Synthesis and Processing of Porous Polymers Using Supercritical Carbon Dioxide (original) (raw)
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Chemistry of Materials, 2003
The synthesis of permanently porous, highly cross-linked, poly(methacrylate) resins using supercritical CO 2 is described. The pressure-adjustable solvent properties associated with supercritical fluid solvents are exploited to fine-tune the average pore size and surface area of the materials. It was found that the materials' properties varied in a discontinuous manner with respect to the CO 2 pressure. A minimum in the BET surface area (and a maximum in the pore diameter) was observed at a reaction pressure of approximately 2600 psi. These trends were rationalized by the fact that the mechanisms of nucleation, aggregation, and pore formation are highly sensitive to the nature of the porogenic solvent environment.
This review is written to fulfill the need of a comprehensive guide for the manufacture of porous polymer particles. The synthesis section discusses and for the first time compares microfluidics, membrane/microchannel, suspension, dispersion, precipitation, multistage polymerizations and a few other less known methods, microfluidics being in greater detail. The comparison includes on one hand simplicity, scaling-up possibilities and the ability to yield nonspherical particles for these methods and on the other hand size, size monodispersity, pore characteristics and chemical functionality of the obtained particles. This extensive comparison certainly makes this review also useful for the preparation of nonporous particles. In addition, functionalization/characterization techniques and applications of porous particles are also discussed, including some visionary recommendations. The review is expected not only to enable individual experts of each field to compare their methods with the other ones, but also to be a handbook for the newcomers to this field to guide them from the synthesis to the applications.
Porous Copolymer Resins: Tuning Pore Structure and Surface Area with Non Reactive Porogens
Nanomaterials, 2012
In this review, the preparation of porous copolymer resin (PCR) materials via suspension polymerization with variable properties are described by tuning the polymerization reaction, using solvents which act as porogens, to yield microporous, mesoporous, and macroporous materials. The porogenic properties of solvents are related to traditional solubility parameters which yield significant changes in the surface area, porosity, pore volume, and morphology of the polymeric materials. The mutual solubility characteristics of the solvents, monomer units, and the polymeric resins contribute to the formation of porous materials with tunable pore structures and surface areas. The importance of the initiator solubility, surface effects, the temporal variation of solvent composition during polymerization, and temperature effects contribute to the variable physicochemical properties of the PCR materials. An improved understanding of the factors governing the mechanism of formation for PCR materials will contribute to the development and design of versatile materials with tunable properties for a wide range of technical applications.
Effect of porogenic solvent on the porous properties of polymer monoliths
Journal of Applied Polymer Science, 2012
Polymer monoliths with open pores and median pore size of about 15 nm-3 lm have been successfully synthesized by photoinitiated polymerization of butyl methacrylate and ethylene glycol dimethacrylate monomers. The solubility of the monomers in a porogenic solvent is determined by Hildebrand solubility parameter, and it is found that it has great effect on the pore size of the polymers synthesized. Polymers with larger pores are usually generated with poorer solvents for the monomers. However, polymers with different pore sizes and porosities have been obtained using porogenic solvents with similar Hildebrand solubility parameters. The evaporation rate of the porogenic solvents might be another critical factor affecting the properties of the polymer monoliths. Moreover, the effect of water as a cosolvent on the pore size and porosity of the polymers have also been investigated. Polymers with larger pore size have been prepared with the presence of water due to the occurrence of earlier phase separation in the polymerization. V
Porous Biomaterials Obtained Using Supercritical CO 2 −Water Emulsions
Langmuir, 2007
Highly porous, hydrophilic porous matrices were fabricated by using a high internal phase supercritical-CO 2 (scCO 2 ) emulsion templating technique. The novel aspect of the work resides in the combination of a natural biopolymer (dextran) as the building component of the matrices and of an environmentally benign solvent (supercritical-CO 2 ) as the pore-generating phase. The synthetic route to the porous biomaterials involved the preliminary functionalization of the dextran chains with methacrylic moieties, formation of a scCO 2 -in-water concentrated emulsion, and curing of the external phase of the emulsion by radical polymerization. As the emulsion stabilizer a perfluoropolyether surfactant was chosen. The matrices obtained exhibit highly interconnected, trabecular morphologies. The porous biomaterial morphologies were qualitatively characterized by scanning electron microscopy (SEM) and the evaluation of void and interconnect sizes was carried out on the micrographs taken with the light microscope. To tailor the morphologies of the porous structures, the influence of the volume fraction of the internal phase and of the surfactant/ internal phase ratio was investigated. It was established that the variation of the volume fraction of the internal phase exerted only a limited influence on void and interconnect sizes. On the contrary the increase of surfactant concentration alters dramatically the distribution of void size, a large proportion of the void space enclosed within the matrix being attributable to voids with a diameter exceeding 100 µm. The free toxic solvent process of fabrication of the porous structures, the high water content, the expected biocompatibility, and the mechanical properties that resemble natural tissues make these porous hydrogels potentially useful for tissue engineering applications. Watson, M. S.; Whitaker, M. J.; Popov, V. K.; Davies, M. C.; Mandel, F. S.; Wang, J. D.; Shakesheff, K. M. Chem. Commun. (Cambridge) 2001, 109-110. (4) (a) Barbetta, A.; Dentini, M.; De Vecchis, M. S.; Filippini, P.; Formisano, G.; Caiazza, S. AdV. Funct. Mater. 2005, 15, 118-124. (b) Barbetta, A.; Dentini, M.; Zannoni, E. M.; De Stefano, M. E. Langmuir 2005, 15, 118-124. (c) Barbetta, A.; Dentini, M.; Massimi, M.; Conti Devirgiliis, L.
Facile fabrication of doubly porous polymeric materials with controlled nano- and macro-porosity
Polymer, 2015
A critical overview of the different parameters affecting the porous features of doubly porous polymeric materials based on poly(2-hydroxyethyl methacrylate-co-ethylene glycol dimethacrylate) (poly(HEMAco-EGDMA)) and designed via a double porogen templating approach is presented. A thorough investigation was accomplished so as to highlight the main advantages of the proposed double porogen approach which relied on the distinct and independent control of both porosity levels, i.e. nano-and macro-porosity. The nanoporosity level was produced via a phase separation phenomenon that occurred during the polymerization of the comonomers in the presence of various porogenic solvents. To generate the macroporosity, three straightforward and versatile strategies were implemented through the use of sodium chloride (NaCl) macro-sized particles. The first one implied the use of non-sintered NaCl particles that allowed for the creation of non-interconnected macropores. The other two strategies involved the sintering of NaCl particles prior to the generation of the poly(HEMA-co-EGDMA) network. In the latter case, NaCl particles were fused through two different methods, either through sintering at 730 C or by Spark Plasma Sintering. Upon porogen removal, doubly porous PHEMA-based materials were obtained with macropores having NaCl particle imprints in the 100 mm order of magnitude, while the second porosity level laid within the 10 nm to 10 mm order of magnitude, as evidenced by mercury intrusion porosimetry and scanning electron microscopy, depending on the solvent structure, its volume proportion, and the cross-linker concentration in the polymerization feed. A full porous characterization was carried out in order to clearly understand the effect of such structural parameters on the porosity of the as-obtained doubly porous polymeric materials and their nanoporous counterparts.
Novel Polymeric Materials with Double Porosity: Synthesis and Characterization
Macromolecular Symposia, 2014
Functional doubly porous polymeric materials based on cross-linked poly(2-hydroxyethyl methacrylate) (PHEMA) were engineered via novel porogen templating methodologies. Two straightforward and versatile strategies were implemented through the use of either CaCO 3 microparticles or poly(methyl methacrylate) beads as macroporogens, in conjunction with either hydroxyapatite nanoparticles of around 200 nm average diameter or a porogenic solvent (e.g., ethanol) as nanoporogens. Upon porogen removal, macropores with dimensions in the 100 mm range were generated, while the second porosity lied within the 1 mm order of magnitude, as evidenced by mercury intrusion porosimetry and scanning electron microscopy. The possibility to further functionalize such biporous PHEMA-based frameworks was investigated through a two-step synthetic approach involving an activation stage, followed by the coupling of propargylamine as a model compound. The success of the functionalization procedure was clearly demonstrated by Raman spectroscopy that indicated the occurrence of alkyne functionality within the biporous materials.
Porous Polymer Networks: Synthesis, Porosity, and Applications in Gas Storage/Separation
Chemistry of Materials, 2010
Three porous polymer networks (PPNs) have been synthesized by the homocoupling of tetrahedral monomers. Like other hyper-cross-linked polymer networks, these materials are insoluble in conventional solvents and exhibit high thermal and chemical stability. Their porosity was confirmed by N 2 sorption isotherms at 77 K. One of these materials, PPN-3, has a Langmuir surface area of 5323 m 2 g -1 . Their clean energy applications, especially in H 2 , CH 4 , and CO 2 storage, as well as CO 2 /CH 4 separation, have been carefully investigated. Although PPN-1 has the highest gas affinity because of its smaller pore size, the maximal gas uptake capacity is directly proportional to their surface area. PPN-3 has the highest H 2 uptake capacity among these three (4.28 wt %, 77 K). Although possessing the lowest surface area, PPN-1 shows the best CO 2 /CH 4 selectivity among them.