Propylene]-ethylene] copolymers - obtd. by polymerisation of propylene using ziegler catalyst, followed by polymerisation of propylene-ethylene mixt. with same catalyst

摘要

Propylene-ethylene copolymers (I) are claimed; (I) are obtd. by 2-stage, gas-phase polymerisation in an agitated solid bed, with a Ziegler-Natta catalyst system contg. Ti-contg. solid components and Al cpd. as co-catalyst; process comprises (i) polymerisation of propylene at 20-40 bar, 60-90 deg.C and a residence time of 1-5 hrs., to give 0.05-2 kg PP/mmol Al cpd., then (ii) polymerisation of a mixt. of propylene and ethylene (ratio of partial pressures P:E = (0.5:1):(5:11) at 5-30 bar (at least 7 bar below the pressure in stage (i), 30-100 deg.C and a residence time of 1-5 hrs.; (a) the wt. ratio between the monomers reacted in stages (i) and (ii) is (2.5:1)-(20:1), or (b) (ii) polymerisation is carried out in the presence of a 1-8C alkanol (II), in which case the above wt. ratio (1:1)-(20:1). The above process is claimed as such. Pref., (II) is a 1-4C alkanol. USE/ADVANTAGE - Useful for the prodn. of film, tubing, coatings, fibre, hollow mouldings, injection moulded articles and moulded pts. for vehicles. Film and moulded prods. produced from (I) are claimed as such. Provides EP copolymers (I) with good rigidity, improved free flowing properties, a satisfactory level of notch impact strength, high bulk density and a low content of catalyst residues.