NO810796L - NEW PROPYLENE POLYMER. - Google Patents

Description

The catalyst systems that have previously been used during propylene polymerization have been an unmodified

cert or an electron-donor-modified titanium halide component, activated with an organoaluminum cocatalyst. Typical examples of commonly known propylene polymerization catalyst systems include co-crystallized titanium trichloride-aluminum trichloride catalysts of general formula n-TiCl 3 -AlCl 3 /activated with diethylaluminum chloride or triethylaluminum. The co-crystallized titanium trichloride-aluminum trichloride may have been modified with a suitable electron-donor compound to increase its activity or stereospecificity. Such compounds include phosphorus compounds, esters of inorganic and organic acid ethers and numerous other compounds.

New catalysts have recently been developed which are far more active than the above-mentioned commonly known catalysts for the polymerization of α-olefins. Briefly explained, said catalysts consist of a titanium halide catalyst component placed on a magnesium dihalide and an alkyl aluminum compound which may be present as a complex with an electron-donor compound. Such catalyst components are, among other things, described in US patent no. 3,830,787, no. 3,953,414, no. 4,051,313, no. 4,115,319

and No. 4,149,990.

The advantages of polymerizing propylene in the presence

of said new catalysts is an improved yield (polymer/

Ti w/w) and stereospecificity (= isotactic index).

or % heptane-insoluble compounds), while the mechanical properties have essentially remained unaffected.

It is a purpose of the present invention

to provide a new propylene polymer which has improved processability when extruded or injection molded compared to conventional propylene polymer.

Furthermore, it is an aim of the invention to provide a new polypropylene that can be processed with wood

low extrusion or molding temperatures and/or low extrusion or molding pressures than conventional known polypropylene resins which have the same melt flow.

Other purposes and advantages of the invention will be apparent from the following description.

The present invention provides a new propylene polymer with a melt flow range between 0.2 and 30 g per 10 minutes, an isotactic index of no less than approx. 92%, a dimer-trimer content that does not exceed 4 g per kg polymer, a crystalline melting point of at least approx. 165°C, and a ratio between the weight average molecular weight and the number average molecular weight of at least 7, a Ti content not exceeding 3 ppm, a Mg content not exceeding approx. 40 ppm, a Cl content that does not exceed approx. 100 ppm and a total ash content that does not exceed approx. 400ppm.

The catalyst components used to prepare the propylene polymer according to the present invention can be any of those that have been recently developed, i.e. the high-activity magnesium halide-supported catalyst components and organoaluminium co-catalyst components which are described, among other things, in US patents no. 3,830,787, no. 3,953,414, No. 4,051,313, No. 4,115,319 and No. 4,149,990 which are incorporated herein by reference.

Such a catalyst composition typically consists of two components, where the components are supplied separately to the polymerization reactor. Component (a) in such a composition is advantageously selected from the group consisting of trialkylaluminum compounds with from 1-8 carbon atoms in the alkyl group, such as triethylaluminum, trimethylaluminum, tri-n-butylaluminum, triisobutylaluminum, triisohexyl-aluminum, tri-n-octylaluminum and triisooctyl aluminum. Most preferably, trialkyl aluminum is complexed with an electron donor before it is fed to the polymerization reactor. The best results are obtained when esters of carboxylic acids or diamines, especially esters of aromatic acids, are used as electron donors.

Some typical examples of such connections

are methyl and ethyl benzoate, methyl and ethyl p-methoxybenzoate, diethyl carbonate, ethyl acetate, dimethyl maleate, triethyl borate, ethyl o-chlorobenzoate, ethyl naphthenate, methyl p-toluate, ethyl toluate, ethyl p-butoxybenzoate, ethyl -cyclohexanoate,

ethyl pivalate, N,N,N<1>,N'-tetramethylenediamine, 1,2,4-trimethyl-piperazine, 2,5-dimethylpiperazine and the like. The molar ratio between aluminum alkyl and electron donor can vary between 1 and 100, preferably between 2 and 5. Solutions of the electron donor and the trialkyl aluminum compound, e.g. in each other or in a hydrocarbon such as hexane or heptane, are preferably pre-reacted for a certain period of time, usually less than an hour, before introducing the mixture into the polymerization reaction zone.

The second component of the catalyst composition is either a titanium tri- or tetrahalide placed on a magnesium dihalide, or a complex of a titanium tri- or tetrahalide with an electron donor compound placed on a magnesium dihalide. The halogen in said halides can be chlorine, bromine or iodine, preferably chlorine. The electron donor, if such is used for the preparation of a complex, is suitably selected from esters of inorganic and organic oxygen-containing acids and polyamines. Examples of such compounds are esters of aromatic carboxylic acids, e.g. benzoic acid, p-methoxybenzoic acid and p-toluic acid and more particularly alkyl esters of said acids, alkylenediamines, e.g. N<1>,N",N'",N""-tetramethylethylenediamine. The molar ratio between magnesium and the electron donor is equal to or higher than 1, preferably between 2 and 10. Generally, the titanium content, expressed in terms of pure titanium metal, will vary between 0.1 and 20% by weight in the supported catalyst component, preferably between 1 and 3% by weight.

The preparation of such catalyst components has been previously described, and they are commercially available.

Said catalyst components (a) and (b) are introduced into the reaction zone in such quantities that the molar ratio between Al/Ti is kept in a range between 1 and 10,000, preferably between 10 and 200.

It is important that the polymerization process used to prepare the polymer according to the present invention is one where the propylene acts both as a diluting liquid as well as starting material for the reaction, except that small amounts of inert hydrocarbons such as hexane, mineral oil, petrolatum etc, to introduce the catalyst components into the reaction zone. The reaction conditions used in the present method include polymerization temperatures from approx. 46.1 to 79.4, preferably between 51.6 and 71.1°C. The pressure must be sufficiently elevated to keep at least part of the propylene in the liquid phase. Suitable pressures are on

14.2 kg/cm 2 higher, e.g. up to 35.7 kg/cm 2. Total amounts of solids in the reaction zone in this system are usually of the order of 15-50%, although of course you can also use higher, e.g. up to 60% polymer solids. However, in order to effectively treat the suspension that is produced, it is preferred to keep the polymerization at such a level that the percentages of solids stated above are obtained. The reaction is continuous and monomer supply and catalyst components are continuously fed to the reactor, after which a suspension of polymer product and liquid propylene is withdrawn, preferably through a cyclic withdrawal valve which simulates continuous operation. If desired, known modifying compounds such as hydrogen can be added.

The pressure in the polymer suspension is dropped to e.g. 3.5 kg/cm 2 or less in a low pressure zone (meaning here a zone that has a pressure lower than that found in the polymerization reaction zone), and due to the pressure drop and the volatile nature of the various ingredients, there will be a blowing out the volatile compounds from the solid polymer. This blowing out, which can be eased by heating, means that you get a polymer powder that is essentially dry, and by this term is meant a polymer that contains 5% or less volatile compounds. An unreacted monomer stream is withdrawn at the top of this low pressure blowdown zone, and at least a portion thereof is compressed, condensed and returned to the reactor. Typically, the polymer is passed to a final drying zone to remove residual volatile compounds.

Alternatively, the liquid polymerization medium can be filtered or centrifuged under pressure, and the liquid propylene can be returned to the reactor after suitable cleaning, thereby saving energy in the form of recompression. This method has the advantage that certain soluble impurities (such as aluminum alkyl compounds and organic esters) are removed from the polymer. This in turn leads to a polymer product with a lower content of impurities.

Because of the generally high productivity

one has on the aforementioned catalyst system expressed in kg of polymer produced per kg titanium metal, then there is no need to remove catalyst residues from the polymer in a washing step, which is the case with ordinary catalysts.

Various additives can, if desired, be incorporated into the polypropylene resin such as fibers, fillers, antioxidants, metal deactivators, heat and light stabilizers, dyes, pigments, lubricants and the like.

The polymers can be advantageously used in the production of fibres, threads and films by extrusion, of solid articles by injection molding and for the production of bottles by a blow molding technique.

The advantages of polymers according to the present invention compared to polymers prepared by common known catalysts and with similar mechanical properties include a wider processing area, lower requirements with regard to energy during processing, superior ability to fill thin sections and molds with many cavities, and in production of continuous threads or fibers has better drawability and higher processing speed.

Based on spiral melting current measurements, it was found e.g. that polymers according to the present invention with melt flows (ASTM 1238) varying from 2-12 g per 10 minutes could be processed at molding temperatures that ranged from 25-15°C lower, and at molding pressures that ranged from 25-10.7 kg/cm<2>lower than ordinary polymers with the same melt flows

(ASTM 1238) .

It is assumed that it is the molecular weight distribution, Mw/Mn, which is the property that best relates to improvements in the polymer's rheological properties and its processability. Typical polymerization with common catalyst systems would give a polymer with a Mw/Mn ratio of a maximum of 6.5, and usually 6, whereas polymers of the present invention have Mw/Mn ratios of at least 7, e.g. between approx. 7 and approx. 10.

The following examples illustrate the invention.

EXAMPLES 1 and 2

Homopolymerizations of propylene were carried out in

a large experimental plant where monomer and catalyst components were continuously fed into a reactor, and where the monomer feed rate corresponded to a residence time of

about. 2 hours in the reactor. The organoaluminum compound in the catalyst system was a hexane solution of either triisobutylaluminum (TIBA) or triethylaluminum (TEA) which had been previously treated with a hexane solution of methyl p-toluate (MPT), an electron donor compound. The solid supported titanium halide catalyst component was a commercially available catalyst. substances. Ethyl benzoate had been used during the preparation of the supported catalyst component. The two catalyst components were added at rates directly proportional to the production rate of polypropylene and in amounts sufficient to maintain the concentration of polymer solids in the reactor suspension at a nominal value of about 40 %. The catalyst productivity (kg polymer per kg titanium metal) was calculated in each case from the withdrawal rate of the polymer suspension, the content of solids in the suspension and the addition rate of the titanium catalyst component. The operating conditions used and the results are shown in Table 1 together with typical characteristics of a control product made from washed polypropylene n obtained using standard catalyst components, i.e. co-crystallized STiCl^-AlCl^ with diethyl aluminum chloride as co-catalyst.

As indicated in the table, standard ASTM test methods were used to determine most of the properties of the polymer product.

The Mw/Mn ratio was determined by liquid chromatography using o-dichlorobenzene as solvent.

The isotactic index was obtained by determining the percent insolubles in heptane after the polymer had been extracted with boiling heptane, and the dimer-trimer content was found by gas chromatographic analyzes of the heptane extract at room temperature.

The crystalline melting point was measured by differential scanning calorimetry.

The contents of Ti, Mg and Al were determined by atomic absorption analysis of the polymer ash dissolved in hydrochloric acid, and the chlorine content was determined by colorimetric determination of a burnt polymer sample using a Parr oxygen bomb.

It goes without saying that one can easily perform

variations and modifications with the propylene polymer according to the present invention. All such variations and modifications are considered to lie within the intention of the invention as it appears from the following claims.

Claims (10)

1. Propylene polymer, characterized by a melt flow range from approx. 0.2 to 30 g per 10 minutes, an isotactic index of no less than approx. 92%, a dimer-trimer content that does not exceed approx. 4 g/kg, a crystalline melting point of at least approx. 165°C, a ratio between the weight average molecular weight and the number average molecular weight (Mw/Mn) of at least approx. 7, a Ti content that does not exceed approx. 3 ppm, a Mg content that does not exceed approx. 40 ppm, a Cl content that does not exceed approx. 100 ppm and a total ash content that does not exceed approx. 400ppm. 2. Polymer according to claim 1, characterized in that said Mw/Mn ratio varies from approx. 7 to approx. 10. 3. Process for the production of polymer according to claim 1, characterized in that one: continuously feed propylene monomer and catalyst components to a polymerization reactor, polymerizes said propylene at a temperature between 46 and 80°C at a sufficiently high pressure so that at least part of the propylene is maintained in the liquid phase, and where the product is removed in an essentially continuous manner as a suspension in liquid propylene, and where the catalyst composition consists of the following components: (a) an aluminum trialkyl or an aluminum trialkyl which is at least partially complexed with an electron-donor compound, and (b) a titanium tri- or tetrahalide supported by a magnesium dihalide, or a complex of a titanium tri- or tetrahalide with an electron donor compound supported on a magnesium dihalide. 4. Method according to claim 3, characterized in that the electron-donor compound in component (a) in the catalyst composition is an ester of a carboxylic acid or a diamine. 5. Method according to claim 3, characterized in that the molar ratio between trialkyl aluminum and electron donor varies from approx. 1 to approx. 100. 6. Method according to claim 3, characterized in that component (a) is prepared by pre-reacting the aluminum trialkyl with the electron donor for less than an hour before the polymerisation. 7. Method according to claim 14, characterized in that said electron donor is an ester of an aromatic carboxylic acid. 8. Method according to claim 3, characterized in that the molar ratio between said magnesium and said electron donor in component (b) is at least approx. 1. 9. Method according to claim 3, characterized in that the titanium content expressed as titanium metal varies from approx. 0.1 to approx. 20% by weight in the supported catalyst component (b). 10. Method according to claim 3, characterized in that the catalyst components (a) and (b) are added to the reaction zone in a molar ratio between Al/Ti of between 1 and approx. 10,000.