Abstract: A rubber-modified styrene type polymer comprising from 1 to 15 parts by weight of a dispersed phase made of a rubber-like elastic material and from 99 to 85 parts by weight of a continuous phase made of a polymer comprising from 35 to 75 wt % of styrene type monomer units and from 65 to 25 wt % of (meth)acrylate type monomer units, wherein the rubber-like elastic material is a styrene (30 to 50 wt %)-butadiene (70 to 50 wt %) block copolymer, the weight average molecular weight (Mw) of the polystyrene portions of this block copolymer is from 45,000 to 75,000, and the ratio (Mw/Mn) of Mw to the number-average molecular weight (Mn) is from 1.20 to 1.80.

Abstract: An isomerization between 3,4-dichlorobutene-1 and 1,4-dichlorobutene-2 is carried out in the presence of a catalyst for isomerization as a combination of a copper compound and a dithiocarbamic acid derivative. The dithiocarbamic acid derivative is a compound having the formula ##STR1## wherein R and R' are the same and different and respectively represent a C.sub.1 -C.sub.8 alkyl group or an aryl group and M represents hydrogen atom or a metal atom or ammonium group and R" represents a C.sub.1 -C.sub.8 alkyl group, an aryl group or a heterocyclic group such as mercaptobenzothiazole.