Polymers In Supercritical Carbon Dioxide Research Articles

Antifouling performance of poly(acrylonitrile)-based membranes: From green synthesis to application

In order to develop clean ultrafiltration membranes able to prevent the fouling of biological compounds in filtration processes, poly(ethylene glycol) methyl ether acrylate (PEGA) was grafted to poly(acrylonitrile) (PAN) by free-radical polymerization in supercritical carbon dioxide (scCO2) and the grafted copolymer was blended with PAN to fabricate porous membranes using scCO2-induced phase inversion method. Fourier transform infrared (FT-IR) analysis, 1H nuclear magnetic resonance (1H NMR) and differential scanning calorimetry (DSC) confirmed that the poly(acrylonitrile)-graft-poly(ethylene oxide) (PAN-g-PEO) was successfully synthesized, for the first time, in scCO2. The effect of increasing PEGA content on the initial monomer feed mixture on graft polymer morphology and average molecular weight was studied. Blended membranes with different PEGA contents were investigated by scanning electron microscopy (SEM), mercury porosimetry and dynamical mechanical analysis (DMA) to characterize their morphological, physico-chemical and mechanical properties. Moreover, water contact angle measurements, pure water permeability and filtration experiments were performed to evaluate membrane hydrophilicity and fouling resistance properties. Permeation experiments of model foulants, bovine serum albumin (BSA) and starch solutions were used to investigate antifouling character of blend membranes at different pHs. PAN:PAN-g-PEO (70:30) showed to be the ultrafiltration membrane with best performance. Furthermore, comparing with conventional technologies blended membranes of PAN:PAN-g-PEO prepared by a scCO2-assisted process showed enhanced hydrophilicity, larger protein and starch solution permeabilities and good resistance to irreversible fouling, indicating that the technology is an efficient process to prepare fouling resistant membranes for biomacromolecule separations.

Grafting modification of ramie fibers with poly(2,2,2-trifluoroethyl methacrylate) via reversible addition–fragmentation chain transfer (RAFT) polymerization in supercritical carbon dioxide

Reversible addition–fragmentation chain transfer (RAFT) polymerization was used to control the grafting of 2,2,2-trifluoroethyl methacrylate (TFEMA) with ramie fibers in supercritical carbon dioxide (scCO 2). The hydroxyl groups of the ramie fibers were converted to 2-dithiobenzoyl isobutyrate as the RAFT chain transfer agent (cellulose-CTA). Then, the subsequent grafting with TFEMA was mediated by RAFT polymerization in the presence of 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate (ECPDB) as the free RAFT chain transfer agent (free CTA). The modified ramie fibers were highly hydrophobic with water contact angles of up to 149°. Size exclusion chromatography showed narrow polydispersity (PDI = 1.28) of the grafted poly(TFEMA) chains. This grafting polymerization process is a novel and environmentally friendly approach for the preparation of functional grafted copolymers utilizing ramie fiber biomass.

Synthesis of Powdered Polymeric Microparticles by Using Supercritical Carbon Dioxide as the Polymerizing Medium

Polystyrene microparticles were synthesized by emulsion polymerization in supercritical carbon dioxide (sc-CO2) using (polydimethylsiloxane) (PDMS) as a surfactant/stabilizer and azobisisobutyronitrile (AIBN) as initiator. The emulsion polymerization was carried out by varying pressures within the range 13.79–17.93 MPa. At the end of polymerization, powdered polymeric micoparticles were collected by depressurizing CO2. The powdered polymeric microparticles were characterized by SEM, GPC, DSC and TGA. The influence of pressure on conversion, molecular weight, particle size and polydispersity index was studied. The molecular weight (Mn) of the polymer is in the range of 35,542 to 45,078 g/mol. Polydispersity index is in the range of 1.45–1.86 and particle size in the range of 3.25 µm–6.3 µm.

Dispersion polymerization in supercritical carbon dioxide using comb-like fluorinated polymer surfactants having different backbone structures

Comb-like fluorinated polymers with different backbone structures, poly(heptadecafluorodecyl acrylate) (PA-R f), poly[oxy[(2-perfluorooctylethylene)thiomethyl]ethylene] (PEO-R f), and poly[ p-[[(perfluorooctylethylene)thio]methyl]styrene] (PS-R f), were used as surfactants in dispersion polymerization to examine the effect of backbone structure on the formation of polymer particles. Dispersion polymerization of monomers with different polarities using these comb-like fluorinated polymer surfactants in CO 2 showed that PEO-R f containing a polar oxyethylene backbone was an effective surfactant for the dispersion polymerization of a polar monomer, such as N-vinyl-2-pyrrolidone, whereas PA-R f was effective for less polar monomers, such as methyl methacrylate and N-vinyl caprolactam.

Preparation of Silica/Poly(divinylbenzene) Composite Particles by Dispersion Polymerization in Supercritical Carbon Dioxide

Silica/poly(divinylbenzene) (PDVB) composite particles were synthesized by the dispersion polymerization of divinylbenzene (DVB) with ultrafine silica particles in supercritical carbon dioxide (scCO2). Silica particles of average diameter 130 nm were pretreated with 3-(trimethoxysilyl) propyl methacrylate in order to be well dispersed in CO2 and participated in the polymerization. Random copolymeric dispersant, poly(diisopropylaminoethyl methacrylate-co-heptafluorobutyl methacrylate) was used as a stabilizer to provide sufficient stabilization to latexes in scCO2 and the silica/PDVB composite powder was obtained in high yield from the polymerization. SEM analysis revealed that the composite particles prepared at 5% silica loading ratio and 6% stabilizer concentration with respect to monomer have the average diameter of 1.60 μm with uniform and spherical morphology. The composites were also characterized by FTIR spectroscopy and TGA.

Synthesis of cross-linked poly(methyl methacrylate) via dispersion polymerization in supercritical carbon dioxide

Cross-linked poly(methyl methacrylate) particles were prepared via dispersion polymerization in supercritical carbon dioxide (scCO2) using poly(heptadecafluorodecyl methacrylate) (PHDFDMA) and 2,2′-azobisisobutyronitrile as the dispersant and the initiator, respectively. The following chemicals were used as cross-linking agents: ethylene glycol dimethacrylate (EGDMA), 1,4-buthanediol di(meth)acrylate (1,4-BD(M)A), and trimethylolpropane trimethacrylate. PHDFDMA was synthesized by solution polymerization in scCO2. We investigated the effect of the chemical structure, concentration of the cross-linking agents, reaction pressure, and CO2 density on the morphology, the polydispersity, and the cross-linking density of polymer particles. The resulting polymer particle was characterized by field emission SEM, differential scanning calorimetry, and thermal gravimetric analysis. The cross-linked PMMA particles is more agglomerate as the cross-linking agent concentration increased and as pressure decreased at constant temperature. Glass-transition temperature (Tg) of the resulting polymer increased as the cross-linking agent increased with temperature and pressure increasing at the same CO2 density. Decomposition temperature is slightly increased as 1,4-BDA concentration increased. From these results, we can confirm that the thermal stability of the polymer increased as the cross-linking agent and EGDMA is the best cross-linking agent in term of the thermal stability.

Effect of Monomer Loading and Pressure on Particle Formation in Nitroxide-Mediated Precipitation Polymerization in Supercritical Carbon Dioxide

The critical degree of polymerization (Jcrit) at which polymer chains become insoluble in the continuous medium and particle formation commences has been estimated under a variety of experimental conditions for the nitroxide-mediated precipitation polymerizations of styrene (St) at 110 °C and tert-butyl acrylate (t-BA) at 118 °C in supercritical carbon dioxide (scCO2) mediated by N-tert-butyl-N-[1-diethylphosphono(2,2-dimethylpropyl)]oxy (SG1). The value of Jcrit increases with increasing target molecular weight, initial monomer loading, and pressure. Under the conditions investigated, Jcrit for t-BA is higher than that for St, which is consistent with greater solubility of poly(acrylates) in neat scCO2. A simple graphical approach has been developed and successfully employed, whereby Jcrit can be predicted as a function of both target molecular weight and initial monomer loading on the basis of a data set of Jcrit versus initial monomer loading.

Pulsed Breakdown and Plasma‐Aided Phenol Polymerization in Supercritical Carbon Dioxide and Sub‐Critical Water

AbstractThis paper deals with two fundamental experimental studies with respect to plasma processes in highly pressurized carbon dioxide (CO2) and water: pulsed discharge phenomena in CO2 up to supercritical condition as a basic study of plasma production and polymerization of phenol with a pulsed discharge plasma in sub‐critical water as an application of a discharge plasma for chemical reactions. The experiments showed that: 1) the measured electrical breakdown voltage in supercritical CO2 had a relatively large dispersion compared with that in the gas and liquid phases, and was almost independent of the CO2 density, 2) the delay time for breakdown increased gradually with increasing density, and there was a large fluctuation around the sub‐critical phase or high‐pressure gas phase, 3) the highest conversion of phenol into products in the water experiments under temperatures of 301 to 525 K and pressures of 0.1 to 20 MPa was about 17% under the experimental condition of 523 K, 20 MPa and 4 000 pulsed discharge shots and 4) phenol synthesis could only be obtained at higher temperatures in pulsed discharge plasma.magnified image

Preparation of silica/perfluoroalkyl methacrylate polymer inorganic/organic particles in supercritical carbon dioxide

Silica/perfluoroalkyl methacrylate polymer (PHDFDMA) particles were prepared using various types of silica by polymerization in supercritical carbon dioxide. There are three steps in the fabrication of inorganic/organic hybrid composites: silane treatment, polymerization, and soxhlet extraction. After these steps, we observed the morphology of silica/PHDFDMA particles using field emission scanning electron microscope and transmission electron microscope. From these analyses, we can confirm that the silica/PHDFDMA core/shell particles were obtained when we used Ludox and silica gel as a silica template. On the other hand, core/shell particles were not formed when using fused silica and precipitated silica. In addition, to confirm the amount of polymer on silica, we performed an analysis using thermogravimetric analysis and electron probe micro-analyzer. In this case, PHDFDMA was approximately 20 wt.% on the silica gel and 40 wt.% on the Ludox, respectively. When using fused silica and precipitated silica as a template, amount of PHDFDMA on silica was maximum 5 wt.% and over 40 wt.%, respectively. From these results, to obtain enough PHDFDMA encapsulated silica particle, colloidal silica, Ludox is the best template in four different types of silica.

NMR study of vinylpyrrolidone polymerization in supercritical carbon dioxide

NMR study of vinylpyrrolidone polymerization in supercritical carbon dioxide

Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: A model for understanding the molecular-weight distribution

Poly(vinylidene fluoride) (PVDF) that is synthesized by precipitation polymerization in supercritical carbon dioxide (scCO 2) has a bimodal molecular weight distribution (MWD) and a very broad polydispersity index (PDI) under certain reaction conditions. Different models have been formulated to account for this behavior. This paper presents a homogenous model for a continuous stirred-tank reactor (CSTR) that includes the change of the termination reaction from kinetic control to diffusion control as the chain length of the polymeric radicals increases, and accounts for the change in the termination rate constant with macroradical chain length in the diffusion-controlled region. The model also includes the chain transfer to polymer reaction. Comparison of the model output with experimental data demonstrates that changes of the MWD, including the development of a bimodal distribution, with such reaction conditions as monomer concentration and average residence time are successfully predicted. In addition, the model can capture the occurrence of gelation, which appears to be responsible for a region of inoperability that was observed in the polymerization experiments. The success of this homogeneous model is consistent with recent research demonstrating that the CO 2-rich phase is the main locus of polymerization for the precipitation polymerization of vinylidene fluoride and vinylidene fluoride/hexafluoropropylene mixtures in scCO 2, at the conditions that have been studied to date.

Silicon‐Based and Fluorinated Polymeric Surfactants for Nitroxide Mediated Dispersion Polymerization in Supercritical Carbon Dioxide

AbstractBlock copolymers based on siloxanes and fluorinated block copolymers were synthesized and tested as surfactants for nitroxide mediated polymerizations (NMP) in supercritical carbon dioxide. Styrene was polymerized in the presence of TEMPO at 130 °C using various surfactants. Siloxane‐based surfactants were synthesized by a new route based on NMP; the perfluorinated surfactants were also synthesized by NMP. The dispersion polymerizations of styrene in scCO2 reveal conversions of up to 35% in 4 hours at 19.1 MPa. The resulting polydispersity indices lie in the range 1.2–1.4. The best results are obtained using a perfluorinated surfactant. Preliminary copolymerization experiments of the polystyrene macroinitiator in scCO2 have shown successful chain‐extension with butyl acrylate (BuA) resulting in the formation of a poly (St‐b‐BuA) block copolymer.

Phase behaviour of l-lactic acid based polymers of low molecular weight in supercritical carbon dioxide at high pressures

The results of investigations of phase behaviour in the systems l-lactic acid based polymers + carbon dioxide at high pressures are presented. The measurements have been performed in wide temperature and composition ranges. Two samples of the polymer differing in molecular weight ( M n: 1080 and 3990 g/mol) have been investigated. Both samples of the polymer were characterized with the gel permeation chromatography and NMR spectroscopy. The influence of the structure of the polymer on the solubility in supercritical carbon dioxide has been discussed. The results obtained suggest that the solubility of low molecular weight l-lactic acid based polymers in supercritical carbon dioxide is not controlled by its size, but to a large extent by the character of its terminal groups. The phase behaviour in the system l-lactic acid + carbon dioxide has been also investigated and the results were compared with those for the systems composed of l-lactic acid based polymers and carbon dioxide.

Controlled/living heterogeneous radical polymerization in supercritical carbon dioxide

AbstractSupercritical carbon dioxide (scCO2) is an inexpensive and environmentally friendly medium for radical polymerizations. ScCO2 is suited for heterogeneous controlled/living radical polymerizations (CLRPs), since the monomer, initiator, and control reagents (nitroxide, etc.) are soluble, but the polymer formed is insoluble beyond a critical degree of polymerization (Jcrit). The precipitated polymer can continue growing in (only) the particle phase giving living polymer of controlled well‐defined microstructure. The addition of a colloidal stabilizer gives a dispersion polymerization with well‐defined colloidal particles being formed. In recent years, nitroxide‐mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition fragmentation chain transfer (RAFT) polymerization have all been conducted as heterogeneous polymerizations in scCO2. This Highlight reviews this recent body of work, and describes the unique characteristics of scCO2 that allows composite particle formation of unique morphology to be achieved. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3711–3728, 2009

Organic–inorganic polypyrrole‐surface modified SiO2 hybrid nanocomposites: a facile and green synthetic approach

AbstractOrganic–inorganic hybrid nanocomposites composed of conductive polypyrrole (PPy) and surface modified silica (SiO2) were successfully prepared through an in situ chemical oxidative polymerization in supercritical carbon dioxide (scCO2). SiO2 nanoparticles were surface modified using 3‐methacryloxypropyltrimethoxysilane (MPTMS) in order to disperse well in the medium. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that the SiO2 nanoparticles were encapsulated into the polymer. UV‐visible spectra of the diluted colloidal dispersions of PPy/SiO2 hybrid nanocomposites were similar to those of PPy system. Fourier transform infrared spectroscopy (FT‐IR) suggested the strong interaction between PPy and SiO2. Surface characterizations of nanocomposites were described by X‐ray photoelectron spectroscopy (XPS). The nanocomposites synthesized in scCO2 have been shown to possess higher electrical conductivity and thermal stability. Copyright © 2009 John Wiley & Sons, Ltd.

A one-pot method to enhance dissolution rate of low solubility drug molecules using dispersion polymerization in supercritical carbon dioxide

The surfactant assisted polymerization of 1-vinyl-2-pyrrolidone in supercritical carbon dioxide in the presence of Piroxicam, selected as a model of a low aqueous solubility drug, was studied in order to prepare in a single step a polymeric composite to enhance the rate of dissolution of the pharmaceutical compound. Reactive entrapping was carried out at 65 °C in the P range 21–38 MPa. Under proper operative conditions we obtained the composite under the form of sub-micron spherical particles with relatively narrow particle size distribution. Drug loadings higher than 12% (w/w) were obtained and XRD and Raman spectroscopy suggest that the anti-inflammatory agent is dispersed in the matrix with a non-crystalline structure. The dissolution rate of the drug from the composites was significantly faster both than that of the pure compound and of its physical mixture with the polymer. Collected results suggest that the proposed one-pot process can be used to prepare polymer based composites to increase bioavailability of low solubility drugs without utilization of toxic solvents and under mild temperature conditions.

Synthesis of conducting polyaniline‐montmorillonite nanocomposites via inverse emulsion polymerization in supercritical carbon dioxide

AbstractA new inverse emulsion polymerization and intercalation procedure in supercritical carbon dioxide (SCCO2) was initially employed to synthesize polyaniline‐montmorillonite (PANI‐MMT) nanocomposites. The effect of chemical groups in MMT galleries on intercalation in SCCO2 was investigated. The MMTs modified by different organic cationic surfactants were incorporated into the composite particles, and in unintercalated, partially delaminated or fully exfoliated state. The aminated MMT or fluorinated MMT were utilized to prepare conducting PANI‐MMT nanocomposites with highly concentrated (12–25 wt% loading to monomer), fully exfoliated MMT platelets in SCCO2. The structure and morphology of PANI‐MMT nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray powder diffraction pattern (XRD), and transmission electron microscope (TEM). Thermogravimetry analysis (TGA) was performed to demonstrate the enhancement of thermal stability of the composites. SCCO2 was shown to be more effective for impregnation, disaggregation and exfoliation of MMTs than isooctane, which indicates that SCCO2 is an alternative solvent for synthesis of some intercalated composite materials, not only based on the environmental friendly characteristic of SCCO2, but also owing to that SCCO2 can play an important role in intercalative polymerization. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Preparation of poly(methyl methacrylate)–TiO 2 nanoparticle composites by pseudo-dispersion polymerization of methyl methacrylate in supercritical CO 2

Poly(methyl methacrylate) (PMMA)–TiO 2 nanoparticle composites and poly(styrene) (PS)–TiO 2 nanoparticle composites are synthesized by pseudo-dispersion polymerization in supercritical carbon dioxide (CO 2) in the presence of 3-(trimethoxysilyl)propylmethacrylate (MPS)-modified TiO 2 nanoparticles. These composites are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, and laser diffraction particle size analysis. On the polymerization of PMMA, the product composites were microparticles, and were PMMA shell on TiO 2 core particles. The formation mechanism of these composite particles in supercritical CO 2 is analyzed by the FT-IR analysis and turbidity measurement of MPS-modified TiO 2. It is found that MPS-modified TiO 2 serves as not only an inorganic filler but also an effective stabilizer for the polymerization of PMMA in supercritical CO 2. On the other hand, the polymerization of PS yields a bulk solid. The morphologies of the PMMA and PS composites are found to be quite different from each other, presumably due to the difference in the interaction mechanisms between the carbonyl group of the monomers and the hydroxyl group on the TiO 2 surface. The degree of aggregation of PMMA–TiO 2 composite particles increases with the MPS-modified TiO 2/MMA monomer ratio.

Ethylene polymerization in supercritical carbon dioxide with binuclear nickel(ii) catalysts

A series of new, highly fluorinated neutral (kappa(2)-N,O) chelated Ni(II) binuclear complexes based on salicylaldimines bridged in p-position of the N-aryl group were prepared. The complexes are single-component catalyst precursors for ethylene polymerization in supercritical carbon dioxide and toluene. Solubility of the catalyst precursors in supercritical carbon dioxide is effected by a large number of up to 18 trifluoromethyl groups per molecule. Semicrystalline polyethylene with a low degree of branching is formed (ca. 10 branches/1000 carbon atoms). Polymer microstructures are independent of the nature of the bridging moiety, while stability of the catalysts appears to differ.

Controlled Dispersion Polymerization in Supercritical Carbon Dioxide

Recent advances in controlled polymerization have led to increased activity in controlled free radical polymerization in unconventional solvents. This short report focuses on the renewed interest in dispersion polymerization in supercritical CO2 brought about by the application of controlled free radical polymerization techniques. The emergence of novel and industrially-applicable materials is discussed, as well as the dependence of material properties and morphology upon factors such as surfactant type and how it is employed during the polymerization.