Tread rubber composition and pneumatic tire

A pneumatic tire, formed from a tread rubber composition comprising:

• (i) a rubber component;
• (ii) silica in an amount of 5 to 150 parts by mass relative to 100 parts by mass of the rubber component;
• and (iii) a silane coupling agent containing a mercapto group,
• (i) the rubber component comprising a conjugated diene polymer (A) in an amount of 20-90% by mass per 100% by mass of the rubber component, the conjugated diene polymer (A) comprising a monomer unit derived from a conjugated diene, a monomer unit derived from a compound represented by the following formula (1), and a monomer unit derived from a compound represented by the following formula (2), at least one end of the copolymer (A) being modified by the following compound (G) or an alkoxysilane compound, the conjugated diene polymer (A) having a vinyl bond content of at least 20 mol % but not more than 70 mol % based on 100 mol % of the constituent unit derived from a conjugated diene,
• V1-S1 (1)
• wherein V1 is a group of the formula (1-V1) and S1 is a group of the formula (1-S);
• wherein R11 represents a hydrogen atom or a hydrocarbyl group;
• n represents 0 or 1;
• and R12 represents a hydrocarbylene group,
• wherein X1, X2, and X3 each independently represent a substituted amino group or an optionally substituted hydrocarbyl group, and at least one of X1, X2, and X3 is a substituted amino group,
• V2-A2 (2)
• wherein V2 represents a group represented by the following formula (2-V1);
• and A2 represents a group represented by the following formula (2-A),
• wherein R21 represents a hydrogen atom or a hydrocarbyl group;
• m represents 0 or 1;
• and R22 represents a hydrocarbylene group,
• wherein R25 and R26 each represent a hydrocarbyl group or a trihydrocarbylsilyl group, or R25 and R26 are joined together to form a hydrocarbylene group optionally containing at least one of a nitrogen atom and en oxygen atom as a hetero atom, or R25 and R26 together form a single group bonded to the nitrogen atom via a double bond,
• Compound (G) being a compound of formula (3) and the alkoxysilane compound being a compound of formula (4):
• wherein E represents an oxygen atom or a sulfur atom;
• and Z1 and Z2 each represent a substituted amino group, a hydrogen atom, an optionally substituted hydrocarbyl group, or an optionally substituted hydrocarbyloxy group, provided that at least one of Z1 and Z1 is a group containing a substituted amino group, or Z1 and Z2 are joined together to for, together with the carbonyl carbon atom, a cyclic structure containing a substituted amino group,
• wherein v represents an integer of 1 to 10;
• R41, R42, and R43 each independently represent an alkyl group or an alkoxy group, and at least one of R41, R42, and R43 is an alkoxy group;
• and A4 represents a substituted amino group,
• (iii) the silane coupling agent being at least one of a silane coupling agent represented by the following formula (I) and a silane coupling agent containing a linking unit B represented by the following formula (II) and a linking unit A represented by the following formula (III),
• wherein R101 to R103 each represent a branched or unbranched C1-5 alkyl group, a branched or unbranched C1-5 alkoxy group, or a group represented by —O—(R111—O)b—R112 where b R111s each represent a branched or unbranched C1-15 divalent hydrocarbon group, and b R111s may be the same as or different from one another;
• R112 represents a branched or unbranched C3-25 alkyl group, a branched or unbranched C3-25 alkenyl group, a C10-20 aryl group, or a C10-20 aralkyl group;
• and b represents an integer of 2 to 20, and R101 to R103 may be the same as or different from one another;
• at least one of R101 to R103 is a group represented by —O—(R111—O)b—R112;
• and R104 represents a branched or unbranched C1-5 alkylene group,
• wherein R201 represents a hydrogen atom, a halogen atom, a branched or unbranched C1-12 alkyl group, a branched or unbranched C2-12 alkenyl group, a branched or unbranched C2-12 alkynyl group, or the alkyl group in which a terminal hydrogen atom is replaced with a hydroxy group or a carboxyl group;
• and R202 represents a branched or unbranched C1-12 alkylene group, a branched or unbranched C2-12 alkenylene group, or a branched or unbranched C2-12 alkynylene group, provided that R201 and R202 together may form a cyclic structure.