United States Patent [19]
Collette et al.
[ii] 4,335,225 [45] Jun. 15,1982
[54] ELASTOMERIC POLYPROPYLENE
[75] Inventors: John W. Collette, Wilmington, Del;
Charles W. Tullock, Landenburg, Pa.
[73] Assignee: E. I. Du Pont de Nemours and Company, Wilmington, Del.
[21] Appl. No.: 240,138
[22] Filed: Mar. 3, 1981
Related U.S. Application Data
[63] Continuation of Ser. No. 917,282, Jun. 20, 1978, abandoned, which is a continuation-in-part of Ser. No. 814,878, Jul. 12, 1977, abandoned.
[51] Int. C1.3 C08F 10/06
[52] U.S. CI 525/240; 526/154;
526/348; 526/348.2; 526/348.3; 526/348.4; 526/348.5; 526/348.6; 526/351; 526/905
[58] Field of Search 525/240; 526/351, 348,
526/348.2, 348.3, 348.4, 348.5, 348.6
[56] References Cited
U.S. PATENT DOCUMENTS
3,112,301 11/1963 Nattaetal 526/351
3,175,999 3/1965 Natta et al 526/351
3,257,370 6/1966 Nattaetal 526/351
3,329,741 7/1967 Schrage et al 526/351
3,511,824 5/1970 Listner 526/351
3,784,502 1/1974 Gobran et al 260/33.6 PQ
3,932,307 1/1976 Setterquist 526/351
3,950,269 4/1976 Setterquist 526/351
FOREIGN PATENT DOCUMENTS
2653379 6/1977 Fed. Rep. of Germany .
1138290 6/1957 France .
44-6827 3/1969 Japan .
856736 12/1960 United Kingdom 526/348
OTHER PUBLICATIONS
Kinsinger et al., Journal of Physical Chemistry, vol. 63, (1959), pp. 2002-2007.
Raff et al., Crystalline Olefin Polymers, Part I, vol. XX, Intersciences Publ., N.Y., (1965), pp. 376, 712-715.
Primary Examiner—Edward J. Smith
[57] ABSTRACT
A fractionable elastic polypropylene which has an inherent viscosity of 1.5-9, exhibits no yield point, has a tensile set not exceeding 150% and contains about 10 to 80% by weight of a diethyl ether-soluble fraction having an inherent viscosity exceeding 1.50. This polypropylene is a direct reaction product and thus need not be separated into its component parts to be a useful elastomer. Also described is the diethyl ether-soluble polypropylene fraction of the direct reaction product which has about 0.5% to about 5% isotactic crystallinity and exhibits birefringence when a film formed from said fraction is viewed under crossed Nicol prisms in a polarizing microscope at about 25° C. or is stretched between crossed polarizing sheets at about 25° C. The diethyl ether-soluble fraction itself is a useful elastomeric material.
15 Claims, 1 Drawing Figure
ELASTOMERIC POLYPROPYLENE
CROSS-REFERENCE TO RELATED
APPLICATION 5
This is a continuation of application Ser. No. 917,282, filed June 20, 1978, which is a continuation-in-part of application Ser. No. 814,878, filed July 12, 1977, both abandoned.
BACKGROUND OF THE INVENTION
This invention relates to elastic polymer consisting essentially of units derived from propylene.
Both crystalline and amorphous polypropylenes are ^ well known. Crystalline polypropylene is generally regarded as consisting at least prevailingly of the isotactic or syndiotactic structure and amorphous polypropylene is generally regarded as consisting at least prevailingly of the atactic structure. U.S. Pat. Nos. 2„ 3,112,300 and 3,112,301, both to Natta et al., describe isotactic and prevailingly isotactic polypropylene, respectively. Structural formulae for isotactic and syndiotactic polypropylene are given in U.S. Pat. No. 3,511,824 to Listner. "Atactic" polypropylene is de- 25 fined as polypropylene in which the substituent methyl groups are arranged randomly above and below the backbone chain of atoms when the latter are all in the same place.
Most commercial grades of polypropylene are highly -jq crystalline and, as is well known, are used in the manufacture of plastic products. Amorphous polypropylenes are also available commercially and are generally gummy materials of little strength. The amorphous polypropylenes are usually present as a small fraction in 35 prevailingly isotactic polypropylene and can be readily extracted. They are normally used in adhesive applications.
Rubbery polypropylenes are also known. Such products have been said to be produced directly by conven- 40 tional polymerization using particular catalysts, by repeated extractions of conventional polypropylene, by chemical treatment of crystalline polypropylene and by sequential polymerization, processes. Representative rubbery polypropylenes are described in U.S. Pat. Nos. 45 3,329,741 to Schrage et al., 3,175,999 to Natta et al., 3,511,824 to Listner and 3,784,502 to Gobran et al. Such polypropylenes, however, have not found significant use in products requiring an elastic polymer.
There is a need, therefore, for a polypropylene with 50 practical elastic properties that can be produced as a direct reaction product by a practical process.
SUMMARY OF THE INVENTION
This invention provides a fractionable, elastic poly- 55 mer consisting essentially of units derived from propylene which has an inherent viscosity of 1.5-9, exhibits no yield point, has a tensile set not exceeding 150% and contains about 10-80% by weight of a diethyl ethersoluble fraction which has an inherent viscosity exceed- 60 ing 1.50 and an isotactic crystalline content of about 0.5 to about 5% by weight and exhibits birefringence when a film formed from the fraction is viewed under crossed Nicol prisms in a polarizing microscope at about 25° C. or is stretched between crossed polarizing sheets at 25° 65 C.
Also included in this invention is the diethyl ethersoluble polypropylene itself.
DESCRIPTION OF THE INVENTION
In one embodiment, this invention provides an elastic, fractionable product in which the "whole polymer", i.e., the direct reaction product itself without separation of any polypropylene components, is elastic, exhibiting properties similar to a vulcanized rubber. This result is achieved without sequential polymerization in which reaction conditions or proportions of monomers are varied during polymerization to produce alternating "blocks" in the polymer structure.
By "fractionable" is meant that the product is nonhomogenous and thus consists essentially of two or more fractions which are readily separable by extraction with solvents such as diethyl ether and hexane. The whole polymers thus consist essentially of about 10-80 weight percent (preferably 40-75%) of diethyl ethersoluble fraction and varying proportions of other fractions, typically about 10-35 weight percent of a fraction soluble in boiling hexane but insoluble in boiling diethyl ether and about 10-55% of a fraction insoluble in boiling hexane.
The diethyl ether-soluble fraction itself is another embodiment of this invention.
"Diethyl ether-soluble" content or "ether-soluble" content as used herein with respect to a polypropylene is determined in boiling diethyl ether by the procedure described hereinafter under "Analytical Methods".
The measure of elasticity used in describing the polypropylenes of this invention is "tensile set" which is defined as the elongation remaining in a compressionmolded specimen after it has been stretched at a rate of 20 inches (51 cm) per minute to 300% elongation at 72°-75° F. (22°-24° C), then immediately allowed to recover at the same rate until the specimen is at zero stress. It is expressed as a percentage of the original length or distance between bench marks. The whole polymers and the preferred diethyl ether-soluble polypropylenes of this invention have a tensile set not exceeding 150% and preferably not exceeding 100%. Some samples have a tensile set of 75% or less.
The whole polymers of this invention do not exhibit a yield point. "Yield point" as used herein means that in the test of ASTM method D412 conducted to break at 20 inches (51 cm) per minute and 25° C. there is a strain (or elongation) value at which the stress (force) required to further increase the elongation decreases.
All tensile and stress-strain measurements referred to herein, including the examples, are carried out on straight or dumbbell specimens 0.25 inch (0.64 cm) wide and 0.018-0.080 inch (0.045-0.20 cm) thick by ASTM Method D 412, with the exception that where averages are specified, two samples of the product are tested.
The attached figure shows a stress-strain (hysteresis) curve of a typical polymer of this invention (the polymer of Example 1) in comparison with a prior art highly isotactic polypropylene, "Pro-fax" 6523 sold by Hercules, Inc., (isotactic content 94%). The polymer of Example 1 has a tensile set of 93% at the stretch rate of 20 inches/minutes (51 cm/min) and relaxation at the same rate. It shows no yield point. The isotactic polypropylene has a tensile set of 300% (i.e., shows no recovery) and does show a yield point at about 15% elongation at a stretch rate of 0.2 inch per minute (0.5 cm/min) and relaxation rate of 20 inches/minute (51 cm/min).
The whole polymers of this invention have an inherent viscosity of 1.5-9, preferably 3-8, and the diethyl ether-soluble fraction has an inherent viscosity greater
than 1.5, and preferably greater than 2.5. Inherent viscosity as used herein is measured in decahydronaphthalene at 135° C. by the procedure described under "Analytical Methods" hereinafter. It is expressed in deciliters per gram (dl/g). The polypropylenes of this invention 5 become increasingly elastic with increasing content and increasing inherent viscosity of the ether-soluble fraction. Birefringence is clearly visible when a film formed by pressing a sample of the ether-soluble fraction between microscope slides is viewed under crossed Nicol 10 prisms in a hot-stage polarizing microscope at about 25° C. When the temperature is raised the birefringence disappears in the region of the melting point of the film. Birefringence is also clearly visible when a film formed from the ether-soluble fraction is pressed or stretched 15 between crossed polarizing sheets at a temperature of about 25° C.
The whole polymers have an isotactic content of 55% or less and preferably about 25-45%. By "isotactic content" is meant the proportion of polymerized propy- 20 lene units which occur in chain segments in which five successive polymerized propylene units have an identical steric configuration. Thus a polypropylene in which 45% of the polymerized propylene units are contained in segments of five or more successive polymerized 25 propylene units, each such unit having the same steric configuration, has an isotactic content of 45%. Isotactic content as reported herein can be measured directly by 13c nuclear magnetic resonance (NMR) according to methods known in the art, a suitable example of which 30 is described under "Analytical Methods" hereinafter. For a given isotactic content, the polymers of this invention are highly elastic as shown by their tensile set and absence of yield point.
The whole polymers also have syndiotactic contents. 35 By "syndiotactic content" is meant that part of the polymerized propylene in which the methyl groups lie alternately above and below the plane of the main chain. Syndiotactic content also can be measured directly by 13c nmr. 40
The whole polymers have a tensile strength in the range from about 400 psi to 2500 psi (28 kg/cm2 to 175 kg/cm2) as determined by ASTM Method D 412; the ether-soluble fractions have tensile strengths from about 100 psi (7 kg/cm2) to 600 psi (42 kg/cm2). 45
Each whole polymer has a major melting point between about 135°-155° C. as determined by the method described under "Analytical Methods" hereinafter.
The diethyl ether-soluble fractions of the new elastic polypropylenes have properties that distinguish them 50 from solvent-extracted fractions of polypropylenes of the art. For example, they have relatively broad molecular-weight distributions, as indicated by relatively high values of the ratio Mw/M„, where Mw is weight-average molecular weight and M„ is number- 55 average molecular weight. See Billmeyer, "Textbook of Polymer Science", pp 6-7 (Interscience/Wiley, 1962). The ratio Mw/M„ is referred to herein as dispersity. It is determined by gel permeation chromatography (gpc).
The diethyl ether-soluble fractions also have rela- 60 tively high inherent viscosities in relation to the inherent viscosities of the corresponding whole polymers! The ratio of the inherent viscosity of the ether-soluble fraction to the inherent viscosity of the whole polymer is usually in the range 0.5-0.9. 65
In addition the diethyl etherrsoluble fractions have isotactic crystalline contents from about 0.5 to about 5% by weight. Crystalline content is strongly suggested
by birefringence, and is demonstrated by and determined from heat of fusion (Ahf) and 13C nmr. The I3C nmr data show that the crystallinity of these fractions is isotactic. The techniques for determining the abovementioned properties are discussed under "Analytical Methods" hereinafter.
The foregoing discussion of properties of the ethersoluble fractions applies in particular to the ether-soluble fractions of whole polymers that have been isolated from the polymerization mixture by methods that do not involve hot melting or extrusion. Generally, such whole polymers as isolated from the reaction show a higher percentage of ether-extractable components, i.e., about 30-80%, than after hot melting, extrusion, or other fabrication techniques. The decrease is believed to be due to interaction of the ether-soluble fraction with more-highly crystalline components in the product.
The high molecular weight, diethyl ether-soluble component is the key factor contributing to the elastic properties of the polymers of the invention. In this regard, the polymers differ from those of the prior art, in which elastomeric properties are limited to the fraction soluble in hexane. The ether-soluble fraction of the polymers of the invention is highly elastic but generally has low tensile strength. It may be combined with more crystalline polypropylenes (i.e., those of higher isotactic content) to provide elastomeric materials with muchimproved tensile strength. It is believed that the isotactic units in the more crystalline polypropylene cocrystallize with the isotactic units in the ether-soluble component to provide a crosslinked elastomeric network.
The polypropylenes of this invention can be prepared by polymerizing propylene in the presence of a catalyst which is the reaction product of an organometallic compound with a partially hydrated surface of a metal oxide such as AI2O3, Ti02, SiC>2, and MgO or physical mixtures thereof. The organometallic compounds are those of the formula ... where M is Ti, Zr or Hf; R is aryl, aralkyl, tertiary alkyl, (e.g., trialkylmethyl), or trialkylsilyl; and the RCH2 group has no hydrogen bonded to the atom in the beta-position to M. The aforementioned alkyl groups can contain from 1-12 carbon atoms.
Typically, the two catalyst components are reacted in the ratio of 0.01-1.0 millimole of the organometallic compound per gram of metal oxide. The preferred catalysts are those resulting from the reaction of organozirconium compounds ... especially tetrarieophylzirconium (TNZ), with hydroxylated alumina (Al2O3) in the ratio of about 0.1-1.0 millimole of organozirconium compound per gram of alumina. Such catalysts and their preparation are described in U.S. Pat. No. 3,932,307 to Setterquist. Preferably, the hydroxylated alumina is prepared by allowing fumed alumina to equilibrate with and thereby adsorb atmospheric moisture followed by heating at about 120°-500° C. for 1 min-10 hrs in a stream of nitrogen. Suitable catalysts also include the reaction product of other organometallic compounds as described above with the aforementioned metal oxides, said catalysts being prepared in the same manner as the preferred "neophylzirconium aluminate on alumina" catalyst described above. Representative organometallic compounds include tetraneopentylzirconium, tetrabenzyltitanium, tetrabenzylzirconium, tetraneopentylhafnium, tetrabenzylhafnium, tetrakis(trimethylsilylmethyl)zirconium, tetraneophyltitanium and tetraneopentyltitanium.
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