The invention provides compositions of chloroprene rubbers having improved vibration-damping properties under low temperature conditions without deterioration of mechanical properties, permanent compression set and tension fatigue in the final product. The chloroprene rubbers of the invention contain a xanthogen-modified chloroprene rubber and/or a mercaptan-modified chloroprene rubber in an amount of 100 parts by mass, a carbon black having an average particle diameter of 70 mn to 600 mn and a DBP oil absorption (as determined by Absorption A method of JIS-K6221) of 15 ml/100 g in an amount of 15 to 150 parts by mass, and a plasticizer represented by the chemical formula R.sub.1COO(CH.sub.2).sub.8COOR.sub.2 wherein R.sub.1 and R.sub.2 each represent an alkyl group having 1 to 7 carbons.

The invention provides compositions of chloroprene rubbers having improved vibration-damping properties under low temperature conditions without deterioration of mechanical properties, permanent compression set and tension fatigue in the final product. The chloroprene rubbers of the invention contain a xanthogen-modified chloroprene rubber and/or a mercaptan-modified chloroprene rubber in an amount of 100 parts by mass, a carbon black having an average particle diameter of 70 mn to 600 mn and a DBP oil absorption (as determined by Absorption A method of JIS-K6221) of 15 ml/100 g in an amount of 15 to 150 parts by mass, and a plasticizer represented by the chemical formula R.sub.1COO(CH.sub.2).sub.8COOR.sub.2 wherein R.sub.1 and R.sub.2 each represent an alkyl group having 1 to 7 carbons.

A chloroprene-based block copolymer, a latex, a latex composition, and a rubber composition that can produce a product with excellent tensile properties and flexibility without the use of a vulcanizing agent or a vulcanizing accelerator having a chloroprene-based block copolymer, contains 5 to 30% by mass of a polymer block (A) and 70 to 95% by mass of a chloroprene-based polymer block (B), wherein the polymer block (A) is derived from a monomer, when the monomer is polymerized alone, a polymer with a glass transition temperature of 80 C. or higher can be obtained and the chloroprene-based polymer block (B) includes a chloroprene monomer unit and a polyfunctional monomer unit.

A chloroprene-based block copolymer, a latex, a latex composition, and a rubber composition that can produce a product with excellent tensile properties and flexibility without the use of a vulcanizing agent or a vulcanizing accelerator having a chloroprene-based block copolymer, contains 5 to 30% by mass of a polymer block (A) and 70 to 95% by mass of a chloroprene-based polymer block (B), wherein the polymer block (A) is derived from a monomer, when the monomer is polymerized alone, a polymer with a glass transition temperature of 80 C. or higher can be obtained and the chloroprene-based polymer block (B) includes a chloroprene monomer unit and a polyfunctional monomer unit.

A method for manufacturing a chloroprene polymer composition, the method including: a polymerization step of polymerizing chloroprene in the presence of at least one rosin acid component selected from the group consisting of a rosin acid and a rosin acid salt to obtain a chloroprene polymer composition containing a chloroprene polymer, in which in the rosin acid component, a mass ratio B1/A1 of a total amount B1 of abietic acid, neoabietic acid, palustric acid, levopimaric acid, and salts thereof with respect to a total amount A1 of dehydroabietic acid, pimaric acid, isopimaric acid, dihydroabietic acid, and salts thereof is 0.10 to 3.00, and a toluene insoluble content of the chloroprene polymer is 50% by mass or more.

A method for manufacturing a chloroprene polymer composition, the method including: a polymerization step of polymerizing chloroprene in the presence of at least one rosin acid component selected from the group consisting of a rosin acid and a rosin acid salt to obtain a chloroprene polymer composition containing a chloroprene polymer, in which in the rosin acid component, a mass ratio B1/A1 of a total amount B1 of abietic acid, neoabietic acid, palustric acid, levopimaric acid, and salts thereof with respect to a total amount A1 of dehydroabietic acid, pimaric acid, isopimaric acid, dihydroabietic acid, and salts thereof is 0.10 to 3.00, and a toluene insoluble content of the chloroprene polymer is 50% by mass or more.