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 MgCl 2 Platelets

Energy calculations relative to the adsorption of several substituted 1,3-diethers on the unsatured (100) and (110) lateral cuts of MgCl 2 are presented. Independent of the particular approach used, coordination of the diethers 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 are able to rationalize the observed dependence on the chemical structure of the 1,3-diethers of the stereoregulating ability for propene polymerization of MgCl 2 /TiCl 4 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 species adsorbed on (100) and (110) cuts, respectively.