Influence of Aliphatic Amine Epoxy Hardener on the Adhesive Properties of Blends of Mono-Carboxyl- terminated poly(2-ethylhexyl acrylate-co-methyl methacrylate) with Epoxy Resin Filiberto Gonza ´lez Garcia, 1,2 Bluma Guenther Soares, 3 Maria Elena Leyva, 1 Alexandre Zirpoli Simo ˜es 2 1 Laboratorio de Biomateriais, Departamento de Fı ´sica e Quı ´mica, Instituto de Cie ˆncias Exatas, Universidade Federal de Itajuba ´ (UNIFEI), Itajuba ´ 37500-903, MG, Brazil 2 Laborato ´rio de Quı ´mica, Universidade Federal de Itajuba ´-Campus Itabira, Itabira 35900-373, MG, Brazil 3 Instituto de Macromole ´culas, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bl. J, Ilha do Funda ˜o, 21945-970 RJ, Brazil Received 7 May 2009; accepted 4 November 2009 DOI 10.1002/app.31720 Published online 27 April 2010 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The adhesive properties have been investi- gated in blends of mono-carboxyl-terminated poly(2-ethyl- hexyl acrylate-co-methyl methacrylate) with diglycidyl ether of bisphenol A and three different aliphatic amine epoxy hardener. The adhesives properties are evaluated in steel alloy substrate using single-lap shear test. The copolymers are initially miscible in the stoichiometric blends of epoxy resin and hardener at room temperature. Phase separation is noted in the course of the polymeriza- tion reaction. Different morphologies are obtained accord- ing to the amine epoxy hardener. The most effective adhesive for steel–steel joints in single-lap shear test is the blends using 1-(2-aminoethyl)piperazine (AEP) as hard- ener. This system shows the biggest lap shear strength. However, the modified adhesives show a reduction in the mechanical resistance. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2762–2770, 2010 Key words: epoxy adhesive; aliphatic amine; lap shear; cohesive fracture; cavitation INTRODUCTION Epoxy resins are some of the most important ther- mosetting polymers used for many applications like coatings, adhesives, insulation, and matrixes for composite materials because of good engineering properties. One major drawback is their poor resist- ance to impact and crack initiation. The fracture re- sistance of the epoxy network can be improved by using different types of modifiers. 1 Another possibil- ity is to change the structure of the epoxy resin 2–6 or on the amine co-monomer. 7–9 Liquid rubber-epoxy systems have been widely studied over 30 years ago. The aim is to increase the toughness of epoxy thermoset with a disperse rub- ber rich phase. 1 Particular attention had received re- active oligomeric compounds, such as carboxyl and amino terminated butadiene-acrylonitrile with low molecular weight. Examples of these compounds include: statistical copolymers, telechelic acrylate copolymers and terpolymers, amine terminated polysiloxanes, and extended chain carboxyl-termi- nated perfluoro polyethers. 10 The liquid rubber that has received the most attention involves carboxyl- terminated butadiene-acrylonitrile (CTBN) liquid polymers. Recently, the adhesion behavior in blends of mono-carboxyl-terminated poly(2-ethylhexyl acry- late-co-methyl methacrylate) random copolymers (MCTEAM) with diglycidyl ether of bisphenol A (DGEBA), and TETA is evaluated as a function of the composition and concentration of the copolymer in steel alloy adherent. 11 In those copolymers, a phase-separation phenomenon induced by a poly- merization reaction takes place. As expect, the size of the dispersed phase depends on the composition and the modifier concentration. The copolymer with 60% molar of methyl methacrylate showed the best adhesive properties. This behavior was related to the small average size of copolymer particle (5.0 lm) homogeneously distributed in the thermoset matrix. In this way, the use of different aliphatic amine epoxy hardener on the adhesive properties of blends of mono-carboxyl-terminated poly(2- Correspondence to: F. G. Garcia (fili@unifei.edu.br). Contract grant sponsor: National Plane of Science and Technology, Sector Natural Gas and Petroleum; contract grant numbers: CT-PETRO, CNPQ (CT-PETRO) 500092/ 02-8. Contract grant sponsor: FAPEMIG; contract grant number: TEC 00242/07. Journal of Applied Polymer Science, Vol. 117, 2762–2770 (2010) V C 2010 Wiley Periodicals, Inc.