Cycloolefin copolymer composition

A cycloolefin copolymer composition (C) obtained by:

• copolymerizing (a) an .alpha.-olefin and (b) a cycloolefin represented by the following formula (I) ##STR10## wherein n is 0 or 1,
• m is 0 or a positive integer,
• r is 0 or 1,
• each of R.sup.1 to R.sup.18, R.sup.a and R.sup.b independently represent a hydrogen atom, a halogen atom or a hydrocarbon group, provided that R.sup.15 to R.sup.18 may mutually bond to form a monocyclic or polycyclic ring structure which may contain a double bond, and a combination of R.sup.15 and R.sup.16 or a combination of R.sup.17 and R.sup.18 may form an alkylidene group, or by the following formula (II) ##STR11## wherein each of p and q is 0 or an integer of 1 or greater,
• each of m and n is 0, 1 or 2,
• each of R.sup.1 to R.sup.19 independently represents a hydrogen atom, a halogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group or an alkoxy group, provided that a carbon atom with which R.sup.9 or R.sup.10 bonds and either a carbon atom with which R.sup.13 bonds or a carbon atom with which R.sup.11 bonds may bond with each other directly or through an alkylene group having 1 to 3 carbon atoms and that, when n=m=0, a combination of R.sup.15 and R.sup.12 or a combination of R.sup.15 and R.sup.19 may mutually bond to form an aromatic monocyclic ring or aromatic polycyclic rings,
• in the presence of component (A) a blend of a styrene/(ethylene/propylene)/styrene block copolymer and styrene/butadiene/styrene block copolymer, wherein the weight ratio of said styrene/(ethylene/propylene)/styrene block copolymer to styrene/butadiene/styrene block copolymer is 42/58 to 58/42,
• the component (A) having an intrinsic viscosity (.eta.), as measured in decalin at 135.degree. C., of 0.5 to 5.0 dl/g, at least one glass transition temperature (Tg), as measured by DSC, of lower than 15.degree. C., polymerizable carbon-to-carbon double bonds in an amount of 2 to 150 (g-iodine/g-polymer) in terms of iodine value, and a refractive index n.sub.D (A), as measured at 25.degree. C., of 1.50 to 1.65;
• wherein the copolymer composition (C) contains 1 to 40% by weight of the component (A), and a difference .DELTA.n.sub.D is not more than 0.015, where .DELTA.n.sub.D is .vertline.n.sub.D (A)-n.sub.D (B) .vertline., n.sub.D (A) being the refractive index of component (A) and n.sub.D (B) being a refractive index of a cycloolefin copolymer component (B) obtained by copolymerizing said .alpha.-olefin (a) and said cycloolefin (b) in the absence of said component (A).