Reaction-Induced Phase Separation and Thermomechanical Properties in Epoxidized Styrene-block-butadiene-block-styrene Triblock Copolymer Modified Epoxy/DDM System Sajeev Martin George,* ,†,‡ Debora Puglia, § Jose M. Kenny, § Jyotishkumar Parameswaranpillai,* ,∥ and Sabu Thomas* ,†,⊥,# † School of Chemical Sciences, Mahatma Gandhi University, Priyadarshini Hills P.O., Kottayam, Kerala 686560, India ‡ Department of Chemistry, St. Thomas College, Pala, Kottayam, Kerala 686574, India § Materials Engineering Centre, University of Perugia, Local Pentima Bassa, 21, 05100 Terni, Italy ∥ Department of Polymer Science and Rubber Technology, Cochin University of Science and Technology, Cochin, Kerala 682022, India ⊥ International and Interuniversity Centre for Nanoscience & Nanotechnology, Mahatma Gandhi University, Priyadarshini Hills, Kottayam, Kerala 686560, India # Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selongor, Malaysia * S Supporting Information ABSTRACT: Styrene-block-butadiene-block-styrene (SBS) triblock copolymer epoxidized with 47 mol % degree of epoxidation (eSBS47) by hydrogen peroxide in a water/dichloroethane biphasic system was blended with epoxy based on diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diaminodiphenylmethane (DDM) as a curing agent. The amounts of eSBS in the blends were 10 and 20 wt %. The evolution of the glass transition temperatures (T g ) of the cured blends at different cure times was analyzed using differential scanning calorimetry (DSC) to understand the thermal behavior of epoxy system under dynamic conditions in the presence of eSBS. Transmission electron microscopy (TEM) analysis revealed core−shell nanodomains of eSBS dispersed in the epoxy matrix. The relationship between rheology and phase separation was carefully explored. Dynamic mechanical analysis (DMA) validated the nanophase-separated structure of the eSBS47-modified epoxy system. Upon addition of eSBS47 to the epoxy system, the fracture toughness of the nanostructured thermosets was improved, and the thermal stability was retained, but the dimensional stability was slightly decreased. 1. INTRODUCTION One of the most commonly used thermosetting polymer, epoxy resin (diglycidyl ether of bisphenol A, DGEBA), is employed in industrial applications in the automotive, aerospace, and electronics industries as an adhesive and structural material, because of its good mechanical and thermal properties, good adhesion to other substrates, good chemical and electrical resistance properties, and so on. 1 These specific properties are due to its cross-linked structure. Nevertheless, cured epoxy resins are highly brittle and have poor fracture toughness because of their extreme cross-linked structures when compared to other engineering thermoplastic polymers. To improve the toughness of epoxy resins, different modifiers can be considered to broaden the final application of this type of thermosetting resin. Epoxy resins are commonly modified with elastomers, which usually leads to a loss in modulus and thermal properties. 2−4 Engineering thermoplastics such as poly(ether sulfone) (PES) and poly(acrylonitrile-butadiene- styrene) (ABS) can be used to replace elastomers with the aim of improving the toughness of the resulting materials. 5−11 Recently, block copolymers have been used as modifiers to toughen epoxy resins. 12−14 One of the most important properties of block copolymers is the ability to self-assemble into different nanoscale structures. 15−17 Nanoscale morpholo- gies such as spherical, wormlike, and vesiclelike structures are formed before or during the curing itself. One of the feasible pathways for generating nanostructures is the use of amphiphilic block copolymers, where one of the blocks is miscible with epoxy resin. 14,18−20 Another concept is the chemical modification of one of the blocks to improve the compatibility of the block copolymer in the thermosetting matrix. 21 One of the first studies on the formation of nanostructures in epoxy resin modified with block copolymers was reported by Hillmyer et al. in 1997. 22 They observed the formation of nanostructures in DGEBA-type epoxy resins, by using poly(ethylene oxide)-block-poly(ethyl ethylene) (PEO− PEE) and poly(ethylene oxide)-block-poly(ethylene propylene) (PEO−PEP) diblock copolymers as modifiers. Later, several studies were carried out by different scientists using reactive and nonreactive diblock and triblock copolymers. 12−17 Ordered and disordered nanostructures are formed in the thermosetting matrix prior to the curing reaction itself, and these nanostructures are further fixed with the subsequent curing Received: December 5, 2013 Revised: March 25, 2014 Accepted: April 8, 2014 Article pubs.acs.org/IECR © XXXX American Chemical Society A dx.doi.org/10.1021/ie404124b | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX