Low molecular weight nitrite rubber

A nitrile rubber having a molecular weight (Mw) in the range of from 25,000 to 200,000 g/mol, a Mooney viscosity (ML 1+4 @ 100 deg. C.) of less than 8 and a polydispersity index of less than about 2.1, wherein the nitrile rubber is prepared by olefin metathesis of at least one conjugated diene, at least one α,β-unsaturated nitrile and optionally further one or more copolymerizable monomers in the presence of one or more compounds of the general formula I, II, III or IV and optionally the presence of a co-olefin and a solvent, wherein,

• wherein:
• M is Os or Ru,
• R and R1 are, independently, hydrogen or a hydrocardon selected from the group consisting of C2-C20 alkenyl, C2-C20 alkynyl, C1-C20 alkyl, aryl, C1-C20 carboxylate, C1-C20 alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy, aryloxy, C2-C20 alkoxycarbonyl, C1-C20 alkylthio, C1-C20 alkylsufonyl and C1-C20 alkylsulfinyl,
• X and X1 are independently any anionic ligand, and
• L and L1 are independently any neutral ligand or any neutral carbine, optionally, L and L1 can be linked to one another to form a bidentate neutral ligand;
• wherein
• M1 is Os or Ru;
• R2 and R3 are, independently, hydrogen or a hydrocarbon selected from the group consisting of C2-C20 alkenyl, C2-C20 alkynyl, C1-C20alkyl, aryl, C2-C20 carboxylate, C1-C20 alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy, aryloxy, C2-C20 alkoxycarbonyl, C1-C20 alkylthio, C1-C20 alkylsulfonyl and C2-C20 alkylsulfinyl,
• X2 is an anionic ligand, and
• L2 is a neutral π-bonded ligand, independent of whether they are mono- or polycyclic,
• L3 is a ligand selected from the group consisting of phosphines, sulfonated phosphines, fluorinated phosphines, functionalized phosphines bearing up to three aminoalkyl-, ammonumalkyl-, alkoxyalkyl-, alkoxylcarbonylaklyl-, hydrocycarbonylalkyl-, hydroxyalkyl- or ketoalkyl- groups, phosphites, phosphinites, phosphonites, phosphinamines, arsines, stibenes, ethers, amines, amides, imines, sulfoxides, thioethers and pyridines,
• Y-is a non-coordinating anion,
• n is an integer in the range of from 0 to 5;
• wherein
• M2 is Mo or W,
• R4 and R5 are, independently, hydrogen or a hydrocarbon selected from the group consisting of C2-C20 alkenyl, C2-C20 alkynl, C1-C20 alkyl, aryl, C1-C20 carboxylate, C1-C20 alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy, aryloxy, C2-C20 alkoxycarbonyl, C1-C20 alkylthio, C1-C20 alkylsulfonyl and C1-C20 alkylsulfinyl,
• R6 and R7 are independently selected from any unsubstituted or halo-substituted alkyl, aryl, aralkyl groups or silicon-containing analogs thereof,
• wherein
• M is Os or Ru,
• R and R1 are independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, and substituted or unsubstituted alkyl,
• X and X1 are independently any anionic ligand, and
• L and L1 are independently any neutral ligand or any neutral carbine, optionally, L and L1 can be linked to one another to form a bidentate neutral ligand.