Supported catalysts for stereospecific polymerization of propylene

Abstract

AbstractTetrabenzyltitanium (B4Ti), tribenzyltitanium chloride (B3TiCl), tetra(p‐methylbenzyl)titanium (R4Ti) and tri(p‐methylbenzyl)titanium chloride (R3TiCl) have been used as catalysts for ethylene and propylene polymerization activated by AlEt2Cl. B4Ti‐AIEt2Cl in solution polymerizes ethylene readily but its activity decays rapidly. B4Ti was also supported on Cab‐O‐Sil, Alon C, and Mg(OH)Cl. The last support was found to give catalyst with longest lifetime with a rate of polymerization, Rp = 7.0 g/hr‐mmole Ti‐atm ethylene. 14CO counting techniques gave 1.13 × 10−3 mole of propagating center per mole of B4Ti; the rate constant of propagation, kp = 540 l./mole‐sec. None of the tetravalent titanium compounds polymerize propylene in solution. However, when supported on Mg(OH)Cl, Cab‐O‐Sil, Alon C, Cab‐O‐Ti, and charcoal, they all polymerize propylene. In this work the supports were characterized by various techniques, including the paramagnetic probe method, to determine the concentration and nature of surface hydroxyls. Those factors controlling the rate and stereospecificity of propylene polymerization were investigated. The system B3TiCl–Mg(OH)Cl–AlEt2Cl is the most active with Rp = 2.89 g/hr‐mmole Ti‐atm propylene. The concentration of propagation center is 0.9 × 10−3 mole per mole of B3TiCl; kp = 32 l./mole‐sec. This catalyst gave only about 70% stereoregular polymer. Diethyl ether is found to raise stereospecificity to 100%, but there is a concommittent tenfold decrease of activity. Other interesting catalyst systems are: (π‐C5H5)TiMe3–Mg(OH)Cl–AlEt2Cl (1.56, 89.5); (π‐C5H5)TiMe2–Mg(OH)Cl–AlEt2Cl (0.075, 94.5); and (π‐C5H5)TiMe3–Alon C–Al‐Et2Cl (0.08,97.2), where the first number in the parenthesis is Rp in g/mmole Ti‐hr‐atm and the second entry corresponds to percentage yield of stereoregular polypropylene. Hafnocene and titanocene supported on Mg(OH)Cl produce only oligomers of propylene.