Abstract: A process for producing a polyethylene material for use in products requiring high mechanical strength and high elastic modulus is disclosed. The process involves the use of a specific class of particulate polyethylenes having an intrinsic viscosity of 5-50 dl/g in decalin at 135.degree. C. and the steps of compression molding, solvent immersing, solid-phase extruding or rolling and finally drawing the material in that order.

Abstract: A process for the production of polyethylene materials oriented at a high level is disclosed in which a selected ethylene polymer as produced is extruded or rolled at a temperature lower than its melting point and subsequently subjected to stretching. The polymer is from 5 to 50 dl/g at 135.degree. C. in decalin in intrinsic viscosity and smaller than 60 .ANG. in crystal size on a plane (110) in the diffraction pattern.

Abstract: A process for producing polyethylene materials in which ultrahigh molecular polyethylene is molded by compression, extrusion or rolling and stretching in a solid phase and at specified temperatures. The polymer is formed by a selected multi-stage polymerization with the use of a composite catalyst of specified compositions. Fibers or films are obtained with improved strength and modulus qualities.

Abstract: Provided is an olefin-polymerization catalyst comprising the combination of the following components [I] and [II]:[I] a solid component obtained by intercontacting and reacting the following components (1) through (4):(1) a compound obtained by treating an oxide of an element of Groups II-IV in the Periodic Table with a compound represented by the general formula R.sup.1.sub.m Si(OR.sup.2).sub.n.sup.X.sub.4-m-n wherein R.sup.1 and R.sup.2 are each a hydrocarbon radical having 1 to 24 carbon atoms, a hydrocarbon radical containing oxygen, sulfur or nitrogen, or hydrogen, X is a halogen atom, m is 0.ltoreq.m<4 and n is 0.ltoreq.n.ltoreq.4, provided 0.ltoreq.m+n.ltoreq.4,(2) a reaction product obtained by the reaction of a magnesium halide and a compound represented by the general formula Me(OR.sup.3).sub.n.sup.X.sub.z-n wherein Me is an element of Groups I-VIII in the Periodic Table, with the limitation that silicon, titanium and vanadium are excluded, R.sup.