335 Full Paper Macromolecular Chemistry and Physics wileyonlinelibrary.com Macromol. Chem. Phys. 2012, 213, 335−343 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/macp.201100497 New Improved Thermosets Obtained From Diglycidylether of Bisphenol A and a Multiarm Star Copolymer Based on Hyperbranched Poly(glycidol) Core and Poly(methyl methacrylate) Arms Mireia Morell, Xavier Ramis, Francesc Ferrando, Àngels Serra* A well-defined multiarm star copolymer, hyperbranched poly(glycidol)- b-poly(methyl meth- acrylate) (PGOH- b-PMMA), is used as a modifier in the curing of diglycidylether of bisphenol A (DGEBA) using 1-methyl imidazole (1MI) as anionic initiator. The effect of the polymer topology on the curing and gelation processes is studied. The addition of the PGOH- b-PMMA to the resin leaves the complex viscosity unaltered. The addition of the modifier decreases the shrinkage after gelation compared to that measured in the curing of the neat resin. By DMTA a single relaxation process in the pure DGEBA and modified thermoset is found. The addi- tion of the star-like modifier led to an improvement on the mechanical characteristics such as the impact strength and microhardness in comparison to the neat material. M. Morell, À. Serra Department of Analytical and Organic Chemistry, Universitat Rovira i Virgili, C/Marcel·lí Domingo s/n, 43007, Tarragona, Spain E-mail: angels.serra@urv.cat X. Ramis Thermodynamics Laboratory, ETSEIB Universitat Politècnica de Catalunya, Av. Diagonal 647, 08028, Barcelona, Spain F. Ferrando Department of Mechanical Engineering, Universitat Rovira i Virgili, C/Països Catalans, 26, 43007, Tarragona, Spain 1. Introduction Chemically induced phase separation (CIPS) is one of the methodologies used to improve the fracture toughness by promoting biphasic nanostructured morphology. In this process, the morphology develops during curing from an initial homogeneous mixture. [1–3] Using block copolymers, one of the blocks is previously insoluble or phase sepa- rates during curing while the other remains soluble. In this case, the nanostructured morphology originated is mainly explained from the nanoparticles of the segregated block fixed by the soluble block to the epoxy resin. [4] Another way to obtain nanostructured thermosets is to take benefit of the heterogeneities generated during the curing process. Although epoxy resins are described as three-dimensional network with a regular structure, the truth is that the curing process is not a perfect process and in some points of the mixture the cross-linking reac- tion proceeds faster generating a non-homogeneous matrix. [5] Epoxy networks obtained by homopolymeriza- tion of epoxy resins by using curing initiators are intrinsi- cally inhomogeneous materials favoring the appearance of nanostructured morphologies. The curing agent, the type of catalyst (if necessary), their concentrations, the different mechanisms that can compete during curing, the temperature and time of curing are parameters, which influence the final morphology of the thermoset. Moreover, the use of linear- or dendritic modifiers has also been proven to play an important role on it. [3,6,7] Hyperbranched polymers (HBPs), as dendritic polymers, could substitute linear polymers as modifiers of epoxy