How Ticl3 Catalysts Control the Texture of As‐Polymerized Polypropylene

Abstract

AbstractWithin a family of catalyst systems wherein TiCl3 was made by mixing TiCl4 and aluminum alkyl solutions, the primary particles of TiCl3 were usually thin, flat polygons with average diameters ranging from 300 to 1000 A. Even in unused catalyst these primary catalyst particles were bound together into large (∼30 μ) secondary particles. A small amount of polyolefin which formed from the aluminum alkyl reducing agent aided in cementing the particles. When propylene monomer was introduced to a slurry of secondary catalyst particles in a liquid hydrocarbon, polymer formed at the surfaces of the ultimate solid particles. The resulting polymer flakes, i.e., particles of as‐polymerized polypropylene, were several times larger than the secondary catalyst particles from which they grew but they retained the same shape. The primary catalyst particles, not visibly altered by the catalytic reaction which they propagated, were distributed uniformly throughout the flake polymer. Each polymer flake consisted of many thousands of cohering roundish flakelets about a 1/2 μ in diameter. How the flakelets are agglomerated and the extent to which they are coalesced accounts for the flakes' texture. The basic morular structure of the flakes, which was manifested further by their papillary surfaces, was not altered by purification procedures which removed catalyst from the nascent polymer. Although all the flakes had the same basic small‐scale structure there were significant coarse textural dissimilarities among them. Some catalysts gave rise to flakes with an open porous texture: other catalysts gave rise to flakes which were dense and compact. In the former, the flakelets were less tightly appressed, and fissures and slits were larger and more numerous than in the latter. The genetic basis for the differences in flake texture resides in the parent catalyst. Secondary catalyst particles whose constituent primary particles are held together in a dense mass produce dense flakes. Conversely, loose aggregates of primary particles produce flakes with loosely aggregated flakelets. Briefly, dissimilarities in catalyst structure carry over to the texture of the flake progeny. Such textural differences contribute importantly to properties of the flake polymer.