Functionalized polymer, rubber composition and pneumatic tire

A functionalized elastomer having the formula

• (P-Bn)q-X
• where P is a polydiene segment, B is a styrenic monomer residue, n is the number of styrenic monomer residues, and Bn is a polystyrenic segment;
• and q is the number of (P-Bn) chains coupled to X;
• wherein for q=1, the weight percent of the functionalized elastomer is at least 90 percent by weight;
• wherein X is a polymerization terminator of formula I
• wherein R1 is C1 to C4 linear alkyl, or C1 to C4 branched alkanediyl;
• in formula I X1, X2, X3 are independently S, a group of formula II, or a group of formula III;
• where R2 is C1 to C18 linear or branched alkyl;
• Z is R3, —OR4, or —R 5—X4;
• R3, R4 are independently C1 to C18 linear or branched alkyl;
• R5 is C1 to C18 alkanediyl or dialkyl ether diyl, with the proviso when R5 is C1 to C18 dialkyl ether diyl, X1, X2, X3 may be independently O, S, a group of formula II, or a group of formula III;
• X4 is halogen or a group of structure IV, V, VI, VII or VIII
• wherein R6, R7, R8, R9, and R10 are independently H or C1 to C8 alkyl;
• R11 is C2 to C8 alkanediyl;
• R12 and R13 are independently H, aryl or C1 to C8 alkyl;
• X5, X6, X7 are independently O, S, or a group of formula II or III where R2 is C 1 to C 18 linear or branched alkyl;
• Q is N or a group of structure IX
• wherein R14 is C1 to C8 alkyl.