Rubber composition, and pneumatic tire

A rubber composition, comprising, based on 100% by mass of a rubber component, not less than 35% by mass of styrene-butadiene rubber, the rubber composition comprising

• a conjugated diene polymer, and
• a silica having a nitrogen adsorption specific surface area of 40 to 400 m2/g,
• the conjugated diene polymer being obtained by polymerizing a monomer component including a conjugated diene compound and a silicon-containing vinyl compound in the presence of a polymerization initiator represented by the following formula (I):
• wherein i represents 0 or 1;
• R11 represents a C7-80 hydrocarbylene group;
• R12 and R13 each are a hydrocarbyl group, or R12 and R13 are joined together to form a hydrocarbylene group;
• and M represents an alkali metal atom, to produce a copolymer, and
• then reacting a compound containing at least one of a nitrogen atom and a silicon atom with an active terminal of the copolymer,
• wherein the silicon-containing vinyl compound is a compound represented by the following formula (II):
• wherein m represents 0;
• X1, X2 and X3 each represent a group represented by the following formula (IIa), or a hydrocarbyl group;
• at least one of X1, X2 and X3 is a group represented by the following formula (IIa),
• wherein R22 and R23 each are an alkyl group,
• wherein the compound containing at least one of a nitrogen atom and a silicon atom is at least one selected from the group consisting of
• a compound represented by the following formula (IIIb),
• a compound represented by the following formula (IIId),
• a compound represented by the following formula (IV), a tris[(alkoxysilyl)alkyl] isocyanurate compound, and
• an N,N-dialkyl-substituted carboxylic acid amide dialkyl acetal compound,
• wherein R32 represents a hydrocarbyl group;
• and R36 represents a hydrocarbylene group, or a group in which a hydrocarbylene group and a group represented by —NR35— are bonded, where R35 represents a hydrocarbyl group or a hydrogen atom,
• where in R31 and R32 each represents a hydrocarbyl group;
• R37 represents a hydrocarbylene group;
• A represents an oxygen atom or —NR35— wherein R35 represents a hydrocarbyl group or a hydrogen atom;
• and R34 represents a hydrocarbyl group or a hydrogen atom,
• wherein R41 represents a hydrocarbyl group;
• R42 and R43 each represent a hydrocarbyl group or a hydrocarbyloxy group;
• R44 and R45 each represents a hydro carbyl group;
• and j represents an integer of 1 to 5,
• wherein an amount of the conjugated diene polymer is 25 to 75% by mass and an amount of a polyisoprene-based rubber is 0 to 40% by mass, each based on 100% by mass of the rubber component, and
• an amount of the silica is 10 to 150 parts by mass for each 100 parts by mass of the rubber component.