CONTROL OF UNSATURATION IN POLYMERS PRODUCED IN SOLUTION PROCESS

Abstract

The copolymerization of ethylene with an optional comonomer is conducted in the presence of a catalyst having a specific aryloxy ether ligand structure. The process enables very high conversions of ethylene to polyethylene at very short residence times when conducted under conditions of pressures of at least 10.3 MPa and high ethylene feed concentrations of from 70 to 150 grams per liter. Using these polymerization conditions, the level of unsaturation may be controlled by the polymerization temperature: for example, a level of 0.09 vinyl groups per 1000 carbon atoms was observed at a polymerization temperature of 160° C. and a level of 0.22 vinyls per 1000 carbon atoms was observed at 220° C.

Claims

1. A process for the (co)polymerization of ethylene and, optionally, at least one C.sub.3 to C.sub.10 alpha olefin comonomer wherein said process is conducted under solution polymerization conditions using a catalyst system comprising: A) a catalyst defined by the formula: ##STR00007## M is titanium, zirconium, or hafnium, each independently being in a formal oxidation state of +4; n is 2; Each X independently is a monodentate ligand; X is chosen in such a way that the metal-ligand complex of formula (I) is, overall, neutral; L is hydrocarbylene or heterohydrocarbylene, wherein the hydrocarbylene has a portion that comprises a 1-carbon atom to 6-carbon atom linker backbone linking the O atoms in formula (I) and the heterohydrocarbylene has a portion that comprises a 1-atom to 6-atom linker backbone linking the O atoms in formula (I), wherein each atom of the 1-atom to 6-atom linker backbone of the heterohydrocarbylene independently is a carbon atom or a heteroatom, wherein each heteroatom independently is O, S, S(O), S(O).sub.2, Si(R.sup.C).sub.2, Ge(R.sup.C).sub.2, P(R.sup.P), or N(R.sup.N), wherein independently each R.sup.C is unsubstituted (C1-C18)hydrocarbyl or the two R.sup.C are taken together to form a (C2-C19)alkylene, each R.sup.P is unsubstituted (C1-C18)hydrocarbyl; and each R.sup.N is unsubstituted (C1-C18)hydrocarbyl, a hydrogen atom or absent; Each of R.sup.1a, R.sup.1b, R.sup.2a, R.sup.2b, R.sup.3a, R.sup.3b, R.sup.4a, R.sup.4b, R.sup.5c, R.sup.5d, R.sup.6c, R.sup.6d, R.sup.7c, R.sup.7d, R.sup.8e, R.sup.8f, R.sup.9e, R.sup.9f, R.sup.10e, R.sup.10f, R.sup.11e, R.sup.11f, R.sup.12e, R.sup.12f, R.sup.13e, R.sup.13f, R.sup.14e, R.sup.14f, R.sup.15e, R.sup.15f independently is a hydrogen atom; hydrocarbyl; heterohydrocarbyl; or halogen atom; B) and an activator, wherein said solution polymerization is conducted under the following conditions: 1) an ethylene feed concentration of from 70 to 200 grams per liter of feed solvent; 2) a pressure of from 10.3 to 31 MPa; 3) a reactor residence time of from 0.5 to 5 minutes, with the proviso that from 50 to 95 weight % of the ethylene in said feed is converted to polymer within said residence time of from 0.5 to 5 minutes, with the proviso that the polymerization is conducted at a temperature of greater than 160° C. so as to produce an ethylene polymer having a degree of unsaturation of greater than 0.1 vinyl groups per 1000 carbon atoms as measured by Fourier Transform Infra Red spectroscopy.

2. The process of claim 1 wherein said L is hydrocarbylene and comprises a 1-carbon atom to 6-carbon atom linker.

3. The process of claim 1 wherein said at least one C.sub.3 to C.sub.10 comonomer is chosen from propylene; 1-butene; 1-hexene and 1-octene.

4. The process of claim 1 wherein said activator comprises a boron ionic activator.

5. The process of claim 1 wherein said activator comprises a boron ionic activator and an alumoxane.

6. The process of claim 1 wherein said M is hafnium.

7. The process of claim 6 wherein said activator comprises a boron ionic activator and an alumoxane.

8. The process of claim 7 wherein the mole ratio of boron in said boron ionic activator to the hafnium in said catalyst is from 1:1 to 2:1 and the mole ratio of aluminum in said alumoxane to the hafnium in said catalyst is from 2:1 to 1000:1.

Description

EXAMPLES

Part 1: Chemicals and Common Procedures Handlings

[0061] Ethylene was purchased from Praxair as polymer grade. The ethylene was purified and dried by passing the gas through a series of purification beds including alumina, 13X molecular sieves, and a conventional deoxygenation bed.

[0062] Purchased 1-octene was dried by storing a 1-liter batch over molesieve 3A.

[0063] Methanol was purchased as GR ACS grade from EMD Chemicals.

[0064] Xylene was purchased from Univar. It was purified and dried by passing through a deoxygenation catalyst, alumina, and 3A and 13X molecular sieve beds). Cylcohexane was purchased from Univar. It was purified and dried by passing through a deoxygenation catalyst, alumina beds, and 3A and 13X molecular sieve beds.

[0065] 13x molecular sieves were purchased from Grace Davison and stored in general lab storage. Before being used as a drying agent, the molecular sieves were heated for 16 hours at 360° C. to activate them and were then pumped into a glovebox at full dynamic vacuum for at least 3 hours. 3A molsieves: Pellets were activated in the same manner.

[0066] Triphenylmethylcarbenium tetrakis(pentafluorophenyl)borate [“trityl borate” ] was purchased from Albemarle and used without further purification.

[0067] Modified methylaluminoxane-7 (MMAO-7) was purchased as a 7 wt % solution in ISOPAR™ E from Akzo Nobel Polymer Chemicals. It was contained in a pyrosafe cylinder and used as received in a glovebox.

[0068] 2,6-di-tert-butyl-4-ethylphenol (BHEB) was purchased as a 99% pure compound and used without further purification.

[0069] The catalyst was made using techniques generally known to those skilled in the art and also disclosed in U.S. Patent Application No. 20150337062 (Demirors et al.; to Dow Global).

Part 2: Polymerization and Polymer Characterizations

[0070] All the polymerization experiments described below were conducted using a continuous solution polymerization reactor. The process is continuous in all feed streams (solvent, monomers and catalyst) and in the removal of product. All feed streams were purified prior to the reactor by contact with various absorption media to remove catalyst killing impurities such as water, oxygen and polar materials as is known to those skilled in the art. All components were stored and manipulated under an atmosphere of purified nitrogen.

[0071] All the examples below were conducted in a reactor of 71.5 cc internal volume. In each experiment the volumetric feed to the reactor was kept constant and as a consequence so was the reactor residence time.

[0072] The catalyst solutions were pumped to the reactor independently and there was no pre-contact between the activator and the catalyst. Because of the low solubility of the catalysts, activators and MAO in cyclohexane, solutions were prepared in toluene. The catalyst was activated in situ (in the polymerization reactor) at the reaction temperature in the presence of the monomers. The polymerizations were carried out in cyclohexane at a pressure of 10.3 MPa. Ethylene was supplied to the reactor by a calibrated thermal mass flow meter and was dissolved in the reaction solvent prior to the polymerization reactor. If comonomer was used it was also premixed with the ethylene before entering the polymerization reactor. Under these conditions the ethylene conversion is a dependent variable controlled by the catalyst concentration, reaction temperature and catalyst activity.

[0073] The internal reactor temperature is monitored by a thermocouple in the polymerization medium and can be controlled at the set point to +/−0.5° C. Downstream of the reactor the pressure was reduced from the reaction pressure 10.3 MPa to atmospheric pressure. The solid polymer was then recovered as a slurry in the condensed solvent and was dried in vacuum oven before analysis.

[0074] The ethylene conversion was determined by a dedicated on-line gas chromatograph. The average polymerization rate constant Kp was calculated based on the reactor hold-up time, the catalyst concentration and the ethylene conversion and is expressed in l/(mmol*min).

Kp is calculated as Kp=(Q/(100−Q))1×(1/TM)×(1/HUT)

where: [0075] Q=the percent ethylene conversion [0076] TM=the reactor catalyst concentration in mM [0077] HUT=the reactor hold-up time in minutes

[0078] Polymerization results are shown in Table 1.

Polymer Analysis

[0079] GPC analysis was carried out using a Waters 150 C GPC using 1,2,4-trichlorobenzene as the mobile phase at 140° C. The samples were prepared by dissolving the polymer in the mobile phase solvent in an external oven at 0.1% (w/v) and were run without filtration. Molecular weights are expressed as polyethylene equivalents with a relative standard deviation of 2.9% and 5.0% for the number average (Mn) and weight average (Mw) respectively. Poly dispersity (“PD”) is Mw/Mn.

[0080] Polymer densities were measured using pressed plaques (ASTM D-1928-90) with a densitometer.

[0081] Polymer branch frequencies (SBr) and polymer unsaturation were determined by Fourier Transform Infra Red (FT-IR) spectroscopy. The instrument used was a Nicolet 750 Magna-IR spectrophotometer.

[0082] Unsaturation data are shown in Table 2. The data in Table 2 illustrate that, under the polymerization conditions of these examples, the level of unsaturation may be controlled (increased) by increasing the polymerization temperature. (The run numbers in Table 2 correspond to those of Table 1.)

TABLE-US-00001 TABLE 1 Catalyst Activity and Polymer Molecular Weight Under Varying Process Conditions Reactor Run Temp. C2 C8/C2 Kp Mw SBr/ Catalyst # (° C.) g/l (wt/wt) Q (%) (1/mM*min) (10.sup.−3) PD 1000C uM Al/Hf 1 220 160 0.3 89.62 677 132.4 2.3 14.6 4.9 4.1 2 220 180 0.3 89.66 463 123.0 2.0 14.9 7.2 2.8 3 190 130 0.3 90.20 1826 203.3 2.1 15.4 1.9 10.3 4 190 180 0.3 90.52 620 154.1 2.2 13.9 5.9 3.4 5 160 100 0.3 90.58 10682 326.6 2.3 16.7 0.35 57.8 6 160 100 0.3 90.28 6449 297.1 2.3 17.1 0.56 36.1 7 160 100 0.5 89.57 5962 295.4 2.3 27.8 0.56 53.9 8 160 100 0.7 89.45 5887 263.6 2.3 35.8 0.56 36.1 C2 = ethylene C8 = octene

[0083] The total flow of solvent and ethylene was 27.5 ml per minute which provides hold up times (HUT) of between 2.1 minutes (for the ethylene flow rate of 75 grams of ethylene per liter of feed) and 1.9 minutes (for the ethylene flow rate of 120 grams of ethylene per liter of feed).

[0084] The catalyst used in all examples is described by the following formula:

##STR00006##

[0085] The catalyst was activated with methylalumoxane (MAO) and trityl borate. The reactor catalyst concentration (expressed as uM of Hf) is shown in Table 1, as is the Al/Hf mole ratio. Trityl borate was used in a B:Hf mole ratio of 1:2/1 in all experiments. BHEB was also used at a mole ratio (BHEB:Al) of 0.3:1 in all experiments.

TABLE-US-00002 TABLE 2 Unsaturation Levels Reactor Temperature Unsaturation Run# (° C.) (Vinyls per 1000 Carbon Atoms) 2 220 0.22 4 190 0.19 6 160 0.1 8 160 0.09

INDUSTRIAL APPLICABILITY

[0086] The copolymerization of ethylene and comonomer(s) is disclosed. The resulting polymers are suitable for the preparation of a wide variety of goods including plastic toys; plastic parts and profiles and plastic films.