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.times.10.sup.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;
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- (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.sub.2 .dbd.CHR aplha-olefin, where R is a C.sub.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.sub.4-8 alpha-olefin or combination thereof in (b+c) is less than 50%;
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- (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.sub.2 .dbd.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.