GB941087A - Modified polypropylene and process for producing it - Google Patents

Abstract

941,087. Polypropylene block copolymers. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. Dec. 20, 1961 [Dec. 22, 1960], No. 45719/61. Drawings to Specification. Heading C3P. A modified polypropylene is made which consists of at least 90% of highly isotactic polypropylene chains uninterrupted by ethylene and having attached to the ends of at least a proportion of the polypropylene molecules a portion of ethylene-propylene copolymer, the total amount of ethylene in the polymer being in the range of 2 to 8% by weight and the proportion of ethylene in the ethylene-propylene copolymer being between 20 and 90% by weight. The modified polypropylene is made by polymerizing propylene in contact with a stereospecific polymerization catalyst until the concentration of the polymer in the reaction mixture is at least 90% of the desired final concentration, continuing polymerization in the presence of ethylene in an amount sufficient to provide the desired amount of combined ethylene in the final polymer, while maintaining the concentration of propylene in excess of that of ethylene until the latter has polymerized, then stopping the polymerization and recovering the polymer. The process may be carried out continuously in a plurality of reactors operated with a series flow of polymer from one reactor to the next, the polymerization of propylene being carried out in all but the last reactor, and in that reactor a mixture of ethylene and propylene is polymerized. The catalysts used are of the Ziegler type, e.g. titanium trichloride+aluminium diethyl chloride. The reaction is carried out in a solvent medium, e.g. heptane. Also present during polymerization may be modifiers, e.g. hydrogen, zinc diethyl, tributyl phosphite, ethyl acetate or dimethyl formamide.