Preparation and morphology of star-shaped copolymers of the AnBn type

Star-shaped copolymers of the A(n)B(n) type composed of polystyrenes and polyisoprenes were prepared by two-stage coupling reactions using 4, 8, and 12-functional chlorosilane compounds as linking agents. At the first stage, living polystyrenes end-capped with 1,1-diphenylethylene were confirmed to react with half or less than half of the chlorines. At the second stage, living polyisoprenes end-capped with a few units of butadiene were used. The final products purified by GPC fractionation were confirmed to be star-shaped copolymers having the objective molecular structures by NMR and osmometry. A(n)B(n) Star-shaped copolymers having arm-molecular weights of M-n similar to 1 x 10(4) showed clear microphase-separated structure. In the samples having arm-molecular weights of M-n-4 x 10(4), however, diffusive domain boundaries were observed. This may be due to bicomponent multibranching and low mobility of arm polymers.