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

Claim 1

A process for making normally solid, high molecular weight, non-linear, substantially gel-free, propylene polymer material with strain hardening elongational viscosity from normally solid, high molecular weight, linear propylene polymer material without strain in harding elongational viscosity, which comprises: (1) irradiating said linear propylene polymer material: (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 1×10 4 megrads per minute for a period of time sufficient for a substantial amount of chain scission of the amorphous content of said material to occur, but insufficient to cause gelation of the material; (2) maintaining the thus irradiated material in such an environment for a period of up to one hour; and (3) then treating the irradiate material while in such environment to deactivate substantially all of the free radicals present in the irradiated material, wherein said normally slid, high molecular weight, non-linear, substantially gel-free propylene polymer material is selected from the group consisting of: (I) a propylene polymer composition consisting essentially of: (a) from 10 to 50% of a propylene homopolymer having an isotactic index of from 80 to 99%, or a copolymer a selected from the group consisting of (i) propylene and ethylene, (ii) propylene, ethylene and a CH 2 ═CHR aplha-olefin, where R is a C 2-8 straight or branched alkyl, and (iii) propylene and an alpha-olefin, as defined above in (a)(ii), wherein said copolymer contains from 85 to 99% propylene and having an isotactic index greater than 80 to 99%, (b) from 5 to 20% of a semi-crystalline, essentially linear copolymer having a crystallinity of about 20 to 60%, by differential scanning calorimetry (DSC), wherein the copolymer is selected from the group consisting of (i) ethylene and propylene containing over 55% ethylene; (ii) ethylene, propylene, and an alpha-olefin, as defined above in (a)(ii), containing from 1 to 10% of the alpha-olefin and over 55% up to 98% of both ethylene and alpha-olefin; and (iii) ethylene and an alpha-olefin, as defined in (a)(ii), containing over 55% up to 98% of said alpha-olefin, which copolymer is insoluble in xylene at room or ambient temperature, and (c) from 40 to 80% of a copolymer selected from the group consisting of a copolymer of (i) ethylene and propylene wherein the copolymer contains from 20% to less than 40% ethylene; (ii) ethylene, propylene, and an alpha-olefin, as defined in (a)(ii), wherein the alpha-olefin is present in an amount of from 1 to 10% and the amount of ethylene and alphaolefin present is from 20% to less than 40%; and (iii) ethylene and an alpha-olefin, as defined in (a)(ii), containing from 20 to less than 40% of the alpha-olefin, and optionally containing 0.5 to 10% of a diene, said copolymer I(c) being soluble in xylene at ambient temperature, and having an intrinsic viscosity of from 1.7 to 3.0 dl/g, wherein the total amount of ethylene units or said alpha-olefin units or of ethylene and said alpha-olefin units when both are present in the composition is from 15 to 35%, and the total content of ethylene or C 4-8 alpha-olefin or combination thereof in (b+c) is less than 50%; and (II) a propylene polymer composition consisting essentially of: (a) 10-60 parts by weight of homopolymer polypropylene having an isotactic index greater than 90 to 99%, or of crystalline propylene copolymer with ethylene, with a CH 2 ═CHR olefin where R is a 2-6 carbon alkyl radical, or combinations thereof, containing over 85% by weight of propylene and having an isotactic index greater than 85 to 94%; (b) 8-40 parts by weight of a crystalline copolymer containing ethylene and propylene, having an ethylene content greater than 50% and insoluble in xylene at room temperature; (c) 30-60 parts by weight of an amorphous ethylene-propylene copolymer containing optionally small proportions of a diene, soluble in xylene at room temperature and containing 40 to 70% by weight ethylene.