An investigation has been made of micelle formation by a polystyrene-polybutadienepolystyrene block copolymer in ethyl acetate, which is a selectively bad solvent for polybutadiene; the number-average molecular weights of the three blocks were 12900,66000 and 13 700, respectively. As the temperature was raised dilute solutions of the copolymer in ethyl acetate showed a distinct cloud-point, which moved to higher temperatures with increases in concentration. On raising the temperature further the solutions gradually became clear again.Light scattering and electron microscopy studies showed that the onset of cloudiness was due to the formation of long worm-like micelles from spherical micelles. The clearing of solutions at higher temperatures occurred because the micelles dissociated to form copolymer molecules in the free-chain form. The cores of both types of micelle were composed of swollen polybutadiene blocks and the outer fringes of the micelles of polystyrene blocks. The spherical micelles had a fairly narrow size distribution. The worm-like micelles had a wide distribution of contour lengths but possessed a narrow size distribution in the radial direction,A second polystyrene-polybutadiene-polystyrene copolymer having shorter blocks than the first copolymer showed a similar type of solution behaviour at lower temperaturs.

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The various levels of organisation which may be distinguished in non-crystalline block Copolymers are considered. An account is given of the application of lowangle X-ray diffraction and electron microscopy to the characterisation of the two-phase morphology and grain texture of some styrenelisoprene copolymers. The first group of copolymers to be considered contains two series of samples of the type S-I, (S-I-)2X, (S-I-)aY, and (S-I-)4Z where I is polyisoprene, S polystyrene and X, Y and Z are di-, tri-and tetra-functional coupling groups. The second group of copolymers which was subjected to a less detailed study than the first consists of just two polystyrene-g-polyisoprene samples.