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Abstract  

The hydrolytic condensation of a precursor synthesized by the reaction of equimolar amounts of (3-aminopropyl)triethoxysilane and phenylglycidylether led to a distribution of polyhedral oligomeric silsesquioxanes (POSS) containing 8–11 Si atoms, functionalized with amine groups. About 57% of the NH functionalities were active for reaction with epoxy groups. The multifunctional amine-POSS was used to modify an epoxy network obtained by the homopolymerization of diglycidylether of bisphenol A initiated by benzyldimethylamine. The main effect of POSS modification was an increase in both the glassy and rubbery modulus explained, respectively, by the increase in cohesive energy and crosslink densities.

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Abstract  

The study of the cure reaction of the epoxy network diglycidyl ether of bisphenol A with amantidine is a useful tool to characterize the industrial behaviour of this material. The total enthalpy of reaction, the glass transition temperature and the partial enthalpies at different cured temperatures have been determined using differential scanning calorimetry in dynamic and isothermal mode. Two models, one based on chemical kinetics and the other accounting for diffusion were used and compared with experimental data. It can be seen that the inclusion of a diffusion factor in the kinetic model is negligible.

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Epoxy resins of DGEBA type were thermally cured with diaminodiphenylmethane as crosslinking agent, and then analysed by Differential Scanning calorimetry (DSC) at various heating rates in order to determine the glass transition temperatureT g of the final networks. First it was shown that during cyclingT g is shifted towards higher values up to a maximum or . Such a change is attributed to an increasing extent of cure which develops during the thermal analysis, and also to relaxation processes thermally activated inside the polymeric matrix. Then the dependence of on the heating rateq imposed by the DSC apparatus was presented forq changing from 0.1 to10‡C min−1. At heating rates exceeding 3‡C min−1 only the classical temperatureT g was detected, but at smallerq values, an additional endothermic transition was revealed, located at higher temperature and linked to a physical aging-like phenomenon, which takes place at low heating rates. The plot of against logq is divided into two quasi-linear parts on each side ofq=3‡C min−1. In conclusions, an equation was given to describe the vs. logq function.

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Journal of Thermal Analysis and Calorimetry
Authors: F. Fraga, V. Soto, J. Blanco-Méndez, A. Luzardo-Alvarez, E. Rodríguez-Núñez, J. Martínez-Ageitos and M. Pérez

Abstract  

Knowledge of the the kinetic study of chitosan/genipin allow to know the different effects that time and temperature have on the cure reaction of the material. The total enthalpy of reaction, the glass transition temperature and the partial enthalpies have been determined using DSC in dynamic mode. Two models, one based on chemical kinetics and the other accounting for diffusion were used. The incorporation of the diffusion factor in the second model allowed for the cure kinetics to be predicted the whole range of conversion.

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Journal of Thermal Analysis and Calorimetry
Authors: M. A. García del Cid, M. G. Prolongo, C. Salom, C. Arribas, M. Sánchez-Cabezudo and R. M. Masegosa

with aromatic diamines, decreases in the T g of the epoxy network have been frequently reported [ 5 , 14 , 17 – 19 ]. This fact has been attributed to the plasticization of the epoxy network by the hydrocarbon chains of the alkylammonium cations [ 5

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Abstract  

Diglycidyl ether of bisfenol-A (DGEBA)/polybenzyl methacrylate (PBzMA) blends cured with 4,4’-diaminodiphenylmethane (DDM) were studied. Miscibility, phase separation, cure kinetics and morphology were investigated through differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Non-reactive DGEBA/PBzMA blends are miscible over the whole composition range. The addition of PBzMA to the reactive (DGEBA+DDM) mixture slows down the curing rate, although the reaction mechanism remains autocatalytic. On curing, initially miscible (DGEBA+DDM)/PBzMA blends phase separate, arising two glass transition temperatures that correspond to a PBzMA-rich phase and to epoxy network. Cured epoxy/PBzMA blends present different morphologies as a function of the PBzMA content.

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Abstract  

In this work the curing kinetics behaviour of a rubber modified epoxy amine system is investigated through calorimetric analysis. This study is part of a wider investigation on new epoxy formulations to be used as matrices of composite materials. The aim is to enhance both the processing behaviour and the mechanical properties of the matrix in order to obtain higher performance composites for more demanding applications. The epoxy system is blended with a high molecular mass rubber containing functional groups reactive towards the epoxies. The formation of a rubber/epoxy network can be achieved by means of a 'pre-reaction' between the epoxy monomers and the rubber functional groups, carried out in the presence of a suitable catalyst and before the resin is cured with the amino hardener. In this work the influence of both the rubber and the catalyst on the resin cure kinetics is analysed.

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Abstract  

Structural relaxation in different epoxy-anhydride and epoxy-diamine resins has been investigated by differential scanning calorimetry using annealing and cooling rate experiments. The annealing experiments lead to the determination of enthalpy loss,δH, at an equivalent annealing temperatureT a=T g-20, and for periods of annealing time, ta, between 1 h and 4 months. The variation ofδH with logta, defines a relaxation rate per decade,rrpd, which is very sensitive to changes of the epoxy network. The cooling rate experiments allow the determination of the apparent activation energy,δh *. The effect of the degree of crosslinking, the addition of a reactive diluent, which acts as flexibilizer, and the length of cross-link onrrpd and δh* was studied.

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Abstract  

The thermal degradation of the epoxy systems diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diamine cyclohexane (DCH) and diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diaminecyclohexane (DCH) containing calcium carbonate filler immersed and not immersed in hydrochloric acid have been studied by thermogravimetric analysis in order to compare their decomposition processes and to determine the reaction mechanism of the degradation processes. The value of the activation energies, necessary for this study, were calculated using various integral and differential methods. Analysis of the results suggests that hydrochloric acid does not affect the decomposition of the epoxy network and that the reaction mechanisms produce sigmoidal-type curves for the systems not immersed in HCl and deceleration curves for the same systems immersed.

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Abstract  

Diglycidyl ether of bisfenol-A (DGEBA)/poly(vinyl acetate) (PVAc)/poly(4-vinyl phenol) brominated (PVPhBr) ternary blends cured with 4,4’-diaminodiphenylmethane (DDM) were investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). Homogeneous (DGEBA+DDM)/PVPhBr networks with a unique T g are generated. Ternary blends (DGEBA+DDM)/PVAc/PVPhBr are initially miscible and phase separate upon curing arising two T gs that correspond to a PVAc-rich phase and to epoxy network phase. Increasing the PVPhBr content the T gof the PVAc phase move to higher temperatures as a consequence of the PVAc-PVPhBr interactions. Different morphologies are generated as a function of the blend composition.

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