Browsing by Author "Giudici, Reinaldo"
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- Development of cyclic propagation kinetics for modeling the nitroxide-mediated radical copolymerization of styrene-divinylbenzenePublication . Aguiar, Leandro G.; Gonçalves, Miguel A.D.; Pinto, Virgínia; Dias, Rolando; Costa, Mário Rui; Giudici, ReinaldoA kinetic model including the cyclic propagation (cyclization) is proposed for the nitroxide-mediated radical copolymerization of styrene–divinylbenzene. The method involves a balance of sequences of units, which connect a radical center and a pendant double bond present in the same polymer chain. The rate constant for cyclization was considered a function of the sequence length. Good agreement between the model predictions and experimental data for solution and suspension controlled copolymerizations was found. The rate constant of cyclization for the smallest ring (3 monomeric units) was estimated to be 700 s−1 at 90 °C, and the activation energy was estimated to be 32 500 cal mol−1
- Gel formation in aqueous suspension nitroxide-mediated radical co-polymerization of styrene/divinylbenzenePublication . Gonçalves, Miguel A.D.; Pinto, Virgínia; Dias, Rolando; Costa, Mário Rui; Aguiar, Leandro G.; Giudici, ReinaldoResults from an experimental study concerning gel formation with nitroxide-mediated radical polymerization (NMRP) of styrene (S) and divinylbenzene (DVB) in aqueous suspension are reported. Influence of certain polymerization parameters on the dynamics of network formation was measured, namely the polymerization temperature and initial composition. Soluble polymer formed at different polymerization times was analyzed by size exclusion chromatography (SEC) with refractive index (RI) and multi angle laser light scattering (MALLS) detection. Concentration of pendant double bonds (PDB) was quantified by means of ICl titration and the morphology of the S/DVB particles was inspected by SEM. Incidence of cyclizations was assessed and the improvement of network homogeneity when using NMRP/FRP is discussed.
- Mathematical modeling of NMRP of styrene–divinylbenzene over the pre- and post-gelation periods including cyclizationPublication . Aguiar, Leandro G.; Gonçalves, Miguel A.D.; Pinto, Virgínia; Dias, Rolando; Costa, Mário Rui; Giudici, ReinaldoNitroxide-mediated polymerization of styrene-divinylbenzene has been modeled using generating functions of length distributions, pseudo-kinetic propagations, and numerical fractionation with the crosslinking rate depending on generation. Cyclization reactions are tackled by balances of sequences, yielding fair predictions of the measured pendant double bond concentration. With reduction in crosslinking, agreement for the experiments at 90 °C between predicted and measured weight-average, molecular weight, and weight fraction of gel is observed. A much higher relative crosslinking reactivity is observed at 130 °C as compared to 90 °C, likely an effect of the chain mobility.
- Mathematical modeling of styrene/divinylbenzene copolymerization comprising diffusional effects and cyclization kineticsPublication . Aguiar, Leandro G.; Gonçalves, Miguel A.D.; Pinto, Virgínia; Dias, Rolando; Giudici, Reinaldo; Costa, Mário RuiMathematical Modeling of Styrene/Divinylbenzene Copolymerization Comprising Diffusional Effects and Cyclization Kinetics
- NMRP of styrene-divinylbenzene: predictions in the pre- and post-gelation periods using different modelling approachesPublication . Aguiar, Leandro G.; Gonçalves, Miguel A.D.; Pinto, Virgínia; Dias, Rolando; Costa, Mário Rui; Giudici, ReinaldoThree 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.