Steric Composition of Polymers

The amount of amorphous polymer, which is generally produced in small percentage (9-16%) contemporaneously with the non-atactic polymer, is independent of reaction time (see Table II). It is on the contrary closely connected with the nature of the catalytic system employed and changes, for instance, when the triethylaluminum is substituted by other metal alkyls (beryllium alkyls, propylaluminum, isobutylaluminum, etc.) 5,28). It also depends on the purity of the a-titanium trichloride, in particular increasing in the presence of other crystalline modifications of titanium trichloride [i.e. -TiCU (27)] and of titanium compounds obtained by reduction of titanium tetrachloride at low temperature with aluminum alkyls. 

In the Tables V-IX we reported the percentages of the fraction of n-hep-tane insoluble polymer at room temperature and the respective intrinsic viscosities. The data concern the polymers obtained from polymerization tests carried out with triethylaluminum concentrations varying from 1.18 X 10 to 14.75 X 10 mol./l., with ratios Al/Ti between 1 and 10, with propylene concentrations included between 0.19 and 0.63 mol./l. at temperatures of 31°, 51° and 70°C. 

In a recent work (48), the influence of the variation of some factors, concerning the polymerization, on the steric composition of the polymer has been studied subjecting the obtained raw polymer to subsequent extractions with the following series of solvents employed at their boiling point ether, n-heptane and n-octane. 

We have examined polymers obtained in polymerization tests carried out at 70°C, with the following catalytic systems  

We have observed that with the decrease of the propylene partial pressure at which the polymerization is carried out, from 1600 mm. Hg to 250 mm. Hg, the percentage of each fraction of polymer extracted with the 

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