New "all-acrylate" block copolymers:: Synthesis and influence of the architecture on the morphology and the mechanical properties

Novel "all-acrylate" block copolymers have been synthesized by ATRP with a simple and cost-effective one-pot-two-step process. The (A-B)(n) copolymers are composed of an elastomer segment (A = P(2EHA-co-MA) = poly(2-ethylhexyl acrylate-co-methyl acrylate)) and a thermoplastic segment (B = PMMA = poly(methyl methacrylate)). To study the relationship between the molecular architecture and the mechanical properties, a four-arm radial block copolymer (A-B)(4) is compared to the linear diblock (A-B)(1) and symmetric triblock (A-B)(2) and compounds of similar composition. Atomic force microscopy (AFM) shows that all block copolymers present a well-defined microphase separation, which is confirmed by the observation of two glass transitions in DSC. Thermomechanical data from viscoelastic, indentation, and tensile measurements are discussed in terms of the structural characteristics of the copolymers. The increase in the complexity of the molecular structure results in an enhanced elastic response, and the stress-strain curves confirm the strengthening effect with increasing molecular connectivity (radial > linear triblock) and end-block length.