The dilute solution properties and association of hydrogenated poly(styrene-isoprene) two-block copolymers in decane and rrans-decalin have been studied by means of viscosity, diffusion and light-scattering measurements. Data were obtained for two samples with molecular weights of 48 000 and 80000, and both with a styrene content of 38%. In frans-decalin the normal behaviour of a non-associating polymer is found. Association occurs in decane with the formation ofcompact micelles, composed (at ambient temperatures) ofabout 80 molecules. In contrast to what is observed in other associating two-block systems, the transition to the completely dissociated state at elevated temperatures causes a drop ofthe intrinsic viscosity. Moreover, and this is not evident from the viscometric results, the diffusion and light scattering studies reveal that in the intermediate region between association and dissociation another kind of structure with very large dimensions is formed that exists over an extended temperature range. A qualitative description of the observed phenomena is given.* ) This cannot be true for very large N owing to the physical link of all branches with the centre, which limits the total volume.
The association of a hydrogenated poly(styrene-isoprene) block copolymer has been studied in mixtures of a selective (decane) and a non-selective solvent (trans-decalin). Viscosity, diffusion and light-scattering studies were made within the temperature range of 25-100°C. Relatively small, compact micelles with a rather monodisperse distribution are found at low temperatures and high decane concentrations; very large, polydisperse associates are formed at intermediate decane concentrations and also at increasing temperature from the compact micelles prior to complete dissociation. These large particles have no particular effect on the inherent viscosity, which shows a gradual, continuous decrease as the polymer passes from the associated to the dissociated state. The association also gives rise to drastic changes in the UV absorption of the polystyrene part of the polymer. Kinetic experiments indicate a time scale of the order of ten seconds for the association-dissociation transition.The authors wish to thank Messrs. M. S. de Groot and J. M. Wortel for their interest, and for the valuable comments they made during discussions in the course of this work.
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