MXPA00011728A - Molecular weight control in olefin polymerization - Google Patents

Abstract

The molecular weight of polyolefins produced using iron or cobalt complexes of 2, 6-pyridinecarboxaldehyde diimines or a 2,6-diacylpyridine diimines as polymerization catalysts may be lowered by carrying out the polymerization in the presence of hydrogen.

Description

CONTROL OF MOLECULAR WEIGHT IN OLEFIN POLYMERIZATION FIELD OF THE INVENTION In polymerizations of olefins in which iron or cobalt complexes of 2,6-pyridinecarboxaldehyde diimines or 2,6-diacylpyridine diimines are used as polymerization catalysts, hydrogen can be used as a chain transfer agent to reduce the molecular weight of the polyolefin. BACKGROUND OF THE INVENTION The polymerization of olefins using catalysts containing early transition metals such as vanadium and zirconium, is a well-known and commercially important technology. In many cases it is desirable to decrease the molecular weight of the polyolefin that would normally be produced. For example, lower molecular weight polymers are usually considered easier for the melting process, since they have lower melt viscosities. While the conditions of the polymerization process can sometimes be altered to change the molecular weight of the resulting olefin, often a chain transfer agent such as hydrogen is desirably added to the process, to decrease the molecular weight of the polyolefin. The polymerization of olefins, especially from Ref: 124141 ethylene and propylene, using catalysts containing iron or cobalt complexes of 2,6-pyridinecarboxaldehyde diimines or 2,6-diacylpyridine diimines, see, for example, US Patent Applications 08 / 991,372, filed December 16, 1997 and 09 / 006,031, filed January 12, 1998. However, methods for decreasing the molecular weight of polyolefins produced in such processes are not known (except that by decreasing the steric loading of the ligand, a weight-bearing polymer is often obtained. lower molecular). BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a process for the polymerization of a polymerizable olefin using a iron or cobalt complex of a 2,6-pyridinecarboxaldehyde diimine or 2,6-diacylpyridine diimine as the polymerization catalyst, wherein the improvement comprises, using chain transfer agent an effective amount of hydrogen. The present invention also relates to a process for the polymerization of one or more polymerizable olefins, which comprises contacting, under polymerization conditions: (a) one or more polymerizable olefins; (b) hydrogen in an amount effective as a chain transfer agent; and (c) an active polymerization catalyst containing an iron or cobalt complex of a 2,6-pyridinecarboxaldehyde diimine or a 2,6-diacylpyridine diimine. DETAILED DESCRIPTION OF THE INVENTION In the polymerization processes and catalyst compositions described herein, certain groups may be present. The term "hydrocarbyl" means a univalent radical containing only carbon and hydrogen. The term "saturated hydrocarbyl" means a univalent radical containing only carbon and hydrogen and does not contain carbon-carbon double bonds, triple bonds or aromatic groups. The term "substituted hydrocarbyl" as used herein means a hydrocarbyl group containing one or more (types of) substituents that do not interfere with the operation of the polymerization catalyst system. Suitable substituents in some polymerizations may include some or all of the following, halo, ester, keto (oxo), amino, imino, carboxyl, phosphite, phosphonite, phosphine, phosphinite, thioether, amide, nitrile and ether groups. Preferred substituents are the halo, ester, amino, imino, carboxyl, phosphite, phosphonite, phosphine, phosphinite, thioether and amide radicals. Substituents that are useful in these polymerizations, in some cases can be determined by reference to US Patent Applications 08 / 991,372, filed on December 16, 1997 and 09 / 006,031, filed on January 12, 1998., which are included herein as a reference. If not stated otherwise, the hydrocarbyl, substituted hydrocarbyl groups and all other groups containing carbon atoms, such as alkyl, preferably contain from 1 to 20 carbon atoms. Non-coordinating ions are mentioned and are useful herein. Such anions are well known to those skilled in the art, see for example W. Beck. , et al. , Chem. Rev., vol. 88, p. 1405-1421 (1988), and S. H. Strauss, Chem. Rev., vol. 93, p. 927-942 (1993), which are incorporated herein by reference. With regard to the coordinating capacities of such non-coordinating anions, these are described in the following references Beck on page 1411 and Strauss on page 932, Table III. Useful non-coordinating anions include SbF <; f, BAF, PF6"or BF4", wherein BAF is tetrakis [3,5-bis (trifluoromethyl) -phenyl] -borate. A neutral Lewis acid or a Lewis or Bronsted cationic acid whose counter ion is a weakly coordinating anion may also be present as part of the catalyst system. The term "neutral Lewis acid" means a compound that is a Lewis acid capable of subtracting X from the compound of the formula (I) to form a weakly coordinating anion.

In formula (I), M is Co or Fe, each X is independently an anion and each X is such that the total of negative charges in X is equal to the oxidation state of M (for R1 to R7, see below) . The neutral Lewis acid originally has no charge (i.e., is not ionic). Suitable neutral Lewis acids include SbF5, Ar3B (where Ar is an aryl group) and BF3. The term "cationic Lewis acid" means a cation with a positive charge, such as Ag +, H + and Na +. A preferred neutral Lewis acid, which can be alkylated to the metal, is an alkylaluminum compound selected from the group consisting of R93A1, R92A1C1, R9A1C12 and "R9A10" (alkylaluminoxanes), wherein R9 is an alkyl radical containing from 1 to 25 carbon atoms, preferably from 1 to 4 carbon atoms. Suitable alkylaluminium compounds include methylaluminoxane (which is an oligomer with the general formula [MeA10] n), (C2H5) 2A1C1, C2H5A1C12 and [(CH3) 2CHCH2j3Al. Metal hydrides such as NaBH 4 can be used to bind hydride groups to metal M. The term "iron or cobalt complex of a 2,6-pyridinecarboxaldehyde diimine or a 2,6-diacylpyridine diimine", as used herein, means a Fe or Co complex of a ligand of the formula: (II! wherein: R1, R2 and R3 each independently are a hydrogen atom, a hydrocarbyl radical, a substituted hydrocarbyl or an inert functional group; R4 and R5 are each independently a hydrogen atom, a hydrocarbyl radical, an inert functional group or a substituted hydrocarbyl group; and R6 and R7 are an aryl or substituted aryl group. For compounds such as those of formulas (I) and (II) and similar compounds, preferred formulas are found in US Patent Applications Nos. 08 / 991,372, filed December 16, 1997 and 09 / 006,031, filed on January 12, 1998, which 5 are incorporated herein by reference and preferred groups and compounds in these applications are also preferred herein. However, the numbers of the compounds and the group (i.e., Rx) in these applications may vary from those of the present, but are easily convertibles. These applications also describe the synthesis of various ligands and iron and cobalt complexes. In a preferred type of compound, such as that of formula (I) or that of formula (II), R1 'R2 and R3 are Hydrogen and / or R4 and R5 are each independently hydrogen or an alkyl group, especially hydrogen or methyl, and / or R6 is a group and / or R7 is áe ^, - wherein: R8 and R13 each independently are a hydrocarbyl radical, substituted hydrocarbyl or an inert functional group; R9, R10, R11, R14, R15 and R16 are each independently a hydrogen atom, a hydrocarbyl radical, a substituted hydrocarbyl or an inert functional group; R12 and R17 each independently are a hydrogen atom, a hydrocarbyl radical, a substituted hydrocarbyl or an inert functional group; and provided that any two of R8, R9, R10, R11, R12 ', R13, R14, R15, R16 and R17 that are neighbors, taken together, can form a ring. There are many different ways of preparing the active iron and cobalt polymerization catalysts that are used herein, many of which are described in US Patent Applications Nos. 08 / 991,372 filed December 16, 1997 and 09 / 006,031. , presented on January 12, 1998 and those »- * ^? A! ^. described are applicable in the present. "Pure" compounds can be used which themselves can be active polymerization catalysts, or the active polymerization catalyst can be prepared in itself by a variety of methods. Other methods for preparing active polymerization catalysts will be found in this patent application and in the examples herein. The active polymerization catalysts will polymerize the olefins (not all catalysts will polymerize all olefins or olefin combinations) will also be found in US Patent Applications Nos. 08/991, 372 filed December 16, 1997 and 09 / 006,031, filed January 12, 1998. Monomers useful herein include ethylene and propylene and ethylene is preferred. When hydrogen is used as the chain transfer agent, it is preferred that the amount of hydrogen present is from about 0.1 to about 80 mole percent of the olefin present, preferably from about to about 20 mole percent. Suitable and preferred conditions for polymerizations can be found in US Patent Applications Nos. 08 / 991,372, filed December 16, 1997 and 09 / 006,031, filed January 12, 1998. Polymerization can be carried out in any way known in the art, for example batch or continuously, in slurry, in gas phase or in solution, and the catalyst may or may not be supported, or any combination thereof. The polymers produced are useful as molding and extrusion resins, for example to prepare packaging films, bottles and mechanical parts. In the Example and the Comparative Example, all pressures are gauge. The term "THF" means tetrahydrofuran. Regarding molecular weights, they were judged by measuring the melt index of the polymer, in accordance with ASTM D1238-95, Procedure A. The higher the Melt Index, the more molecular weight. EXAMPLE 1 POLYETHYLENE (III) A 600 ml Parr ™ shaking autoclave was charged with 200 ml of anhydrous hexane containing 1.0 ml of MMA0-3A (1.7M in heptane, Methylaluminoxane modified by Akzo; contains approximately 30% isobutyl groups) and , K * A & , ... ¿j ^ ia ^ t 0.2 ml of triisobutylaluminum (l.OM in toluene), under a nitrogen atmosphere. The nitrogen was displaced by introducing 1.03 MPa of ethylene under pressure and ventilating three times. A toluene solution of 1 mg of the compound of the formula (III) (0.00147 mmol) was then rapidly injected through an inlet port. The autoclave was sealed and immediately pressurized to 140 kPa with hydrogen; then the pressure was increased to 1.03 MPa with ethylene (giving 13 mol% of hydrogen in the gas phase) and stirred for 30 minutes with continuous ethylene feed (without additional hydrogen). The internal temperature of the autoclave was raised from 18 to 46 ° C in the first minute and subsequently maintained at approximately 50 ° C. After 30 minutes, the ethylene was vented and the resulting clear suspension of fine white polyethylene powder was filtered by suction and dried in a vacuum oven, to obtain 15.0 g of polyethylene powder. melt index (190 ° C, 2160-g wt): 32 g / 10 minutes. COMPARATIVE EXAMPLE 1 POLYETHYLENE (III) A 600 ml Parr ™ shaking autoclave was charged with 200 ml of anhydrous hexane containing 1.0 ml of MMAO-3A (1.7M in heptane, Akzo modified methylaluminoxane containing approximately 30% isobutyl groups) and 0.2 ml of triisobutylaluminum ( .OM in toluene), under a nitrogen atmosphere. The nitrogen was displaced by introducing 1.03 MPa of ethylene under pressure and ventilating three times. A toluene solution of 1 mg of the compound of the formula (III) (0.00147 mmol) was then rapidly injected through an inlet port. The autoclave was immediately pressurized to 1.03 MPa with ethylene and stirred for 30 minutes with continuous ethylene feed. The internal temperature of the autoclave rose from 22 to a peak of 55 ° C in the first three minutes and subsequently remained at approximately 50 ° C. After 30 minutes, the ethylene was vented and the resulting clear suspension of fine white polyethylene powder was filtered by suction and dried in a vacuum oven, to obtain 14.9 g of polyethylene powder. fusion index (190 ° C, 2160-g wt): 1.05 g / 10 minutes. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (6)

1. CLAIMS Having described the invention as an antecedent, the content of the following claims is claimed as property: 1. An improved process for the polymerization of a polymerizable olefin using a iron or cobalt complex of a 2,6-pyridinecarboxaldehyde diimine as the polymerization catalyst. or a 2,6-diacylpyridine diimine, characterized in that the improvement comprises the use, as a chain transfer agent, of an effective amount of hydrogen.
2. 2. A process for the polymerization of one or more polymerizable olefins, characterized in that it comprises contacting under polymerization conditions: (a) one or more polymerizable olefins; (b) hydrogen in an amount effective as a chain transfer agent; (c) an active polymerization catalyst containing an iron or cobalt complex of a 2,6-pyridinecarboxaldehyde diimine or a 2,6-diacylpyridine diimine.
3. The process according to any of claims 1 or 2, characterized in that the 2,6-pyridinecarboxaldehyde diimine or 2,6-diacylpyridine diimine is of the formula (ID wherein: R1, R2 and R3 each are independently a hydrogen atom, a hydrocarbyl radical, a substituted hydrocarbyl or an inert functional group, R4 and R5 are each independently a hydrogen atom, a hydrocarbyl radical, a functional group inert or a substituted hydrocarbyl, and R6 and R7 are an aryl or substituted aryl radical
4. 4. The process according to claim 3, characterized in that: R1, R2 and R3 are a hydrogen atom, R4 and R5 each independently are hydrogen or alkyl; R6 is (IV); and R7 is wherein: R8 and R13 are each independently a hydrocarbyl radical, substituted hydrocarbyl or an inert functional group; R9, R10, R11, R14, R15 and R16 are each independently a hydrogen atom, a hydrocarbyl radical, a substituted hydrocarbyl or an inert functional group; R12 and R17 are each independently a hydrogen atom, a hydrocarbyl radical, a substituted hydrocarbyl or an inert functional group; and provided that any two of R8, R9, R10, R11, R12, R13, R14, R15, R16 and R17 that are neighbors taken together can form a ring.
5. 5. The process according to any of claims 1 or 2, characterized in that the polymerizable olefin is ethylene.
6. 6. The process according to claim 5, characterized in that the complex is an iron complex.