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     

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     

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.     

Synthesis and characterization of styrene–N-butyl maleimide copolymers using iniferters containing thiyl end groups

The radical homopolymerization of styrene or copolymerization of styrene (S) with N-butyl maleimide (I) initiated by tetraethylthiuram disulfide was used to prepare macroinitiators having thiyl end groups. The S–I copolymers from the feeds containing 30–70 mol % I showed approximately alternating composition. The rate of copolymerization and molecular weights decreased with increasing maleimide derivative concentration in the feed; homopolymerization of I alone did not proceed. The macroinitiators served for synthesis of further S–I copolymers. Using polystyrene macroinitiator and the S–I copolymer with thiyl end groups in the polymerization of S–I mixture and styrene, respectively, the copolymers containing blocks of both polystyrene and alternating S–I copolymer were obtained. The copolymerization of S–I mixture initiated with the S–I copolymer bearing thiyl end groups led to the extension of macroinitiator chains by the blocks of alternating copolymer. The presence of the blocks in the polymer products was corroborated using elemental analysis, size exclusion chromatography, and differential scanning calorimetry. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 755–762, 1998     

Porous bead aliphatic–aromatic methacrylate copolymers III. The effect of diluent on porous structure formation of MMA–DMN copolymers

Porous bead copolymers of di(methacryloyloxymethyl)naphthalene and methyl methacrylate have been synthesized using a mixture of isooctane and toluene as a diluent of the monomer system. The copolymers obtained exhibit similar specific surface areas and enhanced specific pore volume as compared to those prepared in the presence of dodecane and toluene. Their submicroscopic structure is visualized as first-order organization of microglobules similarly to PPS-type styrene–divinylbenzene copolymers.     

The influence of the diluent system on the porous structure formation of copolymers based on 2‐vinylpyridine and divinylbenzene. Diluent system. III. heptane/methylethylketone

The effects of the diluent mixture's composition and crosslinking degree [divinylbenzene (DVB)] on the porous characteristics of the anion‐exchange resins based on 2‐vinylpyridine (2VP) and DVB, synthesized by suspension polymerization, in the presence of a diluent mixture constituted of heptane (HEP) and methyl ethyl ketone (MEK) at different proportions, were evaluated. The resins were characterized by mercury porosimetry, nitrogen adsorption (Brunauer–Emmett–Teller (BET) method surface area determination), apparent density, and swelling in methanol. The optical appearance of the copolymer beads was examined by optical microscopy. It was found that the development of porosity was attained whenever the content of methyl ethyl ketone in the diluent mixture was increased for all DVB contents employed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 666–669, 2004     

Characterization of macroporous 1‐vinyl‐2‐pyrrolidone copolymers obtained by suspension polymerization

Radical suspension copolymerization of 1‐vinyl‐2‐pyrrolidone (VP) with three different cross‐linkers: divinylbenzene (DVB), trimethylolpropane trimethacrylate (TRIM), and di(methacryloxymethyl) naphthalene (DMN) was used to prepare macroporous microspheres. During the copolymerization, the mixture of toluene and n‐dodecane as a pore‐forming diluent was used. All samples were characterized in terms of particle size and distribution, nitrogen content, specific surface area total pore volume, and pore size distribution. It was found that specific surface area of the obtained beads is strongly dependent on the diluent system and the type of cross‐linker and achieves value from 27 to 845 m²/g. To determine the influence of chemical structure of cross‐linkers on the selectivity and polarity of the copolymers, inverse gas chromatography was applied. In addition, VP–DVB and VP–DMN copolymers were modified by sulfonation into cation‐exchangers with cation exchange capacity equal 1.98 and 2.31 mmol/g, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and properties of porous copolymers of 4,4′-bismaleimido diphenyl methane and styrene

Porous copolymers of 4,4′-bismaleimido diphenyl methane and styrene of different molar ratio of monomers were synthesized. The copolymers beads were prepared by the suspension polymerization method in the presence of aqueous solution of poly(vinyl alcholo) and calcium chloride as a dispersing medium. Benzyl alcohol-n-decyl alcohol (80 : 20; V/V) mixture was used as the diluent. Independently of the ratio of monomers all copolymer samples indicate stable porosity and high mechanical and thermal stabilities. The results from the SFE show that instead of extraction in a Soxhlet apparatus, some unreacted monomers and diluents remain in the copolymers porous structure. Real compositions of the copolymers found from the results of CHN analyses were different from those assumed. © 1996 John Wiley & Sons, Inc.     

Synthesis,characterization and properties of amphiphilic butadiene-oxyethylene multiblock copolymers

Butadiene-oxyethylene multiblock copolymers were synthesized via coupling reaction of telechelic α,ω-dihydroxypolybutadiene (PB) and poly(ethylene glycol) with tolylene-2,4-diisocyanate. The poly(oxyethylene) (PEO) content of the purified copolymer was determined by elemental analysis and the structural parameters were calculated from number-average molecular weights of the purified copolymer, determined by membrane osmometry, and those of the prepolymers, determined by vapor pressure osmometry. The total number of blocks varied from 60 to 100. Transmission electron microscopy showed the existence of multiphases in the copolymer. Wide angle X-ray diffraction indicated that the crystallinity increased from 0 to 50% with increasing weight ratio of PEO/PB. These multiblock copolymers exhibit excellent emulsifying properties, as compared to the multiblock copolymers or graft copolymer of oxyethylene and styrene. Only 0.1 g of polymer was needed to make 100 mL of a water/toluene (9:1, w/w) mixture form an emulsion completely. When the weight ratio of water/toluene was changed from 9:1 to 7:3 or the molecular weight of PEG from 6000 to 2000, the oil-in-water type emulsion was changed to water-in-oil type. The copolymers also showed a good phase transfer catalytic effect when applied to the Williamson reaction. Conversion of potassium phenolate into butyl phenolate reached over 95% when the multiblock copolymer containing 3 mmol of PEO was used for 1 g potassium phenolate, whereas no reaction occurred without using the multiblock copolymer at 90°C for 4 h.     

Correlations for prediction of specific surface area and bulk and apparent densities of porous styrene‐divinylbenzene copolymers

Macroporous styrene‐divinylbenzene copolymers with different degree of crosslinking were prepared by suspension polymerization in presence of different binary mixtures of toluene and heptane, as diluent. Specific surface area, bulk and apparent densities, and pore volume of the resulting beads were determined experimentally. Applying the least square method to the experimental data, correlations for prediction of these properties were obtained. Effects of divinylbenzene concentration, diluent to comonomer volume ratio, and composition of the diluent mixture were considered in developing the aforementioned correlations. The influence of the reaction recipe on porous structure of the samples was also studied using scanning electron microscope (SEM). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Compositional heterogeneity,thermostable, and shape memory properties of ethylene oxide-ethylene terephthalate segmented copolymer with long soft segment

Ethylene oxide-ethylene terephthalate segmented copolymers (EOET) with long PEO segment or high PET content have showed an obvious compositional heterogeneity. The EOET copolymers with compositional heterogeneity could be separated into soluble and insoluble fractions by extraction with chloroform. ¹H-NMR measurements showed that the former contains much lower PET content than the average content value, and the latter is in reverse. DSC results revealed that PET segments in the latter would crystallize more easily, but in the former PEO segments exhibits more intensive melting peak. The thermogravimetric behaviors of EOET copolymers were between PEO and PET homopolymers. The EOET copolymers with serious compositional heterogeneity showed two stages of weight loss. TGA was sensitive to indicate the compositional heterogeneity in EOET copolymers. The compositional heterogeneity could impart a great influence on the shape memory behavior of EOET copolymers. The recovery curve of EOET copolymers with serious compositional heterogeneity also can exhibit two stages of deformation recovery. Generally, the component with worse memory behavior in EOET copolymer is an unfavorable factor, and the addition of EOET copolymer with better memory behavior into the blend is a favorable factor for the blend system. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 947–955, 1998     

Studies of porous polymer gels. II. Structure and porosity of moderately crosslinked poly(methacrylic acid) gels

The porosity of suspension copolymers of methacrylic acid (MA) and divinylbenzene (DVB) has been studied. The copolymers were prepared both directly from monomer blends and with toluene or n-octane as inert diluents. The pore volume and radii of pores were larger for copolymers containing 5.0% of DVB than those for copolymers containing 9.1% of DVB. The volume and radii of pores increased with increasing diluent content, but the effect of n-octane was more pronounced than that of toluene. Based on considerations of monomer reactivities and copolymer-diluent and copolymer-unreacted monomer interactions, the following model of structure of MA and DVB copolymers has been proposed: The copolymers are composed of microgels interconnected into a rigid skeletonlike structure, surrounded by lightly crosslinked and unentangled poly(methacrylic acid) chains.     

Swelling of porous ethylvinylbenzene–divinylbenzene copolymers and the stability of the pore structure

A series of porous ethylvinylbenzene–divinylbenzene (EVB–DVB) copolymers with DVB contents ranging from 22.0 to 98.4% were prepared using various amounts of toluene as the inert diluent, and studies were made on the copolymers as to their swelling properties, the stability of their pore structure, and the relationship between swelling in nonsolvents and variations in their pore structure. The swelling experiments showed that the ethanol regains of the copolymers were closely related to the course of phase separation, and the increases in both the DVB content and the volume fraction of monomers in the organic phase resulted in enhanced capacity of the highly crosslinked copolymers to keep swelling in solvents having extremely small affinity for these copolymers. The variations in pore structure, sometimes quite considerable, for copolymers pretreated with different solvents were observed even at DVB content up to 98.4% and further studies showed that a consistent relationship existed between pore volume variation and volume swelling ratio in ethanol for toluene modified copolymers.     

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.     

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     

ABA-type block copolymers containing poly(dimethylsiloxane) and ketonic resins

Block copolymer containing segments of poly(dimethylsiloxane) (PDMS) and ketonic resins were synthesized. Dihydroxy-terminated PDMS were reacted with the isophorone diisocyanate (IPDI) to obtain the diisocyanate-terminated PDMSs (urethane). These urethanes were reacted with reactive hydroxyl groups in the cyclohexanone–formaldehyde, acetophenone–formaldehyde, and in situ melamine-modified cyclohexanone–formaldehyde resins. Formation of block copolymers was illustrated by several characterization methods, such as chemical and spectroscopic analysis and gel permeation chromatography. The solubilities of the block copolymers were determined, and their surface properties were investigated by contact angle measurements. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 643–648, 1998     

Preparation and uranyl ion adsorptivity of macroreticular chelating resins containing phosphono groups

Macroreticular copolymer beads were prepared by suspension polymerization of styrene, bis(2-chloroethyl) vinyl phosphonate (CEVP) and divinylbenzene (DVB) in the presence of toluene as diluent. The bis(2-chloroethyl) phosphonate groups on the bead surface were converted into phosphono groups by hydrolysis with dilute nitric acid. For the additional enrichment of phosphono groups, the copolymers were phosphorylated at the phenyl rings with phosphorus trichloride in the presence of aluminum chloride and hydrolyzed and oxidized with dilute nitrics acid. The investigations on metal ion chelation characteristics of the bead-type copolymers revealed that they have very high adsorptivity toward uranyl ions and good chemical resistance under acidic and alkaline media. It was also found that the phosphono group-containing copolymer beads are effective adsorbents for other heavy metal ions such as Pb²⁺, Hg²⁺, Cd²⁺, and Cu²⁺.     

溶剂对rac-Et[Ind]_2ZrCl_2/MMAO催化体系催化乙烯-降冰片烯共聚合的影响

采用乙基桥连二茚基二茚基二氯化锆(rac-Et[Ind]2ZrCl2)/MMAO催化体系催化乙烯/降冰片烯共聚合,比较了甲苯、苯、正己烷、环己烷及其混合溶剂作为反应介质对共聚合活性及共聚物结构的影响。通过差示扫描量热分析(DSC)对共聚产物进行了热力学性质的表征。结果表明,聚合活性和产品的玻璃化转变温度(Tg)在不同溶剂体系中有着显著的差异,在相同聚合条件下,当甲苯/苯体积比为80/20时,聚活活性达到最高,但产品的Tg和降冰片烯的插入率较低。     

Copolymerization and addition of styrene and N‐phenylmaleimide in the presence of nitroxide

The copolymerization and addition reaction of styrene (S) with N‐phenylmaleimide (PMI), either neat or in xylene, have been found to proceed at 125°C in the presence of 2,2,6,6‐tetramethylpiperidin‐1‐yloxy (TEMPO) radicals. TEMPO‐terminated alternating S‐PMI copolymers and comonomer adducts were obtained. The amounts of the low molecular weight compounds increased with the increasing content of PMI in the initial mixture. The reaction suggests formation of monofunctional unimolecular initiators. In the autopolymerization of neat comonomers, a mediating role of TEMPO was observed. The synthesized copolymers containing TEMPO end groups were used as macroinitiators to initiate polymerization of styrene. The molecular weight distributions of resulting poly(styrene‐alt‐N‐phenylmaleimide)‐block‐polystyrene copolymers indicated the presence of both low molecular weight termination products and some copolymer precursor. The copolymers and comonomer adducts were characterized using the nitrogen analysis, size‐exclusion chromatography (SEC), and NMR spectroscopy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1093–1099, 2000     

Reactive Extraction of Levulinic Acid Using TPA in Toluene Solution: LSER Modeling,Kinetic and Equilibrium Studies

Abstract

Levulinic acid, a carboxylic acid containing ketone structure, is a clear to brownish semi‐solid melting at 37°C; soluble in alcohol, ether, and chloroform, levulinic acid can be used as an acidulant in foods and beverages. Organic solutions of amines are being used increasingly to separate organic acids from aqueous mixture solutions by reactive extraction. The design of an amine extraction process requires kinetic data for the acid–amine+solvent system used. Kinetic studies for the extraction of levulinic acid from aqueous solution with tripropylamine (TPA) diluted in toluene were carried out using a stirred cell for kinetic studies. Equilibria for levulinic acid extraction by TPA in toluene as a diluent have been determined. All measurements were carried out at 298.15 K. The equilibrium data were also interpreted by a proposed mechanism of complexation by which (1∶1) and (2∶1) acid‐amine complexes are formed. Kinetics of extraction of levulinic acid by TPA in toluene has also been determined. The results of the liquid‐liquid equilibrium measurements were correlated by a linear solvation energy relationship (LSER).