Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Patent
1998-09-11
2000-12-19
Berman, Susan W.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
522114, C08J 324, C08J 328, C08F 246, C08F11006, C08F25502
Patent
active
061628433
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a process for crosslinking polypropylene polymers. The process employs steps of irradiation and annealing. The invention further relates to crosslinked polypropylene polymers produced by the process.
There have been earlier proposals to crosslink polypropylene polymers, by processes which employ ionizing radiation. However, there is an inherent difficulty as, in parallel with crosslinking, the backbone polymer chains are prone to degradation by ionizing radiation, this degradation being known as chain scission. The overall effect can be a substantial degradation in mechanical properties.
In Japanese Patent Application No. 74 23582 of Japan Atomic Energy Research Institute, referred to in Chemical Abstract 58944V, vol. 82, 1975, page 66, there is disclosed the crosslinking of polyolefins, using ionizing radiation in the presence of both acetylene and a chloride-containing monomer such as vinyl chloride. The process takes place at room temperature, at at least 1 atm. (10.sup.5 Pa) pressure. The radiation level is 10.sup.8 -10.sup.9 Rad., a very high level of radiation.
In U.S. Pat. No. 3,835,004 of Japan Atomic Energy Research Institute there is disclosed the crosslinking of polyolefins including polypropylene, using .gamma.-radiation in the presence of acetylene or 1,3-butadiene, and of a fluorine-containing monomer, for example tetrafluoroethylene. Use of the two crosslinking agents is said to produce polyolefins with better properties than those crosslinked with acetylene or 1,3-butadiene alone. In Example 4 of U.S. Pat. No. 3,835,004 the process as applied to high density polypropylene pellets, using both acetylene and tetrafluoroethylene, and 4.8 Mrads of .gamma.-radiation, gave a product with a gel fraction of 0.536. In comparison, use of acetylene alone gave a gel fraction of 0.474.
In U.S. Pat. No. 4,134,812 of Japan Atomic Energy Research Institute and The Furukawa Electric Co., Ltd., there is disclosed a method of manufacturing shaped articles, by blending a polyolefin with crosslinking agents, moulding to the desired shape, and crosslinking the shaped articles by irradiation, using an electron beam. The crosslinking agents, used together, are tetrakis-[methylene-(3,5-di-t-butyl-4-hydroxy-hydrocinnamate)]-methane and a compound X-Y.sub.m where X is a group free from acetylenic linkage, Y is a group containing acetylenic linkage and m is an integer of 1 or more. Preferred compounds X-Y.sub.m are dipropargyl maleate and dipropargyl succinate. Acetylene gas is said not to be possible for use, "because it is not only little miscible with a poly-.varies.-olefin due to its own gaseous condition, but also gives rise to the formation of an explosive product by reaction with heavy metals". There is one example of the invention as applied to polypropylene, Example 5. In this example a moulded polymer sheet 3 mm thick, containing 100 parts polypropylene, 5 parts tetramethylene dipropiolate and 0.5 parts of the tetrakis compound, was irradiated in the open air at a dose rate of 20 Mrads. The gel fraction of the irradiated product was 0.75.
Experiments on the irradiation of polypropylene using .gamma.-radiation are described in European Polymer Journal, 1979, vol. 15, pp. 379 to 387 (W. K. Busfield and J. H. O'Donnell). Different isotactic polypropylene film samples were irradiated in vacuo at 35.degree. C. at a range of doses, from 5 Mrads to 150 Mrads. After irradiation the samples were stored for more than 3 weeks before being opened to the atmosphere. There was a significant decrease in the tensile breaking stress and strain, attributed by the authors to fairly extensive chain scission.
Experiments on the crosslinking enhancement in polypropylene film by .gamma.-irradiation in the presence of acetylene are described in British Polymer Journal, 1986, vol. 18, No. 5 (W. K. Busfield and R. W. Appleby). Quenched and pre-annealed samples of polypropylene film were irradiated using .gamma.-radiation, at a dose rate from 5 to 40 Mrads, at 35.degree. C., in the
REFERENCES:
patent: 3414498 (1968-12-01), Shinohara et al.
patent: 3835004 (1974-09-01), Kagiya et al.
patent: 4134812 (1979-01-01), Sasaki et al.
patent: 5160464 (1992-11-01), Ward et al.
European Polymer Journal, 1979, vol. 15, pp. 379 to 387 (W.K. Busfield and J.H. O'Donnell).
British Polymer Journal, 1986, vol. 18, No. 5, pp. 340 to 344 (W.K. Busfield and R.W. Appleby).
Polymer Communications, 1986, vol. 27, pp. 45 to 46 (R.W. Appleby and W.K. Busfield).
Chemical Abstract 58944v, vol. 82, p. 66.
Fisher Harold M.
Jones Richard Albert
Ward Ian MacMillan
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