olefin can itself act as a solvent for example 1 hexene in which case no other solvent is necessary the concentration of nbr in the reaction mixture is not critical but should be such that the reaction is not hampered if the mixture is too viscous to be stirred efficiently for example preferably the concentration of nbr is in the range of from 1 to 20 by weight more preferably in the range of from 6 to 15 by weight the process of the present invention usually is carried out at a temperature in the range of from 20 to 140 u00b0 c preferably in the range of from 60 to 120 u00b0 c the reaction time will depend upon a number of factors including cement concentration amount of catalyst used and the temperature at which the reaction is performed the metathesis usually is complete within the first two hours under typical conditions the progress of the metathesis reaction may be monitored by standard analytical techniques for example using gpc or solution viscosity whenever referenced throughout the specification the molecular weight distribution of the polymer was determined by gel permeation chromatography gpc using a waters 2690 separation module and a waters 410 differential refractometer running waters millennium software version 3 05 01 samples were dissolved in tetrahydrofuran thf stabilized with 0 025 bht the columns used for the determination were three sequential mixed b gel columns from polymer labs reference standards used were polystyrene standards from american polymer standards corp the mooney viscosity of the rubber was determined using astm test d1646 the nitrile rubber of the present invention is very well suited for the manufacture of a shaped article such.