Polymerization of a-Methylstyrene by Ziegler Catalyst and Properties of the Polymers Obtained

II. Relation between Molecular Weight Distribution and Mechanism of Polymerization

Abstract

Studies on the polymerization of a-methylstyrene by Al t3-Ti C14 catalytic system at various polymerization conditions, especially relation between aging conditions of catalyst and limiting viscosity number [r] of polymers obtained by the polymerization at -78°C, lead us to suppose that the two active species, i. e.(a) the intermediate complex (Ti C13) + (Al Et3 C1)- and (b) Al Et2 C1, are responsible for the polymerization in this system and the ratio of the two species vary with the progress of aging of the catalyst.
To ascertain this conjecture, the poly-a-methylstyrene samples polymerized using the catalyst aged at four different aging conditions were fractionated by column elution method and the molecular weight distributions (MWD) thus obtained were compared.
Results indicate that the MWD of polymer prepared with catalyst aged at -78°C has quite different charactristics from that of polymers obtained by the polymerization of a-methylstyrene in the presence of catalyst aged at 0°C. The MWD of the former has a peak around the MW of 5×104 and ranged only to ca. 6 x 105, whereas MW of the latter range up to ca. 2×106 irrespective of aging time. This latter is essentially the same distribution range as the sample polymerized in the presence of A1Et2 C1 only. The only difference observed within the latter samples is the shape of MWD curve, i. e. fractions of lower MW range decrease and on the contrary higher MW parts increase with the progress of aging of catalyst, indicating the increase of (b) species on the course of aging.
These two facts obtained clearly indicate the consistence of our previous supposition on active species in the course of polymerization of a-methylstyrene at -78°C in the presenceof Ziegler catalyst.