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European Commission

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I Encontro de Jovens Investigadores do Instituto Politécnico de Bragança: livro de resumos

Publication . Martins, Anabela (Ed.)

Encontro de Jovens Investigadores do Instituto Politécnico de Bragança: livro de resumos

2014Book

Open access

NMRP of styrene-divinylbenzene: predictions in the pre- and post-gelation periods using different modelling approaches

Publication . Aguiar, Leandro G.; Gonçalves, Miguel A.D.; Pinto, Virgínia; Dias, Rolando; Costa, Mário Rui; Giudici, Reinaldo

Three modeling approaches for the NMRP of slyrene-divinylbenzene were used for describing experiments performed at different initial conditions: a rigorous approach (model A) based on balance of species and method of characteristics in terms of generating functions and two simplified approaches based upon mass and moment balances, numerical fractionation and pseudo-kinetic method (models B and C). Balances of paths connecting groups were used for tackling loop formation reactions. A critical comparison of the effect of underlying assumptions of lhe three approaches was carried out. Simulations making use of the concept of path balances presented good results for the predictions of pendant double bonds (PDB) concentration. Numerical fractionation can easily allow for empirical reactivity changes with average molecular size (Through the generation index). Thus, simultaneous agreement for predictions of sol weigh-average molecular weigh (Mw) and gel fraction (Wg) could be found with experiments at 90º C. Experiments at 130 º C implied a higher crosslinking reactivity. which might be related lo a higher mobility of polymer chains.

2013Conference object

Open access

Kinetic studies on RAFT inverse-suspension smart hydrogels formation using a tetra detector array

Publication . Gonçalves, Miguel A.D.; Pinto, Virgínia; Dias, Rolando; Costa, Mário Rui; Hernándes-Ortiz, Júlio

Temperature/pH stimuli-responsive hydrogel particles were synthesized using inverse-suspension polymerization in batch stirred reactor. Different water soluble comonomers were present in the initial mixture (namely N-isopropylacrylamide and acrylic acid) as well as crosslinkers with different functionalities (bi-, tri- and tetrafunctional) so that their effect on the network crosslinking density could be seen. Different operating conditions such as polymerization temperature (in the range 20 to 70 °C), monomers dilution, neutralization and the inilial ratios 01 co-monomers and monomers/crosslinker were also tried. Classical Iree-radical polymerization (FRP) and RAFT polymerization (e.g. using 4-cyano-4-phenylcarbonothioylthio-pentanoic acid) were compared in order to put into evidence the impact of the polymerization mechanism on the hydrogel molecular architecture. Sampling at different polymerization limes allowed the study of the kinetics of gel formalin through the analysis by SEC of the soluble phase. RI, LALLS, Intrinsic Viscosity and UV signals were simultaneously measured using a tetra-detector array, thus yielding absolute molecular weight, branching factors, hydrodynamic radius and radius 01 gyration. The performance 01 hydrogel beads was assessed through drug delivery tests triggered by changes in the environmental temperature/pH. Aiming at the development of tools hopefully useful for the design of such advanced materials, a general kinetic approach (Chem. Eng. Sci. 2005, 60, 423) was used to carry out modeling studies including consideration of finite loop formation reactions.

2013Conference object

Open access