Kinetics of the polymerization of styrene with butoxytitanium trichloride and trialkylaluminium

Abstract

The kinetics of polymerization of styrene in heptane was investigated using butoxytitanium trichloride and triethylaluminium/triisobutylaluminium as cocatalysts. A steady state polymenzation after an initial period of declining rates lasting for 20 -60 min was observed. Both the catalyst systems polymerize styrene at a slow rate (= mole dm-, * s-l). The steady state rates show a maximum at an [All : [Ti] ratio of 1 3 and exhibit a first-order rate law with reference to both the monomer and the catalyst. Addition of triethylamine, an electron donor, greatly influences the rates of polymerization when triethylaluminium is used, whereas in the case of triisobutylaluminium, the rates are not greatly influenced by the presence or absence of triethylamine. The effect of the electron donor on the rates of polymerization can be explained by the competitive complexation of the alkylaluminium and the electron donor at the active site.The overall activation energy of polymerization (44 -46 kJ . mol-' ) is in accord with a coordinated anionic mechanism. An alkylated alkoxytitanium halide species as the chemical entity affecting polymerization is suggested. a) NCL Communication No. 3409. 0025-1 16X/84/$03.00 1118 J. C. Sehra, S. Gundiah polymerization of styrene in heptane, including the effect of triethylamine, an electron donor, initiated by butoxytitanium trichloride and trialkylaluminium compounds, is reported in this communication. Experimental partMaterials: Styrene (C.P. grade) was freed of the inhibitor by treatment with 5% sodium hydroxide solution and repeatedly washed with distilled water. The inhibitor-free monomer was dried over fused calcium chloride and calcium hydride and distilled under reduced pressure. The monomer, distilling at 40-42OC at 27 mbar, was collected and used for polymerization. Heptane (C.P. grade) was extracted with conc. sulfuric acid to remove olefinic impurities, washed with 5% sodium carbonate solution followed by distilled water and stored over fused calcium chloride. Heptane, thus purified, was refluxed over sodium for 10 -12 h and distilled. The fraction boiling at 96 -97 "C was collected.Butoxytitanium trichloride (BuOTiC1, )/Tic4 (= 99(70), refluxed over copper turnings and