Polypropylene with free-end long chain branching, process for making it, and use thereof

Claim 2

Gel-free thermoplastic polypropylene, which has an intrinsic viscosity of at least 0.8 dl/g measured in decahydronaphthalene at 135°C, a branching index of less than 1, and which has strain hardening elongational viscosity, the branching index being defined by the equation: in which g' is the branching index,[IV]Br is the intrinsic viscosity of the gel-free polypropylene, and [IV]- Lin is the intrinsic viscosity of linear polypropylene having substantially the same weight average molecular weight as the gel-free polypropylene, and strain hardening elongational viscosity being defined as meaning that, as said gel-free polypropylene in the molten state at a test temperature is drawn at a constant rate from a fixed point, the elongational viscosity increases until breaking of the elongated melt, and said breaking is by fracture.

Claim 3

Predominantly isotactic, semi-crystalline polypropylene according to Claim 1.

Claim 4

Polypropylene according to Claim 2 in which the branching index is less than 0.9.

Claim 5

Polypropylene according to Claim 3, having an intrinsic viscosity of at least 1 dl/g measured in decahydronaphthalene at 135°C and a branching index of 0.2-0.4.

Claim 6

A continuous process for making gel-free polypropylene having strain hardening elongational viscosity from amorphous to predominantly crystalline solid polypropylene without strain hardening elongational viscosity, which comprises: (1) continuously feeding said amorphous to predominantly crystalline polypropylene (a) to an environment in which the active oxygen concentration is established and maintained at less than 15% by volume of said environment (b) and irradiating said polypropylene in said environment with high energy ionizing radiation at a dose rate from 1 to 1 x 10 4 Mrad/min (0.01 to 100 MGy/min) until substantial chain scission of the amorphous content of the polypropylene has occurred without causing gelation of the polypropylene; (2) maintaining the thus irradiated polypropylene in such an environment until significant formation of long chain branches has occurred, (3) then treating the irradiated polypropylene while in such environment to deactivate substantially all of the free radicals present in the irradiated polypropylene, and (4) continuously removing said irradiated polypropylene from said environment.

Claim 7

A continuous process for making gel-free polypropylene having strain hardening elongational viscosity from amorphous to predominantly crystalline solid polypropylene without strain hardening elongational viscosity, which comprises: (1) continuously feeding said amorphous to predominantly crystalline polypropylene (a) to an environment in which the active oxygen concentration is established and maintained at less than 15% by volume of said environment (b) and irradiating said polypropylene in said environment with high energy ionizing radiation at a dose rate from 1 to 1 x 10 4 Mrad/min (0.01 to 100 MGy/min) until substantial chain scission of the amorphous content of the polypropylene has occurred without causing gelation of the polypropylene; (2) maintaining the thus irradiated polypropylene in such an environment until significant formation of long chain branches has occurred, (3) then treating the irradiated polypropylene while in such environment to deactivate substantially all of the free radicals present in the irradiated polypropylene, and (4) continuously removing said irradiated polypropylene from said environment.

Claim 8

A process according to Claim 5 in which said amorphous to predominantly crystalline polypropylene is a gel-free, predominantly isotactic, semi-crystalline polypropylene.

Claim 9

A process according to Claim 5 or 6 in which the intrinsic viscosity of said semi-crystalline polypropylene is 1-25 dl/g.

Claim 10

A process according to Claim 6 in which the semi-crystalline polypropylene is in finely divided particle form.

Claim 11

A process according to Claim 6 in which prior to irradiation said semi-crystalline polypropylene is established and maintained in said reduced active oxygen environment.

Claim 12

A process according to any one of Claims 5 to 9 in which the active oxygen content of said environment is below 0.004% by volume.

Claim 13

A process according to any one of Claims 5 to 10 in which the high energy ionizing radiation is an electron beam delivered at a dose rate of 1 to 1 x 10 4 Mrad/min (0.01-100 MGy/min).

Claim 14

A process according to any one of Claims 5 to 11 in which the absorbed dose of high energy ionizing radiation is 1 to 9 Mrad (0.01-0.09 MGy).

Claim 15

A process according to any one of Claims 5 to 12 in which the period of time of step (2) is in the range from one minute to one hour.

Claim 16

A process according to any one of Claims 5 to 13 in which step (3) is performed by melting the irradiated polypropylene.

Claim 17

Use of a propylene polymer according to any one of claims 2 to 4 for extrusion coating of articles.

Claim 18

Use of a propylene polymer according to any one of Claims 2 to 4 for the production of propylene polymer film.

Claim 19

A melt processing method for making useful articles from a propylene polymer according to any one of Claims 2 to 4.