High melt strength, ethylene polymer, process for making it, and use thereof

Claim 1

Normally solid, gel-free, polymer material selected from the group consisting of erradiated high density polyethylene, and irradiated random copolymers and terpolymers of ethylene and C 3-10 alpha olefins, the ethylene content of which copolymers and terpolymers is at least about 80% by weight, the weight average molecular weight of each member of the group being at least about 50,000, and each member of the group having been made by low pressure polymerization with a Ziegler-Natta catalyst system and having acquired by the following recited process enough free-end long chain branches to cause the branching index of said member to be less than about 0.9, and to cause said member to have significant strain hardening elongational viscosity, which process comprises: (1) irradiating said ethylene polymer material while in the solid state. (a) in an environment in which the active oxygen concentration is established and maintained at less than about 15% by volume of said environment (b) with high energy ionizing radiation at a dose rate in the range from about 1 to about 10 4 megarads per minute for a period of time sufficient to provide an exposure of up to 2.0 Mrads of radiation, but insufficient to cause gelation of the material; (2) maintaining the thus irradiated material while in the solid state in such an environment for a period of time sufficient for a significant amount of free-end long chain branches to form; and (3) then treating the irradiated material while in such environment to deactivate substantially all of the free radicals present in the irradiated material.