Catalyst component for the polymerization of olefins comprising Mg, Ti and an electron donor of formula (I) ##STR00001## In which X and Y are selected from, R.sup.1, and OR.sup.1 and NR.sub.2, B is oxygen or sulphur S is sulphur, R.sup.1 is selected from C.sub.1-C.sub.15 hydrocarbon groups, optionally contain a heteroatom selected from halogen, P, S, N, O and Si, which can be fused together to form one or more cycles, R is hydrogen or R.sup.1 and A is a bivalent bridging group with chain length between the two bridging bonds being 1-10 atoms.

The present invention provides certain polymeric materials, precursors thereof as well as the preparation and uses thereof.

The present invention provides certain polymeric materials, precursors thereof as well as the preparation and uses thereof.