LOW PRESSURE POLYETHYLENE Introduction of small amounts of higher oleflns into ethylene feed produces more flexible polymers
By incorporating minor amounts of olefins such as propylene and 1-butene into ethylene feed, copolymers can be produced. Feeds containing up to 15% of higher 1-olefins are of most interest for producing flexible, solid polymers. In general, these copolymers are more flexible than homopolymers of ethylene. Most of the copolymerization investigations were carried out in slurry-type operation. Molecular weights for ethylenepropylene copolymer (90210 weight %) are lower for the same reaction temperatures than those of ethylene homopolymers. These copolymerization runs were carried out for 4 hours a t a maximum pressure of 450 pounds/square inch gage with 0.6 weight yo of chromium oxide-silica-alumina catalyst in hydrocarbon solvent. The molecular weights of the copolymers vary from about 65,000 a t 110’ C. to 40,000 a t 132’ C. Flexibility of copolymers, as indicated by elopgation of tensile test specimens, increases with decreasing temperature of polymerization reaction.
Acknowledgment
Grateful acknowledgment is made to Phillips Petroleum Co.
for permission t o publish this work.
literature cited (1) Bailey, G. C., Reid, J. A. (to Phillips Petroleum Co.), U. S. Patents 2,581,228 (Jan. 1, 1952) and 2,606,940 (Aug.9,12, 1952).
Cheney, H. A., McAllister, S. H., Fountain, E. B., Anderson, J., Peterson, W. H., IND. ENG.CHEY.42, 2580-6 (1950). (3) Dienes, J., Klemm, H. F., J . Applied Phys. 17, 458 (1946). (4) Fawcett, E. W., Gibson, R. O., Perrin, M. W. (to Imperial Chemical Industries Ltd.), U. S.Patent 2,153,553 (April 1 1 , (2)
1939). (5) Hogan, J. P., Banks, R. L., Lanning, W. C., Clark, Alfred, IND. ENG.CHEM.47, 752-7 (1955). (6) Modern Plastics 32, No. 5, p. 71 (1955). (7) Natta, G., Corradini, P., Atti acad. nazl. Lincsi, Rend., Classe sei. fiz., mat. e nat., 18, 19-27 (1955). (8) Perrin, M. W., Paton, J. G., Williams, E. G. (to Imperial Chemical Industries Ltd.), U. S. Patent 2,188,465 (Jan. 30, 1940). (9) Peters, E. F., Evering, B. L. (to Standard Oil Co. Indiana), U. S. Patent 2,692,261 (Oct. 19, 1954). (10) Roebuck, A. K., Zlete, Alex (to Standard Oil Co. Indiana), U. S.Patent 2,692,258 (Oct. 19, 1954). (11) Ziegler, K., Angew. Chem. 64, 323 (1952). (12) Ziegler, K., Belg. Patent 533,362 (Nov. 16, 1954). (13) Ziegler, K., Brennstof-Chem. 33, 193 (1952) and 35, 321 (1954). (14) Zletz, Alex (to Standard Oil Co. Indiana), U. S.Patent 2,692,257 (Oct. 19, 1954). RECEIYED for review November 22, 1955. ACCEPTEDApril 11, 1956. Division of Petroleum Chemistry, 129th Meeting, ACS, Dallas, Tex., April 1966.
Properties of Marlex 50 Ethylene Polymer R. VERNON JONES A N D P. J. BOEKE Research Division, Phillips Petroleum Co., Barflesville, Okla.
I
MPROVEMENTS in the basic nature of ethylene polymers have recently been made. These developments, based on polymerizing ethylene a t low pressure utilizing active catalyst systems (8, 18, 25), permit a host of new ethylene polymers with a wide range of physical and chemical properties. In general, physical properties bear a direct relationship to the density of ethylene polymers (84). Certain of the important physical properties which vary with the density spectrum are illustrated in Figure 1. Basic properties such as crystallinity, rigidity, softening temperature, and tensile strength increase as the density increases. Elongation and impact strength show an inverse variation with density; however, it must be considered that these properties are also importantly dependent on chain length. The Phillips process is capable of producing a series of polymers whose properties span this density spectrum. One of the most interesting polymers of this series is a high molecular weight homopolymer of ethylene which has been designated Marlex 50 ethylene polymer. It is a tough, white, opaque, rigid material having a high melting point and density. It possesses high tensile strength and low permeability t o liquids and gases. This article describes various properties of this high density ethylene polymer. Marlex 50 polyethylene is a general-purpose resin. As such it is compared here with typical general-purpose high pressure polyethylenes of the types exemplified by the products marketed under the trade names DYNH and Alathon 10 (density 0.92 and melt index 2). These products are referred to as “conventional” polyethylenes. High pressure polyethylenes of both July 1956
lower and higher melt indexes are commercially available. The former are designed to meet the need for improved stress cracking resistance in certain uses whereas the latter are designed for improved processing characteristics and surface gloss although with some sacrifice in other physical properties. Very recently several companies have announced the availability of intermediate density ethylene polymers which, by implication, may be produced in high pressure processes. Properties of polymer suggest applications i n films, bottles, insulation, industrial moldings, etc.
Physical Properties. That the basic physical properties of this unique ethylene polymer are markedly different from the properties of conventional high pressure type polyethylene is readily apparent. Table I lists a range of some of the more important properties as compared to those for a typical high pressure resin. The physical characteristics of the Marlex 50 polymer are correlatable with the structural picture (83) as presented by infrared spectroscopy, nuclear resonance, and x-ray diffraction. Density and hardness are increased over conventional high pressure polyethylene. With greater intermolecular cohesive forces tensile strength is doubled and elongation is decreased. Impact strength is decreased; yet the notched Izod test specimens still show a typical ductile surface on fracture. Apparently, the crystalline/amorphous ratio and relaxation time prevent the polymer specimen from deforming rapidly enough to absorb the kinetic energy of the pendulum without fracture. Heat dis-
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A . TYPICAL HIGH PRESSURE POLYETHYLENE Ea. A M A R L E X COPOLYMER C . RANGE OF T Y P I C A L ZIEGLER POLYMERS D. MARLEX 50 POLYMER Figure 1.
Density spectrum of ethylene t y p e polymers
tortion temperature, deformation under load, and compressive stress (at lY0offset) are all influenced by the high crystallinity. Brittleness temperature obtained with Marlex 50 polynier was considerably lower than that u.ith high pressure polyethylene. IIigli ASTI1 SIarlex Pressure This property, as pointed out by Richards (IQ), depends on the Method 50 Polyetlij4ene molecular weight of t,he polymer. This is consistent with other Melt index i) 1238-52T 0.6-0.8 1.0-2.0 properties, such as solution viscoPity (10) and melt index, which .. 0.96 0.92 Density 412-61rr 4ooo-4500 1800-2000 also indicate a higher molecular weight for the Marlex polymer. Tensile strengtil, lb./sq, incli D 412-5lT 20-30 400-600 Comparison of physical properties suggests analogies between Elongation, % I m p a c t strength (Izod), ft. 3.0 >16 the high density polyethylenes and certain other rigid and semiD 356-472 lb./inch 140,000 25,000 rigid thermoplastic materials. Table 11 compares several such D 747-50 Stiffness, Ib./sq. inch Compressive stress ( a t 1% 2400 400-600 polymers with Marlex 50. D 695-54 offset), Ib./sq. inch Many applications, some of which are indicated in Figure 2 Deformation under load (122’ P., 100 lb./sq. in.), (title photo p. 1152) are suggested for this rigid ethylene polymer. D 621-51 0 5 It is heat, resistant, chemically resistant’, tough, abrasion reHeat % distortion temperature (68 lb./sq. in.) O F. D 648-45T 110-1 15 sistant, machineable, weldable, and it has high strength, light D 716-55T
