Synthesis, dynamic-mechanical and morphological behavior of styrene/butyl methacrylate diblock copolymers

In order to investigate the structure-property relationship of styrene/butyl methacrylate (PS/PBMA) diblock copolymers, two ranges of polymers with M̄n ≈ 100 000 and M̄n > 200 000, respectively, with polydispersity indexes M̄w/M̄n < 1.15 are synthesized with varying ratios of the block lengths. The molecular weights of these polymers are determined by size exclusion chromatography (SEC). Thermal behavior and morphology are characterized by dynamic-mechanical analysis (DMA) and transmission electron microscopy, respectively. Whereas for unsymmetrical diblock copolymers with an overall molecular weight of M̄n ≈ 100 000 only one broadened glass transition due to their disordered state is found, nearly symmetrical diblock copolymers show a partial miscibility which can be ascribed to the proximity of the order-disorder transition and the annealing temperature of the samples. In the case of unsymmetrical high molecular weight diblock copolymers a partial miscibility is observed as well. The high molecular weight diblock copolymers with M̄n > 200 000 at all compositions show microphase-separated structures in contrast to the diblock copolymers with an overall molecular weight of M̄n ≈ 100 000. Compared with styrene/isoprene diblock copolymers a relatively wide range for lamellar structures is found.