EFFECT OF COMPOSITION AND STRUCTURE ON RHEOLOGICAL PROPERTIES OF STYRENE-BUTADIENE BLOCK COPOLYMERS

Styrene-butadiene copolymers of the S-B-S and S-B-S-B-S types, both unmodified and extended with paraffinic-naphthenic oil, were studied by dynamic mechanical spectroscopy and capillary rheometry. In the triblocks at low deformation rates, an increase in 1-vinylethylene unit content leads to an increase in complex dynamic viscosity \eta*\. This may be explained by their different supermolecular structure with a higher proportion of long relaxation times. The pentablocks show a considerable effect of molecular parameters on their flow behaviour at low deformation rates. In all the systems, steady viscosity-eta shows no significant differences at higher shear rates. Obviously the supermolecular structure is disintegrated in these conditions and the effect of chemical structure is negligible. An expected decrease in viscosity in the whole range of deformation rates was observed with the oil-extended copolymer. The dependences of complex dynamic viscosity on angular frequency were compared with those of steady viscosity on shear state but no unequivocal conclusion as regards the validity of the Cox-Merz rule could be reached.