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

Abstract

Ytterbium and lanthanum triflates were used as cationic initiators to cure mixtures of diglycidyl ether of bisphenol A and 2,2,5,5-tetramethyl-4,6-dioxo-1,3-dioxane in several proportions. The evolution of the epoxy and lactone during curing and the linear ester groups in the final materials were evaluated with Fourier transform infrared in the attenuated total reflection mode. The shrinkage after curing and the thermal degradability of the materials with variations in the comonomer ratios and initiator used were evaluated and related to the chemical structure of the final network. The expandable character of 2,2,5,5-tetramethyl-4,6-dioxo-1,3-dioxane was confirmed. The obtained materials were more degradable than conventional epoxy resins because of the tertiary ester groups incorporated into the network by copolymerization. The kinetic parameters of the curing and degradation processes were calculated with differential scanning calorimetry and thermogravimetric analysis, respectively, with isoconversional procedures applied in both cases.

Anionic copolymerization of diglycidyl ether of bisphenol A with Meldrum's acid derivatives initiated by 4‐(N,N‐dimethylamino) pyridine

“…In previous articles,8, 9 we reported the reduction of the shrinkage on the curing of DGEBA/MCP or DGEBA/MDM mixtures with cationic initiators. Three‐to‐one DGEBA/MDM mixtures led to a shrinkage of 2.2% with Yb(OTf) 3 and 2.7 with La(OTf) 3 .…”

“…In previous articles, we reported the cationic copolymerization of DGEBA epoxy resin with MCP8, 24, 25 or MDM9 using several Lewis acids as cationic initiators, and the reduction in the shrinkage was confirmed. In this work, we study the overall curing process and test if the global shrinkage is reduced under anionic conditions.…”

“…Because of the characteristics of MCP, which has a highly strained cyclopropyl ring, a double ring opening of the skeleton could be suspected and could justify the expandable behavior observed 8. However, MDM has also shown an expandable character 9. Therefore, the opening of the Meldrum's acid ring should be responsible for these results.…”

“…Their use is a suitable strategy to reduce the shrinkage, but the synthesis of these monomers is in some cases very tedious 7. Moreover, Meldrum's acid and its derivatives have demonstrated their expandable character in copolymerization with epoxy resins using lanthanide triflates as cationic initiators, which lead to thermosets with lower global shrinkage than pure epoxy resins 8–10…”

Novel dibenzocycloheptenyl phosphonium salts as thermolatent initiator in cationic polymerization

“…[1][2][3][4] The latent cationic initiators, which exhibit no activity under ambient condition but generate active species on external stimulation such as heating or photoirradiation, have gained momentum over conventional anhydride and amine-based initiators. [5][6][7][8][9][10][11][12] Thus, development of efficient thermolatent cationic initiators having good solubility in monomer and resistance toward air and moisture is more desirable. Several onium salts such as benzyl sulfonium, [13][14][15] benzyl pyridinium, 16,17 benzyl ammonium, 18 hydrazinium, 19,20 and others [21][22][23][24][25] have been developed as potential thermolatent initiator.…”