Styrene → Styrene-butadiene-styrene

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In a 800-ml autoclave preliminarily purged with nitrogen were placed 350 ml of cyclohexane which had been subjected to dehydration and oxygen removal and 0.57 ml of a 0.50 mole/liter solution of tetrahydrofuran. Thereto were added 10 g of styrene and 5.85 ml of a 0.50 mole/liter solution of n-butyllithium (5.85 ml corresponds to 2.93 mM of n-butyllithium). The resulting mixture was subjected to polymerization at 50° C. for 1 hr. 30 g of butadiene was added and polymerization was conducted at 60° C. for 2 hr. 10 g of styrene was added and polymerization was conducted for 1 hr, whereby a styrene-butadiene-styrene block copolymer (SBS) was formed. The polymerization conversion was almost 100%. Without terminating the polymerization, the whole mixture was cooled to 20° C. Then, thereto were added 20 g of butadiene and 7.3 ml of a 0.2 mole/liter solution of cobalt octylate in cyclohexane (7.3 ml corresponds to 1.46 mM of cobalt octylate). Further, 2.92 ml of a 0.5 mole/liter solution of carbon disulfide in cyclohexane (2.92 ml corresponds to 1.46 mM of carbon disulfide) was added. Polymerization was conducted at 20° C. for 2 hr. Then, by adding 10 ml of methanol, the polymerization was terminated. The polymer formed was coagulated in methanol containing 0.1% of BHT and then vacuum-dried at 50° C. overnight, whereby 64.4 g of a polymer was obtained. The polymerization conversion in the second step of 1,2-polymerization of butadiene corresponds to 72%.

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