Polymerization of styrene with TiCl3–Al(C2H5)3 and VCl3–Al(C2H5)3 catalysts

The polymerization of styrene was studied in benzene solution with two catalyst systems: TiCl3–Al(C2H5)3 and VCl3–Al(C2H5)3. The reaction was carried out at atmospheric pressure, temperatures of 40–70°C., [monomer] = 0.695–5.75 moles/l., [TiCl3] = 0.12–1.2 g./l., and [alkyl] = 0.001–0.016 mole/l. For polymerizations with TiCl3–Al(C2H5)3 catalyst, the rate of polymerization was found to be first‐order with respect to TiCl3, proportional to [monomer]1.5 and for [Al(C2H5)3] > 0.002 mole/l., proportional to [Al(C2H5)3]−1/2. For [Al(C2H5)3] < 0.002 mole/l., the rate passed through a maximum and decreased rapidly to a negligible value as the alkyl concentration decreased. The apparent activation energy was 8.1 kcal./mole. The rate of polymerization with VCl3 as catalyst component was generally faster than the rate obtained with TiCl3. A reaction scheme has been postulated to account for the influence of monomer and catalyst on the steady state rate. The model suggests that TiCl3 activation consists of surface alkylation and removal of Cl− ions by reaction with Al(C2H5)3. Monomer adsorption occurs on vacant sites, neighboring alkylated surface sites, in competition with the adsorption of metal alkyl. Vacant and alkylated sites partake in the first coordination sphere of Ti+3 ions in TiCl3. Polymerization follows by monomer insertion into the TiC bond at the alkylated site.