Browsing by Author "Kadhirvel, Porkodi"
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- Assessment of RAFT polymerization in the synthesis of crosslinked materials for energy storagePublication . Tristão, Paulo; Costa, Hugo Davide; Kadhirvel, Porkodi; Dias, Rolando; Costa, Mário RuiThe synthesis and characterization of two different classes of polymer crosslinked materials, useful for energy storage and improving energy efficiency, is here studied. Products resulting from the encapsulation of phase change materials (PCM), which can be used for thermal energy storage/release, are considered as first case study. For this purpose, different kinds of PCM can be considered in the encapsulation process, namely renewable based PCM such as natural fatty acids (e.g. stearic/palmitic acids). The sulfur inverse-vulcanization process, producing materials with useful electrochemical properties, is considered as second case study. This latter process takes advantage of the excess of elemental sulfur that is generated in petroleum refining and allows the synthesis of sulfur-rich copolymers to be applied (e.g.) as active materials in lithium-sulfur (Li-S) batteries.
- Development of high performance and facile to pack molecularly imprinted particles for aqueous applicationsPublication . Oliveira, Daniela; Freitas, Filipa; Kadhirvel, Porkodi; Dias, Rolando; Costa, Mário RuiDifferent kinds of molecularly imprinted particles were synthesized and compared, aiming at the development of materials combining high molecular recognition capabilities and facile use as column packing materials for chromatographic aqueous applications. Solution, inverse-suspension and precipitation polymerization were considered and two different model molecules (5-fluorouracil and caffeine) were used to highlight the effect of the interaction between the template molecule and the functional monomer on imprinting efficiency. Particles synthesized through the proposed inverse-suspension process exhibit facile use for packing columns, allow the stable running of chromatographic systems and present a high performance in drug uptake and release in aqueous media. Frontal analysis measurements highlight these key features of the synthesized particles. Drug sorption capabilities of 0.890 mol/g and 5.774 mol/g were measured for 5-fluorouracil and caffeine, respectively, using frontal analysis with eluents containing the target molecules at concentration 0.1 mM. Due to the lower amount of solvent required than with precipitation polymerization, the developed inverse-suspension process presents high synthesis yields, which can be exploited for the large-scale manufacture and commercialization of molecularly imprinted materials. The combined features of the particles makes possible their direct use in bioseparations or in the development of assays and pharmacokinetic studies concerning the presence of drugs in biological fluids.
- Development of stimuli-responsive smart hydrogels using molecular imprinting and interpenetrating polymer networksPublication . Oliveira, Tânia; Reitor, Patrícia; Oliveira, Daniela; Kadhirvel, Porkodi; Dias, Rolando; Costa, Mário RuiDifferent classes of stimuli-responsive smart hydrogels (SRSH) were synthesized in order to assess the usefulness of molecular imprinting and generation of interpenetrating polymer networks to obtain advanced materials with tailored properties/performance. Reversible Addition-Fragmentation Chain-Transfer (RAFT) polymerisation was exploited as an additional tool to increase the control on the formation process of these materials. Batch adsorption and frontal analysis (e.g. for 3-aminopyridine (3AMP) as depicted in the graphical abstract) techniques were used to quantify the affinity of different drugs with the produced SRSH. Stimulated drug release (e.g. due to temperature/pH changes) and protein immobilisation/release were also tested. Results obtained show that molecular imprinting and generation of interpenetrating networks are effective routes to obtain tailored materials with a particular affinity to selected template molecules.
- Development of tailored hydrogels using RAFT polymerization in continuous flow microreactorPublication . Machado, Carla; Oliveira, Tânia; Reitor, Patrícia; Oliveira, Daniela; Freitas, Filipa; Kadhirvel, Porkodi; Dias, Rolando; Costa, Mário RuiThis research is devoted to the development of tools aiding the production of smart hydrogels with tailored molecular architecture and properties. Molecular imprinting, RAFT polymerization and operation in continuous flow microreactor are individually considered and also simultaneously combined in order to try the synthesis of materials with improved performance.
- Electrochemical activity of sulfur networks synthesized through RAFT polymerizationPublication . Almeida, Carlos M.F.; Costa, Hugo Davide; Kadhirvel, Porkodi; Queiroz, Ana; Dias, Rolando; Costa, Mário RuiNovel results concerning the inverse vulcanization of sulfur using reversible addition–fragmentation chain transfer (RAFT) polymerization are here reported. It is shown that RAFT polymerization can be used to carry out this cross-linking process, with the additional possibility to extend the reaction time from a few minutes as with classical free radical polymerization (FRP) to several hours. Higher control on viscosity and processability of the synthesized networks, as well as, the implementation of semibatch feed policies during cross-linking are important advantages of the RAFT process here explored comparatively to the FRP inverse vulcanization. Using cyclic voltammetry, it was assessed the electrochemical activity of the synthesized sulfur-rich polymer networks. It is shown that the fundamental electrochemical activity of the elemental sulfur was preserved in the produced materials. Testing of electrochemical cells assembled with lithium in the anode and different sulfur based materials in the cathode, including the synthesized RAFT networks, is also shown. The results here presented highlight the new opportunities introduced by reversible-deactivation radical polymerization mechanisms on the control of the synthesis process and in the design of such advanced materials and show also that many potential derivatizing possibilities can be achieved.
- Microreactor generated RAFT imprinted smart hydrogelsPublication . Kadhirvel, Porkodi; Dias, Rolando; Costa, Mário RuiStimuli-Responsive Smart Hydrogels (SRSH) are extensively used in biotechnology and biomedicine amongst many other fields1. SRSH can be obtained conventionally through a batch reactor process resulting in irregular shaped particles, whereas emulsion, inverse-suspension, precipitation polymerizations, etc., lead mostly to spherical shaped particles. Recently micro-reactors have been introduced as an alternative approach to produce spherical/conical particles continuously through implementation of a microfluidic droplet based technique.2 Reversible Addition-Fragmentation Chain Transfer (RAFT) controlled polymerization on the other hand has received a considerable attention in hydrogels provided the potential to produce macromolecules with a narrow molecular weight distribution.3 Having faced some classical deficiencies of conventional Free Radical Polymerization (FRP), owing to the importance of hydrogel particle morphology and the promising behavior of Controlled Radical Polymerization (CRP) using RAFT agent, here we try to combine the continuous flow microreactor and RAFT to overcome the obstacles. Besides, one additional goal is to create molecular memory (imprinting) inside hydrogel network. Pharmaceutical drugs with different classifications are employed as templates to obtain molecular imprinted hydrogels (MIH) in a continuous flow microreactor.
- Molecular imprinting in hydrogels using reversible addition-fragmentation chain transfer polymerization and continuous flow micro-reactorPublication . Kadhirvel, Porkodi; Machado, Carla; Freitas, Ana Filipa Fernandes Lobo; Oliveira, Tânia; Dias, Rolando; Costa, Mário RuiAbstract BACKGROUND Stimuli responsive imprinted hydrogel micro-particles were prepared using reversible addition-fragmentation chain transfer polymerization for targeting genotoxic impurity aminopyridine in aqueous environment using a continuous flow micro-reactor. RESULTS The feasibility of operation with a continuous flow micro-reactor for particles production was demonstrated. A comparative evaluation was carried out between batch and micro-reactor produced imprinted and non-imprinted hydrogels. Experimental results proved that molecular imprints generated by free radical polymerization and controlled radical polymerization showed outstanding performance in adsorption behavior: the q value estimate was about 1000 times higher than the value presented by other researchers. Solid phase extraction results further evidenced the promising imprinting with hydrogels using free radical polymerization and controlled radical polymerization by retaining c. 100% of 3-aminopyridine. The imprinting factor of 4.3 presented in this research appears to be the best value shown so far. CONCLUSION The imprinted materials were successfully prepared both in batch and with a continuous flow micro-reactor. The inclusion of a reversible addition-fragmentation chain transfer agent in controlled radical polymerization was important in optimizing the experimental conditions in the continuous microfluidic approach. Though the reversible addition-fragmentation chain transfer agent was very useful in controlling the reaction kinetics, imprinted micro-particles showed the existence of both non-specific and imprinted sites. It is worth extending this work to demonstrate the impact of reversible addition-fragmentation chain transfer agents in molecular imprinting, considering also operation in a continuous flow micro-reactor to obtain tailored smart hydrogel particles. © 2015 Society of Chemical Industry
- Production of RAFT imprinted smart hydrogel particles in a continuous flow micro-reactorPublication . Machado, Carla; Freitas, Ana Filipa Fernandes Lobo; Kadhirvel, Porkodi; Dias, Rolando; Costa, Mário RuiFeasibility of the production of RAFT imprinted smart hydrogel particles in continuous flow micro-reactor is here showed. Microfluidic continuous operation was combined with RAFT polymerization and molecular imprinting tecniques involving selected template molecules. New strategies for the production of advanced materials with tailored properties are thus developed. Particles syntetized in the continuous flow micro-reactor (set-up scheme depicted in the graphical abstract) were purified and characterized using different techniques, namely batch and continuous drugs adsorption and release processes. Particles were packed in small columns allowing the quick testing of these materials using frontal analysis. Therefore, the usefulness of these particles in biotechnology and biomedicine is likely.
- Synthesis and testing of polymer crosslinked materials for applications in energy storage and Li-S batteriesPublication . Tristão, Paulo; Costa, Hugo Davide; Kadhirvel, Porkodi; Dias, Rolando; Costa, Mário RuiThe feasibility of making polymer crosslinked materials with applications in improving energy efficiency is here demonstrated. The encapsulation of phase change materials (PCM), for thermal energy storage/release, and sulphur inverse-vulcanization (producing materials with useful electrochemical properties) are here used as case studies. Effective thermal properties of the produced encapsulated PCM materials were measured through TG/DSC analysis (see graphical abstract). Designing tools allowing the synthesis of materials with tailored thermal properties were exploited (e.g. use of controlled radical polymerization). Sulphur-rich networks are synthetized using different operation conditions (e.g. considering RAFT/NMRP). Testing of these materials in Li-S batteries to assess the impact of the synthesis conditions in their electrochemical properties is ongoing work.