Method for continuous polymerization of modified diene elastomer with lithium amide initiator

A process for the continuous synthesis of a modified diene elastomer comprising at least one silicon atom directly connected to the elastomer chain, comprising:

• a) a stage of polymerization by means of n reactors r1 to rn, considered to be continuous stirred-tank reactors, which are equipped with an internal stirring system, and which are arranged in series, n varying from 2 to 15,
• the reactor r1 being fed by an input solution comprising a solvent, one or more monomer(s), an anionic polymerization initiator chosen from lithium amides and a polar agent,
• one or more of the reactors r2 to rn additionally being optionally fed by reinjection of a purified solution comprising solvent and/or monomer(s) and/or polar agent,
• the temperature of each reactor varying from 20° C. to 150° C. and being greater than or equal to the temperature of the reactor which immediately precedes it,
• the temperature of the reactor rn being greater than the temperature of the reactor r1,
• the amount by weight W1 of monomer(s) introduced into the reactor r1 being such that:
• 0.1
• <
• W
• 1
• ∑
• j
• =
• 1
• n
• 
• W
• j
• ≤
• 1
• the amount by weight Wi of monomer(s) reinjected into the reactor ri, when Wi≠0, i varying from 2 to n, being such that:
• 0
• <
• W
• i
• ∑
• j
• =
• 1
• n
• 
• W
• j
• <
• 0.9
• and such that Wi represents from 5% to 100% by weight of the weight of the solution reinjected into the reactor ri, when Wi≠0,
• where Wj is the amount by weight of monomer(s) introduced into the reactor rj, j varying from 1 to n,
• the amount by weight of all of the monomers entering the reactors r1 to rn representing from 5% to 25% by weight of the sum of the total inputs by weight of the reactors r1 to rn,
• the intrinsic conversion by weight Cintrinsic,1 in the first reactor being less than 70%,
• where Cintrinsic,1=P1/W1
• where P1 is the weight of polymer formed in the reactor r1,
• the total conversion by weight Ctot at the outlet of the reactor rn being greater than or equal to 70%,
• where:
• C
• tot
• =
• ∑
• i
• =
• 1
• n
• 
• P
• i
• ∑
• j
• =
• 1
• n
• 
• W
• j
• where Pi is the weight of polymer formed in the reactor ri,
• the overall conversion by weight Coverall i in each reactor ri, with i varying from 1 to n, being such that:
• C
• tot
• n
• -
• 0.2
• ×
• C
• tot
• <
• C
• overall
• 
• 
• i
• <
• C
• tot
• n
• +
• 0.2
• ×
• C
• tot
• 
• 
• and
• 
• 
• C
• overall
• 
• 
• i
• >
• 0
• where:
• C
• overall
• 
• 
• i
• =
• P
• i
• ∑
• j
• =
• 1
• n
• 
• W
• j
• where Pi is the weight of polymer formed in the reactor ri, i varying from 1 to n,
• the living diene elastomer obtained exhibiting a polydispersity index varying from 1.1 to 1.7,
• b) a stage of modification of the living diene elastomer obtained in the preceding stage (a) by means of a functionalization, coupling or star-branching agent, which makes it possible to introduce, into the elastomer, a functional group comprising at least one silicon atom directly connected to the elastomer chain.