Influence of 1,3-diethers on the stereospecificity of propene polymerization by supported Ziegler-Natta catalysts. A theoretical investigation on their adsorption on (110) and (100) lateral cuts of MgCl2 platelets

Energy calculations relative to the adsorption of several substituted 1,3-d iethers on the unsatured (100) and (110) lateral cuts of MgCl2 are presente d. Independent of the particular approach used, coordination of the diether s on the (110) cut is always preferred. The energy difference favoring the diether coordination on the(110) cut depends on the substituents on carbon 2 of the 1,3-alkoxypropane skeleton. These calculated energy differences ar e able to rationalize the observed dependence on the chemical structure of the 1,3-diethers of the stereoregulating ability for propene polymerization of MgCl2/TiCl4 catalytic systems. In fact, a semiquantitative relationship has been found in the assumption that xylene-soluble (essentially atactic) and -insoluble (essentially isotactic) fractions of polypropylene obtained by these catalytic systems are prevailingly produced by Ti catalytic speci es adsorbed on (100) and (110) cuts, respectively.