Acceleration mechanisms in curing reactions involving model systems

Abstract

The mechanisms involving some of the most common accelerators in the curing reactions of epoxy resins have been investigated by use of model systems. Phenyl glycidyl ether was used as a model compound. The characterization of the reaction products was mainly carried out by High‐Performance‐Liquid‐Chromatography and by preparative methods. Special attention was paid to the oligomerization reactions of the oxirane ring in the presence of tertiary amines. Three different types of oligomers depending on phenyl glycidyl ethers are discussed. The mechanisms of multifunctional accelerators such as imidazoles or phenol‐MANNICH‐base‐compounds are much more difficult. The extraordinary interaction of imidazoles depends on the formation of different oligomers. Furthermore, the cleavage of the imidazole ring was observed. It is possible that the glycidyl ether oligomerization plays an important role in understanding the network structure. Some aspects of the accelerating effect of tertiary amines in the curing of glycidyl ethers with acid anhydrides were likewise discussed. The results obtained using these model reactions may be applied to influence the curing process in commercial epoxy resin systems.

Polymer-Dispersed Liquid Crystals with Co-continuous Structures Generated by Polymerization-Induced Phase Separation of EBBA−Epoxy Solutions

“…For the particular case of the homopolymerization of a tetrafunctional monomer, it may be written as where DP w is the mass-average degree of polymerization of primary chains. The experimental value of the gel conversion results from DP w = 3.86, which lies in the range of experimental values reported for the homopolymerization of monoepoxides in the presence of tertiary amines. − …”

“…In the presence of a tertiary amine as initiator (benzyldimethylamine, BDMA, Figure ), DGEBA undergoes an anionic polymerization at a relatively slow polymerization rate, leading to a polymer network . The reaction proceeds through a living chainwise mechanism leading to very short primary chains (2−5 epoxy units), due to the high ratio of chain transfer/chain propagation rates. − Gelation takes place at advanced conversions that depend on the initial concentration of initiator and cure temperature . This favors the possibility of producing phase separation previous to the gel formation.…”

Anionic Polymerization of Phenyl Glycidyl Ether in Miniemulsion

“…Phenyl glycidyl ether (PGE) is generally used as a model monomer for the study of epoxy matrix hardening as its structure is close to the common reactant 2,2-bis[4-(glycidyloxy)phenyl]propane (DGEBA). − Solution polymerization of PGE has been reported in the past 40 years using anionic, cationic, or nucleophilic initiators. − In particular, detailed kinetic studies on the anionic polymerization of PGE were quoted mainly by Stolarzewicz , and others. , One major drawback reported by these authors is that numerous chain transfer reactions can coexist with the anionic polymerization of epoxides. Transfer reactions to the initiator 15-17 or to solvent 20 cause end-chain defects, whereas transfer to monomer 18 produces new active centers containing aliphatic double bonds and carbonyl groups.…”

Kinetic Reaction Analysis of Gelation: Investigations of Random Step-Growth and Chain-Initiated Resins

“…Number-average molecular weights were consistently less than expected. This was attributed to impurities, but Steinmann (1990) and Fedtke (1987) state that PGE forms a phenolate C 6 H 5 O + N -R 3 H and acrolein. Phenolate acts as a second initiator, causing time-dependent reductions in average molecular weights with 1-methylimidazole.…”

“…The PGE/NMA/BDMA cure was accurately modeled with an initiation step having the same rate constant as the propagation reaction. However, the 1-methylimidazole resin experienced a distinct initiation rate constant (Fedtke, 1987;Hale and Macosko, 1989;Steinmann, 1990).…”