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Epoxies Modified by Palmitic Acid: From Hot‐Melt Adhesives to Plasticized Networks
Author(s) -
Hoppe Cristina E.,
Galante María J.,
Oyanguren Patricia A.,
Williams Roberto J. J.
Publication year - 2005
Publication title -
macromolecular materials and engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 96
eISSN - 1439-2054
pISSN - 1438-7492
DOI - 10.1002/mame.200400348
Subject(s) - epoxy , materials science , transesterification , adhesive , crystallization , bisphenol a , diglycidyl ether , glass transition , fourier transform infrared spectroscopy , polymer chemistry , chemical engineering , composite material , organic chemistry , polymer , methanol , chemistry , layer (electronics) , engineering
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 ( T g ) without any evidence of crystallization or phase separation. T g 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.