Modified vinylaromatic copolymer, production method therefor, modified conjugated diene copolymer obtained therefrom and composition thereof, crosslinked rubber object, and tire member

1. A modified vinylaromatic copolymer comprising a structural unit (a) derived from

a divinylaromatic compound and a structural unit (b) derived from a monovinylaromatic compound, wherein the structural unit (a) at least partially includes the following crosslinked structural unit (a1):

 wherein R 1 represents an aromatic hydrocarbon group having 6 to 30 carbon atoms; and

one or more terminals are each modified by a modification group having at least one functional group selected from the group consisting of an amino group, an alkoxysilyl group, and a hydroxyl group; a number average molecular weight Mn in terms of standard polystyrene as measured with gel permeation chromatography is 500 to 100,000; 50 g or more of the copolymer is dissolved in 100 g of a solvent selected from toluene, xylene, tetrahydrofuran, dichloroethane, or chloroform; 0.5% by mol to 95.0% by mol of the structural unit (a) is contained and 5.0% by mol to 99.5% by mol of the structural unit (b) is contained, based on the total amount of the structural unit (a) and the structural unit (b); and a content of a structural unit other than the structural unit (a) and the structural unit (b) is at most 50% by mol.

2. The modified vinylaromatic copolymer according to claim 1 ,

wherein the copolymer comprises one or more silane-based functional groups (c) each represented by the following formula (c1) or formula (c2), in a side chain or at a terminal:

 wherein R 2 represents a divalent alkylene group having 1 to 6 carbon atoms, and R 3 , R 4 , R 5 , R 7 , R 8 and R 9 each independently represent a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an octoxy group, a lauryloxy group, a phenoxy group, a benzyloxy group, a methyl group, an ethyl group, a propyl group, a butyl group, a cyclohexyl group, a phenyl group, or a benzyl group, provided that at least one of R 3 , R 4 and R 5 or at least one of R 7 , R 8 and R 9 is a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an octoxy group, a lauryloxy group, a phenoxy group, or a benzyloxy group;

a molar fraction of the crosslinked structural unit (a1) to the structural unit (a) is in a range from 0.05 to 0.90;

1 to 20 of the silane-based functional groups (c) are contained per molecule; and

a number average molecular weight Mn is 500 to 100,000, and a molecular weight distribution (Mw/Mn) represented by a ratio of a weight average molecular weight Mw to the number average molecular weight Mn is 30.0 or less.

3. The modified vinylaromatic copolymer according to claim 2 , comprising one or more copolymers each represented by any of the following formulae (2) to (13):

wherein R 2 represents a divalent alkylene group having 1 to 6 carbon atoms, R 3 , R 4 and R 5 each independently represent a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an octoxy group, a lauryloxy group, a phenoxy group, a benzyloxy group, a methyl group, an ethyl group, a propyl group, a butyl group, a cyclohexyl group, a phenyl group, or a benzyl group, provided that at least one of R 3 , R 4 and R 5 is a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an octoxy group, a lauryloxy group, a phenoxy group, or a benzyloxy group, R 6 is an alkyl group having 1 to 6 carbon atoms, a vinyl group, or hydrogen, and Polymer is a copolymer chain, provided that each benzene ring in the formulae is any aromatic ring; and

wherein R 7 , R 8 and R 9 each independently represent a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an octoxy group, a lauryloxy group, a phenoxy group, a benzyloxy group, a methyl group, an ethyl group, a propyl group, a butyl group, a cyclohexyl group, a phenyl group, or a benzyl group, provided that at least one of R 7 , R 8 and R 9 is a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an octoxy group, a lauryloxy group, a phenoxy group, or a benzyloxy group, R 6 is an alkyl group having 1 to 6 carbon atoms, a vinyl group, or hydrogen, and Polymer is a copolymer chain.

4. The modified vinylaromatic copolymer according to claim 2 , wherein the structural unit (b) derived from a monovinylaromatic compound is a structural unit derived from one or more monomers selected from the group consisting of styrene, vinylnaphthalene, vinylbiphenyl, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, m-ethylvinylbenzene, indene, and p-ethylvinylbenzene.

5. A method for producing the modified vinylaromatic copolymer according to claim 2 , from a polyfunctional vinylaromatic copolymer and a silane-based compound, wherein

the polyfunctional vinylaromatic copolymer comprises 0.5% by mol or more and 95.0% by mol or less of the structural unit (a) derived from a divinylaromatic compound and comprises 5.0% by mol or more and 99.5% by mol or less of the structural unit (b) derived from a monovinylaromatic compound;

the structural unit (a) at least partially includes the crosslinked structural unit (a1) and the following vinyl group-containing structural unit (a2):

 wherein R 1 represents an aromatic hydrocarbon group having 6 to 30 carbon atoms;

a molar fraction of the crosslinked structural unit (a1) to the structural unit (a) is in a range from 0.05 to 0.90;

a molar fraction of the vinyl group-containing structural unit (a2) to the sum of the structural units (a) and (b) is in a range from 0.001 to 0.80;

the polyfunctional vinylaromatic copolymer has a Mn of 300 to 50,000 and a Mw/Mn of 20.0 or less;

the silane-based compound is any silane-based compound represented by the following formula (5) and/or formula (6):

 wherein R 2 , R 3 , R 4 and R 5 are the same as those in the formula (c1); and

 wherein R 6 , R 7 and R 8 are the same as R 7 , R 8 and R 9 in the formula (c2); and

the polyfunctional vinylaromatic copolymer and the silane-based compound are dissolved in a hydrocarbon-based solvent and added at a temperature of 0 to 150° C. in the presence of a catalyst.

6. A modified conjugated diene-based copolymer obtained by reacting the modified vinylaromatic copolymer (A) according to claim 2 , as a modifying agent, with a polymer of a conjugated diene compound (B) having an active terminal, or a copolymer of a conjugated diene compound (B) having an active terminal and an aromatic vinyl compound (C).

7. The modified conjugated diene-based copolymer according to claim 6 , comprising 0.001 to 6% by weight of a structural unit (A1) derived from the modified vinylaromatic copolymer (A), 29 to 99.999% by weight of a structural unit (B1) derived from the conjugated diene compound (B) and 0 to 70% by weight of a structural unit (C1) derived from the aromatic vinyl compound (C).

8. The modified conjugated diene-based copolymer according to claim 6 , wherein an area of a region corresponding to a number average molecular weight (Mn) three times or more of the number average molecular weight (Mn) at a peak at the lowest molecular weight side is 10% or more based on a total area of 100% in a differential molecular weight distribution curve obtained by gel permeation chromatography (GPC) measurement.

9. A modified conjugated diene-based copolymer composition, obtained by compounding at least one reinforcing filling agent selected from the group consisting of a filler or a silica-based inorganic filling agent, metal oxide, metal hydroxide and carbon black to the modified conjugated diene-based copolymer according to claim 6 .

10. The modified conjugated diene-based copolymer composition according to claim 9 , further comprising a crosslinking agent.

11. The modified vinylaromatic copolymer according to claim 1 , wherein

95% by mol or more of the structural unit (a) is the crosslinked structural unit (a1), and

two or more terminals are each modified by a modification group having at least one functional group selected from the group consisting of an amino group, an alkoxysilyl group, and a hydroxyl group.

12. The modified vinylaromatic copolymer according to claim 11 , wherein a number average molecular weight Mn is 500 to 50,000, and a molecular weight distribution (Mw/Mn) is 10.0 or less.

13. The modified vinylaromatic copolymer according to claim 12 , wherein the number average molecular weight Mn is 900 to 10,000.

14. The modified vinylaromatic copolymer according to claim 11 , wherein the average number of functional groups per molecule is in a range from 2 to 20.

15. The modified vinylaromatic copolymer according to claim 11 , wherein the monovinylaromatic compound is one or more monomers selected from the group consisting of styrene, vinylnaphthalene, vinylbiphenyl, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, m-ethylvinylbenzene, indene, and p-ethylvinylbenzene.

16. A method for producing the modified vinylaromatic copolymer according to claim 11 , comprising:

a polymerization step of copolymerizing the divinylaromatic compound with the monovinylaromatic compound, or the divinylaromatic compound and the monovinylaromatic compound with a monomer anionically copolymerizable with these compounds, by use of an alkali metal compound or an alkaline earth metal compound as an anionic polymerization initiator, to obtain a vinylaromatic copolymer having a branched structure and an active terminal, and

a terminal modification step of reacting a compound having at least one functional group selected from the group consisting of an amino group, an alkoxysilyl group, and a hydroxyl group, or a precursor compound thereof with the active terminal of the vinylaromatic copolymer, to form a functional group.

17. A modified conjugated diene-based copolymer obtained by reacting the modified vinylaromatic copolymer according to claim 11 with a polymer of a conjugated diene compound, or a copolymer of a conjugated diene compound and an aromatic vinyl compound.

18. The modified conjugated diene-based copolymer according to claim 17 , comprising 0.001 to 6% by weight of a structural unit (A1) derived from a modified vinylaromatic copolymer, 29 to 99.999% by weight of a structural unit (B1) derived from a conjugated diene compound, and 0 to 70% by weight of a structural unit (C1) derived from an aromatic vinyl compound.

19. The modified conjugated diene-based copolymer according to claim 17 , wherein an area of a region corresponding to a number average molecular weight (Mn) three times or more of the number average molecular weight (Mn) at a peak at the lowest molecular weight side is 10% or more based on a total area of 100% in a differential molecular weight distribution curve obtained by gel permeation chromatography (GPC) measurement.

20. A rubber composition comprising 0.5 to 200 parts by weight of at least one reinforcing filling agent selected from the group consisting of a silica-based inorganic filling agent, metal oxide, metal hydroxide, and carbon black based on 100 parts by weight of the modified conjugated diene-based copolymer according to claim 17 .

21. The rubber composition according to claim 20 , further comprising a crosslinking agent.