EFFECTS OF REGIOCHEMICAL AND STEREOCHEMICAL ERRORS ON THE COURSE OF ISOTACTIC PROPENE POLYINSERTION PROMOTED BY HOMOGENEOUS ZIEGLER-NATTA CATALYSTS

The effects of regiochemical and stereochemical errors on the kinetic course of isotactic propene polyinsertion promoted by two typical homo geneous metallocene catalysts are analyzed in detail. It is shown, in particular, that occasional regioirregular 2,1 insertions not only slo w down chain propagation to a substantial extent-as already reported i n a preliminary communication-but also practically inhibit chain trans fer to the monomer and to the aluminum alkyl cocatalyst. Active center s bearing a growing chain with a 2,1 last-inserted propene unit are th erefore trapped in a ''dormant'' state, in which the only feasible alt ernative to the formation of a sterically demanding head-to-head encha inment, at least at sufficiently high reaction temperatures, is 2,1 to 1,3 isomerization. Experimental data suggesting that chain propagatio n is hindered after a stereoirregular monomer insertion are also discu ssed.