SYNTHESIS AND CHARACTERIZATION OF POLYISOPRENE POLYBUTADIENE A(2)B(2)STAR COPOLYMERS

Two routes for the synthesis of star block copolymers having exactly t wo arms of polyisoprene (PI) and two of polybutadiene (PB) are describ ed. The first route starts by condensing one molecule of silicon tetra chloride with two of poly(isoprenyl)lithium which has been end-capped by a few units of styrene. The second route starts by linking two poly (isoprenyllithium) chains with one molecule of silicon tetrachloride a t a suitably reduced temperature. Both routes are completed by reactio n of the two-armed intermediate (PI)(2)SiCl2 with an excess of poly(bu tadienyllithium). The resulting (PI)(2)Si(PB)(2) star polymer was puri fied by fractionation. The reaction steps were monitored by size exclu sion chromatography and the products characterized by low-angle laser light scattering, osmometry, and NMR.