Abstract: | The effect of CS2 on isoprene polymerization with triisobutylaluminum-titanium tetrachloride catalysts was studied at Al/Ti ratios of optimum (0.9) and higher values. In the absence of CS2, appreciable amounts of low molecular weight oils (“extractables”) were formed at the expense of cis-1,4-polyisoprene with higher than optimum Al/Ti ratios. Small amounts of CS2 were found to prevent extractables formation and allow attainment of higher yields of cis-1,4-polyisoprene. The optimum CS2/Ti chloride molar ratio (0.1) was independent of the Al/Ti ratio of the catalyst. Polymer microstructure and dilute solution viscosity were unaffected by CS2. The results support the theory that the catalyst surfaces hold two types of active sites: p-sites, which initiate polymerization, and o-sites, which lead to oligomerization. CS2 appears to enhance polymerization by coordinating selectively at the o-sites. The predominance of oligomerization at the higher Al/Ti ratios was attributed to a destruction of p-sites by excess trialkyl-aluminum. |