Patent ID: 7781552

Claim:
A styrenic copolymer produced by a living polymerization method comprising an isopropenyl aromatic unit represented by the formula (1): wherein the substituent group R 1 represents hydrogen, or a hydrocarbon radical of —C n H 2n+1 wherein n is an integer number of 1 or more, and a vinyl aromatic unit represented by the formula (2): wherein the substituent group R 2 represents hydrogen, or a hydrocarbon radical of —C n H 2n+1 wherein n is an integer number of 1 or more, and the substituent group R 3 represents hydrogen or a phenyl radical, wherein the content (A) of said isopropenyl aromatic unit in said styrenic copolymer is in a range of 5 to 95% by weight, a ratio (Mw/Mn) of a weight-average molecular weight (Mw) of said styrenic copolymer to a number-average molecular weight (Mn) thereof is in the range of 1.6 to 4.0, and the weight-average molecular weight_(Mw) of said styrenic copolymer is 70,000 or more, and wherein the relationship between the content (% by weight) (A) of said isopropenyl aromatic unit in said styrenic copolymer and the glass-transition temperature (° C.) (Tg) of said styrenic copolymer satisfies the formulae (a): 0.12 A+ 102≦Tg≦0.62 A+ 102 (in case of 5 ≦A≦ 20), −5.25×10 −5 A 3 +1.09×10 −2 A 2 +1.72×10 −1 A+ 97≦Tg≦−5.25×10 −5 A 3 +1.09×10 −2 A 2 +1.72×10 −1 A+ 107 (in case of 20 <A< 60), and 1.04 A+ 73≦Tg≦0.79 A+ 98 (in case of 60 <A≦ 95).