Three polystyrene-block-polyisoprene-block-polystyrenes (SIS) with different compositions were prepared and cyclized by the coupling reaction between two end groups on the same molecules. Ring-shaped polystyrene-block-polyisoprenes (SI) were isolated from the coupling products by GPC fractionation. They were ozonized in order to decompose the polyisoprene blocks selectively referring to the linear molecule. GPC analysis of the decomposed products obtained by ozonolysis quantitatively confirmed that the fractionated products include ca. 90% ring molecules. The morphological transition of the ring-shaped block copolymers depends on composition in essentially the same manner as that of the linear triblock copolymers, whereas the domain spacings of SI ring-shaped block copolymers were all smaller than those of the corresponding SIS linear triblock copolymers, which is attributed to looped chain conformation.

A polystyrene-block-oligo(2-tert-butylbutadiene)-block-polystyrene triblock copolymer was prepared and cyclized by end-to-end ring closure. Ring-shaped polystyrene-block-oligo(2-tert-butylbutadiene) was isolated from the coupling product via gel permeation chromatography (GPC) fractionation. The ring polymer was ozonized for decomposition of the oligo(2-tert-butylbutadiene) sequences selectively referring to the linear molecule. From GPC analysis of the decomposed products by ozonolysis, it was quantitatively confirmed that the fractionated product was 86% ring molecules. Single chain dimensions of the ring and linear molecules in a good solvent, benzene, and in a solvent, cyclohexane, were measured with small-angle neutron scattering. The ratios of the radii of gyration, R g (ring)/R g (linear), were 0.780 in benzene and 0.789 in cyclohexane. These were compared with theoretically predicted values. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1582-1589, 2002