Rubber compound for tire tread and method for the preparation thereof
A crosslinkable or crosslinked rubber composition is described which includes a diene elastomer having a mass content of cyclic vinyl units of greater than 15%, and which may be used to form a tire tread. Also described is a tire tread and a tire incorporating the tread. The composition contains a linear or branched diene elastomer derived from at least one conjugated diene, and a reinforcing filler. The elastomer has cyclic vinyl units according to a mass content of greater than or equal to 15% and a number-average molecular weight of from 30,000 to 350,000 g/mol. The elastomer may be obtained by anionic polymerization of one or more monomers including a conjugated diene in an inert hydrocarbon solvent with a catalytic system including an organolithium initiator and a polar agent with several heteroatoms. The reaction may be performed batchwise where the polar agent:initiator molar ratio is greater than 8, or continuously where the polar agent:initiator molar ratio is greater than or equal to 3.
1 . A preparation process for a crosslinkable or crosslinked rubber composition comprising a linear or branched diene elastomer resulting from at least one conjugated diene, and a reinforcing filler, wherein said elastomer is obtained by a process which comprises the following steps:
a) a linear diene elastomer comprising cyclic vinyl units according to a mass content of greater than or equal to 15% and having a number-average molecular weight of from 10,000 to 60,000 g/mol, is prepared by batchwise anionic polymerization of one or more monomers comprising at least one conjugated diene monomer in an inert aliphatic or alicyclic hydrocarbon solvent with a catalytic system comprising an organolithium initiator and a polar agent comprising several heteroatoms, the (polar agent:initiator) molar ratio being greater than 8; and
b) the linear elastomer obtained is optionally branched with a starring agent to obtain a branched diene elastomer.
2 . A preparation process for a crosslinkable or crosslinked rubber composition comprising a linear or branched diene elastomer resulting from at least one conjugated diene, and a reinforcing filler, wherein said elastomer is obtained by a process which comprises the following steps:
a) a linear diene elastomer comprising cyclic vinyl units according to a mass content of greater than or equal to 15% and having a number-average molecular weight of from 30,000 to 100,000 g/mol is prepared by continuous anionic polymerization of one or more monomers comprising at least one conjugated diene monomer, in an inert aliphatic or alicyclic hydrocarbon solvent with a catalytic system comprising an organolithium initiator, a polar agent comprising several heteroatoms and an alkali metal salt of an aliphatic or alicyclic alcohol, said system satisfying the following relationship:
(i) the (polar agent:initiator) molar ratio is greater than or equal to 3; and
b) the linear elastomer obtained is optionally branched by a starring agent to obtain a branched diene elastomer.
3 . A preparation process for a crosslinkable or crosslinked rubber composition comprising a linear or branched diene elastomer resulting from at least one conjugated diene, and a reinforcing filler, wherein said elastomer is obtained by a process which comprises the following steps:
a) a linear diene elastomer comprising cyclic vinyl units according to a mass content of greater than or equal to 15% and having a number-average molecular weight of from 30,000 to 300,000 g/mol is prepared by continuous anionic polymerization of one or more monomers comprising at least one conjugated diene monomer in an inert aliphatic or alicyclic hydrocarbon solvent with a catalytic system comprising an organolithium initiator, a polar agent comprising several heteroatoms and an alkali metal salt of an aliphatic or alicyclic alcohol, wherein said system simultaneously satisfies the following three conditions:
(i) the (polar agent:initiator) molar ratio is greater than or equal to 3
(ii) the (salt:initiator) molar ratio falls within a range of from 0.01 to 2, and
(iii) the (salt:polar agent) molar ratio falls within a range of from 0.001 to 0.5; and
b) the linear elastomer obtained is optionally branched by a starring agent to obtain a branched diene elastomer.
4 . The process according to claim 2 , wherein the (polar agent:initiator) molar ratio is greater than or equal to 5 for said condition (i) of said step a).
5 . The process according to claim 4 , wherein the (polar agent:initiator) molar ratio is greater than or equal to 10.
6 . The process according to claim 5 , wherein said (polar agent:initiator) molar ratio is greater than or equal to 15.
7 . The process according to claim 3 , wherein the (salt:polar agent) molar ratio falls within a range of from 0.001 to 0.1 for said condition (iii) of said step a).
8 . The process according to claim 3 , wherein the (salt:initiator) molar ratio falls within a range of from 0.01 to 0.6 for said condition (ii) of said step a).
9 . The process according to claim 8 , wherein said (salt:initiator) molar ratio falls within a range of from 0.01 to 0.2.
10 . The process according to claim 9 , wherein said (salt:initiator) molar ratio falls within a range of from 0.3 to 0.6.
11 . The process according to claim 1 , wherein said polar agent is selected from the group consisting of diamines and diethers.
12 . The process according to claim 11 , wherein said polar agent is tetramethylethylenediamine.
13 . The process according to claim 2 , wherein said salt is a sodium salt of an aliphatic alcohol having from 3 to 12 carbon atoms.