Reduction of the shrinkage of thermosets by the cationic curing of mixtures of diglycidyl ether of bisphenol A and 6,6‐dimethyl‐(4,8‐dioxaspiro[2.5]octane‐5,7‐dione)

Abstract

Ytterbium and lanthanum triflates were used as initiators to cure mixtures of diglycidyl ether of bisphenol A and 6,6‐dimethyl‐(4,8‐dioxaspiro[2.5]octane‐5,7‐dione) in several proportions. The evolution of the epoxy and 6,6‐dimethyl‐(4,8‐dioxaspiro[2.5]octane‐5,7‐dione) bands during curing and the linear ester groups in the final materials were evaluated with Fourier transform infrared in the attenuated‐total‐reflection mode. The use of a conventional cationic initiator, boron trifluoride monoethylamine, was also studied to test the advantages of lanthanide triflates. The shrinkage after curing and the thermal degradability of the materials with variations in the comonomer ratio and the initiator were evaluated and related to the chemical structure of the final network. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6869–6879, 2006

Cationic curing of diglycidyl ether of bisphenol A and 2,2,5,5‐tetramethyl‐4,6‐dioxo‐1,3‐dioxane and degradation of the thermosets obtained

“…In a previous work, 8 we studied the curing of mixtures of DGEBA epoxy resin with a cyclopropylic spiranic MA derivative (MCP), using lanthanide triflates as initiators. We observed that the higher the proportion was of MCP in the curing mixture, the lower the global shrinkage was.…”

“…4 The expandable character of MCP was proved and attributed to the change in the dipolar moment by the opening of the lactone ring. 8 Moreover, the amount of shrinkage is related to the size of the ring being opened; in general, the larger the ring is, the smaller the shrinkage is. 20 Therefore, six-membered lactones should produce a larger expansion on polymerizing than five-membered lactones.…”

“…[5][6][7] Among ester groups, the tertiary ones are the most easily broken, and so we considered in a previous study their introduction by the copolymerization of diglycidyl ether of bisphenol A (DGEBA) resins with a Meldrum acid (MA) derivative, 6,6-dimethyl-(4,8-dioxaspiro [2.5]octane-5, 7-dione) (MCP), with a spiranic skeleton. 8,9 MCP was selected because it allows the introduction of tertiary ester groups into the network, which facilitates the degradation process of the thermoset. The expandable behavior of MCP on curing was also demonstrated.…”

Phosphorus-containing thermosets obtained by cationic copolymerisation of glycidyl compounds with a spiroorthoester or γ-butyrolactone

“…The enthalpies (J/g) for g-BL-containing mixtures are higher than SOE-containing samples. The enthalpies per epoxy equivalent are higher for the samples with lactone, and close to enthalpy of pure DGEBA [30,31]. This indicates that the enthalpy is mainly related to the ring opening of oxirane groups.…”

New Thermosets Obtained by Thermal and UV‐Induced Cationic Copolymerization of DGEBA with 4‐Phenyl‐γ‐butyrolactone

“…The improved thermal stability of the photocured materials can be related to their higher degree of cross-linking and to the fact that lanthanide triflates can catalyze the decomposition reactions at high temperatures. [32,33] As in thermally cured samples, it is observed that the presence of PhBL increases the thermal degradability due to the introduction of ester linkages in the network via intermediate SOE formation and polymerization. The degradative process of UV-cured samples takes place in a narrow range of temperatures because volatilization of the decomposition fragments is fast at such high temperatures.…”