| 摘要 |
<p>Modified copolymers of ethylene and of at least one alpha -olefin containing from 3 to 12 carbon atoms, containing from 0.5 to 10 mol% of units derived from the said alpha -olefin. Their measured limiting viscosity is between 1.3 and 1.5 times their limiting viscosity calculated from the molecular mass distribution. They are prepared by continuous copolymerisation of ethylene with at least one alpha -olefin in at least one reactor comprising at least one reaction zone, in the presence of a catalyst system of Ziegler type, at a temperature of 180<o>C to 320<o>C and at a pressure of 300 to 2500 bars in the presence, if appropriate, of up to 2 mol% of hydrogen, the mean residence time of the catalyst system in the reactor is between 1 and 120 seconds, the process being characterised in that from 0.01 to 2 millimoles per kg of copolymer of at least one diaryldialkylalkane are introduced into at least one reaction zone at a temperature of between 220<o>C and 320<o>C at a pressure of between 500 and 1000 bars. The modified copolymers produced have a measured limiting viscosity which is between 1.3 and 10 times their limiting viscosity calculated from the molecular mass distribution.</p> |
