Improvements in the production of solid propylene polymers

Propylene is polymerized in an inert liquid reaction medium using as catalyst an anhydrous chloride of samarium and an aluminium trialkyl, the alkyl groups containing 1 to 8 carbon atoms. The reaction medium is preferably a hydrocarbon, e.g. cyclohexane. Propylene partial pressures of 1-21 kg./cm2. or higher and reaction temperatures of 20 DEG -120 DEG C. are used and the polypropylene produced is mainly isotactic and has a melting point of about 160 DEG -165 DEG C. and a density of about 0,9 g./c.c. Generally 0,01 to 1 gram of catalyst is used per gram of propylene and mole ratios of anhydrous samarium chloride to aluminium trialkyl may be from 1:1 to 1:10.