HYDROGENATED BLOCK COPOLYMER
A hydrogenated block copolymer prepared by hydrogenating a block copolymer that contains a polymer block (A) containing a structural unit derived from an aromatic vinyl compound, a polymer block (B) containing a structural unit derived from farnesene, and a polymer block (C) containing a structural unit derived from a conjugated diene except farnesene, wherein the block copolymer contains at least two above polymer blocks (A), at least one above polymer block (B) and at least one above polymer block (C), and wherein at least one above polymer block (B) is at the terminal, and the hydrogenation rate of the carbon-carbon double bond in the polymer block (B) and the polymer block (C) is 50 mol % or more.
1 . An elastic member produced by molding a thermoplastic elastomer composition comprising a hydrogenated block copolymer (I), wherein:
the hydrogenated block copolymer (I) is a hydrogenate of a block copolymer (P) comprising:
a polymer block (a) comprising a structural unit derived from an aromatic vinyl compound, a polymer block (b) comprising 1 to 100% by mass of a farnesene-derived structural unit (b1) and 99 to 0% by mass of a structural unit (b2) derived from a conjugated diene other than farnesene, and a polymer block (c) having a content of the farnesene-derived structural unit (b1) of less than 1% by mass and a content of the structural unit (b2) derived from a conjugated diene other than farnesene of 1 to 100% by mass,
and comprising at least two of the polymer blocks (a), at least one of the polymer block (b) and at least one of the polymer block (c), wherein at least one of the polymer block (b) exists at the terminal, and wherein:
a ratio by mass of the polymer block (a) to the polymer block (b) [(a)/(b)] is from 1/99 to 70/30, a ratio by mass of the polymer block (a) to a total of the polymer block (b) and the polymer block (c) [(a)/((b)+(c))] is from 1/99 to 70/30,
50 mol % or more of a total of carbon-carbon double bonds derived from farnesene and carbon-carbon double bonds derived from the conjugated diene other than farnesene existing in the block copolymer (P) have been hydrogenated, and
a hysteresis loss rate in one cycle of deformation and restoration of a specimen is 20% or less, the specimen being prepared by blanking a 0.5 mm-thick sheet formed by compression molding of the thermoplastic elastomer composition at 240° C. and under a load of 10 MPa for 3 minutes into a strip specimen having a width of 25 mm and a length of 150 mm, where the specimen is 100% expanded at a temperature of 23° C. and then shrunk in the cycle of deformation and restoration of the specimen.
2 . The elastic member according to claim 1 , further comprising 1 to 50 parts by mass of a polystyrene resin (II) relative to 100 parts by mass of the hydrogenated block copolymer (I).
3 . The elastic member according to claim 1 , further comprising 1 to 150 parts by mass of a softening agent (III) relative to 100 parts by mass of the hydrogenated block copolymer (I).
4 . The elastic member according to claim 1 , wherein the hysteresis loss rate in the second cycle in two cycles of deformation and restoration where the specimen is 100% expanded at a temperature of 23° C. and at a rate of 100 mm/min and then shrunk at a rate of 100 mm/min in each cycle is 15% or less.
5 . The elastic member according to claim 1 , wherein a ratio of the hysteresis loss rate (L 2 ) in the second cycle to the hysteresis loss rate (L 1 ) in the first cycle (L 2 /L 1 ) is 0.40 or more.
6 . The elastic member according to claim 1 , wherein a standard polystyrene-equivalent peak top molecular weight (Mp) of the hydrogenated block copolymer (I), as measured through gel permeation chromatography, is from 4,000 to 500,000.
7 . The elastic member according to claim 1 , wherein the hydrogenated block copolymer (I) is a hydrogenated block copolymer comprising a structure having blocks of the polymer block (b), the polymer block (a) and the polymer block (c) in that order.