Process for producing ethylene-.alpha.-olefin copolymers

A process for producing an ethylene-.alpha.-olefin copolymer which comprises the following steps 1 to 3:

• Step 1:
• subjecting ethylene to an oligomerization reaction in the presence of an oligomerization catalyst to convert a part of the ethylene to .alpha.-olefin, and thereby obtaining a reaction solution, a reaction gas or a mixture of the reaction solution and the reaction gas containing said .alpha.-olefin and unreacted ethylene;
• Step 2:
• distilling the reaction solution, the reaction gas or the mixture of the reaction solution and the reaction gas to obtain a mixture consisting mainly of ethylene and .alpha.-olefin from the top of the distillation column, wherein distillation was performed with at least 3 theoretical plates, reflux ratio of at least 0.05 and a pressure of at least 30 kg/cm.sup.2 ;
• and
• Step 3:
• feeding a starting material comprising the mixture obtained in Step 2 into a polymerization reactor, thereby copolymerizing the ethylene and .alpha.-olefin in the presence of a polymerization catalyst to obtain an ethylene-.alpha.-olefin copolymer.

A process for producing an ethylene-.alpha.-olefin copolymer which consists essentially of the following steps 1 to 3:

• Step 1:
• subjecting ethylene to an oligomerization reaction in the presence of an oligomerization catalyst to convert a part of the ethylene to .alpha.-olefin, and thereby obtaining a reaction solution, a reaction gas or a mixture of the reaction solution and the reaction gas containing said .alpha.-olefin and unreacted ethylene;
• Step 2:
• distilling the reaction solution, the reaction gas or the mixture of the reaction solution and the reaction gas to obtain a mixture consisting mainly of ethylene and .alpha.-olefin from the top of the distillation column so that at least 95% by weight of the mixture obtained from the top of the distillation column consists of ethylene and .alpha.-olefin;
• and
• Step 3:
• feeding a starting material comprising the mixture obtained in Step 2 into a polymerization reactor, thereby copolymerizing the ethylene and .alpha.-olefin in the presence of a polymerization catalyst to obtain an ethylene-.alpha.-olefin copolymer.