Functional diene block elastomer with a low pi and improved cold flow, and rubber composition containing same

Functionalized diene elastomer composed:

• a) of a block copolymer functionalized, at the chain end or in the middle of the chain, by a tin functional group and corresponding to the following formula:
• [A-BnXB-A]m
• where n and m are integers of greater than or equal to 0 and such that n+m=1 or 2,
• b) of a block copolymer star-branched by tin and corresponding to the following formula:
• [A-BoYB-A]p
• where o and p are integers of greater than or equal to 0 and such that o+p≧3 and o+p≦6,
• c) of a content of less than 15% by weight, with respect to the total weight of the functionalized diene elastomer, of a non-tin-functional block copolymer corresponding to the following formula:
• [A-B]
• where:
• all the A blocks are composed of a polyisoprene or all the A blocks are composed of a polybutadiene,
• the B blocks are composed of a diene elastomer, the molar content of units resulting from conjugated dienes of which is greater than 15%, the B blocks being identical to one another,
• X and Y independently represent a tin-comprising group,
• the number-average molecular weight Mn1 of each A block varies from 2 500 to 20 000 g/mol,
• the number-average molecular weight Mn2 of each B block varies from 80 000 to 350 000 g/mol,
• the content of 1,2 linkages in each A block is between 1 and 20% in the case where A is a polybutadiene block,
• the content of 3,4 linkages in each A block is between 1 and 25% in the case where A is a polyisoprene block,
• the A-B copolymer exhibits a monomodal distribution of molecular weights before optional functionalization or optional star-branching and a polydispersity index before optional functionalization or optional star-branching of less than or equal to 1.3.