A modified conjugated diene-based polymer having a nitrogen atom, wherein a content of the nitrogen atom is 25 mass ppm or more based on a total amount of the modified conjugated diene-based polymer, a shrinking factor (g′) is 0.59 or less in a GPC-light scattering measurement method with a viscosity detector, and a weight average molecular weight is 200,000 or more and 3,000,000 or less.

A modified conjugated diene-based polymer having a nitrogen atom, wherein a content of the nitrogen atom is 25 mass ppm or more based on a total amount of the modified conjugated diene-based polymer, a shrinking factor (g′) is 0.59 or less in a GPC-light scattering measurement method with a viscosity detector, and a weight average molecular weight is 200,000 or more and 3,000,000 or less.

A method for producing a synthetic polyisoprene latex, including a step of mixing a latex of synthetic polyisoprene (A) synthesized by use of a Ziegler type catalyst and a latex of synthetic polyisoprene (B) synthesized by use of an organic alkali metal catalyst at a weight ratio of “synthetic polyisoprene (A): synthetic polyisoprene (B)=10:90 to 90:10”. In the method, preferably, the weight average molecular weight of the synthetic polyisoprene (A) is 100,000 to 3,000,000 and the weight average molecular weight of the synthetic polyisoprene (B) is 1,000,000 to 5,000,000.

A method for producing a synthetic polyisoprene latex, including a step of mixing a latex of synthetic polyisoprene (A) synthesized by use of a Ziegler type catalyst and a latex of synthetic polyisoprene (B) synthesized by use of an organic alkali metal catalyst at a weight ratio of “synthetic polyisoprene (A): synthetic polyisoprene (B)=10:90 to 90:10”. In the method, preferably, the weight average molecular weight of the synthetic polyisoprene (A) is 100,000 to 3,000,000 and the weight average molecular weight of the synthetic polyisoprene (B) is 1,000,000 to 5,000,000.

Provided is a rubber crawler including a guide rubber that is reduced in heat generation and excellent in abrasion resistance and an inner peripheral rubber that is excellent in scratch resistance and abrasion resistance and having excellent adhesiveness between the guide rubber and the inner peripheral rubber. The rubber crawler of the present invention includes a guide rubber obtained by crosslinking a guide rubber composition and an inner peripheral rubber obtained by crosslinking an inner peripheral rubber composition, the guide rubber composition containing a rubber component (A) and a carbon black (B), the rubber component (A) containing a butadiene rubber and at least one selected from a natural rubber and isoprene rubber, and containing 50 to 80% by mass of the natural rubber and the isoprene rubber and 20 to 50% by mass of the butadiene rubber, the carbon black (B) containing a carbon black (B-1) having an N.sub.2SA of 60 to 125 m.sup.2/g and a DBP absorption of less than 130 mL/100 g and a carbon black (B-2) having an N.sub.2SA of less than 60 m.sup.2/g and a DBP absorption of 110 mL/100 g or more, and a total content of the carbon black (B-1) and the carbon black (B-2) is 25 to 65 parts by mass based on 100 parts by mass of the rubber component; the inner peripheral rubber composition containing a rubber component (a) and a carbon black (b), the rubber component (a) containing 60 to 100% by mass of SBR and 0 to 40% by mass of a diene-based rubber other than the styrene-butadiene rubber, and a carbon black in an amount of 50 to 70 parts by mass based on 100 parts by mass of the rubber component.

Provided is a rubber crawler including a guide rubber that is reduced in heat generation and excellent in abrasion resistance and an inner peripheral rubber that is excellent in scratch resistance and abrasion resistance and having excellent adhesiveness between the guide rubber and the inner peripheral rubber. The rubber crawler of the present invention includes a guide rubber obtained by crosslinking a guide rubber composition and an inner peripheral rubber obtained by crosslinking an inner peripheral rubber composition, the guide rubber composition containing a rubber component (A) and a carbon black (B), the rubber component (A) containing a butadiene rubber and at least one selected from a natural rubber and isoprene rubber, and containing 50 to 80% by mass of the natural rubber and the isoprene rubber and 20 to 50% by mass of the butadiene rubber, the carbon black (B) containing a carbon black (B-1) having an N.sub.2SA of 60 to 125 m.sup.2/g and a DBP absorption of less than 130 mL/100 g and a carbon black (B-2) having an N.sub.2SA of less than 60 m.sup.2/g and a DBP absorption of 110 mL/100 g or more, and a total content of the carbon black (B-1) and the carbon black (B-2) is 25 to 65 parts by mass based on 100 parts by mass of the rubber component; the inner peripheral rubber composition containing a rubber component (a) and a carbon black (b), the rubber component (a) containing 60 to 100% by mass of SBR and 0 to 40% by mass of a diene-based rubber other than the styrene-butadiene rubber, and a carbon black in an amount of 50 to 70 parts by mass based on 100 parts by mass of the rubber component.

A curable low sulfur liquid rubber composition including at least one polymer which contains, in polymerized form, at least one monomer having a carbon chain of four and a peroxide system which includes at least one organic peroxide and at least one coagent. The polymer has a vinyl content of 1% to 90% and a number average molecular weight of 800 g/mol to 70,000 g/mol. The curable low sulfur liquid rubber composition has a sulfur content of 0 to 1%, by weight, and is curable at a temperature of 100° C. to 190° C.

A curable low sulfur liquid rubber composition including at least one polymer which contains, in polymerized form, at least one monomer having a carbon chain of four and a peroxide system which includes at least one organic peroxide and at least one coagent. The polymer has a vinyl content of 1% to 90% and a number average molecular weight of 800 g/mol to 70,000 g/mol. The curable low sulfur liquid rubber composition has a sulfur content of 0 to 1%, by weight, and is curable at a temperature of 100° C. to 190° C.

A catalyst composition of the present disclosure comprises: a rare earth element-containing compound (A) containing a rare earth element compound or a reaction product thereof with a Lewis base, an organic metal compound (B) of a formula: YR.sup.1.sub.aR.sup.2.sub.bR.sub.c.sup.3 [wherein Y is a metal selected from Group 1, Group 2, Group 12, and Group 13 of the periodic table, le and R.sup.2 are each a hydrocarbon groups having 1 to 10 carbon atoms or a hydrogen atom, R.sup.3 is a hydrocarbon group having 1 to 10 carbon atoms, a is 1 and b and c are 0 when Y is a metal in Group 1, a and b are 1 and c is 0 when Y is a metal in Groups 2 and 12, and a, b, and c are all 1 when Y is a metal in Group 13], and a compound having a polar functional group (C).

Essentially ethylene thiourea free cross linkable composition comprising a chloroprene rubber having defined contents of cations from the second or third main group and resinate anions are provided, which possess improved curing characteristics for increased productivity and lower vulcanization temperatures for energy-saving manufacturing methods and vulcanizates obtained by using said chloroprene rubber.