PROPYLENE POLYMERISATION PROCESS

Abstract: A highly efficient process is disclosed for the production of substantially amorphous ethylene-propylene copolymers which are useful as hot melt adhesives, as blending components in roofing materials, and as cable and wire flooding agents. The process involves reacting from 70 to 96.5 wt. % propylene and from 3.5 to 30 wt. % ethylene at a temperature between 55°C (130°F) and 80°C (175°F) and at a reactor pressure sufficient to maintain propylene in the liquid phase, in the presence of from 0.7 to 3.0 mol % hydrogen based on the monomer feed to the process and employing as catalyst a composition comprising: (a) a solid catalyst component obtainable by (i) co-comminuting magnesium halide support base and aluminium trihalide in a molar ratio from 8:0.5 to 8:3 in the absence of added electron donor and (ii) then co-comminuting the product of step (i) in the absence of added electron donor with sufficient titanium tetrahalide to provide a molar ratio of magnesium halide to titanium tetrahalide from 8:0.4 to 8:1 and (b) a co-catalyst component comprising a mixture of from 15 to 100 mol % of trialkyaluminium having from 1 to 9 carbon atoms in each alkyl group and 85 to 0 mole % of an alkylaluminium halide having at least one halide group per molecule and from 1 to 9 carbon atoms in the alkyl group in a sufficient quantity to provide an Al/Ti ratio in the range from 50:1 to 600:1; and recovering a substantially amorphous, random ethylene-propylene copolymer having a tacticity index m/r in the range of from 2.5 to 4 as determined by ¹³C NMR spectra.

Description: The present invention relates to a process for producing substantially amorphous ethylene-propylene copolymers having an ethylene content of not more than 15% by weight. In the manufacture of propylene homopolymers and copolymers, conventional polymerisation techniques using unsupported catalysts result in the simultaneous production of substantial quantities of atactic polymer in addition to the desired product of high crystallinity 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 utilized commercially as a component in various adhesive compositions, roofing materials, caulking compounds etc. Recently, developments have been made of new catalysts which are highly active and more stereospecific than the aforementioned conventional catalysts. The proportions of atactic polymer in the polymers produced employing these catalysts are substantially reduced and therefore the polymer product generally does not require any purification for removal of the atactic or low crystalline polymer. Because of the rapid adoption in existing polymer production facilities of these new catalysts, there has been generated a serious shortage of low-crystalline, atactic polymers. U.S. Patent No. 3,789,036 to Longi et al. discloses a process for the production of ethylene-propylene elastomers containing between about 20 and 70 wt. % ethylene using a magnesium-supported titanium catalyst, e.g., a co-ground mixture of titanium tetrachloride and magnesium chloride. It has been found that this catalyst is not very active and, therefore, the polymer produced in the process contains undesirably large quantities of catalyst residues. Secondly, the polymer is more crystalline than desired as measured by the m/r ratio described in detail hereinafter. Finally, because of the low catalyst activity, the catalyst costs become prohibitive. EP-A-0251771 describes the production of amorphous ethylene-propylene random copolymers using a magnesium halide catalyst support base and an aluminium trihalide and titanium tetrahalide catalyst with a mixed trialkylaluminium/alkylaluminium halide co-catalyst. This catalyst system permits formation of products having a m/r ratio below 4. However it is unable to provide products meeting the requirements for softening point, open time, needle penetration and/or heat of fusion when the ethylene content is very low. It is therefore an object of the present invention to provide a highly efficient process for the production of substantially amorphous polymers of propylene and ethylene. In accordance with the present invention there is provided a process for producing substantially amorphous ethylene propylene copolymers which comprises reacting up to 96.5 weight % propylene and from 3.5 weight % ethylene at a temperature between 55°C (130°F) and 80°C (175°F) and at a reactor pressure sufficient to maintain propylene in the liquid phase, in the presence of from 0.7 to 3.0 mol % hydrogen based on the monomer feed to the process and employing as catalyst a composition comprising: (a) a solid catalyst component obtainable by (i) co-comminuting magnesium halide support base and aluminium trihalide in a molar ratio from 8:0.5 to 8:3 in the absence of added electron donor and (ii) then co-comminuting the product of step (i) in the absence of added electron donor with sufficient titanium tetrahalide to provide a molar ratio of magnesium halide to titanium tetrahalide from 8:0.4 to 8:1 and (b) a co-catalyst component comprising 100 mol % of trialkyaluminium having from 1 to 9 carbon atoms in each alkyl group in a sufficient quantity to provide an Al/Ti ratio in the range from 50:1 to 600:1; and recovering a substantially amorphous, random ethylene-propylene copolymer having a tacticity index m/r in the range of from 2.5 to 4 as determined by ¹³C NMR spectra, the proportions of ethylene and propylene being selected such that the copolymer has an ethylene content of not more than 15% by weight. Preferably, all the halides used in forming the catalyst composition are chlorides and all the alkyl groups are ethyl groups. The invention will be described hereinafter in connection with these preferred embodiments of the catalyst system; analogous considerations apply to the use of other catalyst systems within the above definition. Although the polymerisation can be carried out in a batch reactor, it is preferred to utilize a continuous process to achieve the most random incorporation of the comonomer. Usually, pressures in the range betwen 2.9 MPa (400 psig) and 3.8 Mpa (550 psig) are suitable for maintaining propylene in liquid phase; the preferred temperature is between 65°C (150°F) and 70°C (160°F). The hydrogen is added to the polymerisation reactor for control of polymer molecular weight and other properties at concentrations generally about 7 to 10 times the amount conventionally used in the manufacture of isotactic polymer. Moreover, as the ethylene content of the copolymer is increased, it is necessary to increase the hydrogen concentration in the reactor to maintain a copolymer having a constant melt viscosity. As an example, for 100% increase in the ethylene content about a 50% to 150% increase in hydrogen is required. The concentration of hydrogen in the total feed to the reaction zone is preferably in the range of from 1.2 to 2.5 mol %. The solid, supported catalyst component should have a molar ratio of magnesium chloride to aluminium chloride of 8:0.5 to 3.0 and preferably from 8:1.0 to 1.5. The molar ratio of magnesium chloride to titanium tetrachloride is from 8:0.4 to 8:1 and preferably from 8:0.4 to 8:0.6. A critical feature of the solid supported catalyst component is that no electron donor compound should be used in any of the catalyst manufacturing steps. Also, the polymerisation process using the catalyst should be carried out in the absence of added electron donors. Any of the general methods described in U.S. Patents Nos. 4,347,158 and 4,555,496 can be used in preparing the solid support catalyst component except that these methods must be modified to exclude the use of electron donor compounds. Briefly, the modified method involves co-comminuting magnesium chloride and aluminium trichloride in the absence of an electron donor and then co-comminuting the catalyst support so formed with titanium tetrachloride, also in the absence of an electron donor. The solid catalyst component is used in conjunction with an organoaluminium co-catalyst, which, as stated above, is 100 mol % of trialkylaluminium. The molar ratio of total organoaluminium co-catalyst to titanium-containing catalyst component i.e., Al/Ti ratio, should be in the range from 50:1 to 600:1, preferably from 90:1 to 300:1. The polymerisation is carried out in a stirred reactor at average residence times between 1 hour and 3 hours. Sufficient catalyst quantities are fed to the reactor to result in a polymer content in the reactor slurry of from 30 wt. % to 60 wt %. The reactor effluent is withdrawn from the reactor, and unreacted monomer and hydrogen is flashed from the product polymer. Specific catalyst used in the process of this invention has the ability to produce propylene units in the polymer with little or no control of the stereochemistry, and also to incorporate ethylene as randomly as possible to provide maximum disorder in the polymer chain. Because of the high activity of this catalyst, the process is highly efficient and typically results in polymer productions of at least 7000 kg polymer /kg Ti catalyst/hour. The products of the process of this invention have a tacticity index m/r between about 2.5 and 4. This is determined directly by ¹³C Nuclear Magnetic Resonance (NMR). The "m" and "r" describe the stereochemistries 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 theoretically will have a ratio approaching infinity and many by-product atactic polymers have sufficient isotactic content to result in ratios of 50 and above. It has been found that the m/r 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 copolymer, 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 is distributed throughout the polymer molecule in the most random fashion. The method used in calculating n for homopolymer is disclosed in J.C. Randall, J. POLYM. SCI. 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.M. Cheng, MACROMOLECULES, 17 , 1950 (1984). The novel polymer has a very low heat fusion, as determined by Differential Scanning Calorimetry techniques (DSC), a further indication of the amorphous nature of the polymer and the lack of significant crystallinity in the polymer structure. The polymer contains very low concentrations of catalyst residues e.g., the total ash content is generally less than 500ppm and the titanium content no more than 2 ppm and generally less than 1 ppm. Various additives can be incorporated into the polymer, such as antioxidants, U.V. stabilizers and pigments. The polymer products of the process of this invention have excellent properties making them useful in a variety of applications, such as for adhesives, caulking and sealing compounds, roofing compositions, cable and wire flooding compounds, and others. By varying the comonomer content in the polymer and hydrogen addition to the reactor, it is possible to tailor the properties for any desired application. The important product properties include melt viscosity, ring and ball softening point, needle penetration, and open time. The melt viscosity at 190.5°C (375°F) is determined by ASTM test method D-3236 using a Brookfield RVT Viscometer and a No.27 spindle. Hydrogen is used to control molecular weight and thus melt viscosity. It has been found that at increased ethylene content more hydrogen is required to maintain a certain viscosity level. For use as wire and cable flooding compounds the preferred viscosity is between 100 and 5000 mPa s. For hot melt adhesives the desired viscosity range is between about 1000 and 5000 mPa s, at 190.5°C (375°F). For other applications such as bitumen-modified product, the polymer component should have a viscosity above 5000 mPa s, preferably in the range from 10,000 to 25,000 mPa s. The ring and ball softening point determinations are carried out using ASTM E-28 test method. The variables affecting the softening point are ethylene content of the polymer and the triethylaluminium concentration in the organoaluminum co-catalyst used in the polymerisation process. A decrease in the ethylene content as well as in diethylaluminium chloride concentration in the co-catalyst both cause an increase in the ring and ball softening point. The preferred range for this property is from 113°C (235°F) to 150°C (300°F). Needle penetration is another test which measures the softness of the material, in this case by the resistance to penetration according to ASTM test method D-1321. Typically, the penetration values of the copolymers of this invention are in the range from 10 to 75 dmm (1 dmm = 0.1 mm). The same process variables affect this property as in the case of ring and ball softening point. Perhaps one of the most important tests of a hot melt adhesive is the open time. This test is an indication of the elapsed time available 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 sheet 21.5 cm x 28 cm (8.1/2" x 11") of kraft paper, rough side up is taped to a drawdown plate. A polymer sample is heated to 190.5°C (375°F) along with a Bird drawdown applicator. 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, pre-cut strips of kraft paper (rough side down tranverse machine direction) are placed across the film and pressed into place with a rubber roller. After the last strip is applied, and a subsequent waiting period of 5 minutes, the strips are removed in a smooth, brisk motion. The open time is defined as the longest time when 90% or more of the fiber remains. The open times should preferably range from 10 to 60 seconds. An additional benefit of the polymers of this invention is that they contain extremely small quantities of catalyst residues because of the very large productivity rates of the specification catalyst used in the polymerisation. There is no need to remove these small amount of catalysts from the polymer. The following examples illustrate the invention. EXAMPLES 1 to 3 Polymers were prepared in large scale continuous pilot plant operations, wherein monomers, hydrogen and catalyst components were separately and continuously charged to a stirred reactor, the total monomer feed rate corresponding to a residence time in the reactor of 1.8 hours. The organoaluminium compound of the catalyst system was fed to the reactor as a pure stream of triethylaluminium (TEA). The solid supported titanium tetrachloride catalyst component had a titanium 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 the absence of any electron donor compounds. The solid catalyst component was pumped into the reactor as a 6 wt.% mixture in pure petrolatum. The two catalyst components were added at rates directly proportional to the polymer production rates and in amounts sufficient to maintain the polymer solids concentration in the reactor slurry at about 40 wt.%. The catalyst productivity (kg polymer/kg 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, stabilised with Isonoz R 129 and then subjected to testing. Table 1 summarizes the nominal operating conditions and the results of physical testing. Example No. 1 2 3 Reactor Temp., °C(°F) 68(155) 68(155) 68(155) Reactor Press.,MPa (psig) 2.9(410) 3.1(435) 3.3(465) Propylene kg/hr (lbs/hr) 1861(4,100) 1589(3,500) 1589(3,500 Ethylene kg/hr (lbs/hr) 39(85) 97(213) 212(468) Hydrogen kg/hr (lbs/hr) 0.7(1.6) 1.1(2.5) 1.5(3.3) Al/Ti mol ratio 250 250 250 Catalyst Activity kg/kg Catalyst/hr 8,300 11,100 13,900 Ethylene Content, wt/% 3.8 6.9 13.6 m/r Ratio 2.6 3.1 3.5 Melt Viscosity @ 195°C(375°F)mPas 7,750 3,185 3,350 Ring and Ball Softening Point,°C(°F) 147(296) 139(283) 129(364) Needle Penetration mm 1.2 2.5 4.5 ΔH f , cal/g (DSC) 3.3 2.3 1.3 Total Ash, ppm 459 344 275 Ti, ppm 1.6 1.2 1.0 Mg, ppm 13.1 9.8 7.9 Al, ppm 230 173 138

Claims: A process for producing substantially amorphous, ethylene/propylene copolymers which comprises reacting up to 96.5 weight % propylene and from 3.5 weight.% ethylene at a temperature of between 55°C (130°F) and 80°C (175°F) and at a reactor pressure sufficient to maintain propylene in the liquid phase, in the presence of from about 0.7 to about 3.0 mol % hydrogen based on the monomer feed to the process and employing as catalyst a composition comprising: (a) a solid catalyst component obtainable by (i) co-comminuting magnesium halide support base and aluminium trihalide in a molar ratio from 8:0.5 to 8:3 in the absence of added electron donor and (ii) then co-comminuting the product of step (i) in the absence of added electron donor with sufficient titanium tetrahalide to provide a molar ratio of magnesium halide to titanium tetrahalide from 8:0.4 to 8:1; and (b) a co-catalyst component comprising 100 mol % of trialkylaluminium having from 1 to 9 carbon atoms in each alkyl group in a sufficient quantity to provide an Al/Ti ratio in the range of from 50:1 to 600:1; and recovering a substantially amorphous, random ethylene-propylene copolymer having a tacticity index m/r in the range of from 2.5 to 4 as determined by ¹³C NMR spectra. the proportions of ethylene and propylene being selected such that the copolymer has an ethylene content of not more than 15% by weight A process according to claim 1 wherein the catalyst composition comprises magnesium chloride, aluminium trichloride, titanium tetrachloride and triethylaluminium. A process according to claim 1 or claim 2 conducted at a pressure from 2.9 Mpa (400 psig) to 3.8 MPa (550 psig) and a temperature from 65°C (150°F) to 70°C (160°F). A process according to any one of claims 1 to 3 wherein the magnesium halide to aluminium trihalide ratio is from 8:1 to 8:1.5. A process according to any one of claims 1 to 4 wherein the magnesium halide to titanium tetrahalide ratio is from 8:0.4 to 8:0.6. A process according to any one of claims 1 to 5 wherein the Al/Ti ratio is maintained at from 90:1 to 300:1. A process according to any one of claims 1 to 6 wherein the hydrogen is maintained from 1.2 to 2.5 mol % based on the total monomer feed to the process. A process according to any one of claims 1 to 7 carried out under continuous conditions at an average residence time of from 1 to 3 hours. A process according to any one of claims 1 to 8 wherein the solids content of the reactor slurry is maintained at from 30 to 60 wt. %. A process according to any one of claims 1 to 9 wherein the catalyst composition has an activity of at least 7000 kg polymer/kg Ti catalyst/hour. A process according to claim 10 wherein the recovered copolymer has a total ash content of less than 500 ppm. A process according to claim 10 or claim 11 wherein the recovered copolymer has a titanium content of no more then 2 ppm. A process according to any one of claims 1 to 12 wherein the recovered copolymer has a melt viscosity of from 100 to 25,000 mPa s @ 190.5°C (375°F). A process according to any one of claims 1 to 13 wherein the recovered copolymer has a ring and ball softening point of from 113°C (235°F) to 150°C (300°F). A process according to any one of claims 1 to 14 wherein the recovered copolymer has a needle penetration value between about 1 and about 7.5mm. A process according to any one of claims 1 to 15 wherein the recovered copolymer has an open time of from 10 to 60 seconds.

Inventors: ALLEN, GEORGE C., HUGHES, MICHAEL P., PELLON, BRIAN J.
Applicants: REXENE PRODUCTS COMPANY (A DELAWARE CORPORATION)
Application year: 1989
Main classification: C08F210
IPC codes: C08F210, C08F4