by aqueous suspension copolymerization of acrylonitrile (AN), styrene (STY) and divinylbenzene (DVB). The influence of diluent used in the suspension polymerization on the structure of the resulting copolymers was evaluated. The diluents employed were heptane (HEP), toluene (TOL) and anisole (ANI). It was found that the AN incorporation into copolymer structure was dependent on the diluent used. Conversion of nitrile groups into the amidoxime was conducted by treatment with hydroxylamine under alkaline solution. The resins were characterized by apparent density, surface area, average pore diameter, elemental analysis (CHN), FTIR and optical microscopy. Based on the results obtained, it was possible to control the porosity by diluent employed in the synthesis and to modify chemically a resin containing nitrile groups by hydroxylamine reaction. Received: 6 October 2001/Revised version: 2 April 2002/ Accepted: 11 April 2002     

Structure and protein separation efficiency of poly(N-isopropylacrylamide) gels: Effect of synthesis conditions

Crosslinked poly(N-isopropylacrylamide) (PNIPA) gels with different crosslink densities in the form of rods and beads were prepared by free-radical crosslinking copolymerization. Solution and inverse suspension polymerization techniques were used for the gel synthesis. The gels were utilized to concentrate dilute aqueous solutions of penicillin G acylase (PGA), bovine serum albumin (BSA), and 6-aminopenicillanic acid (6-APA). The discontinuous volume transition at 34°C observed in the gel swelling was used as the basis of concentrating dilute aqueous protein solutions. PNIPA gels formed below 18°C were homogeneous, whereas those formed at higher temperatures exhibited heterogeneous structures. The water absorption capacity of PNIPA gels in the form of beads was much higher, and their rate of swelling was much faster than the rod-shaped PNIPA gels. It was also found that the polymerization techniques used significantly affect the properties of PNIPA gels. The separation efficiency decreased when the protein molecules PGA or BSA in the external solution were replaced with small-molecular-weight compounds, such as 6-APA. The protein separation efficiency by the gel beads increased to 100% after coating the bead surfaces with BSA. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 805–814, 1998     

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     

Effect of diluents on the porous structure of crosslinked poly(methyl methacrylate) beads

Summary Copolymer beads based on methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) were prepared by suspension polymerization technique. Two different solvents, namely toluene and cyclohexane, were used as the diluents in the polymerization system. It was found that toluene produces pores of radii 2 to 10 nm corresponding to the interstices between the nuclei. In the case of cyclohexane as the diluent, formation of large pores with a broad size distribution from 10 to 1000 nm were observed. These sizes correspond to the spaces between the microspheres and the aggregates forming the copolymer beads. The results indicate that, as in porous styrene-divinylbenzene copolymers, the solvating power of the diluent present during the network formation is mainly responsible for the structural characteristics of porous MMA/EGDM copolymer beads.     

Crosslinking reaction of glycidyl methacrylate copolymers containing oxime-urethane groups using photogenerated pendant amines

Summary Copolymers containing epoxy and oxime-urethane groups were prepared by copolymerization of glycidyl methacrylate (GMA) and benzophenone oxime allylurethane (BAU). The physical properties of these copolymers were characterized by GPC, NMR and DSC analyses. Photo-crosslinking reaction of the copolymers were studied by measuring the insoluble fraction of copolymer films under various reaction conditions. The degree of cross-linking reaction increased with irradiation time, heating temperature and the amount of BAU units in the copolymer. UV and IR absorption spectral studies indicate that thermal cross-linking reaction of the copolymer was catalyzed by the pendant photogenerated amines. Received: 3 March 1998/Revised version: 7 April 1998/Accepted: 15 April 1998     

Macroporous polyamines containing cyclodextrin: Synthesis,characterization, and sorption properties

Macroporous beads containing N-vinyl-tertio-butyl carbamate (NVTBC) have been prepared by suspension copolymerization using divinylbenzene as crosslinking agent. After solvolysis, parent copolymers containing vinylamine (VA) were functionalized by β-cyclodextrin (β-CD) using the mono-tosyl derivative of β-CD as the intermediate (β-CDOTs). Several copolymers with various degrees of substitution were synthesized. Several factors (reaction time, amounts of the reactants, composition of solvent, and temperature) were studied. Characterization was achieved by crosspolarization magic angle spinning nuclear magnetic resonance spectroscopy (CPMAS NMR). The textural features (specific area and porous volume) of the beads were also determined. These insoluble macroporous copolymers containing β-CD were then used for the recovery of various organic pollutants from aqueous solutions. Some preliminary studies (time, concentration, kinetics, and β-CD content) are presented here. The results of sorption experiments show that they exhibit high sorption capacities toward substituted benzene derivatives. The mechanism of sorption is an acid-base interaction due to the amino groups of the polymer network and/or the formation of an inclusion complex due to the β-CD molecules. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1419–1427, 1998     

Porous bead aliphatic-aromatic methacrylate copolymers,II. The estimation of the structure of methyl methacrylate—di(methacryloyloxymethyl)naphthalene copolymers by means of scanning electron microscopy

Scanning electron microscopy was used to obtain complementary data concerning the surface and inner structure of porous aliphatic-aromatic methacrylate copolymers. Depending on the amount of a porogenic (toluene and dodecane) or crosslinking agent, the suspension copolymerization of methyl methacrylate and di(methacryloyloxymethyl)naphthalene (DMN) leads to either porous polymers with measurable surface areas or gel type polymers with no measurable surface areas. Porous polymers are visualized as one or two level organization of microglobules within the beads whereas gel type polymers exhibit no pores or microglobules neither in the surface layer nor in the bead interior.     

Synthesis and characterization of styrene–divinylbenzene loaded with di(2-ethylhexyl)phosphonic acid. I. Influence of diluent mixture on the porous structure of the copolymer

Styrene–divinylbenzene copolymers were synthesized in the presence of di(2-ethylhexyl)phosphonic acid (EHEHPA) to be applied in the separation of rare earths by extraction chromatography. The copolymers were prepared by suspension polymerization in the presence of pure EHEHPA or in a mixture with isooctane, heptane, or toluene. The composition of the diluent mixture employed in the synthesis was varied. The apparent density, fixed pore volume, and surface area of the copolymers were determined. The content of EHEHPA retained in the copolymer beads was also determined, and it was found to be independent of the porous structure of the copolymer matrix. That content was only dependent on the amount of EHEHPA present in the diluent mixture. The toluene/EHEHPA mixtures produced the copolymers with the best properties required for extraction chromatography supports. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:781–787, 1998