Preparation and Characterization of Tapered Block Copolymers

Tapered block copolymers of styrene and isoprene were prepared by anionic copolymerization of monomer mixtures using sec-BuLi as an initiator in benzene/THF (50/50) at 0°C. Analyses based on both gas chromatography and 1H NMR indicated that monomer composition gradually varied from one chain end to the other. Furthermore, the tapered block copolymers were ozonized so as to decompose 1, 4-microstructure in the polyisoprene sequences. The GPC analysis results of the decomposed products by ozonolysis confirmed that the products had tapered regions in the chains. Two tapered block copolymers with different chain lengths in the tapered region and one regular block copolymer were prepared. Their morphologies were investigated by transmission electron microscopy and small angle X-ray scattering. Microphase-separated structures of three copolymers were revealed to show almost the same alternating lamellar structure.