Emulsifier-free emulsion copolymerization of styrene and sodium styrene sulfonate

The kinetics of the emulsifier-free emulsion copolymerization of styrene and sodium styrene sulfonate have been examined over a range of comonomer compositions. The rate of polymerization was found to increase dramatically in the presence of small amounts of sodium styrene sulfonate. This increase is attributed to the increased number of particles formed when sodium styrene sulfonate was present and to a gel effect enhanced by ion association. At low concentrations of functional comonomer, where a monodisperse product was obtained, a homogeneous nucleation mechanism of particle generation is proposed. At higher concentrations, broader and then bimodal size distributions were obtained, and this is ascribed to significant aqueous phase polymerization of sodium styrene sulfonate. The water-soluble homopolymer is supposed to act as a locus of polymerization. The occurrence of this aqueous phase side reaction and the generation of secondary particles makes impossible the preparation of highly sulfonated polystyrene latexes by batch or seeded batch emulsion copolymerization.     

The emulsion copolymerization of styrene and sodium styrene sulfonate

The emulsion copolymerization of styrene and sodium styrene sulfonate has been shown to be a feasible preparative route to ionomeric sulfonated polystyrene. The properties of these copolymers are reported elsewhere. The copolymerization rate was found to be dramatically enhanced when compared to that for the emulsion copolymerization of styrene under identical conditions. This copolymerization was studied in detail and two mechanisms were proposed to account for these rate differences. An increase in the number of polymerizing particles in the copolymerization with consequent rate enhancement was substantiated by electron microscopy. However, the data indicate that the rate differences cannot be fully accounted for by this effect. In addition, a gel effect is proposed as a second contributor to the enhanced rate. This gel effect is believed to result from the intermolecular association of the incorporated metal sulfonate units in the growing polymer particles. When a third monomer that plasticizes the ionic interactions is used the polymerization rate decreases. This supports the gel effect hypothesis.     

Comparisons of styrene ionomers prepared by sulfonating polystyrene and copolymerizing styrene with styrene sulfonate

As part of a continuing study of ion-containing polymers, a comparison has been made on styrene-based sulfonate ionomers obtained by two different processes. Copolymers of styrene with sodium styrene sulfonate (SSS) have been compared with corresponding polymers obtained by the sulfonation/neutralization of preformed polystyrene (S–PS). The former system covered a range of sulfonate level from 1 to 30 mol %, while the latter ranged from about 1 to 7 mol %. The characterization of these materials has been conducted using solubility behavior, dilute solution viscometry, thermal mechanical analysis, density measurements, and water adsorption studies. At low (ca. 1%) levels the solubility behavior of the SSS copolymers and the sulfonated polystyrenes were similar. However, at higher sulfonate levels the solubility behavior in different solvents and the dilute solution viscometry were significantly different for the two systems. Similarly, thermal analysis studies (DSC) showed that the glass transition of the sulfonated polystyrene increased linearly with sulfonate level, while the T_g for the SSS copolymer increased modestly, up to about 7 mol % sulfonate content, and then remained constant. Significant differences in the softening behavior and water absorption characteristics were also observed for these two classes of ionomers. Although molecular weights and molecular weight distributions are not now available for these ionomers, the differences in their behavior does not appear to be due simply to differences in molecular weight. It is postulated that the differences in the copolymer and the S–PS ionomers may originate with differences in sulfonate distribution. It is suggested that the SSS monomer units are incorporated as blocks in the copolymer as opposed to a more random distribution in the S–PS ionomer. Indirect evidence in support of his argument is found, for example, in the case of the copolymer in the solubility behavior, the relative independence of T_g on sulfonate concentration and the apparent existence of a second, high temperature transition tentatively attributable to an ion-rich phase. Additional studies are required to confirm this hypothesis.     

Emulsifier-free emulsion copolymerization of styrene and sodium 1-allyloxy- 2-hydroxypropane sulfonate

Colloidal particles of poly(styrene-co-sodium 1-allyloxy- 2-hydroxypropane sulfonate) with diameters of 508 ∼ 596 nm were synthesized by emulsifier-free emulsion copolymerization, crosslinked with divinylbenzene, and initiated by potassium persulfate/sodium bisulfite in a mixed solvent of water and acetone. The diameters of the submicrometer-sized particles were measured by dynamic light scattering (DLS) and scanning electron microscopy (SEM). The surface charge densities of the particles were determined by condutometric titration. The results showed that the highly surface charged monodispersed submicrometer-sized particles were obtained by two-stage shot growth polymerization. The particle diameters could be reduced and controlled by adding suitable amount of acetone.     

Core-shell emulsion copolymerization of styrene and acrylonitrile on polystyrene seed particles

Seeded emulsion copolymerization of an azeotropic composition of styrene (St) and an acrylinitrile (AN) comonomer mixture in polystyrene (PS) seed at different polymerization temperature of 55–75°C were investigated. The kinetic data showed a transition temperature at 65°C, above which the activation energy of polymerization is low, 6.1 Kcal/mol, compared with 9.8 Kcal/mol below it. The particle-size results and thin layer chromatographic (TLC) data showed two types of particle of different composition and morphology in the final latex system: a smaller size of (St–AN) copolymer and a larger size of core-PS and (St–AN) copolymer shell, with a zone of PS grafted (St–AN) copolymer in between. Various polymerization parameters, that is emulsifier concentration, type of seed particle and its size, and monomer/polymer ratio, were studied and their effects on particle size and particle morphology were examined. The percent of grafted core-PS was 10% below a polymerization temperature of 65°C and 40% above that temperature. By adjusting the size and number of the seed particles, monomer-polymer ratio, and emulsifier concentration conditions were established in which a final copolymer latex with “perfect” core-shell morphology was achieved.     

Automated batch emulsion copolymerization of styrene and butyl acrylate

This article describes a method for carrying out emulsion copolymerization using an automated synthesizer. For this purpose, batch emulsion copolymerizations of styrene and butyl acrylate were investigated. The optimization of the polymerization system required tuning the liquid transfer method, sufficient oxygen removal from the reaction medium and setting a proper sampling procedure. The monomer conversion‐time plots obtained with gas chromatography revealed a good reproducibility of the automated reaction kinetics. Furthermore, the particle size distributions and the properties of the final products were found to be highly reproducible. The performance of the automated reactions was subsequently compared with the conventional ones: similar reproducibility of either synthetic method was observed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Radiation-initiated emulsion copolymerization of styrene and carboxylic acid monomers

The emulsion Copolymerization of styrene and carboxylic acid monomers such as acrylic, methacrylic, and itaconic acids (AAc, MAAc, IAc) was studied by using ⁶⁰Co γ-rays as initiator and sodium do-decylsulfate as emulsifier. The polymerization behavior of these acid monomers was followed by simultaneous conductometric and potentiometric titrations for a latex sample taken in polymerization. The polymerization rate of these acid monomers increases in the following order of hydrophobicity: IAc < AAc < MAAc; this suggests that their polymerization sites are mainly the surface and/or subsurface regions of latex particles. The copolymerization rate of styrene and acid monomer increases with an increase in the acid monomer content for AAc and MAAc, whereas for IAc the rate decreases. The particle sizes determined by the stopped-flow method reveal that this variation of copolymerization rate cannot be explained by the number of growing particles and should be attributed to another factor; for instance, the transfer rate of styrene molecules from oil droplets to growing particles.     

High-impact polystyrene/halloysite nanocomposites prepared by emulsion polymerization using sodium dodecyl sulfate as surfactant

In this work, we report on the phase behavior of 1-ethyl-3-methyl-imidazolium-ethylsulfate ([emim][etSO(4)])/limonene/polyethylene glycol tert-octylphenyl ether (Triton X-114 or TX-114) microemulsions as a function of ionic liquid (IL) content and temperature. Phase diagrams, conductivity measurements, and small angle X-ray scattering (SAXS) experiments will be presented. A hydrophilic IL, instead of water is used with the goal to enlarge the temperature range on which stable microemulsions can be formed. Indeed, the system shows remarkably large temperature stability, in particular down to -35 °C. We will emphasize on a comparison with a recently published work about microemulsions composed of [emim][etSO(4)], limonene, and Triton X-100 that to some extent are stable at temperatures well below the freezing point of water. The key parameter responsible for the difference in phase behavior, microstructure, and temperature stability is the average repeating number of ethylene oxide units in the surfactant head group, which is smaller for Triton X-114 compared to Triton X-100. Among the fundamental interest, how the amphiphilicity of the surfactant influences the phase diagram and phase behavior of IL-based microemulsions, the exchange of Triton X-100 by Triton X-114 results in one main advantage: along the experimental path the temperature where phase segregation occurs is significantly lowered leading to single phase microemulsions that exist at temperatures beneath 0 °C.     

Dynamic mechanical properties of polystyrene ionomers containing both carboxylate and sulfonate anionic groups

Polystyrene‐based ionomers possessing sodium methacrylate (MA) and sodium styrenesulfonate (SS) units in each polymer chain [poly(styrene‐co‐methacrylate‐co‐styrenesulfonate) (PSMA‐SS)] were synthesized. The dynamic mechanical properties of PSMA‐SS ionomers were studied and compared with those of styrene ionomers containing only MA (PSMA ionomer) or SS (PSS ionomer) units. It was observed that the ionic moduli of PSMA‐SS ionomers depended directly on the total ion content and that the ionic modulus was highest for the PSMA ionomer and lowest for the PSMA‐SS ionomer. The matrix T_gs of the three ionomer systems were found to be similar to each other; the cluster T_g of PSMA‐SS ionomer was higher than that of PSS ionomer at low SS contents but became closer to each other at high SS contents. In addition, the small‐angle X‐ray scattering study revealed that the multiplet size might be in the following order: PSMA‐SS > PSS > PSMA. This implied that at the same ion content, the fractions of cluster regions were smallest for PSMA‐SS ionomer in comparison with those of PSS or PSMA ionomers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Modeling of unseeded emulsion copolymerization of styrene and methyl methacrylate

A mathematical model for the unseeded emulsion copolymerization of styrene and methyl methacrylate has been developed. This model, which includes a new rate coefficient for radical desorption, was used to analyze the effect of the styrene/methyl methacrylate molar ratio in the initial charge on the number of particles, overall conversion and copolymer composition. It was found that the number of particles increased with the methyl methacrylate content and that a drift of the copolymer composition resulted during the polymerization of styrene/methyl methacrylate molar ratios other than 50/50. Good agreement between experimental results and model predictions was achieved.     

Morphological investigation of styrene and acrylamide polymer microspheres prepared by dispersion copolymerization

 The morphology of the styrene and acrylamide copolymer microspheres prepared by dispersion copolymerization in an ethanol/water medium was investigated. The effects of the styrene/acrylamide ratio, ethanol/water ratio and stabilizer concentration on the particle size and size distribution were studied. It was found that the initial solubility parameter of the system was the key factor in the process. The comonomer acrylamide also played an important role in the particle size and size distribution in the presence of cross-linking agent (divinylbenzene). Received: 29 October 1999 Accepted in revised form: 29 November 1999     

Emulsifier-free emulsion copolymerization of styrene and acrylamide using an amphoteric initiator

Emulsifier-free emulsion copolymerization of styrene (St) and acrylamide (AAm) has been investigated in the presence of an amphoteric water-soluble initiator, 2,2′-azobis[N-(2-carboxyethyl)-2-2-methylpropionamidine]hydrate (VA057). The kinetics of polymerization and the colloidal properties of the resulting latices were studied and compared with the cases using ionic initiators. When adopting the amphoteric initiator at pHs lower than 10, stable amphoteric poly (St/AAm) latices, evidenced by the electrophoretic mobility, were prepared directly. Meanwhile, almost the same conversion versus time curves appeared and there were no apparent differences in the final particle sizes for those polymerizations, whereas in the polymerization at pH 10, a much lower rate of copolymerization and a larger size of particles were observed. The surface charge density and the growth rate of latex particles produced with VA057 at pH<10 were comparable to those of the particles with a cationic initiator, 2,2′-azobis(2-amidinopropane)dihydrochloride, but were apparently lower than those with an anionic initiator, potassium persulfate, when the polymerizations were carried out under corresponding conditions. The number of initiator fragments incorporated onto the particle surfaces was independent of polymerization pH, except for pH 10. The abnormal performance of VA057 at pH 10 was attributed to its degradation due to hydrolysis. Received: 14 December 1999 Accepted: 22 February 2000     

Coagulum formation and elimination in emulsion copolymerization of tribromostyrene with styrene

Coagulum formation in emulsion polymerization of tribromostyrene and also in its copolymerization with styrene has been shown to be due to thermal polymerization. The latter takes place in the monomer reservoirs, even in the absence of radical generating initiators, converting them into sticky particles which then form the undesired coagulum. The coagulum formation phenomenon can thus be remedied by reducing the thermal initiation level through a semi-batch emulsion polymerization method, by lowering the polymerization temperature, and reduction of the collision frequency of monomer/polymer particles.     

Radiation graft post-polymerization of sodium styrene sulfonate onto polyethylene

Post-irradiation grafting of sodium styrene sulfonate (SSS) in the presence of acrylic acid (AA) has been investigated on polyethylene (PE) pre-exposed to gamma radiation at room temperature in the air. Special attention was paid to the effect of low molecular weight salt additives on the kinetics of graft copolymerization of SSS and AA. The presence of SSS links in the grafted PE copolymers was detected by the methods of UV and FTIR spectroscopy. Based on the FITR spectroscopy and element analysis data, a mechanism was proposed for graft copolymerization of SSS and AA onto PE. The mechanical properties of the graft copolymers were studied. It was established that PE copolymers grafted with sulfonic acid and carboxyl groups have higher strength characteristics (16.3 MPa) compared to the samples containing only carboxyl groups (11 MPa).     

高表面电荷密度单分散苯乙烯磺酸钠纳米微球的制备

利用无皂乳液聚合 ,在苯乙烯 (St)的反应体系中引入适量的苯乙烯磺酸钠 (NaSS)参加共聚合 ,在聚合过程中分两阶段加料 ,第一阶段中NaSS浓度是决定乳胶粒粒径及单分散性的关键因素。当反应达到较高转化率 ( >90 % )时加入第二阶段单体混合物 ,此阶段中NaSS与St的比例决定了最终胶粒的表面电荷密度。利用上述两阶段无皂乳液聚合法成功地制备了粒径小于 10 0nm、单分散性指数小于 1.0 5以及表面电荷密度大于 3 0 μC·cm-2 的一系列乳胶粒     

Kinetics and mechanisms of the seeded emulsion copolymerization of styrene and acrylonitrile

Effects of various operating variables on the kinetic behavior of the seeded emulsion copolymerization of styrene and acrylonitrile and on the monomer concentration in the copolymer particles were examined. Applicability of high-performance liquid adsorption chromatography to determination of the average composition and composition distribution of the resulting copolymer was also examined.     

Preparation of polystyrene/silica nanocomposites by radical copolymerization of styrene with silica macromonomer

A two-stage process has been developed to generate the silica-based macromonomer through surface-modification of silica with polymerizable vinyl groups. The silica surfaces were treated with excess 2,4-toluene diisocynate (TDI), after which the residual isocyanate groups were converted into polymerizable vinyl groups by reaction with hydroxypropylacrylate (HPA). Thus, polystyrene/silica nanocomposites were prepared by conventional radical copolymerization of styrene with silica macromonomer. The main effecting factors, such as ratios of styrene to the macromonomer, together with polymerization time on the copolymerization were studied in detail. FTIR, DSC and TGA were utilized to characterize the nanocomposites. Experimental results revealed that the silica nanoparticles act as cross-linking points in the polystytene/silica nanocomposites, and the glass transition temperatures of the nanocomposites are higher than that of the corresponding pure polystyrene. The glass transition temperatures of nanocomposites increased with the increasing of silica contents, which were further ascertained by DSC.     

Infinite-dilution viscoelastic properties of sodium poly(styrene sulfonate)

The storage and loss shear moduli G′ and G″ of dilute solutions of two samples of sodium poly(styrene sulfonate) with molecular weights (M) of 3.28 × 10⁵ have been measured. The Birnboim–Schrag multiple-lumped resonator technique was used in the frequency range 100–8000 Hz, and the intrinsic moduli were obtained by extrapolation to infinite dilution. Measurements were performed over the temperature range from 1.0 to 25.0°C in aqueous solvents containing from 0 to 60% by weight glycerol and from 0.001 to 0.005M added salt. The large intrinsic viscosities indicated high extension of the polymer, and the frequency dependences of G′ and G″ were matched well by hybrid relaxation spectra combining rodlike and coil-like behavior. In a solvent containing 0.001M sodium ion and no glycerol, the end-over-end rotational relaxation times for the two molecular weights corresponded to proportionality to the 1.7 power of M. With increasing molecular weight, ionic strength, and/or glycerol concentration, the polyelectrolyte appeared to become less extended, and its behavior more nearly coil-like.     

The synthesis of sulfonated polymers by free radical copolymerization. Poly(butadiene-co-sodium styrene sulfonate)

The copolymerization of butadiene with sodium styrene sulfonate was studied and the copolymer products characterized. In general these copolymers contain 0.5–4 mole% of sulfonated monomer. The effects of the following reaction variables are described: emulsifier type and concentration, monomers feed ratio, chain transfer agent concentration, and reaction conversion. The products were heterogeneous with regard to composition, molecular weight, and solubility behavior. Copolymers prepared under certain conditions exhibited strong intermolecular interactions derived from associations of the ionic species as observed in other ionomers.