Resumen
[0001] A method of preparation of copolymers of 1,3-butadiene and styrene, useful for the production of tires or elastic materials, characterized by a reduced rolling resistance without detriment to other properties such as skid resistance. The copolymer is prepared using anionic polymerization of 1,3-butadiene and styrene and coupling of part of the chains in star shape with an appropriate compound of tin or silicon, terminating the remainder of the linear chains without coupling using an appropriately selected different compound. The presence of these linear chains terminated wioh tin yields a beneficial effect in the reduction of rolling resistance when said product is used in tire formulations. The invention also concerns the copolymers of 1,3-butadiene and styrene obtained by said method.
Reivindicaciones
1. A method of preparation of copolymers of 1,3-butadiene and styrene useful for the production of tires with low rolling resistance characterized by: a. anionic polymerization of the styrene and 1,3-butadiene monomers in a solvent using a lithium alkyl initiator and in the presence of a polar modifier, under inert conditions and at temperatures between 0 and 150°C, preferably between 20 and 120°C b. followed by optional reaction until 2% of a terminal monomer selected from among the monomers which comprise the copolymer or another selected from among the conjugated dienes or aromatic vinyl compounds c. followed by coupling reaction of a maximum of 70% of star-shaped chains using the halide compound of tin or silicon of the formula Cl<n> MeR<4-n> (I), where n represents 3 through 4, Me is Si or Sn, and R is an organic radical of the alkyl, cycloalkyl, or aryl type selected from among radicals with 1 to 20 carbon atoms d. followed by optional reaction until 2% of a terminal monomer, with respect to the remainder of the polymer, selected from among one of the monomers which comprise the copolymer and another selected from among the conjugated dienes or aromatic vinyl compounds e. followed by termination reaction of the linear chains using a compound of the type ClSnR<3> (II), where R is an organic radical of the alkyl, cycloalkyl, or aryl type, selected from among compounds with 1 to 20 carbon atoms. 2. A method according to Claim 1, characterized in that step c. is carried out with tin tetrachloride, SnCl<4> . 3. A method according to Claim 1, characterized in that step c. is carried out with silicon tetrachloride, SiCl<4> . 4. A method according to Claim 1, characterized in that the styrene content may be between 5 and 35%. 5. A method according to Claim 1, characterized in that said solvent is cyclohexane or a mixture of cyclohexane with alkane isomers with 5 to 10 carbon atoms. 6. A method according to Claim 1, characterized in that the alkyl lithium compound is sec-butyllithium. 7. A method according to Claim 1, characterized in that the alkyl lithium compound is n-butyllithium. 8. A method according to Claim 1, characterized in that the polar modifier is tetrahydrofuran. 9. A method according to Claim 1, characterized in that the polar modifier is N,N,N',N'-tetramethylethylenediamine. 10. A method according to Claim 8, characterized in that the tetrahydrofuran concentration in the reaction mass is between 0.15 and 5%. 11. A method according to Claim 9, characterized in that the N,N,N',N'-tetramethylethylenediamine concentration in the reaction mass is between 0.01 and 0.5%. 12. A method according to Claim 1, characterized in that said terminal monomer is styrene. 13. A method according to Claim 1, characterized in that said terminal monomer is 1,3-butadiene. 14. A method according to Claim 1, characterized in that said terminal monomer is 2-methyl-1,3-butadiene. 15. A method according to Claim 1, characterized in that said terminal monomer is α-methylstyrene. 16. A method according to Claim 1, characterized in that the linear chains are terminated with tin tributyl chloride. 17. A method according to Claim 1, characterized in that the linear chains are terminated with tin trimethyl chloride. 18. A method according to Claim 1, characterized in that the linear chains are terminated with tin tripentyl chloride. 19. A copolymer of 1,3-butadiene and styrene, prepared according to the method of Claims 1 through 18, formed at a maximum by 70% of polymer with star structure and at least 30% with linear structure, with all the linear chains containing a tin atom at their end. 20. A copolymer of 1,3-butadiene and styrene, prepared according to the method of Claims 1 through 18, which in vulcanized compounds with at least 20 parts per one hundred of said copolymer have a reduced rolling resistance without degrading the skid resistance. 21. A copolymer of 1,3-butadiene and styrene, prepared according to the method of Claims 1 through 18, which in vulcanized compounds with at least 20 parts per one hundred of said copolymer have values of the tangent of the loss angle (tan δ) relatively low in mecanodynamic tests at temperatures between 50 and 70°C and values of the tangent of the loss angle (tan δ) relatively high in mecanodynamic tests at temperatures between -10 and 10°C.
