Living and non-living catalysts have been used to polymerize olefins. In living polymerization, each catalyst molecule initiates a growing polymer chain that does not undergo chain transfer or termination reactions while monomer is present. One can determine whether or not living polymerization has occurred by comparing the number of initiator molecules with the number of polymer chains produced in the final polymer. These two numbers should be equivalent for true living polymerization. If there are a substantially greater number of polymer chains as compared to initiator molecules, then the polymerization is not living.
The basic components of known living polymerization systems include a Lewis acid, a tertiary alkyl initiator molecule containing a halogen, ester, ether acid, or alcohol group, and an electron donor molecule such as ethyl acetate.
Lewis acids of known living polymerization systems include titanium tetrachloride (TiCl.sub.4), boron trichloride (BCL.sub.3), tin tetrachloride (SnCl.sub.4), iron trichloride (FeCl.sub.3), aluminum trichloride (AlCl.sub.3) and the like. These compounds have been described in U.S. Pat. Nos. 4,910,321 and 4,929,683 and European patent application 341,012 for use in living polymerization of olefins. The exact combination of these elements, however, varies with each system. The tertiary alkyl initiators typically used in living polymerization systems are represented by the formula: ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are a variety of alkyl or aromatic groups or combinations thereof, n is the number of initiator molecules, and X is the functional group upon which the Lewis acid affects a change to bring about the carbocationic initiating site. The functional group is typically a halogen, ester, ether, alcohol, or acid group depending on the Lewis acid employed.
As discussed in U.S. Pat. No. 5,169,914, the chosen electron pair donor component of the above systems is believed to directly relate to the ability of these catalysts to stabilize the carbocation formed and to generate living conditions. The electron donor number concept has been used to explain the activity of catalyst systems which employ ether and ester initiators. It is believed that the formation of in situ electron pair donors are responsible for the catalyst characteristics. However, the role of the electron donor is still uncertain and has been challenged. See, M. Gyor, L. Balogh, H. C. Wang, R. Faust, Polym. Prepr. Amer. Chem. Soc., 33(1), 158 (1992).
Such living polymerization systems are useful for production of narrow molecular weight distribution polymers, however, these systems are very sensitive to certain impurities. For example, the presence of water in Lewis acid catalyzed systems has been considered detrimental because water is associated with chain transfer dominated, nonliving polymerization which results in broad molecular weight distribution polymers i.e., polymer with an Mw/Mn greater than 2.0. There is a decrease in desirable physical properties when the polymer has a broad molecular weight distribution. Recently we have found that water can be used to initiate the living polymerization of isobutylene provided that the correct Lewis acid to water ratio is used. Additionally, in co-pending U.S. application Ser. No. 08/044,862 the addition of an amine to this process was found to modify the overall amount of Lewis acid required to bring about living conditions.
Catalyst systems based on BCl.sub.3 and TiCl.sub.4 using a number of combinations of the previously described components have very similar process characteristics. First, the Lewis acid concentrations must exceed the concentration of initiator sites by 16 to 40 times in order to achieve 100 percent conversion in 30 minutes (based upon a degree of polymerization equal to 890) at -75.degree. to -804.degree. C. Much longer polymerization times are required for higher polymerization temperatures. These catalyst systems are also typically used with solvents such as methyl chloride.
For an industrially applicable process, these catalysts and polymerization conditions fall short of commercial usefulness. Improvements in these systems would include reduction in polymerization time while maintaining narrow molecular weight distribution.