Structure and rheology of di- and triblock copolymers of polystyrene and poly(n-butyl acrylate)
Résumé
Block copolymers based on acrylate matrices are expected to be good candidates for pressure sensitive adhesives formulations because (i) all-acrylic block copolymers are known to be stable over a wide temperature range and are more resistant to UV radiation than polydiene copolymers and (ii) the soft block exhibits an elasticity that is lower than that of polydiene and closer to the Dalhquist criterion (tacky properties). This last property is due to a higher molar mass between entanglements. The block segregation is the key parameter for these kinds of systems because it induces a solid-like behavior useful for adhesion applications. In this work, we have explored this point by synthesizing styrene/ n -butyl acrylate (nBA) and methyl methacrylate/nBA block copolymers by nitroxide-mediated controlled radical polymerization. Atomic force microscopy and small-angle neutron scattering analysis have demonstrated the strong connection between the physico-chemical properties (molar mass, nature of the blocks, χ, dispersity, etc.), the microstructure, and the rheological properties of these block copolymers. Furthermore, the rheological behavior expected for good pressure sensitive adhesives performances is obtained under specific conditions. Finally, we will discuss the adherence performances of model formulations derived from these block copolymers.