AGGREGATION OF TELECHELIC TRIBLOCK COPOLYMERS - FROM ANIMALS TO FLOWERS

We present an experimental study of dilute solutions of a polystyrene- polyisoprene-polystyrene block copolymer in a bad solvent of the polys tyrene terminal blocks (heptane). At high temperature, it was previous ly shown that these copolymers associate in polydisperse and loose agg regates having a small association number and a large radius of gyrati on. These aggregates have been called ''animals''. Here, we deal with the change of the aggregate structure as the solvent selectivity is in creased. Actually, scattering experiments show an aggregate compaction as the temperature is decreased. They pass from an ''animal'' to a '' flowerlike'' structure with a dense core and a swollen corona. However , small angle neutron scattering proves that these flowerlike micelles are always linked together. In addition, to account for this compacti on, we present the study of a diblock copolymer, corresponding to roug hly half of the triblock, and measurements of the solubility of homopo lystyrene in heptane. This allows us to quantify the different terms o f the free energy per chain in the aggregates, from which one perceive s how the temperature tunes the balance of interfacial tension and con formational entropy leading to different aggregates conformations.