The microstructure and microphase behaviour of diblock (M-n approximate to 27 and 50 kg mol(-1)) and triblock (M-n approximate to 50 kg mol(-1)) copolymers of polystyrene (PS) and poly(ethylene-alt-propylene) (PEP) were studied by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and dynamic mechanical thermal analysis (DMTA). The composition was varied from 10 wt.% to 50 wt.% PS. The morphology of solution-cast and compression-moulded samples was compared. The common packing arrangements of body-centred-cubic (BCC) spheres, hexagonal-close-packed (HCP) cylinders and alternating lamellae were observed for the PS microdomains using SAXS and TEM. A microphase texture of PS spheres with a liquid-like packing (LLP) was obtained at lower molecular weight and PS content. Coexisting textures of LLP spheres and HCP cylinders of PS were observed in a triblock copolymer with low PS content. An order-order transition between conventional lamellar and perforated lamellar textures was detected in a nearly-symmetric triblock copolymer. Conventional order-disorder transitions were identified for most of the other polymers using DMTA and temperature-resolved SAXS.