CA1282546C - Propylene polymers - Google Patents

Abstract

NOVEL PROPYLENE POLYMERS

ABSTRACT

Novel, substantially amorphous interpolymers of propylene, ethylene and optionally a third alpha-olefin comonomer having between 4 and 8 carbon atoms per molecule are disclosed. The polymers have properties which make them applicable for use, e.g., as hot melt adhesives and as blending components in roofing materials.

Description

1~32546 BACKGROUND OF THE INVENTION
In the manufacture of propylene homopolymers and copolymers, conventional polymerization techniques using unsupported catalyst result in the simultaneous production of substantial quantities of atac~ic polymer in addition to the desired product of high crystal-linity and isotacticity. Various methods have been employed for the purification and separation of these two polymers. The by-product, i.e. the atactic polymer of low crystallinity is being b utilized commercially as a component in various adhesive composi-tion~, roofing materials, caulking compounds, etc.
Recently, developments have been made of new catalysts which are highly active and more stereospecific than the afore-mentioned conventional catalysts. The proportion o~ atactic polymer in the polymers produced employing these catalysts are substantially re-duced and therefore the polymer product generally does not require any pur~ication for removal of the atactic or low crystalline polymer. Because of the rapid adaptation of existlng polymer facilities to the use of these new catalysts, there has been O generated a serious shoxtage of low crystalline, atactic polymers.

;~

lZ~3~546 It is therefore an object of the present irvention to provide a no~el, substantially amorphous polymer of propylene and ethylene It is another object of the present invention t^ provide a llnovel amorphous polymer of propylene and ethylene, having improved 1¦ physical properties.
11l THE FIGURES
Figures lA and lB are comparative hot stage micrographs of two different polymers and Figures 2A and 2B are films of the same~
llsamples exposed to wide angle x-ray diffraction.

THE INVENTION
In accordance with the present invention there is provided a I
substantially amorphous random interpolymer of from about 10 wt ~ ¦
llto about 30 wt % of ethylene, from about 65 to about 90 wt % of ¦lpropylene and from about 0 to about 15 wt % of a C4 - Cg alpha-¦~olefin, said interpolymer having a tacticity index m/r ranging between about 3 and about 5 as determined by 13C NMR spectra. In ~the absence of the third C4 - C8 alpha-olefin comonomer the m/r ~ratio should range between about 3 and about 4. When a third mon l omex is included, the preferred amount is between about 5 and abou~
¦ 15 wt % based on the total polymer weight.
The tacticity index m/r is determined directly by 13C Nuclear Magnetic Resonance (NMR). The "m" and "r" describe the stereo-chemist~ies of pairs of contiguous propylene groups bonded to one or more ethylene groups, "m" referring to meso and "r" to racemic.
An m/r ratio of 1.0 describes a syndiotactic polymer and an m/r ratio of 2.0 a truly atactic material. An isotactic material ¦theorectically will have a ratio approaching infinity and many by-product atactic polymers have sufficient isotactic content to re-¦Isult in ratios of 50 and above. It has been found that the m/r 1l ratio substantially agrees with the number average sequence length ~¦n of like groups i.e. meso and racemic groups in case of propylene homopolymer produced under the same conditions as the random ~Z54~
Icopolymer, except for the absence of ethylene in the feed. Thus, ¦it was established that the tacticity is independent of comonomer content in the polymer. Also, the comonomer such as the ethylene llis distributed throughout the polymer molecule in the most random Ifashion. The method used in calculating n for homopolymer is ;disclosed in J. C. Randall, J. POLYM. SCI., POLYM. PHYS. ED., 14, 2083 (1976). The tacticity index m/r is obtained by inverting the r'/m' ratio calculated according to the method devised by H. N.
Cheng, MACROMOLECULES, 17, 1950 (1984).
I The interpolymers of this invention are unique in that al-though they exhibit a birefringent spherulitic granular structure ;when examine~ by hot stage microscopy, they are substantially amorphous. Usually, truly amorphous materials will show no struc-Iture by this method. The formation of these granules upon cooling implies that there is enough tacticity for short portions of the chain, i.e. ordered arrays of monomer without long range order, which would tend to form crystallites. The average length of the granules range between about 15 and about 50 microns, although occasionally larger grain sizes might be observed. The hot stage 1 microscopy method is described in "The Light Microscopy of Synthe-tic Polymers", D. A. Helmsley, Oxford University Press, Oxford, England, 1984. The determinations are made by heating the samples ¦on glass slides in a hot stage to 170C and then slowly cooling llthem by turning off the heaters, ~hile viewing the samples througn lla crossed polarizer. Photomicrographs (~00X) are made of the cooled samples, and measurements are made of the largest dimension (=the length) of the granules. Figure lA shows a hot stage photo-micrograph of a typical interpolymer of this invention (Example 3 lof Table 1), Figure lB that of commercially available product I ~Commercial Sample C of Table 2) believed to be a purified atactic ~by-product polymer.
~he interpolymers exhibit no significant crystallinity under wide angle x-ray diffraction ("X-Ray Diffraction Methods In Polyme~

1'~8'~546 i Science", L. E. Alexander, Krieger Publishing Company, Huntington,;
New York, 1979). In these tests the samples are placed between two thin fllms of Mylar ~ and placed at the exit collimator of the !lx-ray tube. A beam stop is used to block out the primary beam and ¦flat films record the scattered radiation with a sample-to-film jdistance of 3Omm. The presence of no more than 2 concentric rings on the exposed film indicates the presence of no significant ~polymer crystallinity.
Il Figure 2A shows an exposed film using the same interpolymer ¦~of this invention as in Figure lA, while Figure 2B is an exposed film of the same sample as of Figure lB. As seen in Figure 2A, ~there are no rings present .indicating an amorphous nature of the polymer sample, while in Figure 2B there are 4 clearly defined l¦rings, which indicate a high degree of crystalline order of the 1I sample.
¦ The novel polymer has a very low heat of fusion, typically less than about 0.6 cal/g, as determined by Differential Scanning Calorimetry techniques (DSC), a further indication of the amorphous;
~Inature of the polymer and the lack of significant crystallinity in ~the polymer structure.
The polymers of this invention are prepared by a process which comprises polymerizing from about 65 to 90 wt % propylene, from about 10 to about 30 wt % ethylene and from O to about 15 wt % of a C4 - Cg alpha-olefin at a temperature between about 130 and about 175F in the presence of a particular catalyst composition. When a third monomer is used the preferred amount is between about 5 and ~about 15 wt % based on the total polymer weight. ~lthough the polymerization can be carried out in a batch reactor, it is pre-ljferred to utilize a continuous process to achieve the most random l¦incorporation of the comonomer(s).
The pressure should be sufficient to maintain propylene in ¦the liquid phase, usually pressures in the range between about 400 Ipsig and about 550 psig are suitableO The preferred temperature 1.

~ 2 ~4 is between about 150 and about 160F.
Hydrogen i~ added to the polymerization reactor for control of polymer molecular weight and other properties at concentration3 generally about 7 to lO times the amount conventionally used in the manufacture of isotactic polymer. Moreover, as the ethylene content o~ the interpolymer i~ increased it is necessary to in-crease the hydrogen concentration in the reactor to maintain a constant melt viscosity. As an example, for a 100~ increase in ethylene content about a 50 to lS0~ lncrease in hydrogen is re-quired. The concentration of nydrogen in the total feed to the reaction zone generally ranges between about 0.7 and about 3.0 mol and preferably between about 1.2 and about 2.5 mol %.
The specific catalyst composition contains a solid, supported catalyst component and an organoaluminum component. The supported catalyst component is comprised of an active transition metal com-pound such as titanium tetrahalide mixed with an enhanced support comprised of magnesium halide and aluminum trihalide. The molar ratio of magnesium halide to aluminum trihalide is about ~:0.5-3.0 and preferably about ~:l.0-1.5.
The molar ratio of magnesium halide to titanium tetrahalide i~ between about 8:0.1-1.0 and pre~erably about 8:0.4-0.6. A
critical feature of the solid supported catalyst component is that no electron donor compounds should be used in any of the catalyst manufacturing steps. Also, the polymerization process using the cataly~t should be carried out in the absence af added electron donors. The preferred halides are chlorine.

Any of the general meth ~ d~x~ in u.S. ~tents No. 4,347,158 and 4,555,496 can be used in prepar ~ the solid ~ ported catalvst ~0 component except that these-m~thods must be modified to exclude the use of electron donor compounds. Briefly, the modified method involves co comminuting magnesium halide and aluminum trihalide in the absenc~ o~ an electron donor and then co-comminuting the . . , ¦catalyst support so formed with titanium tetrahalide, also in the absence of an electron donor.
The solid catalyst component is used in conjunction with an iorganoaluminum co-catalyst, which is a mixture of trialkylaluminum Iand alkylaluminum halide, wherein each alkyl group contains be-tween 1 and 9 carbon atoms, and wherein the alkylaluminum halide contains at least one halide group. The preferred halide is chloride and the alkyl groups are preferably ethyl groups. The 'invention will be described hereinafter in connection with the Ipreferred catalyst system. The triethylaluminum content ranges between about 15 and about 90 mol ~ in the total organoaluminum component. At lower than 15% triethylaluminum concentrations, the polymer productivity is drastically reduced and diethylaluminum!
Ichloride alone fails completely to promote polymerization. At ;higher than 90 mol % some of the physical properties of this polymer are affected in an undesirable manner. The use of diethyl-aluminum chloride is not for the purpose of promoting polymeriza-tion but very importantly, to impart to the catalyst system the ability to produce polymer with desirable properties. The pre-~ ferred co-catalyst is a mixture containing from about 40 to 60 mol % triethylaluminum and about 60 to about 40 mol % diethylaluminum chloride. The molar ratio of total organoaluminum co-catalyst to l!titanium-containing catalyst component, i.e. Al/Ti ratio should ¦Irange between about 50:1 and about 600:1, preferably between about I90:1 and about 300~
The polymerization is carried out in a stirred reactor at average residence times between about 1 hour and about 3 hours.
Sufficient catalyst quantities are fed to the reactor to result in l¦a polymer content in the reactor slurry of from about 30 wt % and Iabout 60 wt %. The re~;tor effluent is withdrawn from the reactor, lland unreacted monomer and hydrogen is flashed from the product polymer.
Various additives can be incorporated into the polymer, such I i l! i 1~8;~5fL6 las antioxidants, U.V. stabilizers, pigments, etc.
The compositions of this invention have excellent properties making them useful in a variety of applications, such as for ad-hesives, caulking and sealing compounds, roofing compositions and others. By varying the comonomer content in the polymer and hy-drogen addition to the reactor, it is possible to tailor the pro-perties for any desired application. The important product pro-perties include melt viscosity, ring and ball softening point, llneedle penetration and open time.
~I The melt viscosity at 375F is determined by ASTM test method D-3236 using a Brookfield RVT Viscometer and a #27 spindle. Hy-`drogen is used to control molecular weight and thus melt viscosity~
¦ It has been found that at increased ethylene content more hydrogen llis required to maintain a certain viscosity level. For hot melt ~adhesives the desired viscosity range is between about 1000 and about 5000 cps at 375F, while for other applications such as bitumén-modified product, the polymer component should have a viscosity above 5000 cps, preferably in the range between about l 10,000 and about 25,000 cps.
1 The ring and ball softening point determinations are carried out using ASTM E-28 test method. The variables affecting the soft-ening point are ethylene content of the polymer and the triethyl-aluminum concentration in the organoaluminum co-catalyst used in l the polymerization process. A decrease in the ethylene content ¦ as well as in diethylaluminum chloride concentration in the co-lcatalyst both cause an increase in the ring and ball softening Ipoint. The preferred range for this property is between about ¦l235F and about 270F for the hot melt adhesive application.
Il ~leedle penetration is another test which measures the softnesq ~of the material, in this case by the resistance to penetration ac-¦cording to ASTM test method D-1321. Typically, the penetration values of the interpolymers of this invention range between 25 and about 75 dmm (1 dmm-O.lmm). The same process variables affect 1ll !

5~6 this property as in the case of ring and ball softening point.
Perhaps the most important test of a hot melt adhesive is the open time. This test is an indication of the elapsed time avail-able between adhesive application to kraft paper and bonding of a kraft paper laminate. This is a very important property for the user, as he must know how soon after applying the adhesive he must add the second sheet of paper. In this test, an 8~" x 11" sheet of kraft paper, rough side-up is taped to a drawdown plate. A
~polymer sample is heated to 375F along with a Bird drawdown ap-plicator. When at temperature, the applicator is placed at the top of the kraft paper and a small puddle of molten polymer is poured near the edge. The polymer is drawn into a smooth film, and as soon as the bottom of the paper is reached, a stopwatch is started. At 10 second intervals, precut strips of kraft paper I~rough side down, transverse machine direction) are placed across the ilm and pressed into place with a rubber roller. After the last strip i5 applied, and a subsequent waiting period of 5 min-~utes, the strips are removed in a smooth, brisk motion. The open time is deined as the longest time when 90% or more of the iber remains. The open times should preferable range between 10 and 60 seconds.
An additional benefit of the polymers of this invention is ~that they contain extremely small quantities of catalyst residues llbecause of the very large productivity rates of the specific cata-l~lyst used in the polymerization. There is no need to remove these ¦~small amounts of catalysts from the polymer.
The following examples illustrate the invention.

EX~lPLES 1 - 8 I Polymers were prepared in large scale continuous pilot plant l'operations, wherein monomers, hydrogen and catalyst components were separately and continuously charged to a stirred reactor, the' total monomer feed rate corresponding to about a 2 hour residence l l l .

~time in the reactor. The organoaluminum compound of the catalyst ¦system was a heptane solution of an eauimolar mixture of triethyl-~
aluminum (TEA) and diethylaluminum chloride (DEAC). The solid lsupported titanium tetrachloride catalyst component had a titanium 1 content of about 2.5 wt % and was prepared by a modification of the preferred technique disclosed in U. S. Patent No. 4,347,158 ~ i.e., modified only in that all process steps were carried out in jlthe absence of any electron donor compounds. The solid catalyst licomponent was pumped into the reactor as a 10 wt ~ mixture in a Iblend of petrolatum and mineral oil in a 50/50 weight ratio. The I two catalyst components were added at rates directly proportioned ,to the polymer production rates and in amounts sufficient to main-tain the polymer solids concentration in the reactor slurry at ,values usually in the range between about 40% and about 60%. The !¦catalyst productivity (lb polymer/lb of Ti-catalyst component) was calculated in each case from the polymer slurry withdrawal rate, solids content in the slurry and the titanium catalyst addition rate. The product polymer was separated from unreacted monomer, Istabilized with Isonox ~ 129 and then subjected to testing. Table l summarizes the pertinent operating conditions and the results of physical testing. The product characteristics of Example 1-6 fall within the claimed limits of this invention, while those of Com-¦parative Examples 7 and 8 reflect the insufficient amount of lethylene groups in the interpolymers, i.e. high softening point, ¦low needle penetration, high heat of fusion.
Table 2 lists the physical properties of Examples 1-8 and also of fifteen atactic polymers (Commercial Examples A-O) ob-~¦tained from various manufacturers ln the United States, Europe and IAsia. Commercial 5ample A is a terpolymer of ethylene, propylene ~'and a major proportion of butene-l, while the remaining samples are either propylene homopolymers or ethylene-propylene copolymers.
~ISamples B, C, G and H are believed to have been produced in pro-¦cesses under conditions deliberately selected to yield relatively ~Z8Z5~6 U) ~ ~ I 1~ o o ~ o ~ r~ o o ~
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lZ8'~546 lax~e concentrations of atactic polymer in the total polymer pro-! duct. It is further believed that the atactic portions have sub-sequently been removed from the isotactic by-product by solvent lltreatment. Samples D F and I-O are believed to be atactic poly-` propylene by-products. None of these commercial samples have the physical properties required of the polymer products of this in-~vention.

EXAMPLES 9 and 10 Il Both experiments were performed in a l-liter, jacketed auto- .
l¦clave equipped with a magnetically coupled stirrer. The tempera- j ture of the autoclave was controlled by the use of a mixture of equal weights of glycol and water as the heat transfer fluid flow-.ing through the jacket. The temperature of this fluid was con-ltrolled by a microprocessor whose temperature indicator was an iron/constantin thermocouple inside the autoclave.. With this ~ z546 system, set point temperature could be maintained + 0.2C. All monomers were polymerization grade, 99.9% pure, and were also passed through molecular sieve beds, as well as beds of copper catalyst for oxygen removal, prior to use. Hydrogen was ultra-high purity, 99.99% and used as is. Aluminum alkyl solutions were purchased as 25% W/W in normal heptane and were used as is. One wt % catalyst slurries were prepared in degassed mineral oil using catalysts of the same type as that of in Examples 1-8. Prior to each use, the autoclaves were heated to 90C with a slow nitrogen purge for 30 minutes. After cooling to 30C, the nitrogen atmos-phere was replaced with a propylene pur~e. Alkyl solutions and catalyst slurries were prepared in septum vials in dry boxes (nitrogen atmosphere), purged with nitrogen upon removal, and pres surized slightly to avoid contamination. Alkyl solutions and catalyst slurries were introduced into the reactors using hypo-dermic syringes, previously cleaned with de-ionized water, dried at 120C, and purged with nitrogen prior to use. In Example 9, 0.34 ml TEA, 0.3~ ml DEAC (Al - 1.77 x 10-3 mole/l), and 0.58 ml of 1% W/W catalyst slurry (2.5% W/W titanium content) were added to the autoclave. Hydrogen was added to equal a partial pressure of 70 psi~. 0~6 liters of propylene was introduced using a sight guage and nitrogen pressure. The reactor content was heated to 60C and maintained while stirring at 500 rpm. As soon as the temperature stabili ed at 60C (5-10 minutes), ethylene was added to the reactor to maintain a constant overpressure of 50 psig greater than the reactor pressure. After 1 hour, the temperature was lowered and excess propylene vented. The ethylene-propylene copolymer was dried under va~uum at ~0C overnight. Example 10 was carried under the conditions of the previous example except that 0.1 liter of butene-l and 0.5 liter of propylene was charged to the autoclave instead of the 0.6 liters of propylene of Example 9. The resulting terpolymer was dried as before.
Table 3 lists the pertinent physical properties of the pro-ducts of Examples 9 and 10.

lZ8Z5~6 1~

Ethylene - wt % 21.1 23.3 Butylene - wt % ---- 9.2 5 m/r 3.3 4.8 Average Granule Length-microns 22 20 No. of Rings - X-ray 0 0 ~HF-cal/g 0-03 -Melt Viscosity @ 375F cps2810 3250 10 Open Time - secs >60 >60 Softening Point - F 260 237 Needle Penetration - 0.1 mm 71 72 Catalyst Efficiency Kg/g41.2 34.6 COMPARATIVE EXAMPLES 11 and 12 These examples were carried out using the procedure described in connection with Example 9 except for the alkyl co-catalyst addition. In Example 11 0.68 ml TEA was used exclusively while in Example 12 the same amount of DEAC only was added. Table 4 lists the pertinent data of these comparative examples.

EX~MPLE NO COMP. 11 COMP. 12 Co-Catalyst TEA 100% ----DEAC ---- 100%
Catalyst Efficiency Kg/g 40.0 0.0 Ethylene - wt % 18.1 ----m/r 4.2 ----Melt ~iscosity @ 375 cps 3700 ----Open Time - secs >60 ----Softening Point - F 275 ----Needle Penetration - 0.1 mm 43 ----As seen from the above data, the use of 100% TEA instead of a mixture of TEA and DEAC (as in Example 9) resulted in a higher m/r ratio of the polymer procluct. Also, the softening point and needle penetration values were affected in a detrimental way.
The use of 100% DEAC as co-catalyst resulted in no formation of polymer.

1~3Z5~6 It is to be understood that many alterations and modification~
can be made to the polymers of this invention. All such departureg are considered within the scope of this invention as defined by th~
specifications and appended claims.

Claims (8)

1. A substantially amorphous binary random copolymer consisting essentially of from about 10 to about 30 wt.% of ethylene and from about 70 to about 90 wt.%
of propylene, said copolymer having a tacticity index m/r ranging between 3.0 and 4.0 and having a propylene inversion value of about 0.15 and below as determined by 13C NMR Spectra.

2. The copolymer of Claim 1 having a heat of fusion of less than about 0.6 cal/g.

3. The copolymer of Claim 1 having a viscosity in the range between about 1000 and about 25,000 cps at 375° F.

4. The copolymer of Claim 1 having a ring and ball softening point between about 235° F and about 300°F.

5. The copolymer of Claim 1 having a needle penetration in the range between about 10 and about 75 dmm.

6. The copolymer of Claim 1 having an open time between about 10 and about 60 seconds.

7. The copolymer of Claim l having a total ash content of less than about 500 ppm.

8. The copolymer of Claim 1 having a titanium content of no more than about 2 ppm.