A kind of styrene-butadiene (S／B) multi-block copolymer was bulk-polymerized in a twin-screw extruder with the anion initiators and mixed S／B monomers．The effects of screw rotational speed

feed rate of monomers and St content on the conversion of styrene and S／B mixture were researched．S／B block copolymer was characterized by 1H-NMR

IR

DMA．It is shown that a lot of short polybutadiene blocks and a little random structure coexist in the copolymer．It also can be seen in TEM photographs that the polybutadiene blocks

while being less than 15％ in whole composition

can retract into the ball shape 30～50 nm in diameter．On lhe other hand

the toughness

especially the elongation at break

of the copolymer grows stronger with the increase of butadiene content．