Synthesis of Poly(N-isopropylacrylamide) in Supercritical Carbon Dioxide and Properties of Aqueous Solutions of the Obtained Polymers

Preliminary Evaluation of Polymer-Based Drug Composite Microparticle Production by Coacervate Desolvation with Supercritical Carbon Dioxide

'This report summarizes the results of work done during the first 1.3 years of a three year project. During the first nine months effort focussed on the design, construction and testing of a closed recirculating system that can be used to study photochemistry in supercritical carbon dioxide at pressures up to 5,000 psi and temperatures up to about 50 C. This was followed by a period of work in which the photocatalytic oxidation of benzene and acetone in supercritical, liquid, and gaseous carbon dioxide containing dissolved oxygen was demonstrated. The photocatalyst was titanium dioxide supported on glass spheres. This was the first time it was possible to observe photocatalytic oxidation in a supercritical fluid and to compare reaction in the three fluid phases of a solvent. This also demonstrated that it is possible to purify supercritical and liquid carbon dioxide using photochemical oxidation with no chemical additions other than oxygen. The oxidation of benzene produced no intermediates detectable using on line spectroscopic analysis or by gas chromatographic analysis of samples taken from the flow system. The catalyst surface did darken as the reaction proceeded indicating that oxidation products were accumulating on the surface. This is analogous to the behavior of aromatic compounds in air phase photocatalytic oxidation. The reaction of acetone under similar conditions resulted in the formation of low levels of by-products. Two were identified as products of the reaction of acetone with itself (4-methyl-3-penten-2-one and 4-hydroxy-4-methyl-2-pentanone) using gas chromatography with a mass spectrometer detector. Two other by-products also appear to be from the self-reaction of acetone. By-products of this type had not been observed in prior studies of the gas-phase photocatalytic oxidation of acetone. The by-products that have been observed can also be oxidized under the treatment conditions. The above results establish that photocatalytic oxidation of organic compounds in supercritical carbon dioxide can be achieved. Until recently it was not possible for us to obtain high quality, quantitative kinetic data. The original flow cell used to obtain UV-Visible spectra on the recirculating fluid did not provide quantitative concentration data because the sapphire windows did not have adequate transmission characteristics below about 240 nm. A pair of windows with better transmission properties arrived as this report was being prepared. While waiting for the replacement windows for the flow cell, the concentration of reactants was monitored by withdrawing samples of the fluid stream for gas chromatographic analysis. This allowed progress to be made in determining some of the factors that affected the rates of reaction in a qualitative sense but the results had large error bars due to the difficulty in obtaining reproducible samples from the pressurized system using gas tight syringes. This problem was recently solved by incorporating a gas chromatograph with automatic sampling valves into the flow system. The two on line analytical methods will now result in reliable analytical data that can be used to follow the reaction kinetics and detect and identify reaction intermediates and by-products, if any are formed.'

Integration and conversion of supercritical carbon dioxide coal-fired power cycle and high-efficiency energy storage cycle: Feasibility analysis based on a three-step strategy

We report the formation of self-assembled monolayers (SAMs) on gold substrates by exposure to n-alkanethiols [CH3(CH2)n-1SH; n = 8, 10, 12, 16, and 18] in liquid and supercritical carbon dioxide. The results of this novel study show that an environmentally friendly solvent can be used to form highly crystalline SAMs with few gauche defects and that pressure as well as exposure time can be used to affect the structural and barrier properties of the monolayer film. Reflectance infrared spectroscopy, electrochemical impedance spectroscopy, and wetting measurements were used to characterize the SAMs. The effects of pressure (76−300 bar) and adsorption time (3−90 min) on the formation of the SAMs were explored. The overall chain density of these SAMs was greater than that for SAMs formed in common organic solvents such as ethanol. The properties of the SAMs were slightly affected by the pressure during formation. At 35 °C, as the carbon dioxide pressure increased (from 76 to about 140 bar), the packing density and resistance of the SAM increased. SAMs prepared at higher pressures ranging from about 140 to 300 bar exhibited similar resistances, capacitances, and canted structures. There was also no significant difference in using liquid (25 °C and 103 bar) or supercritical (35 °C and 103 bar) carbon dioxide for SAM formation. Supercritical carbon dioxide also enabled the formation of SAMs using polar adsorbates (−OH- and −CO2H-terminated thiols) to prepare high-energy surfaces that are wet by water.

ABSTRACTThe findings of this study suggests that chemical composition, essential oil yield, antioxidant and antimicrobial activity of Boswellia serrata oleo gum resin essential oils extracted by hydro distillation, steam distillation and supercritical fluid carbon dioxide methods vary greatly from each other. The optimum essential oil yield was obtained using hydro distillation method (8.18 ± 0.15 %). The essential oils isolated through different extraction methods contained remarkable amounts of total phenolics and total flavonoids. Essential oil isolated through supercritical fluid carbon dioxide extraction exhibited better antioxidant activity with highest free radical scavenging potential (96.16 ± 1.57 %), inhibition of linoleic acid oxidation (94.18 ± 1.47 %) and hydrogen peroxide free radical scavenging potential (68.25 ± 1.02 %). Moreover, the antimicrobial activity of essential oils was performed through well diffusion, resazurin microtiter plate and micro dilution broth assay assays. The essential oil isolated through steam distillation method revealed highest antimicrobial activity with maximum inhibition zone (24.21 ± 0.34 to12.08 ± 0.30 mm) and least MIC values (35.18 ± 0.77 to 281.46 ± 7.03 µg/mL). The comparison of chemical composition of essential oils isolated at different extraction methods have shown that the concentration of α-thujene, camphene, β-pinene, myrcene, limonene, m-cymene and cis-verbenol was higher in steam distilled essential oil as compared to hydro and supercritical fluid carbon dioxide extracted essential oils. These compounds may be responsible for the higher antimicrobial activity of Boswellia serrata oleo gum resin steam distilled essential oil.

The study of currently known methods and devices for processing plant materials has shown that during the study period, the greatest interest (about 31%) of patent holders is manifested in increasing the yield of extractive substances. If we take as an example a tea leaf, then indeed, the formation of conditions for a more complete release of the target components into the aqueous phase during brewing can provide a more profitable and economical consumption of tea raw materials. The study of the thermodynamic principles of the use of supercritical fluid media and carbon dioxide, in particular, in the processing of plant materials and the processing of tea raw materials, as well as the development of methods for intensifying mass transfer to the aqueous phase when “brewing” tea leaves, are uniquely relevant tasks. An important section of thermodynamics is the concept of phase equilibria in systems of different composition. And one of the key characteristics of phase equilibria is such a thing as the solubility of a substance, including in supercritical fluid media. Since solutions of substances in supercritical fluids are diluted, the dependence of the solubility of substances on temperature, pressure, and density of a pure solvent near its critical point is of practical interest. The results of experimental studies of measuring the solubility of tannin in supercritical carbon dioxide by the dynamic method at a temperature of 308 and 333 K, in the pressure range from 8 to 26 MPa, are presented. The data obtained, firstly, indicate a low solubility of tannin in supercritical carbon dioxide, which is a positive moment for the implementation of the tea leaf pretreatment process in order to improve its biological potential, and secondly, a clear suppression of isolines is observed, which in turn indicates the presence of crossover behavior on solubility isotherms. Based on the results of the obtained experimental data on the solubility of tannin in supercritical carbon dioxide, a mathematical description of the solubility of tannin was carried out by the Peng-Robinson equation of state.

s and Presentations: 1. Jung Jae Koh. Versatile Methods of Synthesis for Blue Light-Emitting Pyrylium Salts. ACS Southern Nevada Section Poster Competition (November, 2014) 2. Tae Soo Jo, Jung Jae Koh, Haesook Han, Jongwon Park, Bidyut Biswas, andPradip K. Bhowmik.Synthesis of poly(pyridinium salt)s containing fluorene moieties in the main- chain with various organic counterions. ACS Southern Nevada Section Poster Competition (November, 2013) 3. Tae Soo Jo, Jung Jae Koh, Alexi K. Nedeltchev, Haesook Han, Pradip K. Bhowmik,and Hari D. Mandal. Synthesis and characterization of poly(pyridinium salt)s containing dioxyethylene units in the main-chain and their sensing performance toward acids in organic solvents. Poster Presentations, American Association for the Advancement of Science, Pacific Division 94 th Annual Meeting, Las Vegas, June 2013. 4. Tae Soo Jo, Jung Jae Koh, Haesook Han, Jongwon Park, Bidyut Biswas, andPradip K. Bhowmik.Synthesis of poly(pyridinium salt)s containing fluorene moieties in the main- chain with various organic counterions. Abstracts of Papers, 245 th ACS National Meeting & Exposition, New Orleans, LA, United States, April7−11, 2013. 5. Tae Soo Jo, Jung Jae Koh, Haesook Han, Pradip K. Bhowmik, and Hari D. Mandal. Synthesis of poly(pyridinium salt)s containing heterocyclic pyridine and triphenylamine moieties in the main-chain and their solution, thermal and optical properties. Abstracts of Papers, 245 th ACS National Meeting & Exposition, New Orleans, LA, United States, April 7−11, 2013. 6. Tae Soo Jo, Jung Jae Koh, Alexi K. Nedeltchev, Haesook Han, Pradip K. Bhowmik,and Hari D. Mandal. Synthesis and characterization of poly(pyridinium salt)s containing dioxyethylene units in the main-chain and their sensing performance toward acids in organic solvents. Abstracts of Papers, 245 th ACS National Meeting &Exposition, New Orleans, LA, United States, April 7−11, 2013. 7. Tae Soo Jo, Jung Jae Koh, Haesook Han, Jongwon Park, Bidyut Biswas, andPradip K. Bhowmik.Synthesis of poly(pyridinium salt)s containing fluorene moieties in the main- chain with various organic counterions. Poster Presentations, UNLV's First Annual Stem Summit – January 15th, 2013. 8. Tae Soo Jo, Jung Jae Koh, Haesook Han, Jongwon Park, Bidyut Biswas, andPradip K. Bhowmik.Synthesis of poly(pyridinium salt)s containing fluorene moieties in the main- chain with various organic counterions. Poster Presentations, American Chemical Society (ACS) Southern Nevada Local Section Poster Competition – December 13th, 2012.

Erratum: Preparation of Poly(pentafluorophenyl acrylate) Functionalized SiO2 Beads for Protein Purification.

Synthesis of poly(vinyl pivalate) by atom transfer radical polymerization in supercritical carbon dioxide

The dispersion polymerization of poly (L-lactide)(PLLA) in supercritical carbon dioxide (ScCO2) with stannous octoate (Sn(Oct)2) as a catalyst and n-butanol as an initiator was studied. An amphiphilic triblock copolymer was synthesized by the ring-opening polymerization ofe-caprolactone (e-CL) with the hydroxylpropyl-terminated polydimethylsiloxane (HTPDMS) as the macromolecule initiator and then chosen as the stabilizer in the synthesis of PLLA. With the concentrations of 3 wt % (stabilizer/monomer), fine powder formed PLLAs were obtained. The effects of operating parameters such as pressure, temperature and stirring rate on the properties of the synthesized PLLAs were investigated. The results showed that the temperature had the greatest effect on the conversion and the stirring rate was the most important factor which determined the morphology of the products. An obvious increase of conversion was observed when the temperature increased from 80 °C to 100 °C. The influence of stirring rate on the morphology was achieved through the anchoring of the stabilizer with the growing polymer chains. The stirring rate of 300 rpm was turned out to be necessary and adequate. When the stirring rate increased or decreased out of the range of (300 ± 100)rpm, only agglomerates were obtained.

Controlled dispersion atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out in supercritical carbon dioxide in the presence of aminated fluoropolymers. These materials played the dual role of macroligand for the copper bromide and also steric stabilizer to support formation of polymer microspheres. The livingness of the PMMA beads was confirmed by the one-pot two-step PMMA chain extension and the synthesis of poly(methyl methacrylate)-b-poly(2,2,2-trifluoroethyl methacrylate) (PMMA-b-PFMA) diblock copolymer in scCO2. Successful activator generated by electron transfer (AGET) for ATRP of MMA, using tin ethylhexanoate as a reducing agent, is also discussed, and the concept of dispersion ATRP of MMA was successfully extended to the controlled dispersion polymerization of styrene by ATRP leading to the formation of PS microparticles. Finally, due to the high solubility of the catalyst in scCO2, the purification of PMMA was investigated by supercritical fluid ext...

Poly(p-dioxanone)–poly(ethylene glycol)–poly(p-dioxanone) triblock copolymers (PPDO–PEG–PPDO) were first synthesized by suspension ring-opening polymerization (ROP) of p-dioxanone (PDO) in supercritical carbon dioxide (scCO2) using different molecular weights (2–10 K) of poly(ethylene glycol) (PEG) as macroinitiators. White and fine flow powders were successfully obtained when the molecular weight of PEG was below 6 K and its feed content below 20 wt.%. The 1H nuclear magnetic resonance (NMR) result indicated the formation of PPDO–PEG–PPDO block structure even in a confined polymerized environment of particles. All the powderous samples contained irregular shaped particles that were observed by scanning electron microscope (SEM). Except for the copolymer with 10 wt.% PEG10K feed content, the mean particle sizes of other powderous samples showed identical values close to 15 μm. This fact was in agreement with the crystallinity of PPDO in the copolymers measured by differential scanning calorimetry (DSC). The water absorption of these copolymers was also measured, and as compared with PPDO homopolymer, the introduction of PEG increased the water absorption of the copolymers. The green and environmentally friendly method disclosed in this work is attractive to directly synthesize biodegradable polymeric particles with potential biomedical applications.

Synthesis of poly(2,2,2-trifluoroethyl methacrylate) by supported ATRP was investigated in supercritical carbon dioxide using a copper salt ligated to a polymeric ligand immobilised onto silica; after polymerisation, fluorinated polymers with well defined molecular weight and low polydispersity were obtained.

The reaction between poly(4,4′-isopropylidene-2,2′-diphenylene (tere)isophthalate) copolymer and 3-aminopropyltriethoxysilane was investigated in supercritical carbon dioxide at 150 atm and 100° C. It was found that ester bonds in the copolyarylate undergo aminolysis under the above conditions to give rise to the formation of siloxane-containing amides, whose interaction with phenol groups of the macromolecules and moisture affords an insoluble poly(arylate-co-siloxane) fraction. Under the action of moisture, three-dimensional structures containing polyarylate and polysiloxane fragments are formed in the soluble fraction of the copolymer via the combined hydrolysis of ethoxysilane groups. The formation of the siloxane network affects the properties of the polymers. In particular, thermomechanical and thermal tests showed that sample deformation at 250°C decreases from 80 to 15%, while the carbon residue at 725°C increases twofold as compared to that of an initial polyarylate sample.

Triblock (A-B-A) oligomers of e-caprolactone (e-CL) (A) and poly(ethylene glycol) with an average molecular weight of 400 (PEG400) (B) were synthesized with three different molecular weight in the range of 2–6 kDa by changing the ratio of PEG400/e-CL. These oligomers were then used in dispersion polymerization of L-lactide in supercritical carbon dioxide (scCO2) as stabilizers. 5% stabilizer in the polymerization recipe allowed synthesis of poly(L-lactide) (PLLA) in scCO2 in the powder form with a weight average molecular weight of around 60 kDa with polymerization yields around 80%. Interestingly, there was almost no effect of stabilizer molecular weight on polymerization. L-lactide polymerization in scCO2 without any stabilizer was also possible but both the PLLA molecular weight and polymerization yield were lower, and the product was as aggregates instead of powders. A stabilizer concentration of 5% in the polymerization recipe was found adequate. Further increases in the stabilizer load resulted lower molecular weights and lower yields.