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Polymer Synthesis and Processing in Supercritical Carbon Dioxide
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Polymer Synthesis
The use of supercritical carbon dioxide (scCO2) as a reaction media and reactant offers the opportunity to manipulate the outcome od reactions, including the polymer structure. Our goal is to synthesise polymers with biomedical applications using scCO2 both as solvent and co-monomer.
Selected publications: Green synthesis of a temperature sensitive hydrogel, M. Temtem, T. Casimiro, J. F. Mano, A. Aguiar-Ricardo, E. J. Cabrita, A. Aguiar-Ricardo, Green Chemistry, 2007, 9, 75-79.
Synthesis of highly cross-linked poly(diethylene glycol dimethacrylate) microparticles in supercritical carbon dioxide, T. Casimiro, A. M. Banet-Osuna, A. M. Ramos, M. N. da Ponte, A, Aguiar-Ricardo, European Polymer Journal, 2005, 41, 1947-1953.
Fluorinated graft stabilizers for polymerization in supercritical carbon
dioxide: The effect of stabilizer architecture
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Membrane Production
A number of different techniques are available to prepare porous polymeric films, such as sintering, stretching, track estching, phase separation, sol–gel process, vapour deposition and solution coating. However, the majority of porous flat membranes are prepared from a homogenous polymer solution by the wet-phase inversion method in which a polymer solution (polymer plus solvent) is cast on a suitable support and immersed in a coagulation bath containing a non-solvent. Since the precipitation occurs due to the exchange of solvent and non-solvent, the correct choice of the pairs of solvents is a very important parameter to control the morphology of the membrane. Other important preparation parameters are: polymer concentration, temperature, humidity, evaporation time, and the composition of the casting solution (e.g. additives). Unfortunately many organic solvents used in membrane preparation are volatile, flammable and may pose a risk to health and the environment. Alternative approaches are being developed, and one with growing areas of application is the use of supercritical fluids, of which the most common is carbon dioxide.
Apparatus for membrane production and high-pressure cell (left) and examples of membranes obtained using a CO2-assisted phase inversion method (right).
Schematic diagram of the high-pressure apparatus for the membrane formation: (1) Gilson 305 piston pump; (2) temperature controller; (3) high-pressure cell; (4) pressure transducer; (5) back pressure regulator.
Selected publications: Development of pH-responsive poly(methylmethacrylate-co-methacrylic acid) membranes using scCO2 technology. Application to protein permeation, M. Temtem, T. Barroso, T. Casimiro, A. Aguiar-Ricardo, The Journal of Supercritical Fluids, 2009, 51, 56-66.
Development of PMMA membranes functionalized with hydroxypropyl-β-cyclodextrins for controlled drug delivery using a supercritical CO2-assisted technology, M. Temtem, D. Pompeu, G. Jaraquemada, E. J. Cabrita, T. Casimiro, A. Aguiar-Ricardo, International Journal of Pharmaceutics, 2009, 376, 110-115.
Development and characterization of a thermoresponsive polysulfone membrane using an environmental friendly technology, M. Temtem, D. Pompeu, T. Barroso, J. Fernandes, P. C. Simões, T. Casimiro, A. M. B. Rego, A. Aguiar-Ricardo, Green Chemistry, 2009, 11, 638-645.
Solvent power and depressurization rate effects in the formation of polysulfone membranes with CO2-assisted phase inversion method, M. Temtem, T. Casimiro, A. Aguiar-Ricardo, Journal of Membrane Science, 2006, 283, 244-252.
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Spectroscopy
Due the importance of knowing the nature of stabilizer-growing polymer interactions for the development of new stabilizers, we applyied high-pressure nuclear magnetic resonance, HP-NMR, to investigate the CO2-philicity of Krytox and the molecular interactions between the stabilizer and scCO2. HP-NMR offers unique, highly localized structural molecular information and has shown to be a very powerful tool for the investigation of molecular interactions under the influence of high pressure. We found that the HP-NMR technique is suitable to investigate the solubility of a high molecular weight perfluorinated surfactant in scCO2 by combining CO2 13C chemical shift and Krytox 19F chemical shift variations with medium density. For this purpose a new high-pressure mobile and versatile apparatus was assembled with the capability to change in situ the sample composition and all the relevant operational conditions (p, ρ, T) for the NMR measurements.
Apparatus for HP-NMR measurements.
Schematic diagram of the HP-NMR apparatus: (1) Hand pump compressor; (2) molecular sieves; (3) filter; (4) check-valve; (5) syringe; (6) HPLC valve; (7) pressure transducer; (8) temperature controller; (9) cell with sapphire windows; (10) thermostated water bath; (11) HP-NMR tube; (12) spectrometer Bruker, ARX400; (13) recirculating pump; (14) thermostated pipe.
Selected publications: High-Pressure NMR Characterization of Triacetyl-beta-Cyclodextrin in Supercritical Carbon Dioxide, G. Ivanova, E. R. Vão, M. Temtem, A. Aguiar-Ricardo, T. Casimiro, E. J. Cabrita, Magnetic Resonance in Chemistry, 2009, 47, 133-141.
Molecular interactions and CO2-philicity in supercritical CO2. A high-pressure NMR and molecular modeling study of a perfluorinated polymer in scCO2, M. Temtem, T. Casimiro, A. G. Santos, A. L. Macedo, E. J. Cabrita, A. Aguiar-Ricardo, Journal of Physical Chemistry B, 2007, 111, 1318-1326.
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Pharmaceuticals
Controlled drug delivery products, using biocompatible or biodegradable polymers, have received considerable attention in the last years. These substances provide in general a more controlled release rate and consequently assumption of the drug by the body improving its therapeutic action. In fact, there is a growing interest of the pharmaceutical industry in the development of these systems. Molecular imprinting is a new method to synthesise materials with sites of specific molecular arrangements that act as artificial receptors, on an otherwise uniform matrix. The design of a precise macromolecular structure that is able to recognize specific molecules has indeed a large number of potential applications. There is a tremendous interest in analytical applications, such as biosensors, immunoassays, separation media and affinity supports among others. Molecular imprinting has already given proofs of its enormous potential in the field of pharmaceutical applications. In fact, in the last few years, the development of this technology has moved towards the preparation of new controlled release systems, where it may enhance the drug loading.
Scheme of an imprinting process.
High-pressure cell used for impregnation (left) and examples of a molecular imprinted matrix (center), and PNIPAAm impregnated chitosan scaffold (right).
Schematic representation of the impregnation apparatus.
Selected publications: Supercritical fluid polymerisation and impregnation of molecularly imprinted polymers for drug delivery, A. R. C. Duarte, T. Casimiro, A. Aguiar-Ricardo, A. L. Simplicio, C. M. M. Duarte, Journal of Supercritical Fluids, 2006, 39, 102-106.
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Solubility Measurements
Supercritical fluids might be called “phenomenal fluids” due to their potential as media suitable to develop new processes in chemical engineering. The solvent power of the supercritical fluid can be finely tuned by small changes of temperature and pressure and for that very reason supercritical processes are often restricted to narrow regions of phase diagrams which implies the need to study the phase envelopes and critical points of the complex mixtures that are used in the chemical processes. Measurements of phase envelopes are usually performed by visual methods or by sampling. Both methods have disadvantages; accurate sampling is difficult and time-consuming, while determining a phase transition in a view cell is often constrained by the subjectivity of the experimenter. In principle, the determination of vapor–liquid equilibrium by an acoustic method overcomes these disadvantages.
Apparatus for solubility/VLE measurements: using a sapphire windowed cell - internal volumes ranging from 1 to 30 mL (left) and using a sapphire tube cell (right).
Schematic representation of a cloud point measurements apparatus: HPC - high-pressure cylinder, MC - manual controller, C - cell, M - manometer, DB - decantation blister.
Selected publications: Visual and acoustic investigation of the critical behavior of mixtures of CO2 with a perfluorinated polyether, A. Aguiar-Ricardo, T. Casimiro, T. Costa, J. Leandro, N. Ribeiro, Fluid Phase Equilibria, 2006, 239, 26-29.
Phase behavior studies of a perfluoropolyether in high-pressure carbon dioxide, T. Casimiro, A. Shariati, C. J. Peters, M. N. da Ponte, A. Aguiar-Ricardo, Fluid Phase Equilibria, 2004, 224, 257-261.
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Critical Data Aquisition
The carbon dioxide molecule is small and compact, with a strong quadrupole, which makes it also a relevant testing ground for theory. Apart from this interest for theory testing, CO2 has also been much studied recently, due to its possible applications as an alternative “green” solvent in extraction, reaction, and particle formation processes in supercritical media. In particular, the effect on reactivity of a solvent with a tunable density, such as a supercritical fluid, has recently attracted much attention. Thus the measurement of critical parameters for complex multicomponent fluid mixtures is of both theoretical and industrial interest. Recently, the accuracy of the acoustic technique, when applied to study the critical behavior of multicomponent systems, was evaluated by comparing the critical data measured acoustically and simultaneous visual detection of critical opalescence. In practice, there is good agreement, within experimental error, between the results of acoustic and other methods described in the literature to determine critical points. In those cases, the maximum uncertainty came from the precise composition of the mixtures, not from the acoustic measurements themselves.
Apparatus for acoustic determination of critical parameters.
Schematic representation of an acoustic apparatus: Comp, compressor; HP, hand pump; HBP, high-pressure bomb; M, multimeter; O, oscilloscope; PG, pulse generator; PT, pressure transdutor; RU, refrigeration unit; T, platinum resistance thermometer; V, valves; WB, water bath.
Selected publications: Can the speed of sound be used for detecting critical states of fluid mixtures? J. C. R. Reis, N. Ribeiro, A. Aguiar-Ricardo, Journal of Physical Chemistry B, 2006, 110, 478-484.
Vapor-liquid equilibrium and critical line of the CO2+Xe system. Critical behavior of CO2+Xe versus CO2+n-alkanes, N. Ribeiro, T. Casimiro, C. Duarte, M. N. da Ponte, A. Aguiar-Ricardo, M. Poliakoff, Journal of Physical Chemistry B, 2000, 104, 791-795.
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Research Collaborations
Industry:
Nutraceuticals and Controlled Delivery
Academic:
Clean Technology Group - University of Notthingham Laboratory for Applied Thermodynamics and Phase Equilibria - Delf University of Technology Paula Hammond - MIT Linda Griffith - MIT Manuel M. Abecasis - Bone Marrow Transplantation Unit, IPO Claudia Lobato da Silva - Bioengineering Research Group, IST-UTL Catarina Duarte - Nutraceutical and Delivery, ITQB-UNL Mariana Gomes Pinho - Bacterial Cell Biology, ITQB-UNL João F. Mano - 3B's, Dept. of Polymer Engineering, University of Minho
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