Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-11-02
2002-09-03
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S158000, C522S161000, C522S114000, C522S120000, C522S122000, C522S125000, C525S244000, C525S259000, C525S261000, C525S266000, C525S284000, C525S302000
Reexamination Certificate
active
06444722
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for making graft copolymers of propylene polymer materials.
BACKGROUND OF THE INVENTION
Polyolefin graft copolymers can be made by any one of various methods, including forming active sites on the polyolefin either in the presence of the grafting monomers, or followed by treatment with the monomer. The grafting sites can be produced by treatment with a peroxide or other chemical compound that is a free radical polymerization initiator, or by irradiation with high energy ionizing radiation. The free radicals produced in the olefin polymer as a result of the chemical or irradiation treatment act as initiators for the polymerization of the monomer, as well as active sites for grafting.
For example, U.S. Pat. No. 5,411,994 discloses making polyolefin graft copolymers by irradiating olefin polymer particles and treating with a vinyl monomer in liquid form. A non-oxidizing environment is maintained throughout the process. U.S. Pat. No. 5,817,707 discloses a process for making a graft copolymer by irradiating a porous propylene polymer material in the absence of oxygen, adding a controlled amount of oxygen to produce an oxidized propylene polymer material and heating, dispersing the oxidized polymer in water in the presence of a surfactant, adding a redox initiator system, and then adding a vinyl monomer.
Various additives have been used to modify certain characteristics of graft copolymers such as the morphology of the polymer particles. For example, U.S. Pat. No. 5,916,974 discloses graft polymerizing in the presence of an organic peroxide and a polymerization rate modifier (PRM) to increase the polymerization induction time on the polymer surface, consequently facilitating monomer diffusion into the interior of the polymer particles so that surface polymerization of the monomer is inhibited. Suitable PRMs include sulfur, benzoquinone and its derivatives, and hydroxylamine and its derivatives. The PRM has no significant impact on the number average and weight average molecular weight of the product.
There is a need for a process for controlling the molecular weight of the polymerized monomer side chains of polypropylene graft copolymers made from irradiated propylene polymer materials, so that low molecular weight side chains are produced without adversely affecting the overall physical properties of the graft copolymer.
SUMMARY OF THE INVENTION The process of this invention for making graft copolymers comprises:
(1) irradiating a propylene polymer material in an environment in which the concentration of active oxygen is equal to or less than 0.004% by volume,
(2) adding a controlled amount of oxygen to the irradiated propylene polymer material so that the polymer is exposed to an amount of oxygen greater than 0.004% and less than 15% by volume at a temperature of about 40° C. to about 140° C., to produce an oxidized propylene polymer material containing greater than 1 mmol total peroxide per kilogram of propylene polymer material,
(3) optionally, heating the oxidized propylene polymer material in a substantially non-oxidizing atmosphere at a temperature of at least 80° C. but below the softening point of the polymer,
(4) treating the oxidized propylene polymer material in a substantially non-oxidizing atmosphere at a temperature of about 110° to about 140° C. with about 5 to about 240 parts per hundred parts of the propylene polymer material of at least one grafting monomer that is capable of being polymerized by free radicals to form side chains on the propylene polymer material, in the presence of about 1 part to about 10,000 parts per million parts of monomer of at least one additive to control the molecular weight of the side chains of the polymerized grafting monomer, selected from the group consisting of (a) at least one hydroxylamine derivative polymerization inhibitor and (b) at least one chain transfer agent selected from the group consisting of (i) thio-substituted aliphatic and aromatic compounds, (ii) halogen-substituted aliphatic and aromatic compounds, (iii) nitro-substituted aliphatic and aromatic compounds, and (iv) aliphatic and aromatic phosphine derivatives, and
(5) simultaneously or successively in optional order, (i) deactivating substantially all residual free radicals in the resultant grafted propylene polymer material, and (ii) removing any unreacted vinyl monomer from the material.
Carrying out the graft polymerization reaction in the presence of a hydroxylamine derivative polymerization inhibitor and/or the specified chain transfer agents produced graft copolymers with low molecular weight side chains without adversely affecting the physical properties of the graft copolymer.
DETAILED DESCRIPTION OF THE INVENTION
The propylene polymer material that is used as the backbone of the graft copolymer can be:
(1) a crystalline homopolymer of propylene having an isotactic index greater than 80, preferably about 85 to about 99;
(2) a crystalline copolymer of propylene and an olefin selected from the group consisting of ethylene and 4-10 C alpha-olefins, provided that when the olefin is ethylene, the maximum polymerized ethylene content is about 10%, preferably about 4%, and when the olefin is a 4-10 C alpha-olefin, the maximum polymerized content thereof is about 20% by weight, preferably about 16%, the copolymer having an isotactic index greater than 85; or
(3) a crystalline terpolymer of propylene and two olefins selected from the group consisting of ethylene and 4-8 C alpha-olefins, provided that the maximum polymerized 4-8 C alpha-olefin content is 20% by weight, preferably about 16%, and, when ethylene is one of the olefins, the maximum polymerized ethylene content is 5% by weight, preferably about 4%, the terpolymer having an isotactic index greater than 85.
The 4-10 C alpha-olefins that can be used when the propylene polymer material is a copolymer or terpolymer of propylene include, for example, 1-butene; isobutylene; 3-methyl-1-butene; 3,4-dimethyl-1-butene; 1-pentene; 1-hexene; 4-methyl-1-pentene; 3-methyl-1-hexene; 1-heptene; 1-octene, and 1-decene.
Propylene homopolymer is the preferred propylene polymer backbone material.
When the monomer add level is high, i.e., greater than 20 parts of monomer per hundred parts of the olefin polymer material, it is preferable for some applications to use spherical particles having a weight average diameter of about 0.4-7 mm, a surface area of at least 0.1 m
2
/g, and a pore volume fraction of at least about 0.07, and wherein more than 40% of the pores in the particle, preferably more than 50%, and most preferably more than 90%, have a diameter greater than 1 micron. The pore volume fraction is preferably at least 0.12, most preferably at least 0.20.
The propylene polymer material used as the backbone of the graft copolymer is exposed to high energy ionizing radiation in an essentially oxygen-free environment, i.e., an environment in which the active oxygen concentration is established and maintained at 0.004% by volume or less. The ionizing radiation should have sufficient energy to penetrate to the extent desired the mass of propylene polymer material being irradiated. The ionizing radiation can be of any kind, but the most practical kinds are electrons and gamma rays. Preferred are electrons beamed from an electron generator having an accelerating potential of 500-4000 kilovolts. Satisfactory results in terms of grafting level are achieved with an ionizing radiation dose of about 0.5-12 Mrad, preferably about 0.5-9 Mrad, and most preferably about 0.5 to about 4 Mrad.
The term “rad” is usually defined as that quantity of ionizing radiation that results in the absorption of 100 ergs of energy per gram of irradiated material, regardless of the source of radiation. In the usual practice of the method described herein, energy absorption from ionizing radiation is measured by the well know conventional dosimeter, a measuring device in which a strip of polymer film containing a radiation-sensitive dye is the energy absorption sensing means. Therefore the term “ra
Dang Vu A.
Song Cheng Q.
Basell Poliolefine Italia S.p.A.
Berman Susan W.
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