Summary: Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and polarized light microscopy (PLM) were used to study the curing reaction of diglycidyl ether of 4,4′‐bisphenol P (DGEBP) epoxy resin with aromatic amine, 4‐nitro‐1,2‐phenylenediamine (4‐NPDA). Two exothermic peaks were observed on the DSC curves. The first peak was assigned to the curing process of DGEBP with 4‐NPDA. The second peak was associated with the decomposition that may partially be overlapped with self‐curing. Kinetic analysis was performed by using an advanced isoconversional method, which suggests that the effective activation energy for the first process is around 50 kJ · mol?1, and for the second process, it changes from 160 to 120 kJ · mol?1. The curing process (first peak on DSC curve) is associated with the formation of a liquid crystalline phase that can be converted to another mesophase on cooling if the system is not completely cured. The transition between the two mesophases becomes irreversible on further heating.
DSC curves of repetitive heat‐cool cycles for DGEBP/4‐NPDA system at 10 °C · min?1. 1: heating (1′) and cooling (1) of fresh (uncured) sample; 2: heating (2′) and cooling (2) of partially cured sample; 3: heating (3′) and cooling (3) of cured sample. 相似文献
Summary: Differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis and polarized light microscopy were used to study the curing reaction of diglycidyl ether of 4, 4′‐bisphenol P epoxy resin with an aromatic amine, 3‐nitro‐1,2‐phenylenediamine. Because of different reactivity of the two amino groups, the curing gives rise to two processes represented by two peaks on a DSC curve. It is demonstrated that the amine group in position 1 is more reactive than the one in position 2. Kinetic analysis was performed by using an advanced isoconversional method, which suggests that the effective activation energy for the first process is around 50 kJ · mol?1, and for the second process, is about 100 kJ · mol?1.
Dependence of activation energy on the extent of conversion (points) and the dependence of the extent of conversion on temperature (line) at the heating rate of 10 °C · min?1 for DGEBP/3‐NPDA system. Stars correspond to the stoichiometric system, open circles and squares represent respectively the 1st and 2nd peak for the system with an excess of amine. 相似文献
Summary: Differential scanning calorimetry (DSC), thermogravimetry and isoconversional kinetic analysis were used to study the curing reaction of diglycidyl ether of 4,4′‐bisphenol P epoxy resin with an aromatic amine, 2,4‐dinitroaniline. Two exothermic peaks have been observed on a DSC curve. The first one corresponds to the cure and the second one represents decomposition. Advanced isoconversional method shows an activation energy of cure (90–115 kJ · mol−1) which is markedly higher than the typical activation energy of epoxy‐amine cure reaction. The effect is explained by electrostatic repulsion of the NO2 group that shields NH2 from nucleophilic attack and creates an extra energy barrier to the curing reaction.
Dependence of activation energy on the extent of conversion (scatter plot) and the dependence of the extent of conversion on temperature (line plot) at the heating rate of 10 °C · min−1of DGEBP/2,4‐DNA system. 相似文献
Fluorescence resonance energy transfer (FRET) sensitized emission of perylene by pyrene in a joint‐linker type gel is observed for the first time. The joint‐linker type organic‐inorganic hybrid gels containing pyrene and perylene synthesized from multi‐functional cyclic siloxane, 1,3,5,7‐tetramethylcyclotetrasiloxane (TMCTS), or cubic silsesquioxane, 1,3,5,7,9,11,13,15‐octakis(dimethylsilyloxy)pentacyclo‐[9,5,1,1,1,1]octasilsesquioxane (POSS), as joint molecules, and α,ω‐nonconjugated dienes, 1,5‐hexadiene (HD), or 1,9‐decadiene (DD), as linker molecules, are involved in a photo hydrosilylation reaction with a bis(acetylacetonato)platinum catalyst in a toluene solution of pyrene and perylene. FRET from pyrene (donor) to perylene (acceptor) in the gels is studied quantitatively. The FRET efficiencies (E) of gels containing 300 or 30 x 10–6 m of pyrene and perylene are about 0.6–0.8 or 0.5, respectively, independent of the monomer concentration. Sensitized acceptor emission is observed in the gels, especially in the gels containing 300 x 10–6 m of pyrene and perylene molecules. The ratio of the increase of the sensitized acceptor emission to the loss of donor fluorescence, the G factor, is determined to evaluate the efficiency of the sensitized emission of the acceptor in the gels. The G factors of the gels containing 300 or 30 x 10–6 m of pyrene and perylene molecules are 0.4–0.75 or 0.07‐0.1, repectively, and the gels with TMCTS or DD have a slightly higher G factor than gels with POSS or HD.
The cationic copolymerization of 2‐phenoxymethyl‐1,4,6‐trioxaspiro[4,4]nonane with DGEBA under microwave irradiation using ytterbium and lanthanum triflates as initiators is described. A comparison with thermal heating showed a great enhancement in the reaction rates and a higher SOE incorporation in the network. The double ring opening of SOE reduces the usual shrinkage of epoxy resins on curing, and it was lower under microwave irradiation. Moreover, the ytterbium triflate initiator lead to a higher incorporation of linear ester moieties in the network than lanthanum triflate.
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