Separated aluminum alkyl–titanium tetrachloride catalysts for isoprene polymerization

• Published in: Journal of polymer science. Part A. General papers 1963-01, Vol.1 (1), p.373-384
• Main Author: Saltman, William M.
• Format: Article
• Language: English
• ISSN: 0449-2951; 1542-6246
• DOI: 10.1002/pol.1963.100010133

The liquid portions of triisobutyl–aluminum TiCl 4 catalysts were partially or completely removed from catalysts formed at Al/Ti ratios of 0.5, 0.6, 1.0, 1.2, 2.0, 3.0, and higher. The partially separated catalysts (0.5–1.2 Al/Ti) are still highly active for the polymerization of isoprene to a high cis polymer. The completely separated solid is inactive, but regains polymerization activity if triisobutyl aluminum or diisobutyl‐aluminum chloride is added back. Polymer yield quickly reaches a maximum and then falls off sharply on addback of more trialkyl; the drop in yield is much slower on addback of excess dialkyl halide. The results indicate that trialkyl or dialkyl halide plus β‐TiCl 3 make active catalyst systems for cis ‐polyisoprene; the alkyl dihalide is not satisfactory. Excess trialkyl changes the solid surface or mechanism and results in lowered solid polymer yield and increased oily oligomer formation. Completely separated high ratio (2.0 and 3.0 Al/Ti) catalysts are more active than those only partially separated but still much less active than catalysts formed at lower ratios. Addbacks of either aluminum trialkyl or dialkyl halide depress the solid cis polymer yield. Without any separation no solid polymer at all forms. The results suggest that the catalyst at these high ratios is a solid complex of β‐TiCl 3 with an organometallic. A simple coordination mechanism is sufficient to correlate all the experimental results.