Process for making low crystallinity polyolefins

A process for the production of high molecular weight polyolefins having a degree of crystallinity less than about 25%, which process comprises polymerizing at least one 1-olefin containing at least 3 carbon atoms or a mixture of at least one of said olefins with up to about 67 weight % of ethylene in an inert liquid hydrocarbon diluent at a temperature ranging from about 25.degree. C. to about 90.degree. C. in the presence of a catalytic amount of a catalyst system consisting essentially of

• (a) a hydrocarbon soluble transition metal component derived by contacting in an inert liquid hydrocarbon
• (1) a soluble, halide free magnesium-carboxylate having the general formula Mg(OOCR').sub.2 where each R' is alike or different and is derived from a carboxylic acid containing at least 2 carbon atoms with
• (2) a soluble salt of a transition metal selected from the group consisting of tetravalent titanium, zirconium and hafnium, and
• (b) an alkylaluminum halide activator having the general formula R.sub.n AlX.sub.3-n where R is a 1 to 18 carbon alkyl group and n is a number from 1.5 to 2.5,
• the molar ratio of transition metal salt to magnesium carboxylate being 0.003 to 3, the molar ratio of alkylaluminum halide activator to transition metal salt being at least 1 and the molar ratio of alkylaluminum halide activator to magnesium carboxylate being greater than 2.5.