Abstract: Provided is a thioester modified polymer, wherein a polymer having an intramolecular double bond is modified with at least one of thiocarboxylic acid and dithiocarboxylic acid. The above thioester modified polymer can be manufactured by allowing a polymer having an intramolecular double bond to react with thiocarboxylic acid, dithiocarboxylic acid or a metal salt thereof, and used to be compounded in a diene-based rubber. When this thioester modified polymer is compounded in a diene-based rubber, in particular a silica containing diene-based rubber, tensile strength and breaking elongation, in particular tensile strength and breaking elongation at a high temperature (100° C.), can be improved without decreasing modulus, hardness, exothermicity and the like. Therefore, the rubber composition having excellent thermal resistance and toughness can be effectively used as a rubber compound for forming a cap tread or a side tread of a pneumatic tire.

Abstract: Provided is a thioester modified polymer, wherein a polymer having an intramolecular double bond is modified with at least one of thiocarboxylic acid and dithiocarboxylic acid. The above thioester modified polymer can be manufactured by allowing a polymer having an intramolecular double bond to react with thiocarboxylic acid, dithiocarboxylic acid or a metal salt thereof, and used to be compounded in a diene-based rubber. When this thioester modified polymer is compounded in a diene-based rubber, in particular a silica containing diene-based rubber, tensile strength and breaking elongation, in particular tensile strength and breaking elongation at a high temperature (100° C.), can be improved without decreasing modulus, hardness, exothermicity and the like. Therefore, the rubber composition having excellent thermal resistance and toughness can be effectively used as a rubber compound for forming a cap tread or a side tread of a pneumatic tire.