LOW PRESSURE POLYETHYLENE transmission, gas and liquid permeability, and improved stiffness, along with antiblocking tendency and excellent chemical resistance are of considerable interest to film extruders and converters. The film can be heat sealed by conventional equipment, and established methods for printing polyethylene film are applicable. Properties of Fiber. Polyethylenes possess certain properties such as low density, excellent chemical and electrical properties, nonabsorbency of water and mildew, microorganism and insect resistance that are desirable for filaments or fibers. The chief disadvantage which high pressure polyethylene has is its low softening temperature. Marlex 50 polymer, having a softening point some 40” F. above that for the high pressure polymer, thus becomes a candidate for an important place in the fiber field. Table X gives limited data on a monofilament made from Marlex 50 polymer and compared to literature values ( 2 1 ) for high pressure polyethylene. The over-all balance of Marlex 50 properties should permit the fabrication of many interesting textile products such as automobile interiors, curtains, furniture covers, tarpaulins, filter cloth, rugs, rope, and fish neb. Acknowledgment
The data presented here result from a cooperative program including a large segment of the Research and Development Department of Phillips Petroleum Co., and the authors are appreciative of each contribution. They especially wish to thank the individual members of the Plastics Group for their excellent cooperation in the fabrication and evaluation of samples and Phillips Petroleum Co. for permission to publish this report. literature cited (1) Ballantine, D., others, J . Polymer Sci. 13, 410 (1954). (2) Bockhoff, F. J., Neumann, J. A., SOC.Plastics Engrs. 10,;“io. 5 , 17-19 (1954).
(3) Boyp, C. D., Sisman, D., Oak Ridge National Laboratory, Rept. 1373, June 1953. (4)
Brubaker, D. W., Kammermeyer, Karl, IND.EXG.CHEM.45, 1148 (1953).
(5) Carey, R. H., A S T M Bull. 167, 56 (July 1950). (6) Carey, R. H., Soc. Plastics Engrs. 10, 16-21 (1954). (7) Charlesby, A., Proc. Roy. SOC.(London) 215A, 187 (1952). (8) Clark, Alfred, Hogan, J. P., Banks, R. L., Lanning, W. C., IND. ENQ.CHEM.,48, 1152 (1956). (9) De Coste, J. B., Malm, F. S., Wallder, V. T., Ibid., 43, 117-21 (1951). (10) Dienes, G. J., Klemm, H. F., J . AppZiedPhys. 17, 458 (1946). (11) Dow Chemical Co., Midland, Mich., “Vinylidine Chloride Polymers,” 1942. (12) Dreisbach, R. R., “Physical Properties of Chemical Substances,” vol. 11, Dow Chemical Co., Midland, Mich., 1953. (13) Jones, R. Vernon, Moberly, C. Wayne, Reynolds, W. B., ISD. ENG.CHEM.45, 1117 (1953). (14) Manufacturing Chemists’ Assoc., Washington, D. C., “Technical Data on Plastics,” 1952. (15) Modern Plastics Encyclopedia, vol. 32, NOIA, Plastics Proper: ties Chart, Breskin, Bristol, Conn., 1954. (16) National Bureau of Standards, Washington 25, D. C., Circ. 525, 1953. (17) Parliman., J. H., Modern Packaging 21, No. 11, 198-20, 2402 (1948). (18) Phillips Petroleum Co. Belg. Patent 530,617 (July 22, 1954): (19) Richards, R. B., J . Applied Chem. (London) 1 , 370 (1951). (20) Schmidt, Alois X., Marlies, Charles A., “Principles of High Polymer Theory and Practice,” p. 436, 3IcGraw-Hill, New York, 1948. (21) Sherman, Joseph V., Sherman, Signe Lidfeldt, “The S e w Fibers,” p. 135, Van Nostrand, New York, 1946. (22) Sisman, D., Boyp, C. D., Oak Ridge National Laboratory, 928, June 1951. (23) Smith, D. C., IND. ENG.CHEM.48, 1161 (1956). (24) Sperati, C. A., Franta, W. A., Starkweather, H. W., J . Am. Chem. SOC.75, 6127 (1953). (25) Ziegler, Karl, Belg. Patent 533,362 (Xov. 16, 1954). Received for review November 22, 1955. ACCEPTED dpril 11, 1956. Division of Petroleum Chemistry, 129th Meeting, ACS, Dallas, Tex., April 1956.
Molecular Structure of Marlex Polymers D. C. SMITH Research Division, Phillips Petroleum Co., Bartlesville, Okla.
T
HE possibility of computing all the gross physical properties of a polymer of known composition from a complete knowledge of its molecular and microstructure constitutes a real challenge to polymer chemists and physicists. For with this ability and the aid of mechanized computing they could predict the properties of hypothetical polymers and thus greatly facilitate the search for better polymeric materials. Polyethylene is of considerable interest in this connection because of its structural simplicity, it being generally regarded as structurally similar to normal paraffin hydrocarbons. The fact that polyethylenes prepared by the Xarlex process described in two accompanying articles ( 1 , 2 )have properties differing markedly from those of conventional polyethylenes indicates that relatively small structural differences are of practical importance. This has prompted us to make structural studies on a rather large number of polyethylenes and related olefin polymers. These studies have been based largely on infrared spectroscopy, nuclear resonance, and x-ray diffraction, supplemented by work on polymer solutions. This report presents data on a few typical polymers and summarizes some of the initial results. A more complete account of each phase of the work is planned for subsequent reports. July 1956
Marlex 50 is unique among all synthetic olefin polymers so far examined in ow laboratories in that it possesses a remarkably high degree of structural simplicity and homogeneity. All of the data obtained to date indicate that it consists mainly of unbranched polymethylene chains that terminate a t one end in a vinyl group and a t the other end in a methyl group. This simple structure, which is that of a normal 1-olefin hydrocarbon, evidently results from a combination of a specific catalytic effect and mild polymerization conditions, such as are employed in the Marlex process. As is to be expected of a polymer composed of molecules having such high structural homogeneity, it is highly crystalline and correspondingly dense. Polyethylenes prepared under more severe conditions, such as in the high pressure systems, have less structural homogeneity in that they contain either alkyl branches or branched vinyl structures, or both. These structures, and perhaps also the transolefin groups, break the regularity of the chain and prevent spatial ordering of the molecules, thus leading to polymers of lower crystallinity and lower density. Less homogeneous polymeric structures, in which both the length and number of branches can be controlled, can also bp obtained by copolymerizing ethylene and higher olefins by the
INDUSTRIAL AND ENGINEERING CHEMISTRY
1161
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT hlarlex process. Preliminary results indicate that incorporation of 21 methyl branches per thousand carbons in a propyleneethylene copolymer (6.25 weight yo propylene) lowers the crystallinity by approximately 20y0. Similarly, incorporation of 14 ethyl branches per thousand carbons in a copolymer of 1-butene and ethylene (corresponding to 5.6 weight yo 1-butene) also lowers the crystallinity by about 20%. This suggests that one ethyl branch is equivalent to about 1.5 methyl branches in so far as lowering of crystallinity is concerned. Additional data are required to verify this conclusion.
Unsaturation pattern points up differences in polymers made by different processes
Figure 1 shows portions of the infrared spectra of a conventional commercial polyethylene (DYNH) made by a high pressure process, a new commercial polyethylene (Super Dylan) presumably made by the Ziegler process ( 6 ) , the new Phillips polyethylene Marlex 50, and txyo experimental olefin copolymers made
WAVE NUMBER cm-l
5000 100 I
2000
1000
700
I
I
I
50 -
A- TYPICAL HIGH-PRESSURE POLYETHYLENE (DYNHI
100
t
by the Marlex process. Pressed films of the polymers and a Perkin-Elmer Model 21 spectrometer rrere used. Like most infrared spectra, the Epectra s h o r n are rich in structural information, enough of which can be extracted to give a general quantitative picture of the structural differences among these polymers. The more conspicuous real differencesin the spectra of the homopolymers-Le., those not resulting from differences in film thickness-are due to diff erences in the type of unsaturation present Terminal vinyl groups absorb near 10.1 and 11.0 microns, branched vinyl near 11.25 microns, and internal transolefinic double bonds a t 10.35 microns. Table I gives the total number of these structures per thousand carbon atoms of sample and also relative concentrations for the polymers represented in Figure 1 and for two additional Marlex copolymer samples (designated A and C). The internal cis-olefin structure, if present, is too dilute for quantitative measurement and has not been included in the tabulation. It ordinarily absorbs near 14.5 microns and a t 6.05 microns, but there is no definite evidence of a band a t the former position, and the absorption a t the latter appears to be adequately accounted for by the other olefin structures (vinyls) which are known to be present and absorb a t that position. The unsaturation pattern often forms an effective basis for characterizing polymers prepared by different procewes. Thua, conventional polyethylenes prepared by the IC1 high pressure process have olefin structures that are predominantly of the branched vinyl type, accounting for about 70 to 9570 of the double bonds present. Marlex 50, on the other hand, has mainly terminal vinyls with only a few per cent of trans structures and essentially no branched vinyls. The unsaturation in polyethylenes prepared by the Ziegler process is somediat variable and intermediate betm-een those of the IC1 and the Marlex polyethylenes, both in total amount and in distribution between terminal and branched vinyls. However, Ziegler polyethylenes usually have greater amounts (20 to 40%) in internal trans configurations. Experimental Marlex copolymers of ethylene with either propylene or 1-butene have sho~vnless total unsaturation than Marlex 50, with relatively f e m r terminal vinyl structures and correspondingly more branched vinyl structures. Only in copolymer D, which contains higher 1-butene content, has any evidence of significant trans olefin structure been found in Marlex polymers, and this result is somewhat uncertain because of the possibility of interference from nonolefinic structures in the infrared measurements on this particular polymer. The total unsaturation in these ethylene polymers is very low, ranging from 0.5 to 1.5 double bonds per thousand carbon atoms, but it may have some importance for chemical characteristics such as aging and susceptibility to certain cross-linking reactions which, in turn, might produce significant changes in properties.
Table 1. D - MARLEX COPOLYMER
0 100
Unsaturation Distribution, 70 H R‘ H RY Double \ \ Bonds/1000 ‘C=CH* c=c / Carbon / Atoms R R/C=CHn R/ \H
PROPYLENE-ETHYLENE
t DYh-H Super Dylan Marlex 50
50
0 2
5
IO WAVELENGTH IN MICRONS
Figure 1.
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Unsaturation of Olefin Polymers
0.6 0.7 1.5
15 43 94
68 32 1
17 25 5
15 1-Butene-ethylene
Infrared spectra of olefin polymers-solid films
INDUSTRIAL AND ENGINEERING CHEMISTRY
