TAPERED TRIBLOCK COPOLYMERS

A tapered triblock copolymer having controlled vinyl distribution, enlarged middle block with intermediate composition and microstructure, increased compatibility between its adjacent blocks, good processing characteristics and a peak average molecular weight between 25,000 and 300,000 is made by anionically polymerizing conjugated diene and monovinyl aromatic monomers, polar modifier and initiator to make a first block rich in conjugated diene, forming a second block that is a copolymer of the conjugated diene and the monovinyl aromatic monomer and which is less rich in the conjugated diene than the first block, and forming a third block that is a homopolymer of the monovinyl aromatic monomer. The first, second and third blocks comprise 30 to 60, 20 to 50 wt % and 10 to 40 wt % of the tapered triblock copolymer, respectively. The tapered triblock copolymers may be used as asphalt modifiers, adhesives, sealants, compatibilizers, reinforcing agents and impact modifiers.