Dispersion Polymerization in Supercritical CO2with a Siloxane-Based Macromonomer: 1. The Particle Growth Regime (original) (raw)
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Macromolecules, 1998
Particle growth rates were analyzed for the dispersion polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide at 65°C stabilized with a poly(dimethyl siloxane)-methyl methacrylate (PDMS-mMA) macromonomer. Although pure CO 2 is a mediocre solvent for PDMS even at 4000 psia, the monomer behaves as a cosolvent to prevent flocculation. As pressure is decreased, the dispersion flocculates sooner, as expected due to the reduced solvent quality of CO2. Final particle size is only mildly dependent on pressure as a result of the solvation from the high monomer concentration during the particle formation stage, however particle coagulation increases with decreasing pressure. There exists both a minimum pressure (∼3000 psia) and stabilizer concentration (∼2 wt % stabilizer/ monomer) below which particles are highly coagulated due to insufficient steric stabilization. Here polymerization rates are reduced due to diffusional restrictions. This threshold pressure and stabilizer concentration are required to change the mechanism from precipitation polymerization to dispersion polymerization, as indicated by product morphology, molecular weight, and molecular weight polydispersity. Final particle size and number density determined from the model of Paine {Macromolecules 1990, 23, 3109} agree with the measured values.
In-Situ Investigation on the Mechanism of Dispersion Polymerization in Supercritical Carbon Dioxide
Macromolecules, 2000
The effect of stabilizers on the particle formation stage in dispersion polymerization of methyl methacrylate in supercritical CO2 has been studied by in-situ turbidimetry. The average particle diameter (250 nm) and particle number density are similar at the end of this formation stage for the stabilizers poly(dimethylsiloxane)-b-poly(methyl methacrylate-co-methacrylic acid) (PDMS-b-P(MMA-co-MA)) and poly(1,1-dihydroperfluorooctyl acrylate)-b-polystyrene (PFOA-b-PS). Particle diameters are only about twice as large for perfluoropolyether acid (PFPE-COOH) but become much larger for grafted PDMSmonomethacrylate due to less effective surface coverage. The final particle number density changes little for conversions from 1% to completion for PDMS-b-P(MMA-co-MA) but increases for PFOA-b-PS due to formation of new particles in block copolymer micelles.
Macromolecular Symposia, 2007
Vinyl monomers that consist of carbonyl group and -OH group are found to be act as surfmers (surfactant + monomer) in the polymerization process that uses supercritical CO 2 (scCO 2 ) as a solvent. By co-polymerization of methyl methacrylate (MMA) with methacrylic acid (MAA) and acrylic acid (AA) in scCO 2 , micropowder of poly(MMA) (pMMA) was successfully obtained. The polymerization mechanism was examined with the MMA/MAA systems. From the experiments, it was revealed that the addition of surfmer MAA forms dispersion phase in the scCO 2 that enables the dispersion polymerization of MMA without fluorinated surfactants.
Polymer International
Free radical dispersion polymerization of methyl methacrylate (MMA) was carried out in supercritical carbon dioxide (scCO2) using poly{(heptadecafluorodecyl acrylate)-co-3-[tris(trimethylsilyloxy)silyl]propyl methacrylate} (p(HDFDA-co-SiMA)) as stabilizer. Dry, fine powdered spherical poly(methyl methacrylate) (pMMA) particles with well-defined sizes were produced. The resulting high yield of spherical and relatively uniform micron-size pMMA particles was formed utilizing various amounts of p(HDFDA-co-SiMA) random copolymer. The particle diameter was shown to be dependent on the weight percent of the stabilizer added to the system. The effects of varying the concentration of stabilizer (1–7 wt%), reaction time (4–12 h) and pressure (15–35 MPa) upon the polymerization yield, molar mass and morphology of pMMA were investigated. Copyright © 2005 Society of Chemical Industry
Macromolecules, 2005
Vinyl monomers that consist of carbonyl group and -OH group are found to be act as surfmers (surfactant + monomer) in the polymerization process that uses supercritical CO 2 (scCO 2 ) as a solvent. By co-polymerization of methyl methacrylate (MMA) with methacrylic acid (MAA) and acrylic acid (AA) in scCO 2 , micropowder of poly(MMA) (pMMA) was successfully obtained. The polymerization mechanism was examined with the MMA/MAA systems. From the experiments, it was revealed that the addition of surfmer MAA forms dispersion phase in the scCO 2 that enables the dispersion polymerization of MMA without fluorinated surfactants.
Macromolecular Rapid Communications, 2006
Vinyl monomers that consist of carbonyl group and -OH group are found to be act as surfmers (surfactant + monomer) in the polymerization process that uses supercritical CO 2 (scCO 2 ) as a solvent. By co-polymerization of methyl methacrylate (MMA) with methacrylic acid (MAA) and acrylic acid (AA) in scCO 2 , micropowder of poly(MMA) (pMMA) was successfully obtained. The polymerization mechanism was examined with the MMA/MAA systems. From the experiments, it was revealed that the addition of surfmer MAA forms dispersion phase in the scCO 2 that enables the dispersion polymerization of MMA without fluorinated surfactants.
The polymerisation of functionalised methacrylate monomers in supercritical carbon dioxide
European Polymer Journal, 2003
This paper describes the homopolymerisations of isobornyl methacrylate (IBMA) and poly(ethylene glycol) methacrylate (PEGMA) in supercritical carbon dioxide (scCO 2 ) and copolymerisation with methyl methacrylate (MMA). We have used two different stabiliser systems poly(dimethyl siloxane) monomethylacrylate (PDMS-MMA) and Krytox 157FSL, both of which have been shown previously to be highly effective stabilisers for dispersion polymerisation in scCO 2 . The effect of initiator concentration and copolymer composition is studied. For the copolymerisation of IBMA and MMA, under optimised conditions it is possible to form discrete particles with diameters in the range 1.4-3.6 lm. The PDMS-MMA macromonomer was found to be less effective as a stabiliser, causing particle aggregation due to the low solubility of this stabiliser in the monomers. The copolymers of PEGMA and MMA are also studied. The materials have interesting solubility properties with a transition in solubility from aqueous to organic media on increasing the MMA content.
Macromonomer surfactants for the polymerisation of methyl methacrylate in supercritical CO2
Polymer, 2000
Free radical polymerisation of methyl methacrylate in supercritical CO 2 requires addition of a surfactant (amphipathic macromolecule) to produce poly(methyl methacrylate) (PMMA) in high yield and molar mass and with well-defined particle sizes. This paper describes the use of poly(dimethylsiloxane)monomethacrylate macromonomers in stabilising the free radical polymerisation of methyl methacrylate in supercritical CO 2. In particular, the effects of surfactant molar mass (2-10 kD) and concentration on the nature of the product PMMA are examined. It is found that the 2 kD surfactant is the most effective at low (wt./wt.) concentrations and may be a more viable option for industrial production than the higher molar mass surfactants, although the particle sizes of the PMMA products are different.
Particle encapsulation with polymers via in situ polymerization in supercritical CO2
Powder Technology, 2004
Fine Dechlorane (DCR) particles with an average size of 12 Am were successfully encapsulated with poly(methyl methacrylate) (PMMA) and poly(1-vinyl-2-pyrrolidone) (PVP) polymers via in situ dispersion polymerization in supercritical carbon dioxide (scCO 2 ). Adjusting the process parameters can control the coating thickness, surface morphology, and degree of particle agglomeration. A uniform thin-film encapsulation of the host particles has been achieved under appropriate operating conditions, which is very difficult to obtain using other methods of supercritical fluid processing.
Chemical Engineering and Processing: Process Intensification
PMMA has applications on the medical, pharmaceutical and engineering areas. Different processes may be employed for its production. Here, MMA polymerization was performed by supercritical carbon dioxide dispersion. CO 2 is inert, easily retrievable and separated from the product. The monomer is soluble in dense CO 2 , unlike PMMA, requiring a stabilizer to maintain the dispersion. Here, vinyl terminated PDMS was used as a dispersing agent. The reactions were conducted at 16 MPa/80 C for 4 h. Product characterization was performed by SEM, to evaluate the morphology at estimate the particle size, SEC, to determine the molar mass and polydispersion index, 1 H NMR and FTIR spectroscopy, in order to verify the chemical structure of the product, and also gravimetric analyses, to determine the residual monomer. The results confirmed the adequacy of the process and of the stabilizer for PMMA particles production. 2015 Elsevier B.V. All rights reserved.