Poly spherical butadiene domains

Figure 5-33. Electron micrographs of films of two-block and three-block copolymers of styrene and butadiene cut vertically (left) or parallel (right) to the film surface (M. Matsuo). Top row SBS polymer with S/B= 80/20 mol/mol. Spherical domains of poly(butadiene) segments embedded in a matrix of poly(styrene) segments center row SB polymer with S/B = 60/40 mol/mol. Rods (cylinders) of poly (butadiene) segments in a matrix of poly (styrene) segments bottom row SBS polymer with S/B = 40/60 mol/mol. Lamellae of poly(butadiene) segments alternate with lamellae of poly(styrene) segments.

The polystyrene blocks typically have block weights of about 20 000 whilst the polydiene blocks are in the range 35 OOO-ISO 000. In this range the product at room temperature behaves very much like a reinforced vulcanized rubber. It is also observed, by electron microscopy, that a two-phase system exists in which polystyrene-rich spherical domains are embedded in a continuous phase poly-butadiene-rich rubbery matrix (Fig. 17.2). 

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