Diffusion‐Controlled Particle Growth and its Effects on Nucleation in Stirred Emulsion Polymerisation Reactors

Summary: Particle formation and growth in the batch emulsion homo‐polymerisation of styrene and methyl methacrylate monomers under diffusion‐controlled conditions were studied. The polymerisations started with two stratified layers of a monomer and water containing an initiator and a surfactant, with the water layer being gently stirred. Because of limitations in monomer transport, the rate of particle growth was substantially reduced and as a result a large number of polymer particles formed.

Schematic presentation of the highly diffusion‐controlled polymerisation.     

Macroporous Polymers with Hierarchical Pore Structure from Emulsion Templates Stabilised by Both Particles and Surfactants

Inspired by natural porous materials, such as wood, bamboo and spongy bone consisting of individual structural units that are hierarchically arranged to optimise mechanical properties such as strength and toughness, synthetic macroporous polymers with enhanced physical properties were created by emulsion templating. Hierarchical poly(merised) high internal phase emulsions (HIPE) were created from HIPEs stabilised simultaneously by particles and a surfactant. In these HIPEs, surfactant stabilised and particle stabilised water droplets coexist, which upon polymerisation of the minority oil phase gives rise to macroporous polymers with a hierarchical pore structure. An improvement of the mechanical properties of our hierarchically structured macroporous polymers at equal porosity was observed, due to a more efficient packing of pores in a configuration that improves mechanical strength despite the presence of interconnecting pore throats. Moreover, the permeability of the hierarchically structured polyHIPEs are exceeding those measured for conventional polyHIPEs made from surfactant only stabilised HIPEs.

     

Bifunctional catalysts supported on polymers for the preparation of Bisphenol A

This work is relative to attempts for obtaining acid‐thiol supported polymers that may be used as solid bifunctional catalysts, active in the Bisphenol A synthesis. Five approaches are tested with modified sulphonic styrene‐based polymers obtained either by multi‐polymerisation in one or several steps and derivatization. The objective is to get simultaneously sufficient capacity and high selectivity, by using an adequate acid/thiol ratio, and enhanced sites accessibility via an optimisation of the morphology. Reactivity results are favourably compared to those obtained in a homogeneous process.     

Polymerisation of styrene in microemulsion with catanionic surfactant mixtures

The use of aqueous catanionic surfactant mixtures in the oil-in-water (o/w) microemulsion polymerisation of styrene is reported. Catanionic surfactant mixtures of dodecyltrimethylammonium bromide 1 and sodium dodecylsulfate 3, or decanediyl-1,10-bis(dimethyldodecylammonium bromide) 2, a gemini surfactant, and the anionic surfactant 3 were used. Phase behaviour and polymerisation properties of the microemulsions were studied as a function of the total surfactant concentration and the cationic/anionic surfactant ratio. Single-phase o/w microemulsions were only formed if either the cationic or anionic surfactant were present in large excess. Upon -irradiation, polymer nanoparticles were obtained. Using dynamic light scattering, the particle radii were determined to be 10 to 20 nm, the size depending on the total surfactant concentration, the cationic/anionic surfactant ratio and the surfactant/styrene ratio. Size exclusion chromatography indicated molecular weights of polystyrene of between 3×10⁵ and 1.4×10⁶ Daltons. Catanionic 1/3 and 2/3 mixtures differ in their styrene solubilizations. In a 1- or 3-rich system, the solubilization efficiency can be improved by increasing the concentration of the oppositely charged minor surfactant component, while in a 2-rich system the addition of 3 only diminishes the efficiency. Possible reasons for the different behaviours are discussed.     

Polymerisation of liquid crystalline phases in binary surfactant/water systems

The self-assembly behaviour of the polymerisable surfactant -undecenyltrimethylammonium bromide (-UTAB) both before and after polymerisation has been investigated. In addition polymerisation of the liquid crystalline phases formed by this surfactant in aqueous solution has been studied. Introduction of the carbon-carbon double bond at the end of the hydrocarbon chain increases the rigidity of the paraffinic chains such that the Krafft curve is shifted to higher temperatures compared with that of dodecyltrimethylammonium bromide, a nonpolymerisable analogue. Both the polymerised and non-polymerised forms have been observed to have the same phase progression, with the polymer being more soluble in water such that the liquid crystalline phases formed at high surfactant concentration are accessible at room temperature. Polymerisation of the liquid crystalline phases of -UTAB indicate that polymerisation proceeds to approximately 40% (in comparison) with 80% in a non-aggregated form) and that the original monomeric matrix is undisturbed upon partial polymerisation.     

Role of a Surface Active Agent in the Sol-Emulsion-Gel Synthesis of Spherical Alumina Powders

Spheroidal alumina particles of tailor-made size were prepared by the sol-emulsion-gel method under simultaneous mechanical agitation and sonication and by systematic variation of the concentration of a non-ionic surfactant in the organic solvent (oil phase) above or below the critical micelle concentration (CMC). The CMC of the surfactant in the organic solvent of low dielectric constant was determined from discernible breaks in surface tension, viscosity, optical absorption and dye fluorescence vs. concentration curves. The CMC of the surfactant played an important role in controlling the sol droplet size and accordingly, the size of the alumina particles obtained therefrom. Transmission electron microscopy (TEM) revealed that near (but below) CMC the nanospheroids (10–50 m) were in the state of chain-like agglomerates. Beyond CMC, spheroidal particles of larger dimensions were obtained. Particle size analysis showed a sharp decrease in mean size with increasing concentration of the surfactant up to CMC, above which a gentle upward trend was noticed.     

Hybrid particles of polystyrene and carboxymethyl cellulose as substrates for copper ions

The synthesis of hybrid particles was carried out by emulsion polymerization of styrene in complexes formed by carboxymethyl cellulose (CMC), a polyanion, and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). CMC chains with variable molecular weights and degrees of substitution were tested. The polymerization condition chosen was that corresponding to CMC chains fully saturated with CTAB and to the onset of pure surfactant micelle formation, namely, at the critical aggregation concentration. The hybrid particles were characterized by zeta potential and light scattering measurements. The period of colloidal stability in the ionic strength of 2.0 mol L(-)(1) NaCl was observed visually. Upon increasing the CMC chain length, the particle characteristics remained practically unchanged, but the colloid stability was increased. The increase in the CMC degree of substitution led to particles with more negative zeta potential values. The adsorption of copper ions (Cu(2+)) on the surface of hybrid particles could be described by the Langmuir model, as determined by potentiometric measurements. The increase in the mean zeta potential values and X-ray absorption near-edge spectra evidenced the immobilization of Cu(2+) ions on the hybrid particles.     

Novel method for in-situ surfactant-based solid-phase extraction: application to the determination of Co(II) and Ni(II) in aqueous samples

We report on a completely new kind of solid phase extraction which we term in-situ surfactant-based solid-phase extraction (ISS-SPE). It represents a simple and rapid method for extraction from aqueous samples and preconcentration of compounds containing hydrophobic (alkyl) groups. A cationic surfactant containing alkyl chain is dissolved in the aqueous sample. Following the addition of hexafluorophosphate (HFP; an ion-pairing anion), solutions turn cloudy due to the interaction between the surfactant and the HFP ion. This is due to the formation of fine solid particles composed of the HFP salt of the cationic surfactant. The alkyl groups of the surfactant in the solid particles strongly interact with hydrophobic groups of analytes and become bound. The solid particles are centrifuged, and the sedimented particles can be either dissolved in an appropriate organic solvent, or leached with a solvent to recover the absorbed analyte(s). The method presented here has distinct advantages in that the extraction times are short and recoveries are high, probably a result of the formation of very fine particles of large specific surface, and of their good dispersion in the sample solution. The performance of ISS-SPE was demonstrated by extracting chelates of Co(II) and Ni(II) from water samples. Under the optimized conditions, the preconcentration factors are 51 and 45, respectively, and the detection limits are 0.9 and 0.6???g?L^?1. The method was validated by the analysis of a certified reference material and by comparing results with those obtained by electrothermal AAS.

Morphology control of magnetic latex particles prepared from oil in water ferrofluid emulsion

The use of magnetic latex particles as solid support in biomedical applications is favourable when homogeneous and well-defined core–shell polymer particles are used. Accordingly, this paper concerns with the synthesis of magnetic poly(styrene–divinylbenzene) latex particles using emulsion polymerization of styrene (St) and divinylbenzene (DVB) monomers in the presence of preformed oil in water organic ferrofluid emulsion droplets as seed. The key parameters which affect on formation and morphology of the prepared magnetic latexes were investigated, including type of magnetic emulsion, St/DVB monomers ratio, DVB amount, type of initiator and surfactant nature. In this study, two different magnetic emulsions were used, low and high octane content magnetic emulsions. The magnetic emulsions were stabilized using different types of surfactants including AP, Triton X 405 and SDS. In addition, four different initiators, including AIBN, V50, ACPA and KPS were examined. The morphology of the prepared magnetic latexes was investigated using transmission electron microscopy. In addition, particle size and size distribution, magnetic content and magnetic properties of the prepared magnetic latexes were also examined, using various techniques, e.g. dynamic light scattering, thermal gravimetric analysis and vibrating sample magnetometer, respectively. The results showed that the morphology type (Janus like, moon like and/or core–shell) of the prepared magnetic latex particles could be controlled depending mainly on the used formulation. In fact, the use of styrene monomer leads to anisotropic morphology. Whereas, the progressive use of DVB in presence of KPS intiator leads to a well-defined magnetic core and polymer shell structure.

Comparison of Syndiotactic Polystyrene Morphology Obtained Via Heterogeneous and Homogeneous Polymerization with Metallocene Catalyst

Summary: Supported catalyst system for the slurry phase polymerization of styrene in toluene was prepared by the immobilization of 2-methylindenyltrichlorotitanium(2-MeIndTiCl₃) on silica and activation of this catalyst was performed by methylaluminoxane(MAO) in polymerization media. Homogeneous polymerization of styrene with 2-methylindenyltrichlorotitanium activated by MAO was performed in toluene. The morphology of obtained syndiotactic polystyrene (sPS) via heterogeneous and homhgeneous catalyst system was compared. Polymerization of styrene by homogeneous catalyst lead to formation of gel and resultant polymers presented a compact and dense texture while the global gelation do not occur with silica supported catalyst at different Ti/SiO₂ mol ratios and sPS was obtained as separated particles. Unlike to the homogeneous catalyst, obtained polymers showed a porous texture. Highly porous texture of sPS was obtained with Ti/SiO₂ = 0.5% mol ratio.     

Sol-Emulsion-Gel Synthesis of Shaped Powders in the System BaO-TiO2

Shaped tetragonal barium titanate (BaTiO₃) particles were prepared by the sol-emulsion-gel method with systematic variation of the concentration of a non-ionic surfactant in the organic phase (oil phase) of water-in-oil (w/o) emulsions above or below the critical micelle concentration (CMC). An acetate-based sol with equivalent oxide ratio BaO : TiO₂ = 1 : 1 was selected for the study. Micelle formation of the surfactant and their self-aggregation apparently played an important role in controlling the shape and size of the droplets and accordingly shape and size of the final barium titanate particles resulting therefrom. Transmission electron microscopy (TEM) revealed that with low concentration of the surfactant (2–5 vol%) ill-formed spheres were obtained. Spherical particles were formed with increasing the surfactant concentration to 7 vol%. At 12 vol% of the surfactant, rod-like particles were first found to form, which with further increase in surfactant concentration to 15–20 vol%, gradually transformed to cube-like/lamellar type particles. Attempts have been made to explain the various particle shapes in terms of surfactant aggregation.     

Polymerisation of liquid crystalline phases in binary surfactant/water systems

The binary phase behaviour of two potentially polymerisable quaternary ammonium surfactants in water has been investigated. Allyldodecyldimethylammonium bromide (ADAB) a single-chain surfactant displays a conventional phase progression upon increasing concentration. Whereas the doublechain analogue allyldidodecylmethylammonium bromide (ADDAB) forms two lamellar liquid crystalline phases built from surfactant bilayers, which transform via a first order phase transition. The formation of two distinct lamellar phases and their coexistence has been evidenced by optical microscopy, small-angle x-ray scattering and D₂O deuterium quadrupolar nuclear magnetic resonance spectroscopy. The lamellar phase formed at higher surfactant compositions is a normal lamellar phase (typeL ) consisting of bilayers which are on average parallel and flat. The lower compositional lamellar phase (typeL ) in contrast may not be comprised of planar bilayers but rather aggregates having a high degree of curvature in comparison to those of theL phase. The presence of the allyl polymerisable moiety in the head group position of these surfactants has the effect of reducing the rigidity of the surfactant and increasing its solubility in comparison to nonpolymerisable analogues. Polymerisation of the surfactants was attempted by using thermal and photochemical initiation in isotropic and self-assembled systems. Polymerisation occurred to approximately 30% for DADB but did not occur for ADDAB. Where polymerisation did occur the polymer was incorporated into the monomer matrix by interweaving between the surfactant aggregates. The polymers had a molecular wieght not greater than 8000 Daltons, independent of the monomer concentration of the original solution and type of polymerisation.     

Radical polymerisation of styrene in porous coordination polymers

The first radical polymerisation of styrene in porous coordination polymers has been carried out, providing stable propagating radicals (living radicals), and a specific space effect of the host frameworks on the monomer reactivity is demonstrated.     

Facile fabrication of polymer-inorganic hybrid particles with various morphologies by combination of hydrolytic condensation process with radiation seeded emulsion polymerization

A novel approach was proposed to the synthesis of poly(styrene-divinyl benzene-acrylic acid)/poly [3-(methacryloxy)propyl trimethoxysilane-styrene] [P(St-DVB-AA)/P(MPS-St)] hybrid particles. The morphologies of the particles could be tuned from raspberry-like to snowman-like by simply changing the feeding amount of second monomer or inorganic precursor. The fabricated raspberry-like ones could be modified to obtain hydrophobic surface with a contact angle up to 146°. And the snowman-like ones could be used as solid surfactant to stabilize water/styrene (W/St) mixtures, thus hierarchical porous materials could be obtained after the polymerization of monomer phase. The preliminary application of such soap-free block materials in oil-polluted water treatment was also investigated.

Properties of complexes and particles of gelatin with ionic surfactants

 The properties of soluble gelatinionic surfactant complexes and insoluble particles were evaluated. It was found that colloidal particles of gelatin A – cationic surfactant (dodecyltrimethyl-ammonium bromide, DTAB, and cetyltrimethylammonium bromide, CTAB) were formed. Binding isotherms showed that these particles are obtained above the CMC of each surfactant, while cooperative binding takes place. Surface tension measurements conducted for both gelatin/DTAB and gelatin/anionic surfactant, SDS (sodium dodecyl sulfate) showed a break in the curve describing surface tension vs number of bound surfactant molecules, (ν) at concentrations below the CMC of each surfactant alone. This break, which is attributed to CMC 1, is observed at the same number of bound surfactant mol ecules ν∼2 for both gelatin/surfactant couples. Contact angle measurements showed that the maximal hydro-phobicity of the gelatin-surfactant particles is obtained at the same concentration range in which the precipitation occurs. It was also found that the hydrophobicity of gelatin-SDS particles, is higher than that of the gelatin-cationic surfactants, due to a different composition of the resulting particles. The zeta potential of the particles indicated charge neutralization and even charge reversal for gelatin-CTAB at high surfactant concentration. Received: 4 April 1997 Accepted: 15 December 1997     

Preparation of microlatex dispersions using oil-in-water microemulsions

The preparation of microlatex dispersions from microemulsions of a monomer (styrene, methylmethacrylate or vinyl acetate) is described. A simple method for preparing the microemulsion has been devised. This consists of forming a water-in-oil (w/o) emulsion using a low (HLB) surfactant (nonylphenol with 5, 6 or 7 moles ethylene oxide) and then titrating with an aqueous solution of a high HLB surfactant (nonylphenol with 15 or 16 moles ethylene oxide). A small amount of anionic surfactant (sodium lauryl sulphate, sodium dodecyl benzene sulphonate or dioctyl sulphosuccinate) was also incorporated to enhance the stability of the w/o emulsion and facilitate the inversion to an o/w microemulsion. The droplet-size distribution of the resulting microemulsion was determined using photon-correlation spectroscopy.Three different methods of polymerising the microemulsion were used. These were thermally induced polymerisation using potassium persulphate, azobis-2-methyl propamidinium dichloride (AMP-water-soluble initiators) or azobisisobutyronitrile (AIBN, an oil-soluble initiator). All these initiators required heating to 60°C, i.e. above the stability temperature of the microemulsion. In this case, the microlatices produced were fairly large (37–100 nm diameter) and had a broad particle-size distribution. The second polymerisation procedure was chemically induced using a redox system of hydrogen peroxide and ascorbic acid. This produced microlatices with small sizes (18–24 nm diameter) having a narrow-size distribution. The microlatex size was roughly two to three times the size of the microemulsion droplets. This showed that collision between two or three microemulsion droplets resulted in their coalescence during the polymerisation process. The third method of polymerisation was based on UV irradiation in conjunction with K₂S₂O₈, AMP or AIBN initiators. In this case, the microlatex size was also small (30–63 nm) with a narrow particle-size distribution.Microlatex particles were also prepared using a mixture of monomers (styrene plus methylmethacrylate) or mixture of monomers and a macromonomer, namely methoxy (polyethylene glycol)methacrylate. The latter was used to produce hairy particles, i.e. with grafted polyethylene oxide (PEO) chains.The stability of the microlatices was determined by adding electrolytes (NaCl, CaCl₂, Na₂SO₄ or MgSO₄) to determine the critical flocculation concentration (CFC). The nonionic latices were very stable giving no flocculation up to 6 mol dm^–3 NaCl or CaCl₂ and a CFC of 0.6 mol dm^–3 for Na₂SO₄ or MgSO₄. Charged latices were less stable than the nonionic ones. The critical flocculation temperatures (CFT) of all latices were determined as a function of electrolyte concentration. With the nonionic latices, CFC was higher than the -temperature for polyethylene oxide at the given electrolyte concentration. This indicated enhanced steric stabilisation as a result of the dense packing of the chains and hence an elastic contribution to the steric interaction. This was not the case with the charged latex, which showed CFT values lower than the -temperature. The hairy latices [i.e. those containing methoxy polyethylene glycol (PEG) methacrylate] were also less stable towards electrolyte (CFT was much lower than -temperature), indicating a low density of PEO layers.     

Influence of the polymerisation time on the porous and chromatographic properties of monolithic poly(1,2-bis(p-vinylphenyl))ethane capillary columns

In order to elucidate the effect of the polymerisation time on the morphology of styrene based monolithic support materials, continuous poly(1,2-bis(p-vinylphenyl))ethane (BVPE) rods were synthesised in 1.0 ml glass vials by thermally initiated free radical polymerisations of BVPE in the presence of porogens (toluene, decanol) and a,a′-azoisobutyronitrile (AIBN) as initiator at 65 °C for different polymerisation times (60, 90, 150, 300 and 600 min). Porosity parameters like pore-size-distribution and total porosity were investigated by mercury intrusion porosimetry, while the specific surface area of the BVPE monolithic supports was determined by N₂-adsorption (BET) measurements. An untypical bimodal pore-size-distribution comprising a high fraction of both mesopores (2–50 nm) and macropores (mainly flow-channels in the micrometer range) was observed as a result of the stepwise decrease of the polymerisation time. In consequence of the significant changes of the pore-size-profile, shortening the polymerisation time also resulted in enhanced total porosity due to enlarged flow-channel diameters and increased surface area according to the presence of a considerable amount of mesopores. Results upon the porosity profile of the support are further confirmed by SEM images of monoliths polymerised for different time periods. Since mesoporosity and high surface area of the chromatographic support material play key roles in the interaction and thus retention of low-molecular-weight compounds, polymerisation time should also affect the chromatographic properties and applicability of these polymers. To study the influence of the polymerisation time towards the separation efficiency of small molecules on BVPE capillary columns (200 μm I.D., 8 cm), a mixture of homologous alkylbenzenes was chosen for column evaluation. In accordance with the observations of the porous properties of BVPE stationary phases, the rapid and high resolution separation of a range of low-molecular-weight compounds on monolithic BVPE supports were successfully realised. The methodical reduction of the polymerisation time has been demonstrated to be a simple and effective tool to tailor the porous properties of organic monoliths to provide novel polymer-based stationary phases with porous properties adequate for the rapid and high resolution chromatography of small organic molecules.     

Formation of Polyolefin‐block‐polystyrene Block Copolymers on Phenoxyimine Catalysts

Summary: PE‐block‐PS and P(E‐co‐P)‐block‐PS block copolymers were synthesised via sequential monomer addition during homogeneous polymerisation on various phenoxyimine catalysts. One phenoxyimine catalyst was tailored to produce high molecular weight block copolymers containing both, polyolefin and polystyrene segments. According to chromatographic analysis and TEM morphology studies, blends of block copolymers and PE homopolymers [or P(E‐co‐P), respectively] were formed. The direct olefin/styrene block copolymer synthesis on phenoxyimine catalysts represents an attractive, new one‐pot route to styrenic block copolymers which are commercially prepared by anionic styrene/diene block copolymerisation followed by hydrogenation.

     

Role of the nonionic surfactant Triton X-405 in emulsion polymerization. I. Homopolymerization of styrene

The emulsion polymerization of styrene was studied using the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol). Two separate nucleation periods were noted in these polymerizations resulting in bimodal final latex particle size distributions. The partitioning of the surfactant between the phases was found to play the major role in determining the nucleation mechanism(s) in these polymerizations. Although the total concentration of the emulsifier was always added at a level above its critical micelle concentration (CMC) based on the water phase in the recipe, it was found that the portion of the surfactant initially present in the aqueous phase was below its CMC due to the partitioning. This CMC was also found to increase with increasing total surfactant because the distribution of the surfactant (varying ethylene oxide chain length) depended on the partitioning between the phases. Under these conditions, the first of the two nucleation periods was attributed to homogeneous nucleation, while the second was attributed to micellar nucleation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3813–3825, 1997     

Facile fabrication of snowman-like Janus particles with asymmetric fluorescent properties via seeded emulsion polymerization

This paper presents a facile method for the preparation of snowman-like Janus particles (SJP) with asymmetric fluorescent property via seeded emulsion polymerization, in which in situ formed raspberry-like cadmium sulfide/poly(styrene–divinylbenzene–acrylic acid) nanocomposite particles (RNP) were used as the seeds. The as-prepared RNP and SJP have been thoroughly characterized by transmission electron microscopy, field-emission scanning electron microscopy, thermogravimetric analysis, X-ray powder diffraction, Fourier transform infrared, ultraviolet visible, and photoluminescent spectrometry. It is found that the size ratio of the polymer bulge/inorganic seed part could be continuously tuned as well as the composition of polymer bulges by changing the composition of monomer mixtures and monomer/seed weight ratio. The obtained Janus particles possess amphiphilic properties which can be further used as solid surfactants to stabilize W/O emulsions and successively to construct hierarchical structured materials. Meanwhile, their asymmetric fluorescent properties may be exploited to detect their assembled situation and orientation at the oil–water interface of emulsions as well as at the surface of hierarchical structured materials.