Styrene In Supercritical Carbon Dioxide Research Articles

Modelling of polymerization kinetics and molar mass development in the nitroxide‐mediated polymerization (NMP) of styrene in supercritical carbon dioxide using the PC‐SAFT equation of state

AbstractA mathematical model for polymerization kinetics and molar mass development in the nitroxide‐mediated polymerization (NMP) of vinyl monomers in supercritical carbon dioxide (scCO2) has been developed. The method of moments is used for molar mass development. The perturbed‐chain statistical associating fluid theory (PC‐SAFT) equation of state is used to estimate the number of stable phases present at equilibrium in the reaction mixture, critical number average chain length at which polymer particles are formed, and monomer concentration in each phase. Pure and binary PC‐SAFT interaction parameters are estimated from liquid–liquid equilibrium (LLE) and liquid–vapour equilibrium (LVE) experimental data at 60 to 129°C. The effect of pressure on monomer conversion and molar mass development in the polymerization of styrene (Sty) using benzoyl peroxide (BPO) and 2,2,6,6‐Tetramethylpiperidinyl‐1‐oxyl (TEMPO) at 120°C and 300–500 bar is studied. It was observed that increasing pressure increases polymerization rate without significantly affecting molar mass development.

Synthesis of fluorinated alkoxyamines and alkoxyamine-initiated nitroxide-mediated precipitation polymerizations of styrene in supercritical carbon dioxide

The first controlled/living precipitation NMP in supercritical carbon dioxide in the absence of nitroxide and comparisons with fluorinated alkoxyamines.

Synthesis of new perfluorinated binaphthyl Mn(III) complexes and epoxidation of styrene in supercritical carbon dioxide

In this article, new perfluorinated binaphthyl Mn(III) complexes have been synthesized by template effect. The synthesized complexes were characterized by elemental analysis, FT-IR, LC/MS, UV–vis spectroscopy. After the solubility of the catalysts in scCO2 was observed through the high pressure reactor, catalytic activities of the catalysts have been tested in homogeneous asymmetric epoxidation of styrene in both dichloromethane (organic solvent) and supercritical carbon dioxide (scCO2). In order to determine and compare to complexes, the effect of synthesized catalysts to conversion and selectivity was investigated. Reaction parameters such as; reaction time, solvent type and position of substituents were also assessed during the analysis.

Iodine transfer dispersion polymerization (dispersion ITP) with CHI3 and reversible chain transfer catalyzed dispersion polymerization (dispersion RTCP) with GeI4 of styrene in supercritical carbon dioxide

Submicrometer-sized, polystyrene (PS) particles with controlled molecular weight distribution (MWD), were successfully obtained directly as powder state by iodine transfer dispersion polymerization (dispersion ITP) and reversible chain transfer catalyzed dispersion polymerization (dispersion RTCP) in supercritical carbon dioxide (scCO2) for the first time. These dispersion polymerizations proceeded similarly reaching 80% conversion in 21 h. In the dispersion ITP, the number-average molecular weight (Mn) nonlinearly increased with the conversion, which were always higher than theoretical values, and the MWD at each conversion was comparatively narrow (Mw/Mn = 1.5–1.7) throughout polymerization. In the dispersion RTCP, Mn also nonlinearly increased with increasing conversion and Mw/Mn values were in the range of 1.3–1.5, which were lower than those of the dispersion ITP. In chain extension tests in bulk systems, the degrees of livingness of PS prepared by the dispersion ITP and the dispersion RTCP in scCO2 systems were, respectively, estimated to be 56% and 48%. From these results, while more investigation is necessary, it was concluded that both polymerizations with scCO2 proceeded in a partly controlled manner.

The solubility of styrene in supercritical carbon dioxide

Possible reasons for the existing differences in styrene solubilities in supercritical carbon dioxide obtained using the dynamic (flow) method are analyzed. The results of an experimental study of the solubility of styrene in supercritical CO2 with the use of the static method of measurements and an improved dynamic cell are given. The influence of styrene polymerization under experimental conditions on measurement results at elevated pressures is analyzed. A mathematical formulation for the description of solubility data with the use of the Peng-Robinson equation and three adjustment parameters is presented. The experimental data on the solubility of styrene in supercritical carbon dioxide are described.

Dispersion copolymerization of methyl methacrylate and styrene in supercritical carbon dioxide

A method for producing finely dispersed powders of methyl methacrylate (MMA)-styrene copolymer by radical polymerization in a supercritical carbon dioxide medium (SC-CO2) was proposed, studied, and experimentally implemented. The dispersing agent (surfactant), which made it possible to obtain nearly monodisperse size distribution of polymer particles, was poly(dimethylsiloxane methacrylate), a SC-CO2-soluble substance. The copolymer, synthesized with a molecular mass of Mw ∼ 36000 in the form of spherical particles with a characteristic size of ∼1 μm, exhibited a higher thermal stability as compared to poly(methyl methacrylate) with a similar molecular mass. Varying the percentage ratio between MMA and styrene monomers, it was possible effectively control the integral hydrophobicity and physicomechanical characteristics of the methacrylate-styrene copolymer.

Preparation of polymer microspheres in supercritical carbon dioxide and their evaluation as cold‐flow improvers in diesel

AbstractPolymeric microspheres were synthesized by the precipitation copolymerization of methacrylic acid and styrene in supercritical carbon dioxide. Scanning electron microscopy showed that the products were spherical microparticles. The mean diameter of the particles was 0.2–2 μm. The synthesis conditions affecting the particle size and morphology were examined in detail. The well‐distributed copolymer microspheres were applied as low‐temperature improvers for diesel. The results showed excellent performance for high‐paraffin diesel at low temperatures. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effect of stabilizer concentration and controller structure and composition on polymerization rate and molecular weight development in RAFT polymerization of styrene in supercritical carbon dioxide

An experimental study on the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene in supercritical carbon dioxide is presented. A 38 mL, high-pressure view cell with two frontal and two lateral sapphire windows was used as reactor. Poly(styrene-block-dimethylsiloxane) was used as stabilizer. The performance as RAFT controllers of S-thiobenzoyl thioglycolic acid, methyl naphthalene dithiobenzoate, 4-methyl allyl dithiobenzoate, and benzyl-N,N-dimethyldithiocarbamate was compared. The effect of stabilizer concentration and controller structure and concentration on polymerization rate and molecular weight development was analyzed. Good performance was obtained with the first three controllers, although simultaneous high polymerization rates and low polydispersities were not possible with either of them. The performance of the fourth RAFT controller was poor.

Fluorinated rhodium-phosphine complexes as efficient homogeneous catalysts for the hydrogenation of styrene in supercritical carbon dioxide

A fluorinated trisphenylphosphine ligand was reacted with [(COD)CIRh]2 (COD = cyclooctadiene) and [(COD)2Rh]+BArF− {BArF = tetrakis[(3,5-bistrifluoromethyl)phenyl]borate} to synthesize new fluorinated derivatives of the well-known Wilkinson catalyst as {[P(Ph(CF3)2)3]3RhBArF}, {[P(Ph)3]3RhBArF} and {[P(Ph(CF3)2)3]3RhCl}. BArF anion was used to synthesize cationic complexes. All the synthesized complexes were tested and found to be soluble in supercritical carbon dioxide (scCO2) media. The catalytic activities of the rhodium complexes were examined for hydrogenation of styrene in scCO2. The catalysts showed different activities between 47.9–77.4%. The most effective result among the synthesized Rh-catalysts was obtained with a conversion of 77.4% corresponding to {[P(Ph(CF3)2)3]3RhBArF} under the reaction conditions of 343K temperature and 123 bar pressure after 8 h in scCO2 (molar ratio of substrate to catalyst = 500).

Nitroxide-mediated precipitation polymerization of styrene in supercritical carbon dioxide: Effects of monomer loading and nitroxide partitioning on control

Abstract Nitroxide-mediated solution and precipitation polymerizations of styrene in toluene and supercritical carbon dioxide (scCO2), respectively, using the nitroxides N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)]nitroxide (SG1) and 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO) are presented. Solution polymerizations are compared with simulations using PREDICI software, revealing that differences in the polymerization behaviours between the SG1- and TIPNO-mediated systems cannot be rationalized based on literature rate coefficients and the ideal mechanism for nitroxide-mediated polymerization. Nitroxide and monomer partitioning between the polymer particles and the continuous phase play important roles in the precipitation polymerizations in scCO2. Loss of control (broader molecular weight distributions) as a result of nitroxide partitioning is accentuated at low monomer loading, and is significantly more pronounced for TIPNO than SG1. However, at higher monomer loading the level of control was superior in scCO2 compared to in the corresponding solution polymerizations for both nitroxides, most likely caused by an increase in the number of activation-deactivation cycles experienced by any given chain during its growth.

Synthesis of polyhedral particles by dispersion polymerization in supercritical carbon dioxide

The novel synthesis of polyhedral particles was attained by the dispersion polymerization of styrene in supercritical carbon dioxide using a polydimethylsiloxane-based macroazoinitiator as a precursor of the surfactant. The macroazoinitiator, VPS-1001, composed of poly(dimethylsiloxane) and 6-8 molecules of the azo groups served as a precursor of the surfactant for the dispersion polymerization by azobisisobutylonitrile as an initiator to produce 0.8-4 μm polyhedral particles. The size of the particles decreased as a result of increasing the VPS-1001 concentration. Too high a concentration of VPS-1001 caused coagulation of the particles. A decrease in the temperature increased the particle size and size distribution, while a decrease in the pressure produced particles with nonspecific shapes. An increase in the stirring rotation speed tended to increase the size and size distribution. However, too high a speed of rotation also caused coagulation of the particles.

Palladocarbosilane dendrimers as catalysts for the asymmetric hydrovinylation of styrene in supercritical carbon dioxide

The palladocarbosilane dendrimers 2 and 3, containing the P-stereogenic phosphine [P(2-biphenylyl)PhCH 2] fragment, and the model compound Me 3Si(P(2-biphenylyl)PhCH 2)(PdCl(η 3-2-MeC 3H 4)), 1, were tested as precatalysts in the hydrovinylation of styrene, in supercritical CO 2 medium. Na[BARF] was used as a cocatalyst. In all cases, the activity was somewhat less than that observed in CH 2Cl 2, but the selectivity and enantiomeric excess were excellent and comparable with the results obtained using the conventional solvent.

Synthesis of polystyrene microspheres by dispersion polymerization in supercritical carbon dioxide using a poly(dimethylsiloxane)-based macroazoinitiator

The synthesis of polystyrene microspheres was achieved by the dispersion polymerization of styrene in supercritical carbon dioxide using azobisisobutylonitrile (AIBN) and a poly(dimethylsiloxane) (PDMS)-based macroazoinitiator, VPS-1001. VPS-1001 contained seven to nine molecules of the azo groups and the PDMS blocks with a molecular weight of 10,000 per molecule. The polymerization in the presence of both VPS-1001 and AIBN produced polystyrene microspheres with a diameter below 4 μm in over 85% yields, whereas the polymerization with VPS-1001 in the absence of AIBN provided a nonspecific polystyrene in only 20% yield. The particle size decreased as a result of increasing the concentration of VPS-1001. It was confirmed that the polystyrene particles were stabilized by the PDMS-block-polystyrene formed through the polymerization initiated by VPS-1001 because the polymerization using a PDMS homopolymer provided nonspecific polystyrene as a precipitate during the polymerization.

Nitroxide‐Mediated Radical Precipitation Polymerization of Styrene in Supercritical Carbon Dioxide

AbstractNitroxide‐mediated controlled/living radical precipitation polymerization of styrene in supercritical carbon dioxide has been performed using SG1 and AIBN as mediator and initiator, respectively. The equivalent bulk polymerization proceeded at a rate ≈1.58 times faster than the precipitation polymerization. The number of chains increased with conversion to a similar extent in precipitation and bulk systems. A chain transfer mechanism to the Diels‐Alder dimer is used to explain the increase in numbers of chains. High conversions were also achieved for a conventional precipitation polymerization of styrene in scCO2 at 110 °C. The polymer was obtained as a powder, which contained cavities when observed under an SEM.magnified image

Dispersion polymerization of styrene in supercritical CO 2 in the presence of non-fluorous random copolymeric stabilizers

The non-fluorous random copolymers, poly (3-[tris(trimethylsilyloxy)silyl]propyl methacrylate- co-2-dimethylaminoethyl methacrylate) (poly(SiMA- co-DMAEMA)) and poly (3-[tris(trimethylsilyloxy)silyl]propyl methacrylate- co-diisopropylaminoethyl methacrylate) (poly(SiMA- co-DPAEMA)) were prepared with different comonomer compositions and utilized as stabilizers in the dispersion polymerization of styrene in supercritical carbon dioxide (scCO 2). The copolymers were found to provide an effective stabilization on the polystyrene (PS) latexes in scCO 2. Poly(SiMA- co-DMAEMA) (71:29) were proved to be optimal among (86:11), (71:29), and (57:33) comonomer compositions to produce micron-sized spherical PS particles with higher yields. Poly(SiMA- co-DPAEMA) having higher methyl branching in the DPAEMA pendant group provided a better stabilization compared to poly(SiMA- co-DMAEMA). The effect of varying concentration of stabilizer and monomer upon the polymerization yield, molar mass, and morphology of PS have been investigated.

Nitroxide-Mediated Radical Dispersion Polymerization of Styrene in Supercritical Carbon Dioxide Using a Poly(dimethylsiloxane-b-methyl methacrylate) Stabilizer

Nitroxide-mediated controlled/living dispersion polymerization of styrene in supercritical carbon dioxide (scCO2) has been performed successfully to high conversion using N-tert-N-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide (SG1) and a poly(dimethylsiloxane-b-methyl methacrylate) stabilizer at 110 °C. The molecular weight distributions were narrow (Mw/Mn = 1.12−1.43), and the number-average molecular weight (Mn) values agreed well with theory. A large excess of free SG1 was required to obtain satisfactory control in the dispersion polymerization, possibly due to SG1 partitioning. The critical degree of polymerization at which the polymer precipitates (Jcrit) was determined as 28 by visual observation using a novel approach. Polymerizations conducted in solution (toluene) proceeded at a similar rate (∼20% faster) to those in scCO2. The number of chains increased with conversion in both dispersion and solution, with the greater increase being observed in the dispersion system.

Nitroxide‐Mediated Radical Dispersion Polymerization of Styrene in Supercritical Carbon Dioxide Using a Poly(dimethylsiloxane‐block‐styrene) Alkoxyamine as Initiator and Stabilizer

AbstractSummary: Nitroxide‐mediated dispersion polymerization of styrene in supercritical carbon dioxide has been performed successfully at 110 °C using a new polymeric so‐called inistab species, which fulfils the dual functions of an initiator and a colloidal stabilizer. The inistab species comprised a poly(dimethylsiloxane) block and a polystyrene block end‐capped with the nitroxide N‐tert‐N‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] nitroxide (SG1). The dispersion polymerization resulted in sub‐micron sized polymer particles and polymers of narrow polydispersity.TEM micrograph of PS particles prepared in the dispersion polymerization of S in scCO2 in the presence of PDMS(\overline M _{\rm n} = 6 500)‐b‐PS(\overline M _{\rm n} = 4 500)‐SG1 at 110 °C.magnified imageTEM micrograph of PS particles prepared in the dispersion polymerization of S in scCO2 in the presence of PDMS(\overline M _{\rm n} = 6 500)‐b‐PS(\overline M _{\rm n} = 4 500)‐SG1 at 110 °C.

Asymmetric Hydroformylation of Styrene in Supercritical Carbon Dioxide

Hydroformylation reactions in supercritical carbon dioxide can provide an environmentally conscious method of producing aldehydes for fine-chemical and pharmaceutical products. Asymmetric ligands, such as (R)-BINAP, can be used to provide an enantioselective product. When these reactions are performed in environmentally benign solvents, such as supercritical carbon dioxide (scCO2), additional environmental benefits are derived, such as ease of recycling of the solvent and unconverted reactants and elimination of the need for organic solvents. Rhodium-based catalysts have been prepared through the solid-phase reaction of catalyst precursors in supercritical carbon dioxide and evaluated for the hydroformylation of styrene to produce 2-phenylpropionaldehyde. Triphenylphosphine and (R)-BINAP were tested as ligands, and their effects on the reaction were examined. The catalyst, formed in situ in supercritical carbon dioxide (scCO2), was found to promote the hydroformylation of styrene with enantiomeric selecti...

First nitroxide-mediated free radical dispersion polymerizations of styrene in supercritical carbon dioxide

Controlled/living character has been demonstrated for the first time in nitroxide-mediated free radical dispersion polymerizations in supercritical carbon dioxide. Styrene was polymerized in the presence of N- tert-butyl- N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1) at 110 °C. Stabilization was achieved using the inistab concept (initiator+stabilizer), employing a poly(dimethylsiloxane) (PDMS) based azo initiator as well as a polymeric alkoxyamine macroinitiator with the expected structure SG1-polystyrene-PDMS-polystyrene-SG1. In the presence of sufficient amounts of the inistab, the polymerizations proceeded to high conversion to yield the polymeric product as a powder. Control was indicated by the number-average molecular weights increasing linearly with conversion in reasonable agreement with the theoretical values. Although the molecular weight distributions were broad in many cases, chain extensions in bulk and solution using styrene indicated high degrees of ‘living’ character.

Dispersion polymerization of styrene in supercritical carbon dioxide using monofunctional perfluoropolyether and silicone-containing fluoroacrylate stabilizers

The free radical dispersion polymerization of styrene was carried out in supercritical carbon dioxide (scCO 2) using two different stabilizers. The polymerizations are performed in the presence of poly(heptadecafluorodecyl acrylate- co-tris(trimethylsilyloxy)silyllpropyl methacrylate) p(HDFDA- co-SiMA) and a commercially available carboxylic acid-terminated perfluoropolyether (Krytox ® 157FSL) as polymerization stabilizers. Dry, fine powdered spherical polystyrene particles were produced under optimised conditions. The resulting high yield of spherical and relatively uniform micron-size polystyrene particles were formed utilizing various amounts of p(HDFDA- co-SiMA) random copolymer. However, it was observed that Krytox ® 157FSL was not a good stabilizer as p(HDFDA- co-SiMA) for the dispersion polymerization of styrene. The particle diameter was shown to be dependent on the type of the stabilizer and the weight percent of the stabilizer added to the system. The effect of varying the concentrations of stabilizers and initiator, reaction time and reaction pressure upon the polymerization yield, molar mass and morphology of polystyrene have been investigated.