This invention relates to the polymerization catalyst systems and polymerization processes for mono-1-olefins.
It is well known that mono-1-olefins, such as ethylene, can be polymerized with catalyst systems employing vanadium, chromium or other metals on inorganic oxide, or refractory, supports. Initially, such catalyst systems were used primarily to form homopolymers of ethylene. It soon developed, however, that many applications required polymers which were more impact resistant than ethylene homopolymers. Consequently, in order to produce polymers having short chain branching, like the more flexible free radical polymerized polymers, comonomers such as propylene, butene, hexene or other higher olefins were copolymerized with the ethylene to provide resins tailored to specific end uses. The copolymers, however, are more expensive to produce since inventories of different monomers must be kept and also the comonomers are generally more expensive than ethylene. Linear ethylene polymers with short chain branching can be formed from a pure ethylene feed using the old free radical high pressure process, but the conditions necessary to do this make the product too expensive to be commercially viable at this time.
Additional control over the polymerization process and the resultant polymer is also desired. A process to consistently reduce the density of linear olefin polymers and to more efficiently produce and incorporate comonomers into the linear olefin polymer is economically advantageous. A shift in the polymer branch distribution, wherein the branch length is decreased and the amount of branching is increased, is also economically desirable.