Catalytic control of bond exchange reactions enables healing of cross-linked polymer materials under a wide range of conditions. The healing capability at high temperatures is demonstrated for epoxy–acid and epoxy–anhydride thermoset networks in the presence of transesterification catalysts. At lower temperatures, the exchange reactions are very sluggish, and the materials have properties of classical epoxy thermosets. Studies of model molecules confirmed that the healing kinetics is controlled by the transesterification reaction rate. The possibility of varying the catalyst concentration brings control and flexibility of welding and assembling of epoxy thermosets that do not exist for thermoplastics.

Metal-catalyzed transesterification for healing and assembling of thermosets.

Polymer engineering based on reversible covalent chemistry: A promising innovative pathway towards new materials and new functionalities

This review is on the use of differential scanning calorimetry as a method of monitoring and investigating the kinetics of epoxy resin curing reactions. Some instrumental and experimental aspects are discussed, including methods of analysing the kinetic data. A brief survey is made of epoxy resin curing reactions and results of DSC studies are reviewed. These results are concerned with the use of carboxylic acid anhydrides, primary and secondary amines, dicyanodiamide, and imidazoles as curing agents.

The application of differential scanning calorimetry (DSC) to the study of epoxy resin curing reactions

High Biobased Content Epoxy–Anhydride Thermosets from Epoxidized Sucrose Esters of Fatty Acids

Epoxy resins constitute an important class of thermosets which are used extensively in the field of composites, adhesives surface coatings, etc. They are of aliphatic, cycloaliphatic or aromatic backbones. Epoxy resins based on bisphenol A are commercially available and they have good thermal and mechanical properties. They are cured by a variety of curatives, such as amines and anhydrides, and the mechanism of curing largely depends on the type of curing agent used. They show comparatively low cure shrinkage. Cured epoxies are brittle with poor resistance to crack initiation and growth. Their mechanical properties, in particular toughness, can be modified by incorporating a rubbery phase into the resin matrix. The epoxy matrix can also be modified by various other methods such as incorporation of thermoplastics and particulate fillers. The toughening process leads to improvement in fracture toughness and impact resistance. This review examines the various options and the state-of-the-art vis-a-vis epoxy ...

https://www.tandfonline.com/doi/pdf/10.1163/156855506776382664

Toughening of epoxy resins

The mechanism of acid curing of epoxy resins catalyzed with tertiary amines was investigated by using model systems composed of phenylglycidyl ether and benzoic acid or acetic acid anhydrides in the presence of benzyldimethylamine. The reaction was studied by NMR spectrometry, liquid chromatography, and ozone absorption. The main findings are that (1) the tert-amine is bound chemically and irreversibly during the reaction under the formation of a quaternary ammonium salt 

and (2) 1-phenyloxypropanediol-2,3-dibenzoate or diacetate is the main reaction product. The suggested reaction mechanism involves initiation in which the tertiary amine reacts with the epoxy group, giving rise to a zwitterion that contains a quaternary nitrogen atom and an alkoxide anion; the latter immediately reacts with the anhydride and quaternary salt is formed. In a later stage the carboxy anion of the quaternary salt reacts first with the epoxy group, then with the anhydride. By this reaction diester is formed and the carboxy anion is regenerated.

J. Lövy

Papers

Curing epoxy resins with anhydrides. Model reactions and reaction mechanism