Process for the preparation of crystalline vinylaromatic polymers with a predominantly syndiotactic structure

Process for the preparation of crystalline vinylaromatic polymers with a predominantly syndiotactic structure which comprises polymerizing a vinyl-aromatic monomer, either alone or mixed with at least one other copolymenizable ethylenically unsaturated monomer, in the presence of a catalytic system consisting essentially of:

• a) a complex of titanium having the formula (I)
• Ti (OCONRR').sub.n (I)
• wherein R and R', being the same or different, represent a C.sub.1 -C.sub.12 aliphatic radical or C.sub.6 -C.sub.20 aromatic radical;
• and wherein n is an integer equal to 3 or 4;
• b) a cocatalyst selected from aluminoxane and a compound of boron having formula (II):
• BX.sub.1 X.sub.2 X.sub.3 (II)
• or one of its salts, wherein X.sub.1, X.sub.2 and X.sub.3, being the same or different, represent a C.sub.1 -C.sub.20 perfluorinated hydrocarbon radical.