Epoxies Modified by Palmitic Acid: From Hot‐Melt Adhesives to Plasticized Networks

Abstract

Summary: Reactions taking place in a homogeneous solution of an epoxy monomer based on the diglycidyl ether of bisphenol A (DGEBA) and palmitic acid (PA), in the presence of benzyldimethylamine (BDMA), were investigated using Fourier‐transformed infrared spectroscopy (FTIR) and size exclusion chromatography (SEC). In the stoichiometric formulations prepared with equal molar ratios of epoxy (E) to carboxyl groups, E/PA = 1, the main reaction was the carboxyl addition to the epoxy giving a β‐hydroxy ester. This reaction was followed by transesterification that occurred to a very small extent. In the formulations prepared with an epoxy excess, E/PA > 1, the transesterification reactions were very significant as well as the homopolymerization of the epoxy excess that took place to an almost complete conversion. Reaction products synthesized in the range of 1 < E/PA < 2 were solids at room temperature due to the crystallization of a fraction of fatty acid chains. Above the melting temperature, reaction products recovered the liquid state. The formulation synthesized with E/PA = 2 exhibited a good behavior as a hot‐melt adhesive of steel sheets with a single lap‐shear strength of 2.5 MPa and an interfacial‐cohesive failure. For E/PA > 3, the gelation took place leading to the networks exhibiting a single glass transition temperature (Tg) without any evidence of crystallization or phase separation. Tg varied from 90 °C for the neat epoxy to 0 °C for the formulation with E/PA = 3.Single lap‐shear strength values of hot‐melt adhesives corresponding to reaction products synthesized with E/PA = 1.6, 1.8, and 2.magnified imageSingle lap‐shear strength values of hot‐melt adhesives corresponding to reaction products synthesized with E/PA = 1.6, 1.8, and 2.

Chain extension and branching of poly(L-lactic acid) produced by reaction with a DGEBA-based epoxy resin

“…(3) Dicarboxylated PLLA reacting with DGEBA to prepare PLLA/ DGEBA copolymers. The epoxy-acid reaction is complex in the presence of TABA [17]. The reaction mechanism of dicarboxylated PLLA reacting with DGEBA may be described as Figure 2.…”

Control of reactions and network structures of epoxy thermosets

“…Among classical efficient base catalysts are: (i) imidazoles [142][143][144], (ii) tertiary amines [138,145,146], (iii) phosphonium bromide [140,147] and (iv) some metal salts [80][81][82]. For instance, 1,2-dimethylimidazole [142] and dimethylbenzylamine [145] as well as tetrabutylphosphonium bromide [140] and zinc acetate [82] have been reported as very efficient catalysts (Fig. 28).…”

Self‐Assembly of Epoxy‐Based Polymers

“…Glass transition temperatures decreased from about 90 ° C for the neat epoxy to 0 ° C for the formulation with E/PA = 3. Although some degree of nanostructuration can be expected in these materials, no crystalline structures were observed [17] .…”

“…As an example of the epoxy -fatty acid chemistry, palmitic acid ( PA ) was reacted with DGEBA in the presence of BDMA to give products whose properties were controlled by the molar ratio of epoxy ( E ) to carboxyl groups (E/PA) [17] . In the presence of tertiary amines and in formulations containing an epoxy excess, transesterifi cation of the β -hydroxy ester formed through the epoxy -acid addition is very signifi cant as well as the homopolymerization of the epoxy excess.…”

“…Above the melting temperature the product behaved like a liquid; below the melting temperature a physical gel was formed with crosslinks introduced by the micrometer -size fatty ester crystals. These systems showed interesting properties as hot -melt adhesives which are liquids at the application temperature and solidify at room temperature [17] .…”