Atomic force microscopic studies of novel arborescent block and linear triblock polystyrene–polyisobutylene copolymers

This paper reports the investigation of the nanostructured surface morphology of novel arborescent polyisobutylene-block-polystyrene (PIB–PS) copolymers, in comparison with linear PS–PIB–PS triblock copolymers, using atomic force microscopy (AFM) in tapping mode. Arborescent PIB–PS samples displayed interesting new phase morphologies, which changed dramatically upon annealing but remained irregular. Linear PS–PIB–PS samples showed morphologies similar to those previously found by transmission electron microscopy (TEM) in cryomicrotomed bulk samples, ranging from spherical/cylindrical to lamellar nanometer-sized discreet PS phases dispersed in a continuous PIB matrix. Annealing the samples resulted in more ordered structures. Three-dimensional AFM image and section analysis indicated a height difference between PIB and PS in the block copolymers, which became more prominent during annealing. This feature was verified on compression moulded and protein coated samples. The arborescent PIB–PS materials displayed thermoplastic elastomeric behaviour with a tensile strength between 7 and 10 MPa and elongation ranging from 1000% to 1830%. In comparison, linear triblock samples had a tensile strength between 7 and 20 MPa and elongation ranging from 380% to 640%. Block copolymers with irregular elastomeric midsegments may emerge as a new class of TPEs.