Browsing by Author "Trigo, Ivone"
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- Copolimerização radicalar por transferência de átomo de metacrilato de metilo com dimetacrilato de etilenoglicolPublication . Trigo, Ivone; Dias, RolandoNos anos mais recentes a polimerização radicalar por transferência de átomo (ATRP) de monómeros acrílicos e metacrilatos, na presença de uma pequena quantidade de reticulador, tem sido investigada com o objectivo de produzir materiais solúveis com estrutura não linear ou mesmo polímeros insolúveis (gel). Estes materiais apresentam diversas aplicações em microelectrónica, indústrias dos revestimentos ou biomedicina. Neste contexto, tem sido explorada a produção por ATRP de polímeros não lineares com um menor grau de heterogeneidade do que aqueles obtidos por polimerização radicalar convencional (FRP). Este trabalho apresenta estudos experimentais sobre a polimerização por ATRP de de metacrilato de metilo (MMA) com dimetacrilato de etilenoglicol (EGDMA) usando α-bromofenilacetato de metilo (MBPA) como iniciador e mediada por brometo de Cobre (CuBr) usando como ligante 1,1,4,7,10,10-hexametiltrietiletetramina (HMTETA). Os polímeros sintetizados foram analisados por cromatografia de exclusão de tamanhos (SEC) com detecção simultânea do índice de refracção (RI) e da dispersão multi-ângulo da luz (MALLS). Foram medidos detalhes importantes da arquitectura molecular destes materiais, nomeadamente massas moleculares absolutas e raio de giração médio z. Foram realizadas diferentes experiências de síntese com o objectivo de investigar a influência das condições de operação, nomeadamente temperatura de polimerização e razões molares iniciais de MMA/EGDMA/MBPA/CuBr/HMTETA, na estrutura dos materiais obtidos. In the last few years, atom transfer radical polymerization (ATRP) of acrylate and methacrylate monomers in the presence of a small amount of cross-linker has been investigated in order to produce branched polymers and gels with applications in microelectronics, coatings industries or biomedicine. In this context, it is being explored the production by ATRP of branched/crosslinked polymers with a lower degree of heterogeneity than that obtained by conventional free radical polymerization (FRP). This work reports an experimental study on the ATRP of methyl methacrylate (MMA) + ethylene glycol dimethacrylate (EGDMA) initiated by MBPA (methyl-bromophenylacetate) and mediated by copper bromide (CuBr) ligated with HMTETA (1,1,4,7,10,10- hexamethyltriethylenetetramine). The synthesized copolymers were analyzed by size exclusion chromatography (SEC) with simultaneous detection of refractive index (RI) and multi-angle laser light scattering (MALLS) signals. Important details of the molecular architecture of these materials can therefore be measured, namely absolute molecular weights and z-average radius of gyration. Different experimental runs were performed in order to investigate the influence of the operating conditions (e.g. temperature and initial molar ratios MMA/EGDMA/MBPA/CuBr/HMTETA) on the structure of the products.
- Kinetic modeling of the molecular architecture of cross-linked copolymers synthesized by controlled radical polymerization techniquesPublication . Gonçalves, Miguel A.D.; Trigo, Ivone; Dias, Rolando; Costa, Mário RuiKinetic Modeling of the Molecular Architecture of Cross-Linked Copolymers Synthesized by Controlled Radical Polymerization Techniques
- Kinetic modeling of the molecular architecture of cross-linked copolymers synthesized by controlled radical polymerization techniquesPublication . Gonçalves, Miguel A.D.; Trigo, Ivone; Dias, Rolando; Costa, Mário RuiA recently developed general kinetic approach, based on population balances in terms of generating functions, is applied to the modeling of the molecular architecture of branched copolymers produced through controlled radical polymerization (CRP) techniques, namely nitroxide-mediated radical polymerization (NMRP) and atom-transfer radical polymerization (ATRP). Thanks to this method, it is possible to carry out dynamic predictions of distributions of molecular weights, sequence lengths and z-average mean square radius of gyration of the products, both before and after gelation (whenever it occurs) with consideration of complex kinetic schemes. The model chemical systems styrene + divinylbenzene (S/DVB) and methyl methacrylate + ethylene glycol dimethacrylate (MMA/EGDMA) are experimentally investigated in order to assess the prediction capabilities of the aforementioned approach. Measurements of absolute molecular weights and z-average radius of gyration of the copolymers are performed for different times of polymerization using a SEC system with a refractive index detector coupled with MALLS. It is shown that the proposed computational tool can enhance the possibility of better design of these complex materials but additional studies concerning the impact of intramolecular cyclizations on the structure of materials synthesized at diluted conditions are needed.
- Molecular architecture of non-linear polymers: kinetic modeling and experimental characterization of the system methyl methacrylate + ethylene glycol dimethacrylatePublication . Trigo, Ivone; Gonçalves, Miguel A.D.; Dias, Rolando; Costa, Mário RuiMolecular Architecture of Non-Linear Polymers: Kinetic Modeling and Experimental Characterization of the System Methyl Methacrylate + Ethylene Glycol Dimethacrylate
- Molecular architecture of non-linear polymers: kinetic modeling and experimental characterization of the system methyl methacrylate + Ethylene Glycol DimethacrylatePublication . Trigo, Ivone; Gonçalves, Miguel A.D.; Dias, Rolando; Costa, Mário RuiA general kinetic approach allowing the prediction of the molecular architecture of non-linear polymers is applied to the study of the copolymerization of methyl methacrylate (MMA) with ethylene glycol dimethacrylate (EGDMA). Dynamic predictions of molecular weight distributions, sequence length distributions and mean square radius of gyration are possible before and after gelation. A set of experiments concerning the copolymerization of MMA and EGDMA was carried out in toluene solution at 60 8C for which classic radical kinetics is a good approximation. The time evolution of key polymer properties was followed using a SEC system with a refractive index detector coupled with MALLS allowing the determination of absolute weight average molecular weight and apparent molecular size distributions as well as z-average radius of gyration. Special focus was given to assess the influence of the initial amount of cross-linker on the dynamics of the non-linear structure build-up of these products. A kinetic scheme comprising 23 different chemical species and 76 chemical reactions was used in the modeling studies of this chemical system. Most of the kinetic parameters used in the simulations have been collected from previous studies. For experiments at low monomer conversion (up to about 0.5) a good agreement between predictions and experimental measurements is observed for molecular weights and z-average radius of gyration by fitting a small number of parameters describing gel effect (with a conversion dependent but chain length independent termination rate parameter) and the relative propagation on pendant double bonds. However, predicted values of weight-average molecular weights and z-average radius of gyration before gelation are too low at higher monomer conversions with non-linear systems. The likely cause is the presence of intramolecular reactions which should not be neglected in these circumstances.
- SEC/MALLS measurement of the branched structure of methyl methacrylate + ethylene glycol dimethacrylate copolymers synthesized by atom transfer radical polymerizationPublication . Trigo, Ivone; Gonçalves, Miguel A.D.; Dias, Rolando; Costa, Mário RuiIn the last few years, atom transfer radical polymerization (ATRP) of acrylate and methacrylate monomers in the presence of a small amount of cross-linker has been investigated in order to produce branched polymers and gels with applications in microelectronics, coatings industries or biomedicine (Wang and Zhu, 2005; Gao et al., 2007). In this context, it is being explored the production by ATRP of branched/crosslinked polymers with a lower degree of heterogeneity than that obtained by conventional free radical polymerization (FRP). This work reports an experimental study on the ATRP of methyl methacrylate (MMA) + ethylene glycol dimethacrylate (EGDMA) initiated by MBPA (methyl -bromophenylacetate) and mediated by copper bromide (CuBr) ligated with HMTETA (1,1,4,7,10,10- hexamethyltriethylenetetramine). The synthesized copolymers were analyzed by size exclusion chromatography (SEC) with simultaneous detection of refractive index (RI) and multi-angle laser light scattering (MALLS) signals. Important details of the molecular architecture of these materials can therefore be measured, namely absolute molecular weights and z-average radius of gyration. Different experimental runs were performed in order to investigate the influence of the operating conditions (e.g. temperature and initial molar ratios MMA/EGDMA/MBPA/CuBr/HMTETA) on the structure of the products.