Polymerisation and structure–property relationships of Ziegler–Natta catalysed isotactic polypropylenes

Polypropylene homopolymer samples were prepared with a Ziegler–Natta catalyst using two different external donors, namely diphenyldimethoxysilane (DPDMS), and methylphenyldimethoxysilane (MPDMS). Each donor was used in varying molar ratios to the catalyst in order to prepare samples for physical testing. The polymers were fully characterised and also fractionated by preparative TREF with characterisation of the fractions. In terms of the polymerisation reactions the DPDMS external donor exerts greater influence at the active sites than the MPDMS and produces polymer of higher molar mass and lower polydispersity. The physical properties of the polymers were investigated using microhardness measurements. It is revealed that the microhardness is strongly dependent on the stereoregularity of the samples.