PROCESS FOR PREPARING PROPYLENE 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 0.5 to 15 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 formula (I)

(R.sup.3).sub.z(R.sup.2O).sub.YSi(R.sup.1).sub.X  (I).

Claims

1. An olefin polymerization process comprising: reacting propylene and 1-butene and optionally ethylene 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 0.5 to 15 wt % and optionally ethylene-derived comonomer units in an amount of up to 3 wt %, and wherein the polypropylene has XS at most 3 wt %, when the only comonomer is 1-butene, 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  (I) wherein x is 1; y is 2 or 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): ##STR00008## wherein the carbon atom C bonded to the Si atom is a tertiary carbon atom and each of the residues R.sup.4, R.sup.5 and R.sup.6 bonded to the tertiary carbon atom is, independently from each other, a linear C.sub.1-4 alkyl, or two of R.sup.4, R.sup.5 and R.sup.6, together with the tertiary carbon atom C they are attached to can be part of a carbocycle of 4-10 carbon atoms; R.sup.2 is a linear C.sub.1-4 alkyl; R.sup.3 is linear C.sub.1-4 alkyl, preferably methyl or ethyl.

2. The process according to claim 1, wherein x is 1, y is 2 and z is 1, R.sup.4, R.sup.5, R.sup.6 are methyl, R.sup.2 is methyl or ethyl and R.sup.3 is methyl or ethyl.

3. The process according to claim 1, wherein, x is 1, y is 3, z=0, R.sup.4, R.sup.5 and R.sup.6 are methyl and R.sup.2 is methyl.

4. The process according to claim 1, wherein the polypropylene does not comprise any monomer units derived from a C.sub.5-10 alpha-olefin.

5. The process according to claim 1, wherein the amount of 1-butene-derived comonomer units in the polypropylene is 1 to 12 wt %.

6. The process according to claim 1, wherein the polypropylene is a 1-propylene-1-butene-ethylene terpolymer, wherein the 1-butene content is 1 to 12 wt %, and ethylene content is 0.5 to 2.5 wt %.

7. The process according to claim 1, wherein the MFR.sub.2 of the propylene polymer is in the range of 0.5 to 100 g/10 min.

8. The process according to claim 1, wherein the process is operated in liquid phase or by mixed liquid-gas techniques.

9. The process according to claim 1, wherein the Ziegler-Natta catalyst system comprises: a Ziegler-Natta procatalyst comprising a titanium and a magnesium compound, and an organometallic cocatalyst comprising an aluminum compound.

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

11. The process according to claim 1, wherein the Ziegler-Natta procatalyst is obtainable or 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 b) reacting the product of stage a) with a dialkylphthalate of formula (I): ##STR00009## 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 of formula (I) takes place; c) optionally washing the product of stage b) and/or d) optionally reacting the product of step b) or step c) with additional TiCl.sub.4.

12. A polypropylene, obtainable by the process according to claim 1.

13. An article, comprising the polypropylene according to claim 12.

14. An article according to claim 13, wherein the article is a film, a blown film, a cast film, a biaxially oriented film, or any combination thereof.

15. The process of claim 1, further comprising: processing the polypropylene to a film.

16. (canceled)

Description

EXAMPLES

I. Measuring Methods

[0075] If not otherwise indicated, the parameters mentioned in the present application are measured by the methods outlined below.

1. Comonomer Content by IR Spectroscopy

[0076] The 1-butene content of the propylene-butene copolymer was determined by quantitative Fourier transform infrared spectroscopy (FTIR) on films. Thin films were pressed to a thickness of between 260 and 300 μm at 210° C. and spectra 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 I.sub.767 (absorbance value) and the thickness (T, in cm) of the pressed film using the following relationship:

mol % C4=(I.sub.767/T−1,8496)/1,8233

[0077] 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.−1-750 cm.sup.−1 and the ethylene content was determined using the baseline corrected peak at 748 cm.sup.−1 to 710 cm.sup.−1, using the following relationships:

mol % C4=(I.sub.780-750/T−3,1484)/1,5555

mol % C2=(I.sub.748-710/T−0,6649)/1,2511

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

[0078] The amount of xylene solubles was determined at 25° C. according ISO 16152; first edition; 2005 Jul. 1.

3. MFR.SUB.2

[0079] Melt flow rate MFR.sub.2 was measured according to ISO 1133 (230° C., 2.16 kg load).

4. Melting Temperature

[0080] The melting points (T.sub.m) were determined on a DSC Q2000 T A 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

II. Polymerization Experiments

[0081] In the Inventive Examples, the following external donors were used:

##STR00004##

[0082] tert-butyl trimethoxy silane, marked in the examples as ID0. CAS no 18395-29-4.

##STR00005##

[0083] tert-butyl dimethoxy(methyl) silane, marked in the examples as ID3. CAS no 18293-81-7.

[0084] In the Comparative Examples, the following external donors were used: [0085] Dicyclopentyldimethoxysilane, marked in the examples as D. CAS no126990-35-0, [0086] Thexyltriethoxysilane, marked in the examples as CD2. CAS no 142877-46-1

##STR00006## [0087] di-tert-butyldimethoxy silane, marked in the examples as CD4. CAS no 79866-98-1

##STR00007##

[0088] The donors ID0, ID3, CD2 and CD4 were prepared according to the procedures reported in the literature.

[0089] The same Ziegler-Natta procatalyst was used in all Examples and was prepared as follows:

[0090] First, 0.1 mol of MgCl.sub.2×3 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. The amount of Ti in the catalyst was 1.9 wt-%.

[0091] In all Examples, triethylaluminium (TEA) was used as the organometallic cocatalyst.

[0092] 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 treated catalyst was fed last by means of a liquid propylene flow. No additional monomers were fed during the polymerization.

Catalyst Preactivation:

[0093] 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

Polymerization:

[0094] A stirred autoclave (double helix stirrer) with a volume of 21.2 dm.sup.3 containing 0.2 bar-g propylene was filled with additional 4.33 kg propylene or with 3.45 kg propylene and the chosen amount of 1-butene. After adding 0.5 mmol TEA with 250 g propylene, the chosen amount of hydrogen 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 in case of terpolymerization experiments) and pre-polymerization was run for 5 to 6 min at 20° C. The polymerization temperature was then increased to 75° C., and held constant throughout the polymerization.

[0095] When producing propylene-butene-ethylene terpolymers, a constant flow of 0.5 g/min of ethylene was fed via MFC throughout the polymerization in order to achieve the target ethylene concentration in the resultant polymer (in Comparative Example 6 and Inventive examples 4 and 5). For these experiments the reactor pressure was kept constant by adding propylene via mass flow controller. 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.

[0096] After flushing the reactor twice with N2 and one vacuum/N2 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.

[0097] The polymerization conditions/results are shown in Tables 1, 2, 3 and 4.

TABLE-US-00001 TABLE 1 Polymerization conditions in propylene-butene polymerization average calculated C4/(C3 + C4) Catalyst weight ratio in External Amount liquid phase H2 Example donor mg wt-% NL InvEx1 ID0 24.2 22.96 12 InvEx2 ID0 24.8 20.59 12 InvEx3 ID3 25.0 23.08 12 CompEx1 D 24.6 24.68 27 CompEx2 D 24.1 27.96 27 CompEx3 D 24.9 34.97 27 CompEx4 CD4 24.0 18.03 12 CompEx5 CD2 25.0 22.81 6

TABLE-US-00002 TABLE 2 Polymer properties of propylene-butene copolymers External total MFR.sub.2 C4 (IR) XS T.sub.m Example Donor g/10 min wt % wt % ° C. InvEx1 ID0 7.7 6.1 2.1 148.5 InvEx2 ID0 4.4 5.3 2.1 150.3 InvEx3 ID3 7.7 6.8 2.4 147.0 CompEx1 D 9.0 6.1 2.3 147.3 CompEx2 D 8.8 6.6 2.4 146.7 CompEx3 D 11 8.7 3.0 142.9 CompEx4 CD4 1.8 5.0 3.9 150.1 CompEx5 CD2 12.3 7.2 6.7 144.5

TABLE-US-00003 TABLE 3 Propylene-1-butene-ethylene polymerisation conditions Average calculated C4/(C4 + C3) Total Catalyst weight ratio in H2 in External amount liquid phase C2 feed bulk donor mg wt % g NL InvEx4 ID0 25.5 21.0 30 12 InvEx5 ID3 24.0 21.0 30 12 CompEx6 D 25.5 21.8 30 12

TABLE-US-00004 TABLE 4 Polymer properties of propylene-1-butene-ethylene terpolymers C4 total C2 total External MFR.sub.2 (IR) (IR) XS Tm Example donor g/10 min wt % wt % wt % ° C. InvEx4 ID0 5.3 6.3 1.2 3.5 140.5 InvEx5 ID3 7.9 7.5 1.1 4.1 140.2 CompEx6 D 3.6 5.5 0.9 2.8 143.9

[0098] 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:

[00001]$R=\frac{{\left(\frac{C_4}{C_3}\right)}_{\mathrm{polymer}}}{{\left(\frac{C_4}{C_3}\right)}_{\mathrm{liq}.\mathrm{phase}}}$

[0099] R is specific for a given catalyst, monomer pair and temperature. As liquid phase composition values, the average of the initial and final calculated values was used.

[0100] The values of R determined for propylene-1-butene polymerisations with the Ziegler-Natta catalyst system comprising external donor D (R=0.18-0.19) and the Ziegler-Natta catalyst system comprising external donor ID0 or ID3 (R=0.22 to 0.24) show that the external donor of the present invention increases the 1-butene reactivity of the Ziegler-Natta catalyst system and still the XS value is low. In comparative example 5 R is on the same level as in inventive examples, however, XS values are clearly higher than in inventive examples. In comparative examples 1 to 3 XS values are on the same level as in the inventive examples, but the R values are lower, i.e. 1-butane reactivity of the inventive examples is higher.

[0101] 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.

[0102] 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.