Preparation, Characterization of Cyclic Block Copolymers and Their Bulk Structures

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Three polystyrene-block-polyisoprene-block-polystyrenes with different compositions were prepared and cyclized by the coupling reaction between two end groups on the same molecules. Ring-shaped polystyrene-block-polyisoprenes were isolated from the coupling products by GPC fractionation. They were ozonized so as to decompose the polylyisoprene blocks selectively referring to the linear molecule. From GPC analysis of the decomposed products obtained by ozonolysis, it was quantitatively confirmed that the fractionated products include c.a. 90% ring molecules. It has been found that the morphological transition of the ring-shaped block copolymers takes place depending 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.