Process for preparing propylene/1-butene copolymers

Abstract

The present invention relates to an olefin polymerization process, wherein propylene and 1-butene and optionally ethylene are reacted in the presence of a Ziegler-Natta catalyst system so as to obtain a polypropylene, wherein the polypropylene comprises 1-butene-derived comonomer units in an amount of from 5 to 20 wt % and optionally ethylene-derived comonomer units in an amount of up to 3 wt %, and the Ziegler-Natta catalyst system comprises an external donor of the following formula (I): (R.sup.3).sub.z(R.sup.2O).sub.ySi(R.sup.1).sub.x.

Claims

1. An olefin polymerization process comprising reacting propylene, 1-butene, and ethylene in the presence of a Ziegler-Natta catalyst system to obtain a polypropylene, wherein the polypropylene is a terpolymer and comprises 1-butene-derived comonomer units in an amount of from 5 to 20 wt % and ethylene-derived comonomer units in an amount of up to 3 wt %, and wherein the Ziegler-Natta catalyst system comprises an external donor of the following formula (I)
(R.sup.3).sub.z(R.sup.2O).sub.ySi(R.sup.1).sub.x(I) wherein x is 1 or 2; y is 2or 3; and z is 0 or 1; under the provision that x+y+z=4; R.sup.1 is an organic residue of the following formula (II) ##STR00006## wherein a carbon atom bonded to the Si atom is a tertiary carbon atom and each of the residues R.sup.4 and R.sup.5 bonded to the tertiary carbon atom is, independently, a C.sub.1-2 alkyl; each of the residues R.sup.6 and R.sup.7 is, independently, a C.sub.1-2 alkyl; R.sup.8 is hydrogen or a C.sub.1-4 alkyl; R.sup.2 is C.sub.1-2 alkyl; and R.sup.3 is C.sub.1-4 alkyl.

2. The process according to claim 1, wherein R.sup.3 is methyl or ethyl.

3. The process according to claim 1, wherein x is 1, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are methyl, and R.sup.8 is hydrogen or C.sub.1-2 alkyl.

4. The process according to claim 1, wherein the polypropylene has an amount of xylene solubles XS of 10.0 wt % or less and/or a melt flow rate MFR.sub.2 of from 1.0 to 100 g/10 min.

5. The process according to claim 1, wherein the Ziegler-Natta catalyst system comprises: a Ziegler-Natta procatalyst which comprises a titanium compound, and an organometallic cocatalyst which comprises an aluminium compound.

6. The process according to claim 1, wherein a molar ratio of aluminium to Ti in the Ziegler-Natta catalyst system is from 10/1 to 1000/1 and/or a molar ratio of the external donor to Ti in the Ziegler-Natta catalyst system is from 1/1 to 100/1.

7. The process according to claim 5, wherein the Ziegler-Natta procatalyst is obtained by a) reacting a spray crystallized or emulsion solidified adduct of MgCl.sub.2 and a C.sub.1-C.sub.2 alcohol with TiCl.sub.4 and b) reacting the product of a) with a dialkylphthalate of formula: ##STR00007## wherein R.sup.1 and R.sup.2 are independently an alkyl group having at least 5 carbon atoms, under conditions where a transesterification between said C.sub.1 to C.sub.2 alcohol and said dialkylphthalate takes place; a) optionally washing the product of b) and/or b) optionally reacting the product of b) or c) with additional TiCl.sub.4.

8. A process for preparing a film comprising preparing a polypropylene by the olefin polymerization process according to claim 1 and processing the polypropylene to a film.

9. The process according to claim 3, wherein the polypropylene has an amount of xylene solubles XS of 10.0 wt % or less and/or a melt flow rate MFR.sub.2 of from 1.0 to 100 g/10 min.

10. The process according to claim 3, wherein the Ziegler-Natta catalyst system comprises: a Ziegler-Natta procatalyst which comprises a titanium compound, and an organometallic cocatalyst which comprises an aluminium compound.

11. The process according to claim 3, wherein a molar ratio of aluminium to Ti in the Ziegler-Natta catalyst system is from 10/1 to 1000/1 and/or a molar ratio of the external donor to Ti in the Ziegler-Natta catalyst system is from 1/1 to 100/1.

12. The process according to claim 3, wherein the Ziegler-Natta procatalyst is obtained by a) reacting a spray crystallized or emulsion solidified adduct of MgCl.sub.2 and a C.sub.1-C.sub.2 alcohol with TiCl.sub.4 and b) reacting the product of a) with a dialkylphthalate of formula: ##STR00008## wherein R.sup.1 and R.sup.2 are independently an alkyl group having at least 5 carbon atoms, under conditions where a transesterification between said C.sub.1 to C.sub.2 alcohol and said dialkylphthalate takes place; a) optionally washing the product of b) and/or b) optionally reacting the product of b) or c) with additional TiCl.sub.4.

Description

EXAMPLES

(1) I. Measuring Methods

(2) If not otherwise indicated, the parameters mentioned in the present application are measured by the methods outlined below.

(3) 1. Comonomer Content by IR Spectroscopy

(4) The 1-butene content and, if present, the ethylene content of the copolymers or terpolymers has been measured by FT-IR spectroscopy.

(5) Before measuring, the stabilized powder was pressed in the IR press as follows:

(6) Press Settings to Homogenise the Material: press temperature: 210 C. melting time: 90 sec cooling rate: 12 C/min de-moulding temperature between 35 and 45 C.

(7) TABLE-US-00001 step 1 2 (cooling) duration (sec.) 90 900 Temperature ( C.) 210 30 pressure (bar) 0 0

(8) Press Settings for IR Plate: press temperature: 210 C. melting time: 45 sec press pressure: 3 steps (10/30/90 bar) cooling rate: 12 C./min de-moulding temperature: between 35 and 45 C.

(9) TABLE-US-00002 1 2 3 4 5 (cooling) duration (sec.) 45 15 15 15 900 Temperature ( C.) 210 210 210 210 30 pressure (bar) 0 10 30 90 90

(10) The films had a thickness of between 260 and 300 m

(11) Spectra have been recorded in transmission mode. Relevant instrument settings include a spectral window of 5000 to 400 wave-numbers (cm.sup.-1), a resolution of 2.0 cm.sup.-1 and 16 scans. The butene content of the propylene-butene copolymers was determined using the baseline corrected peak maxima of a quantitative band at 767 cm.sup.-1, with the baseline defined from 1945 to 625 cm.sup.1. The comonomer content in mol % was determined using a film thickness method using the intensity of the quantitative band 1767 (absorbance value) and the thickness (T, in cm) of the pressed film using the following relationship:
mol % C4=(1767/T1.8496)/1.8233

(12) In case of a propylene-ethylene-butene terpolymer, the 1-butene content was measured as described above but determined using the baseline corrected peak at 780 cm.sup.-1750 cm.sup.-1 and the ethylene content was determined using the baseline corrected peak at 748 cm.sup.-1 to 710 cm.sup.-1.

(13) 2. Amount of Xylene Solubles (XS, wt.-%)

(14) The amount of xylene solubles was determined at 25 C. according to ISO 16152; first edition; 2005-07-01.

(15) 3. MFR.sub.2

(16) Melt flow rate MFR.sub.2 was measured according to ISO 1133 (230 C., 2.16 kg load).

(17) 4. Melting Temperature

(18) The melting points (T.sub.m) were determined on a DSC Q2000 TA Instrument, by placing a 5-7 mg polymer sample, into a closed DSC aluminum pan, heating the sample from 30 C. to 225 C. at 10 C./min, holding for 10 min at 225 C., cooling from 225 C. to 30 C., holding for 5 min at 30 C., heating from 30 C. to 225 C. at 10 C./min. The reported values are those of the peak of the endothermic heat flow determined from the second heating scan

(19) II. Polymerisation Experiments

(20) In the Inventive Examples, the following external donors were used: Thexyltrimethoxysilane (in the following referred to as Donor ID1 or ID1), CAS no 142877-45-0

(21) ##STR00004## Thexyltriethoxysilane (in the following referred to as Donor ID2 or just ID2), CAS no 142877-46-1

(22) ##STR00005##

(23) Donors ID1 and ID2 were prepared according to the procedure described in EPO488595.

(24) In the Comparative Examples, the following external donor was used: Dicyclopentyldimethoxysilane (in the following referred to as Donor D or just D). CAS no126990-35-0

(25) In all Examples, triethylaluminium (TEA) was used as the organometallic cocatalyst. The same Ziegler-Natta procatalyst was used in all Examples and was prepared as follows:

(26) First, 0.1 mol of MgCl.sub.23 EtOH was suspended under inert conditions in 250 ml of decane in a reactor at atmospheric pressure. The solution was cooled to the temperature of 15 C. and 300 ml of cold TiCl.sub.4 was added while maintaining the temperature at said level. Then, the temperature of the slurry was increased slowly to 20 C. At this temperature, 0.02 mol of dioctylphthalate (DOP) was added to the slurry. After the addition of the phthalate, the temperature was raised to 135 C. during 90 minutes and the slurry was allowed to stand for 60 minutes. Then, another 300 ml of TiCl.sub.4 was added and the temperature was kept at 135 C. for 120 minutes. After this, the catalyst was filtered from the liquid and washed six times with 300 ml heptane at 80 C. Then, the catalyst was filtered and dried. Catalyst and its preparation concept is described in general e.g. in patent publications EP491566, EP591224 and EP586390.

(27) Polymerizations have been carried out in a 20-L bench scale reactor. The same Al/Ti and external donor/Ti molar ratios were used in all Examples: Al/Ti=250 mol/mol and external donor/Ti=25 mol/mol. A prepolymerization was carried out at 20 C., and liquid phase copolymerization was carried out at 75 C. Propylene and 1-butene have been fed to the reactor before the catalyst, and treated with 0 5 mmol TEA, in order to remove the remaining traces of impurities. The activated catalyst was fed last by means of a liquid propylene flow.

(28) Catalyst Preactivation:

(29) In the glovebox a defined amount of solid catalyst was transferred in a 20 ml stainless steel vial, with 10 ml hexane. Then 0.5 mmol triethylaluminium (TEA, 1 molar solution in hexane) was injected in a second steel vial with a total volume of 2 ml. Afterwards 2 mmol TEA+0.25 mmol donor (0.3 molar solution in hexane) were mixed for 5 minutes in a 5 ml syringe and added in the catalyst vial. In the following step, both vials were mounted on the autoclave

(30) Polymerization:

(31) A stirred autoclave (double helix stirrer) with a volume of 21.2 dm.sup.3 containing 0.2 barg propylene was filled with additional 4.33 kg propylene or with 3.45 kg propylene and the chosen amount of 1-butene (quality 2.6; supplier: AIR-Liquide) After adding 0.5 mmol TEA with 250 g propylene, a certain amount of H2 was added via mass flow controller (MFC). The solution was stirred at 20 C. and 250 rpm. After a total contact time of 5 min between the solid catalyst and the TEA/Donor solution, the catalyst was injected by means of 250 g propylene. Stirring speed was increased to 350 rpm (250 rpm for the terpolymerisation examples) and pre-polymerisation was run for 5 to 6 min at 20 C. The polymerisation temperature was then increased to 75 C. and held constant throughout the polymerization. In producing propylene-butene-ethylene terpolymer in addition a constant flow of 0.5 g/min of ethylene was fed via MFC throughout the polymerization (in Comparative Example 4 and Inventive example 6). For these experiments the reactor pressure was held at 29 bar-g by adding propylene via MFC.

(32) The polymerization time was measured starting when the temperature reached 73 C. After 1 hour the reaction was stopped by adding 5 ml methanol, cooling the reactor and flashing the volatile components.

(33) After flushing the reactor twice with N2 and one vacuum/N.sub.2 cycle, the product was taken out and dried overnight in a fume hood. 100 g of the polymer was additivated with 0.2 wt % Ionol and 0.1 wt % PEPQ (dissolved in acetone) and then dried overnight in a hood plus 2 hours in a vacuum drying oven at 60 C.

(34) The polymerization conditions/results are shown in Tables 1 and 2, and Tables 3 and 4.

(35) TABLE-US-00003 TABLE 1 Polymerization conditions average calculated TEA1 added C4/(C3 + C4) External to monomers weight fraction Average H2 Catalyst External Al/Ti Donor/Ti (1 molar) in liquid phase temperature amount mg Donor mol/mol mol/mol mmol wt % C. NL CompEx1 24.6 D 250 25 0.5 24.7 75 27.3 CompEx2 24.1 D 250 25 0.5 28.0 75 27.3 CompEx3 24.9 D 250 25 0.5 35.0 75 27.3 InvEx1 25.0 ID1 250 25 0.5 18.2 75 10 InvEx2 24.8 ID1 250 25 0.5 24.0 75 10 InvEx3 25.4 ID1 250 25 0.5 30.8 75 10 InvEx4 24.6 ID2 250 25 0.5 17.5 75 6 InvEx5 25.0 ID2 250 25 0.5 22.8 75 6

(36) TABLE-US-00004 TABLE 2 Polymerization results total C4 total MFR.sub.2 (IR) XS T.sub.m Donor g/10 min wt % wt % C. CompEx1 D 9 5.8 2.3 147.3 CompEx2 D 8.8 6.2 2.4 146.7 CompEx3 D 11 8.3 3.0 142.9 InvEx1 ID1 6 5.0 2.2 148.8 InvEx2 ID1 4.8 6.8 2.6 145.6 InvEx3 ID1 6.2 9.1 3.6 141.1 InvEx4 ID2 12.9 4.9 5.7 148.5 InvEx5 ID2 12.3 7.2 6.7 144.5

(37) TABLE-US-00005 TABLE 3 Propylene-butene-ethylene polymerisation conditions Average calculated Average Catalyst External C4/(C4 + C3) C2 temp Total H2 amount External Donor/Ti Al/Ti in liquid phase feed in bulk in bulk Activity mg donor mol/mol mol/mol wt % g C. NL kgPP/gcat/h CompEx4 25.5 D 25 250 21.8 30 75 12 66 InvEx6 25.5 ID1 25 250 20.8 30 75 12 64

(38) TABLE-US-00006 TABLE 4 Polymer properties of Propylene-butene-ethylene terpolymers C4 C2 External MFR.sub.2 total (IR) total (IR) XS Tm donor g/10 min wt % wt % wt % C. CompEx4 D 3.6 5.5 0.9 2.8 143.9 InvEx6 ID1 5.5 7.3 1.0 3.6 139.8

(39) When evaluating a catalyst for its copolymerization performance, the most useful parameter to determine is the relative comonomer reactivity ratio R, which is defined by:

(40) $R=\frac{{\left(\frac{C_4}{C_3}\right)}_{\mathrm{polymer}}}{{\left(\frac{C_4}{C_3}\right)}_{\mathrm{liq}.Math.\mathrm{phase}}}$

(41) R is specific for a given catalyst and monomer pair. Since the concentration of 1-butene increases over the polymerization time while that of propylene decreases, there is a significant difference in liquid phase composition between start and end of the polymerisation experiment. For this reason, as liquid phase composition values, the average of the initial and final calculated values was used.

(42) The results are shown in FIG. 1 (i.e. relative C4/C3 reactivity ratio determination for Ziegler-Natta catalyst systems comprising external donor ID1, ID2, or D).

(43) The values of R determined for the Ziegler-Natta catalyst system comprising external donor D (R=0.17) and the Ziegler-Natta catalyst system comprising external donor ID1 or ID2 (R=0.23) show that the external donor of the present invention increases the butene reactivity of the Ziegler-Natta catalyst system.

(44) Turning the chart of FIG. 1 into wt % values provides the curves shown in FIG. 2 (correlation between wt % of C4 in the liquid phase and the copolymer composition). From FIG. 2, it can be concluded that, in order to produce a copolymer containing 9 wt % butene, the monomer feed requires 20% less butene when the ID1 donor is used (Inventive Examples 1-3), compared to the D donor (Comparative Examples 1-3).

(45) The same can be concluded based on the melting point of the copolymers. The correlation between comonomer content and melting point of propylene-butene copolymers is well known,see for example Cimmino, Martuscelli, Nicolais, Silvestre in Polymer 1978,19,1222; Crispino, Martuscelli, Pracella in Makromol Chem 1980,181,1747; Abiru, Mizuno, Weigand in J Appl Polym Sci 1998;68:1493.

(46) By comparing the melting points to the comonomer feed ratio, one can see that, at the same comonomer feed ratio, lower melting point (that is, higher butene content) is obtained using the catalyst system of the present invention compared to the catalyst system with the D donor. On the other hand, compared to the catalyst system with the D donor, the catalyst system of the present invention requires a lower butene/propylene ratio in the feed to produce a copolymer with the same melting point.

(47) So, as demonstrated above, the Ziegler-Natta catalyst system comprising the external donor of the present invention has a very high reactivity for 1-butene, thereby requiring less 1-butene in the monomer feed.

(48) This means that less unreacted 1-butene has to be removed from the final polymer, with the operability advantage of reducing the degassing time, resulting in a higher throughput.