Filiberto González Garcia

Determination of the epoxide equivalent weight of epoxy resins based on diglycidyl ether of bisphenol A (DGEBA) by proton nuclear magnetic resonance

Abstract A methodology for the determination of epoxide equivalent weights (EEW) in liquid epoxy resins based on the diglycidyl ether of bisphenol A (DGEBA) using proton nuclear magnetic resonance ( 1 H-NMR) spectroscopy is described. The data obtained are in good agreement to those obtained from the classical titration procedure with HBr in glacial acetic acid. The 1 H-NMR method constitutes an alternative for the characterization of epoxy resin, since it is rapid and free of interfering chemical reagents.

Grafting of polymethyl methacrylate from poly(ethylene-co-vinylacetate) copolymer using atom transfer radical polymerization

Abstract Atom transfer radical polymerization was employed for the first time to prepare graft copolymer having by ethylene–vinyl acetate (EVA) copolymer as backbone and poly(methyl methacrylate) (PMMA) as branches. The polymerization of MMA was initiated by EVA carrying chloropropionate groups as macroinitiator, in the presence of copper chloride (CuCl) and bipyridine (bpy) at 80 °C. The macroinitiator was prepared by esterification of partially hydrolyzed EVA with 2-chloropropionyl chloride. Successful graft copolymerizations were performed both in toluene/γ-butyrolactone mixed solvent and in toluene solution, with grafting efficiency of 12% and 6%, respectively. Molecular weight distribution of the PMMA segments around 1.2 has been achieved with pure toluene solution. The ATRP graft copolymerization was supported by an increase of the molecular weight of the graft copolymers, as compared to that of the macroinitiator and also by their monomodal molecular weight distribution.

The compatibilization of SBR/EVA by mercapto-modified EVA

Abstract Styrene–butadiene copolymer/ethylene–vinyl acetate copolymer (SBR/EVA) blends with different ratios were prepared by using a Haake internal mixer. These blends were compatibilized with mercapto-modified EVA (EVALSH), which promotes bonding between the SBR phase and the EVALSH through a chemical reaction between the mercapto groups of the reactive compatibilizing agent and the double bond of the unsaturated rubber. The presence of EVALSH resulted in an improvement of the tensile strength of the unvulcanized SBR/EVA blends and also a more uniform dispersion of the EVA phase inside the SBR matrix for blends containing higher amount of the rubber phase. The formation of insoluble material in the blends containing EVALSH indicates reactive compatibilization, which was confirmed by Fourier transform infrared analysis and also by dynamic mechanical analysis. In this case, a decrease in damping properties of the SBR phase was observed as a consequence of decreasing chain mobility. EVALSH also caused a decrease in degree of crystallinity of the EVA phase as observed by differential scanning calorimetry analysis.

Separação de fases induzida por meio de reação química no sistema éter diglicidílico do bisfenol A e piperidina com poli(metacrilato de metila)

The phase separation and gelification behavior of epoxy system based on diglycidyl ether of bisphenol-A (DGEBA) and piperidine modified with poly(methyl methacrylate) (PMMA) were studied in the range between 60 °C and 120 °C. The morphology is influenced by the PMMA content in the blend and also by the cure temperature. The molecular weight of PMMA provokes slight changes on cloud point and does not affect the reaction rate. The systems modified by PMMA exhibited kinetic retardation effect but the cloud point rate was higher than the polymerization rate.

Estudio de la reacción de curado del sistema éter diglicidílico del bisfenol-A (DGEBA) y la dietilentriamina (DETA) por calorimetría diferencial de barrido

The curing reaction of diglycidyl ether of bisphenol-A (DGEBA) and diethylentriamine (DETA) system was studied by differential scanning calorimetry (DSC). Different kinetics expressions were found by isothermal and dynamic experiments that they justify mechanism changes with the temperature. The reaction follows a second order kinetics and has activation energy of 90 kJ mol-1 at high temperatures (non-catalytic mechanism). The kinetics of the reactions at low temperatures manifested the existence of two competitive mechanisms, the constants rate were determined at 60 and 70°C and has activation energy in the range of 56.9 to 63.0 kJ mol-1 that is in perfect agreement with the reported to low temperatures (autocatalytic mechanism ).