Process for the polymerization of .alpha.-olefins, a catalyst used in the polymerization and its preparation

In the polymerization of C.sub.3 -C.sub.12 -.alpha.-olefins, the activity of the catalyst and the isotacticity and molecular weight of the polymer product can be adjusted and improved in a controlled manner by a new process wherein PA1 A) a catalyst system is prepared by bringing a support which comprises magnesium chloride, a derivative thereof or a reagent forming it into contact with at least titanium tetrachloride or a reagent forming it, in order to produce a titanated support; by bringing the titanated support into contact with at least a group 1, 2 or 13 metal compound which contains a C.sub.1 -C.sub.10 -alkyl and activates titanium tetrachloride to a catalytically active titanium group, in order to produce an activated support; and by bringing a substance selected from among the said support, titanated support and activated support into contact with at least one donor or a reagent forming it, in order to produce a catalyst system PA1 B) polymerization is carried out using the catalyst system by bringing it into contact with at least a C.sub.3 -C.sub.12 -.alpha.-olefin, whereupon poly-C.sub.3 -C.sub.12 -.alpha.-olefin chains are formed in the catalytically active titanium groups, and preferably by bringing the said catalyst system, the said C.sub.3 -C.sub.12 -.alpha.-olefin and the said poly-C.sub.3 -C.sub.12 -.alpha.-olefin chains into contact with hydrogen or some other similar chain transfer agent, whereupon a poly-C.sub.3 -C.sub.12 -.alpha.-olefin terminated with hydrogen or suchlike is formed. In the process the improvement is achieved so that, in step A), PA1 i) a first controlled amount of a less soluble internal donor and a second controlled amount of a more soluble internal donor are provided on the surface of the said support, titanated support or activated support, in order to produce an internal donoration product, and PA1 ii) the internal donoration product is brought into contact with at least one eluant eluting the more soluble internal donor and with at least one external donor or a reagent forming it, in order to produce an external donoration product, the catalyst system thereby formed having at least catalytically active titanium groups, the said first controlled amount of the less soluble internal donor and the said second controlled amount comprising external donor.

FIELD OF THE INVENTION
 The invention relates to a process for the polymerization of C.sub.3
 -C.sub.12 -.alpha.-olefins, wherein
 A) a catalyst system is prepared by bringing a support which comprises
 magnesium chloride, a derivative thereof or a reagent forming it into
 contact with at least titanium tetrachloride or a reagent forming it, in
 order to produce a titanated support, by bringing the titanated support
 into contact with at least a compound of a metal of group 1, 2 or 13 of
 the Periodic Table of the Elements (IU 1990), which compound contains a
 C.sub.1 -C.sub.10 -alkyl and activates titanium tetrachloride to a
 catalytically active titanium group, in order to produce an activated
 support, and by bringing a substance selected from among the said support,
 titanated support and activated support into contact with at least one
 donor or a reagent forming it, in order to produce a catalyst system;
 B) polymerization is carried out by using the catalyst system by contacting
 it with at least a C.sub.3 -C.sub.12 -.alpha.-olefin, whereupon
 poly-C.sub.3 -C.sub.12 -.alpha.-olefin chains are formed in the
 catalytically active titanium groups, and preferably by contacting the
 said catalyst system, the said C.sub.3 -C.sub.12 -.alpha.-olefin and the
 said poly-C.sub.3 -C.sub.12 -.alpha.-olefin chains with hydrogen or some
 other similar chain transfer agent, whereby a poly-C.sub.3 -C.sub.12
 -.alpha.-olefin terminated with hydrogen or suchlike is formed.
 The invention also relates to a method for the preparation of a catalyst
 system intended for the polymerization of C.sub.3 -C.sub.12
 -.alpha.-olefins, in which process a support which comprises magnesium
 chloride, a derivative thereof or a reagent forming it is contacted with
 at least titanium tetrachloride or a reagent forming it, in order to form
 a titanated support; the titanated support is contacted with at least a
 compound of the said group 1, 2, or 13 metal, which compound contains a
 C.sub.1 -C.sub.10 -alkyl and activates titanium tetrachloride to a
 catalytically active titanium group, in order to produce an activated
 support; and a substance selected from among the said support, titanated
 support and activated support is contacted with at least one donor or a
 reagent forming it, whereby the said catalyst system is formed.
 By titanated support is meant a contact product of a support and titanium
 tetrachloride or a reagent forming it. By activated support is meant a
 support which has first been contacted with titanium tetrachloride or a
 reagent forming it, and thereafter with a metal compound which contains a
 C.sub.1 -C.sub.10 -alkyl and activates titanium tetrachloride.
 Finally the invention relates to a catalyst system intended for the
 polymerization of C.sub.3 -C.sub.12 -.alpha.-olefins, the catalyst system
 being prepared by the above method for the preparation of a catalyst
 system.
 1. Discussion of Related Art
 The conventional process for the polymerization of poly-C.sub.3 -C.sub.12
 -.alpha.-olefins has the disadvantage that all of the donors used therein
 participate in a random equilibrium system. Thus the quantity and quality
 of the poly-C.sub.3 -C.sub.12 -.alpha.-olefin fractions depending on
 equilibrium cannot be regulated. This has resulted, for example, in that,
 when the isotacticity of the product is raised by using a larger donor
 quantity, the hydrogen sensitivity of the catalyst system has decreased
 and its activity has dropped.
 2. Summary of the Invention
 In the said step A) of the polymerization process, when a support
 comprising magnesium chloride, a derivative thereof or a reagent forming
 is contacted with titanium tetrachloride or a reagent forming it, there is
 formed a titanated support having at least titanium tetrachloride
 coordinated to its magnesium chloride.
 Thus, when the said titanated support is contacted with a metal compound
 containing a C.sub.1 -C.sub.10 -alkyl, there is formed an activated
 support having catalytically active titanium groups coordinated to its
 magnesium chloride.
 Finally, when a substance selected from among the said support, titanated
 support and activated support is contacted with at least one donor or a
 reagent forming it, a catalyst system is formed the activated support of
 which has, coordinated in its magnesium chloride, catalytically active
 titanium groups and at least one type of donor.
 An object of the present invention is to provide a poly-C.sub.3 -C.sub.12
 -.alpha.-olefin as isotactic as possible, without reducing the hydrogen
 sensitivity or activity of the catalyst system.
 The above-mentioned objects of the invention have now been achieved by a
 novel process for the polymerization of C.sub.3 -C.sub.12
 -.alpha.-olefins, the process being primarily characterized in that in
 step A):
 i) on the surface of the said support, titanated support or activated
 support there is provided a first controlled amount of a less soluble
 internal donor and a second controlled amount of a more soluble internal
 donor to produce an internal donoration product, and
 ii) the internal donoration product is contacted with at least one eluant
 eluting the more soluble internal donor and with at least one external
 donor or a reagent forming it, in order to produce an external donoration
 product,
 the catalyst system thereby formed containing at least catalytically active
 titanium groups, the said first controlled amount of the less soluble
 internal donor, and the said second controlled amount comprising the
 external donor.

DETAILED DESCRIPTION OF INVENTION
 According to one embodiment, two eluants are used.
 In this case, the internal donoration product is contacted with a first
 eluant, which primarily removes only the coordinated more soluble internal
 donor, in order to produce a first elution product, which contains, on the
 surface of the support, treated support, or further treated support, at
 least the said controlled amount of the less soluble internal donor.
 There-after the first elution product is contacted with at least the
 external donor or the reagent forming it, in order to produce an external
 donoration product, which contains, on the surface of the support, treated
 support, or further treated support, at least the said controlled amount
 of the less soluble internal donor and external donor, i.e. the external
 donor has replaced the more soluble internal donor.
 Finally the external donoration product is contacted with a second eluant,
 which removes external donor from the surface of a support of the type
 concerned and yields external donor back to the surface concerned, in
 order to produce a second elution product, which contains, on the surface
 of the support, treated support or further treated support, at least the
 said controlled amount of the less soluble internal donor and additionally
 external donor in a thermodynamic equilibrium.
 In the obtained catalyst system, on the surface of the support of the
 external donoration product or optionally the second elution product there
 is thus, coordinated, at least catalytically active titanium groups, the
 said controlled amount of the less soluble internal donor and external
 donor in equilibrium, the second eluant maintaining the said equilibrium.
 Although it is possible in the invention to elute in step ii) substantially
 all of the more soluble internal donor from surface of the support
 concerned, according to one embodiment it is also possible in step ii) to
 use such an amount or type of eluant that it removes only a portion of the
 more soluble internal donor, in which case the catalyst system obtained
 contains, coordinated, a catalytically active titanium group and, in a
 controlled ratio, less soluble internal donor, more soluble internal
 donor, and external donor.
 The present invention is thus based on the realization that, instead of one
 internal donor or a reagent forming it, two internal donors or reagents
 forming them are used, one of the donors being a less soluble internal
 donor or a reagent forming it and the other a more soluble internal donor
 or a reagent forming it. By contacting a substance selected from among a
 support, a titanated support and an activated support with the less
 soluble internal donor or a reagent forming it and with the more soluble
 donor or a reagent forming it, in a controlled ratio, and by replacing the
 more soluble internal donor with the external donor, the ratio desired in
 the given case is always obtained between the internal donor and the
 external donor.
 As it has been observed in the invention that the different fractions of
 poly-C.sub.3 -C.sub.12 -.alpha.-olefins are adjustable and that an
 isotactic material can be prepared with a greater hydrogen sensitivity and
 a greater yield than previously, in its widest scope the invention relates
 only to the procedures stated in the foregoing and hereinafter.
 Typical C.sub.3 -C.sub.12 -.alpha.-olefins usable in the polymerization
 process according to the invention include propylene, 1-butene,
 4-methyl-1-pentene, 3-methyl-1-butene, 4,4-dimethyl-1-pentene, etc. They
 may also be copolymerized with one another and with other monomers,
 preferably ethylene. The most preferred C.sub.3 -C.sub.12 -.alpha.-olefin
 is propylene.
 According to a preferred embodiment of the invention, in polymerization
 step B) the said catalyst system, the said C.sub.3 -C.sub.12
 -.alpha.-olefin and the said poly-C.sub.3 -C.sub.12 -.alpha.-olefin chains
 are contacted with hydrogen or other such chain transfer agent, whereupon
 a hydrogen-terminated poly-C.sub.3 -C.sub.12 -.alpha.-olefin is formed.
 In the polymerization process according to one embodiment of the invention,
 there are two internal donor types, of which the first is poorly soluble
 in trialkylaluminum and the second is more soluble in trialkylaluminum,
 which acts both as the activating C.sub.1 -C.sub.10 -alkyl metal compound
 and as an eluant. Thus the polymerization system is controlled and the
 amount of internal donor eluted by alkylaluminum is no longer random but
 controlled. It is to be noted in this context that the above systems also
 enable eluants other than trialkylaluminum to be used, a fact which in
 turn increases the controllability of the polymerization process. An
 embodiment in which at least two eluants are used has also been described
 above. The invention thus relates to a control method by which various
 desired poly-.alpha.-olefin products are achieved and not to a certain set
 of parameter values by the use of which only a specific
 poly-.alpha.-olefin product is arrived at.
 Donors or reagents forming them do not compete with titanium tetrachloride
 or a reagent forming it for the coordination sites of magnesium chloride
 or a derivative thereof. Furthermore, since according to the invention it
 is possible to use an eluant which is not necessarily a metal compound
 which contains a C.sub.1 -C.sub.10 -alkyl and activates titanium
 tetrachloride, the donoration and elution steps according to the
 invention, described above, can be carried out completely independently of
 the titanation and activation. Thus, in principle the donoration/elution
 can be carried out on a support, a titanated support, or an activated
 support. Also, there is no obstacle to carrying out or continuing the
 donoration and elution also in the said polymerization step B).
 According to one preferred embodiment of the invention, the titanation and
 activation of step A) are combined with one or more donoration and elution
 runs of steps i) and ii) according to the invention in such a manner that
 in step A)
 i') a support which comprises magnesium chloride, a derivative thereof or a
 reagent forming it is contacted with at least titanium tetrachloride or a
 reagent forming it, with a first separate amount of a less soluble
 internal donor or a reagent forming it, and with a second separate amount
 of a more soluble internal donor or a reagent forming it, in order to
 produce an internally donorated and titanated support containing the said
 first controlled amount of the less soluble internal donor and the said
 second controlled amount of the more soluble internal donor. In this case
 the magnesium chloride of the support contains at least coordinated
 titanium tetrachloride and the above-mentioned less soluble internal donor
 and more soluble internal donor. Thereafter
 ii') the internally donorated and titanated support is contacted with at
 least a compound of a group 1, 2 or 13 metal, which compound contains a
 C.sub.1 -C.sub.10 -alkyl and activates titanium tetrachloride to a
 catalytically active titanium group; with at least one eluant, which may
 be a compound of the said metal, and with at least one external donor or a
 reagent forming it, in order to produce a catalyst system which contains
 at least catalytically active titanium groups and, in a controlled ratio,
 the less soluble internal donor and the external donor.
 By the terms presented above, "a first separate amount of a less soluble
 internal donor or a reagent forming it" and "a second separate amount of a
 more soluble internal donor or a reagent forming it" is meant the use of
 two different internal donors or two different reagents forming internal
 donors, as a mixture or separately, or the use of the same substance
 separately as a reagent forming one internal donor (cf. hereinafter
 transesterification) and as a second internal donor. By "amount" is meant
 in this context the added amount, not the amount associated with the
 support.
 According to one embodiment, the more soluble internal donor is removed and
 possibly equilibrated by means of one eluant and the external donor is
 equilibrated by means of another eluant, in which case in the
 above-mentioned step ii') the internally donorated and titanated support
 is contacted with at least a compound of a metal of group 1, 2 or 13,
 which compound contains a C.sub.1 -C.sub.10 -alkyl and activates titanium
 tetrachloride to a catalytically active titanium group, and with a first
 eluant, which primarily removes only the more soluble internal donor, in
 order to produce an internally donorated, eluted and activated support
 having catalytically active titanium groups and a poorly soluble internal
 donor, as well as uncoordinated coordinative sites left by the removed
 more soluble internal donor. Thereafter the said internally donorated,
 eluted and activated support is contacted with at least an external donor
 or a reagent forming it, which is capable of coordinating to the said
 coordinative sites, and with a second eluant, which removes external donor
 from the said coordinative sites and yields it back, in order to produce a
 catalyst system which has, in the magnesium chloride of its twice
 donorated and eluted and activated support, at least coordinated
 catalytically activated titanium groups and, in a controlled ratio, the
 less soluble internal donor and the external donor in equilibrium, the
 said second eluant maintaining the equilibrium.
 When in step B) the said catalyst system is contacted with a C.sub.3
 -C.sub.12 -.alpha.-olefin, there form, in the catalytically active
 titanium groups adjacent to the coordinated less soluble internal donor,
 long, completely isotactic poly-C.sub.3 -C.sub.12 -.alpha.-olefin chains
 and, in the catalytically active titanium groups adjacent to the
 coordinated external donor and the coordinative sites in equilibrium with
 it, there form isotactic chain sequences of poly-C.sub.3 -C.sub.12
 -.alpha.-olefins or short atactic chains or chain sequences, depending on
 whether the external donor is respectively linked to the coordinative
 sites or separate therefrom.
 When in step B) the said catalyst system, the said C.sub.3 -C.sub.12
 -.alpha.-olefin and said poly-C.sub.3 -C.sub.12 -.alpha.-olefin chains are
 contacted with hydrogen or other such chain transfer agent, there occurs
 linking of a first atom of hydrogen to the catalytically active titanium
 groups adjacent to the coordinative sites and of a second atom of hydrogen
 to the atactic poly-C.sub.3 -C.sub.12 -.alpha.-olefin chains and sequences
 in the said groups, whereby hydrogen-terminated poly-C.sub.3 -C.sub.12
 -.alpha.-olefin is formed.
 By the use of at least two internal donors of clearly different
 solubilities it is thus possible better to control the polymerization
 process according to the invention. According to one embodiment, the
 proportion of purely isotactic and larger-molecule material in the
 poly-C.sub.3 -C.sub.12 -.alpha.-olefin containing it and a less isotactic
 and smaller-molecule material is controlled by means of the ratio of the
 less soluble internal donor to the more soluble internal donor so that
 with larger proportions of less soluble internal donor a larger proportion
 of purely isotactic and larger-molecule material is obtained.
 Respectively, with smaller proportions of less soluble internal donor a
 smaller proportion of purely isotactic and larger-molecule material is
 obtained.
 Depending on whether or not, during the polymerization, the external donor
 participating in the equilibrium is attached to the support, alternating
 isotactic and atactic sequences are formed. Since chain transfer by means
 of hydrogen occurs only at the stage of growth of atactic sequences,
 isotactic sequences are in general longer than atactic sequences.
 According to one embodiment of the invention, the proportion of isotactic
 material in the form of chain sequences in the less isotactic and
 smaller-molecule (thus not purely isotactic) material of poly-C.sub.3
 -C.sub.12 -.alpha.-olefin is controlled by means of the ratio of the
 external donor to the second eluant so that with a larger amount of
 external donor in proportion to the second eluant a larger proportion of
 an isotactic and larger-molecule material in the form of sequences is
 obtained. Thus there forms a material which is isotactic but at the same
 time more hydrogen-sensitive than when a large amount of the less soluble
 internal donor is used. Respectively, when less eluant and more external
 donor is used, a larger proportion of atactic and smaller-molecule
 material in the form of sequences is obtained. Thus there also forms a
 larger amount of the said xylene-soluble, completely atactic material
 having a very small molecular size.
 Above, the control of the different fractions of poly-C.sub.3 -C.sub.12
 -.alpha.-olefins by means of donors and eluants, in accordance with the
 invention, has been described. The said fractions can also be affected by
 means of other parameters, such as the reaction time, the reaction
 temperature and the amount of the chain transfer agent, such as hydrogen.
 It is thus preferable to adjust the length and molecular weight of the
 chain sequences and/or chains of the less isotactic and smaller-molecule
 material of the poly-C.sub.3 -C.sub.12 -.alpha.-olefin by means of
 hydrogen and/or the temperature so that with a lower hydrogen amount and a
 lower temperature a higher molecular weight is obtained, and vice versa.
 The molecular weight is in general measured by using the melt index, MFR,
 a lower MFR being obtained with higher molecular weights.
 A wide molecular weight distribution can be achieved by using, for example,
 approximately equal amounts of the less soluble internal donor and the
 external donor, the latter splitting off in a state of equilibrium,
 whereupon approximately equal amounts of a larger-molecule isotactic
 material and a smaller-molecule atactic material are formed. Furthermore,
 the molecular weight of the atactic material can be decreased further by
 using a large amount of hydrogen. By the control method according to the
 invention, poly-.alpha.-olefins suitable for different uses can thus be
 obtained.
 In steps i) and i') stated above, the said less soluble internal donor is
 preferably a Lewis base less soluble in a hydro-carbon. Internal donors
 are well known in the art, and lists thereof have been presented widely in
 the patent literature and in scientific literature. Thus a person skilled
 in the art will know what is meant by an internal donor. The internal
 donor is thus a Lewis base, which means that its molecule has one or more
 electron-donor heteroatoms, such as oxygen, nitrogen, phosphorus or sulfur
 atoms. In general, bidentate (=two electron-donor heteroatoms) Lewis bases
 are used in the polymerization of poly-C.sub.3 -C.sub.12 -.alpha.-olefins,
 and thus it is advantageous to use a bidentate Lewis base poorly soluble
 in a hydrocarbon. Respectively, the more soluble internal donor is
 preferably a Lewis base more soluble in a hydrocarbon, most preferably a
 bidentate Lewis base more soluble in a hydro-carbon. By "less soluble" and
 "more soluble" are meant within the widest scope of the invention
 materials that are less soluble or more soluble than the other in the
 eluant used. It is clear that, when an eluant is added according to the
 invention, the purpose is in general to remove the more soluble internal
 donor but to leave as much as possible (preferably all) of the less
 soluble internal donor in the solid catalyst.
 According to one preferred embodiment, the less soluble internal donor is a
 C.sub.1 -C.sub.6 -alkyl ester of an organic carboxylic acid, preferably a
 C.sub.1 -C.sub.4 -alkyl ester of an organic dicarboxylic acid, and most
 preferably diethyl phthalate. It is known that a low-alkyl diethyl
 phthalate attached to a solid catalyst is very difficult to elute. This
 may be due to the fact that the small alkyl groups, i.e. ethyls, of
 phthalate are not solvated as strongly with a hydrocarbon solvent or a
 hydrocarbon-containing solvent, i.e. the eluant, as are the larger alkyls
 of a phthalate. When phthalates are used, the preferred difference in the
 alkyls between the less soluble and the more soluble internal donors is at
 least 3, preferably at least 6, carbon atoms.
 Since it is difficult to attach di-C.sub.1 -C.sub.4 -alkyl phthalate,
 preferably diethyl phthalate, directly to a support, a titanated support
 or an activated support, it can advantageously be formed by using as the
 magnesium chloride derivative in step i) or i') a complex according to
 Formula I:
EQU MgCl.sub.2.nROH (I)
 where ROH is an aliphatic C.sub.1 -C.sub.4 -alcohol, preferably ethanol, or
 a mixture of such alcohols, n is 1-6, preferably approx. 3. A di-C.sub.7
 -C.sub.20 -alkyl phthalate, preferably dioctyl phthalate, is used as the
 reagent forming the less soluble internal donor. Thereafter they are
 transesterified to a di-C.sub.1 -C.sub.4 -phthalate, preferably diethyl
 phthalate, coordinated to magnesium chloride, and to a removable C.sub.7
 -C.sub.20 -alcohol byproduct, preferably octanol. Transesterification can
 be effected not only by the above-mentioned reagent selection but also by
 using a high temperature, i.e. a temperature of approx. 128-200.degree.
 C., preferably approx. 130-150.degree. C.
 According to one preferred embodiment, the more soluble, i.e. elutable,
 internal donor or step i) and i') is a C.sub.7 -C.sub.20 -alkyl ester of
 an organic carboxylic acid, preferably a di-C.sub.8 -C.sub.16 -alkyl ester
 of organic dicarboxylic acid, such as dioctyl phthalate, dinonyl
 phthalate, didecyl phthalate, diundecyl phthalate, didodecyl phthalate,
 ditridecyl phthalate or ditetradecyl phthalate. The most preferable
 phthalate is dioctyl phthalate. Since the low solubility of the less
 soluble internal donor was probably due to the short alkyl group of the
 phthalate, the higher solubility of the more soluble internal donor is
 most likely respectively due to the greater length of the alkyl group of
 the phthalate, enabling the donor to be solvated by a hydrocarbon and be
 removed.
 Since the substance forming the less soluble internal donor may be the more
 soluble internal donor, the first-mentioned internal donor can
 advantageously be prepared by partial transesterification. In this case
 the said controlled amounts of the less soluble and more soluble internal
 donor are obtained by carrying out the said transesterification in a
 limited manner, in which case the unreacted amount of di-C.sub.7 -C.sub.20
 -alkyl phthalate constitutes the said amount of the more soluble donor.
 Preferably the limited transesterification is carried out by adjusting the
 ratio of the complex to di-C.sub.7 -C.sub.20 -alkyl phthalate, the
 reaction temperature and/or the pressure.
 It is preferable to use in step i) and i') a molar ratio of the less
 soluble+the more soluble internal donor to magnesium which is within a
 range of 0.10-0.50, preferably 0.10-0.40, and most preferably 0.15-0.30.
 As was pointed out above, the one or more eluants in step ii) and ii') may
 either be a separate eluant or be of the same metal compound which
 contains C.sub.1 -C.sub.10 -alkyl and activates coordinated titanium
 tetrachloride to a catalytically active titanium group. The eluant is thus
 an organic substance which dissolves the more soluble internal donor but
 does not dissolve the less soluble internal donor. Thus the more soluble
 internal donor and the less soluble internal donor together with the
 eluant form a dissolution system which elutes out most or all of the more
 soluble internal donor but leaves most of the less soluble internal donor
 in the support, the titanated support or the activated support. By organic
 material is meant in this context both purely organic and organometallic
 materials.
 According to one preferred embodiment, the eluant is a group 1, 2 or 13
 metal compound which contains a C.sub.1 -C.sub.10 -alkyl, preferably such
 an excess of the metal compound containing a C.sub.1 -C.sub.10 -alkyl, and
 being used in step A) for activation purposes, that it does not
 participate in the activation of the coordinated titanium tetrachloride to
 a catalytically active titanium group. A preferred eluant is tri-C.sub.1
 -C.sub.10 -alkylaluminum, a more preferable eluant is tri-C.sub.1 -C.sub.6
 -alkylaluminum, and the most preferred is tri-C.sub.1 -C.sub.4
 -alkylaluminum, such as triethylaluminum. The molar ratio Al/Ti is
 preferably within a range of 1-2000, preferably within a range of 50-500,
 and most preferably within a range of 100-200.
 In steps ii) and ii') a treatment with an external donor and an eluant is
 carried out. The said external donor is according to a preferred
 embodiment a Lewis base partly soluble in hydrocarbon, and preferably a
 bidentate Lewis base partly soluble in hydrocarbon. By "partly soluble" is
 meant that the external donor is partly attached to a solid catalyst and
 partly, eluted by the said eluant, in solution, i.e. the external donor,
 together with the catalyst and the eluant, forms an equilibrium system.
 The external donor is a typical external donor used in the art. Lists of
 external donors can be found in the literature of the field, and a person
 skilled in the art will be capable of selecting from them suitable
 external donors the solubility of which corresponds to the criteria stated
 above. A typical external donor is a dialkyl-dialkoxysilane, such as
 cyclohexyl-methyl-dimethoxysilane.
 As was pointed out, in the process according to the invention for the
 polymerization of C.sub.3 -C.sub.12 -.alpha.-olefins, such as propylene, a
 support is used which comprises magnesium chloride, a derivative thereof
 or a reagent forming it. The support itself may be magnesium chloride, a
 derivative thereof or a reagent forming it, or the support may be, for
 example, of an inert substance, such as an inorganic oxide, coated with
 magnesium chloride, a derivative thereof or a reagent forming it. Some
 typical inert supports are silica, alumina, their mixtures or mixed oxides
 with each other or with other oxides. A preferred magnesium chloride is
 .beta.-magnesium chloride, which coordinates titanium tetrachloride well.
 .beta.-magnesium chloride is formed, for example, by grinding or through
 chemical reactions. Examples of derivatives of magnesium chloride include
 its complexes with alcohols and examples of reagents forming magnesium
 chloride include alkyl magnesium compounds and magnesium alkoxy compounds,
 which together with a chlorinating substance form .beta.-magnesium
 chloride. According to a preferred embodiment, the magnesium chloride
 derivative comprised by the support is a complex according to generic
 Formula (I)
EQU MgCl.sub.2.nROH (I)
 where ROH is an aliphatic C.sub.1 -C.sub.4 alcohol or a mixture of such
 alcohols, and n is 1-6, preferably approx. 3, in which case in step A)
 this complex is caused to react with titanium tetrachloride or a complex
 forming it. R is preferably methanol and/or ethanol, most preferably
 ethanol.
 A. typical reaction in which a reagent according to Formula (I) reacts with
 titanium tetrachloride occurs according to the following reaction
 equation:
EQU MgCl.sub.2 *EtOH+3TiCl.sub.4 =MgCl.sub.2 *3TiCl.sub.3 OEt+3HCl
 where Et is the ethyl group C.sub.2 H.sub.5. It should be pointed out that
 the alcohol, which is sometimes called an electron donor in the
 literature, is not an internal electron donor, since it leaves the
 catalyst system during titanation. The same, of course, concerns all
 compounds reacting in this manner.
 In this reaction, three moles of TiCl.sub.3 OEt are formed for each mole of
 MgCl.sub.2. The TiCl.sub.3 OEt formed must be removed by washing as
 completely as possible, since this byproduct is a catalyst poison in the
 polymerization of propylene or any other C.sub.3 -C.sub.12
 -.alpha.-olefin. Therefore the reaction is performed in the presence of a
 large TiCl.sub.4 excess, the hot TiCl.sub.4 washing out the TiCl.sub.3 OEt
 byproduct. According to a preferred embodiment, titanium tetrachloride or
 a reagent forming it is used in such an excess that the molar ratio
 Ti/Mg=1-100, preferably 5-40, most preferably 10-25.
 In the titanium chloride wash, magnesium chloride in its coordinative form,
 i.e. .beta.-form, is released according to the following reaction
 equation:
EQU MgCl.sub.2 *3TiCl.sub.3 OEt-3TiCl.sub.4 =.beta.-MgCl.sub.2 +3TiCl.sub.4 - -
 - TiCl.sub.3 OEt
 A portion of the titanium tetrachloride coordinates to .beta.-MgCl.sub.2
 and forms active centers during activation. To make the titanium
 tetrachloride wash more effective, preferably at least two, and most
 preferably three, titanium tetrachloride treatments are used.
 By the reagent which forms titanium tetrachloride used in the titanation is
 meant, for example, titanium alkoxide or titanium alkoxychloride, which
 together with a chlorination reagent form titanium tetrachloride which can
 be activated.
 According to a preferred embodiment of the invention, in step A) at least
 three steps are performed, in the first of which the support is contacted
 with titanium tetrachloride or a reagent forming it and with the less
 soluble internal donor or a reagent forming it; in the second the solid
 obtained from the first step is contacted with titanium tetrachloride or a
 reagent forming it and with the more soluble internal donor or a reagent
 forming it; and in the third the solid obtained from the second step is
 contacted with titanium tetrachloride or a corresponding washing solvent.
 Most preferably, in the first step a complex of magnesium chloride and
 alcohol (cf. Formula (I) above) is used as the magnesium chloride
 derivative and di-C.sub.7 -C.sub.20 -alkyl phthalate as the reagent
 forming the less soluble internal donor, and the conditions used are such
 that, in the first step, there occurs forming and linking in situ of the
 less soluble internal donor (cf. transesterification above), in which
 case, in the second step, the second, more soluble internal donor is
 linked to the solid catalyst intermediate by normal coordination.
 Preferably the said steps are combined, i.e. a partial transesterification
 to a less soluble C.sub.1 -C.sub.4 -alkyl ester and a more soluble C.sub.7
 -C.sub.20 -alkyl ester is carried out.
 In step A) of the process according to the invention, the preferable molar
 ratio of the less soluble internal donor to magnesium is within a range of
 0.05-0.30, most preferably within a range of 0.10-0.20. When step A) is
 carried out in three steps, it is preferable to use in the first step a
 molar ratio of the less soluble internal donor to magnesium which is
 within a range of 0.05-0.30, preferably within a range of 0.10-0.20.
 Respectively, it is advantageous to use in general, and preferably in the
 said second step, a molar ratio of the more soluble internal donor to
 magnesium which is within a range of 0.05-0.30, most preferably within a
 range of 0.10-0.20. Most preferably, substantially equal amounts of the
 less soluble and of the more soluble internal donor are used, i.e. the
 molar ratio of the less soluble internal donor to the more soluble
 internal donor is preferably within a range of 0.5-2.0, more preferably
 within a range of 0.7-1.3, and most preferably approx. 1.0.
 In the step in which the coordinated titanium tetrachloride is activated by
 means of a group 1, 2 or 13 metal compound containing a C.sub.1 -C.sub.10
 -alkyl it is preferable to use a compound which reduces and C.sub.1
 -C.sub.10 -alkylates the coordinated titanium tetrachloride to a
 catalytically active titanium group. Thereby the titanium tetrachloride is
 reduced and the C.sub.1 -C.sub.10 -alkyl group of the said metal compound
 links to it; during the polymerization, C.sub.3 -C.sub.12 -.alpha.-olefin
 monomers are linked to the C.sub.1 -C.sub.10 -alkyl group.
 These compounds, defined as cocatalysts, which are capable of reducing and
 alkylating titanium tetrachloride to a catalytically active titanium
 group, are well known in he art. A typical metal compound which contains
 C.sub.1 -C.sub.10 -alkyl is a tri-C.sub.1 -C.sub.10 -alkylaluminum,
 preferably a tri-C.sub.1 -C.sub.6 -alkylaluminum, and most preferably a
 tri-C.sub.1 -C.sub.4 -alkylaluminum, such a triethylaluminum. When
 reagents to be chlorinated, forming magnesium chloride and/or titanium
 chloride, are used, it is possible to use C.sub.1 -C.sub.10 -alkylaluminum
 chlorides, which both activate and chlorinate the said reagents. A
 preferred Al/Ti molar ratio is 1-2000, more preferable 50-500, and the
 most preferable 100-200.
 As was mentioned at the beginning, the invention relates not only to the
 polymerization process described above but also to a method for the
 preparation of the catalyst system used in the polymerization and to the
 said catalyst system. The catalyst system according to the invention and
 its preparation are evident from the polymerization process described
 above, if steps A), i), i'), ii), and ii') of the polymerization process
 are taken into account. In this context we also refer to accompanying
 claims 24 and 25.
 Experiments, in which 21 examples were performed, are described below. The
 description is of the empirical progress towards the invention, and thus
 Examples 1-4, A and J are reference examples, whereas Examples 5, 6 and
 B-O describe the present invention, using two internal donors D.sub.1.
 EXAMPLES
 In the research, larger donor amounts in one and the same titanation step
 (cf. for example 1 and 2) and different donor amounts in two successive
 titanation steps were used. The investigation thus related not only to the
 effect of increasing donor amounts in one and the same titanation step but
 also to their division among different titanation steps.
 In Reference Examples 1 and 2 of the preliminary experiment series, an
 investigation was made whether it was possible to use larger donor amounts
 together with transesterification to raise the isotacticity index II
 without a decrease in the hydrogen sensitivity (MFR) or the activity of
 the catalysts. In these experiments, two normal titanation runs were
 performed, an internal donor being added to the first of them and the
 second one being carried out as a washing step without a donor. The ratio
 of internal donor D.sub.1 to magnesium Mg used was D.sub.1 /Mg=0.15 and
 0.3 (Examples 1 and 2).
 In Reference Example 3 of the preliminary experiment series, three
 titanation steps were experimented with; only to the first of them was one
 type of internal donor added to investigate whether it was possible to
 wash off the detrimental byproducts of catalyst preparation without the
 isotacticity index II decreasing owing to the repeated titanium
 tetrachloride washes.
 In Reference Example 4, the increasing of the donor amount in comparison to
 Example 3 in the first titanation step of the titanation was experimented
 with in order to determine whether such a procedure would provide any
 advantages with respect to the isotacticity--hydrogen
 sensitivity--activity equilibrium. In this example, a D.sub.1 /Mg ratio of
 0.3 was used.
 In Embodiment Example 5, two internal donors were added in different steps,
 in the first titanation step and in the second titanation step, whereas
 the third titanation step, i.e. rinsing titanation, was carried out using
 titanium tetrachloride without an addition of internal donor. The idea of
 two internal donors according to the invention was thus implemented in
 these examples. The adding of the less soluble internal donor in the first
 step was carried out by transesterifying the alcohol of MgCl.sub.2.nROH
 and an added substance forming the first internal donor, this substance
 being dioctyl phthalate (DOP), whereby diethyl phthalate (DEP) was
 obtained, which adhered strongly to the catalyst. The more soluble
 internal donor (DOP) was added in connection with the second titanation
 step, without transesterification, whereupon the DOP could be eluted out.
 In this manner, the system of two donors according to the invention is
 formed, of which donors one is easily eluted and the other is closely
 linked to a solid catalyst component, in which case there are better
 possibilities for controlling the hydrogen sensitivity of the catalyst and
 the isotacticity, molecular weight and molecular weight distribution of
 the polymer.
 In Embodiment Example 6, the more soluble internal donor used was a
 compound having a larger hydrocarbon group (in the case of esters, the
 alkyl group of the alcohol residue). In this example, the aim was also to
 determine whether these larger molecules could be used in the second donor
 addition to produce a more soluble activation byproduct TiCl.sub.3 -OR.
 Thus, in Example 2, dioctyl phthalate (DOP) was used as the reagent
 forming the less soluble internal donor (DEP) and diundecyl phthalate
 (DUP) was used as the more soluble internal donor.
 Preparation of Procatalyst
 Unless otherwise mentioned, the procatalyst was prepared according to the
 following recipe:
 45 g of MgCl.sub.2.3EtOH support was introduced into the synthesis reactor
 together with 150 ml of heptane. The slurry was cooled to -10.degree. C.
 (stirrer speed was 200 rpm). 300 ml of cold (-12.degree. C.) titanium
 tetrachloride TiCl.sub.4 was added into the reactor. The molar ratio
 TiCl.sub.4 /EtOH was 4.8. The temperature was raised within 3 hours to
 20.degree. C. Thereafter a compound forming the internal donor was added,
 the compound being dioctyl phthalate (DOP). The amount of dioctyl
 phthalate added during the first titanation is shown in Table 1. The
 temperature of the mixture was thereafter raised to 130.degree. C. Af ter
 1.5 hours the liquid was removed and the temperature was lowered to
 120.degree. C. After an addition o f fresh titanium tetrachloride
 (TiCl.sub.4) (300 ml), the temperature was maintained at 120.degree. C.
 for one hour. In Examples 7-10 the second internal donor was add ed after
 the said second titanium tetrachloride amount had been added. In Examples
 4-10 a third titanium tetrachloride treatment was carried out after the
 said second titanium tetrachloride treatment. Finally the catalyst was
 washed 3 times with 300 ml of hot heptane (&gt;90.degree. C.) and was dried
 by blowing nitrogen through the catalyst bed until the catalyst turned
 into a freely flowing powder.
 Bulk Homopolymerization of Propylene
 Propylene was polymerized in a stirred tank reactor having a volume of 5
 liters. 0.6 ml of triethylaluminum cocatalyst (TEA), approx. 0.2 ml of a
 25 wt. % n-heptane solution of cyclohexyl-methyl-dimethoxysilane (external
 donor), and 30 ml of n-heptane were mixed together and were reacted for 5
 minutes. One-half of the mixture was fed into the polymerization reactor
 and the other half was mixed with approx. 20 mg of the above-mentioned
 procatalyst. After another 5 minutes the procatalyst/TEA/external
 donor/n-heptane mixture was fed into the polymerization reactor. The Al/Ti
 molar ratio was 500 and the ratio Al/external donor was 20 mol/mol. 70
 mmol of hydrogen and 1400 g of propylene were fed into the reactor, and
 the temperature was raised within 15-30 minutes to the desired
 polymerization temperature of 70.degree. C. The polymerization time was 60
 min, whereafter the formed polymer was withdrawn from the reactor. The
 isotacticity index II and melt index MFR.sub.2 (g/10 min, with a load of
 2.16 kg) of the polymer were determined.
 Results
 Below is a description of the six laboratory catalyst synthesis experiments
 describing the synthesis differences when a shift is made from two to
 three titanations, from 0.15 to 0.30 D.sub.1 /Mg addition, and from one to
 two donor additions.
 Table 1
 Results of bulk homopolymerization of propylene when 2 or 3 titanations
 (titanium tetrachloride treatments), D.sub.1 /Mg=0.15 and 0.3, and the
 addition of 1 or 2 donors are used.

Ref. Ref. Ref. Ref.
 Quantity Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6
 Titanation times 2 2 3 3 3 3
 Donor DOP DOP DOP DOP 2*DOP DOP +
 DUP
 D.sub.1, D.sub.1 /Mg, mol/mol 0.15 0.3 0.15 0.3 0.15 + 0.15 +
 0.15 0.15
 Activity kg/g cat. 24.1 24.6 44.9 34.3 38.5 45.3
 II % 96.8 98.3 96.2 98.0 97.3 98.2
 MFR.sub.2, g/10 min 6.4 4.4 7.3 4.7 7.3 8.2
 Examination of the Results
 Reference Example 1. In this example, which represents the classical
 synthesis, two titanation runs and a D.sub.1 /Mg ratio of 0.15 are used.
 Owing to the low washing efficiency, the activity is only of the order of
 25 kg PP/g cat, and owing to the low donor concentration, the isotacticity
 index II % is lower than 97%. (It can be assumed that the slightly higher
 MFR is due to the corresponding isotacticity.)
 Reference Example 2. When an attempt is made to correct the situation in
 Example 1 with respect to isotacticity by raising the donor amount to 0.3,
 isotacticity rises to a good value of 98.3, but at the same time hydrogen
 sensitivity decreases (molecular weight is not decreased, i.e. MFR does
 not rise), since a larger amount of well-attaching DEP takes up donor
 sites in the catalyst, and only a lower number of active sites are
 involved in the hydrogen-sensitive equilibrium of the external donor. This
 is seen as a low melt index (MFR=4.4). The large amount of DEP also has
 the effect that activity remains low.
 Reference Example 3. When a third titanation is added to the synthesis, the
 washing efficiency increases. Owing to the improved washing efficiency,
 the byproduct, TiCl.sub.3 OEt, of the procatalyst is washed out more
 effectively, and thus the poison effect of this byproduct on the catalyst
 is reduced. This is seen as a considerable increase in activity (A=44.9).
 The efficient wash is also seen as a lower donor concentration in the
 catalyst, which leads to lower isotacticity. The smaller donor amount, for
 its part, is seen as a higher hydrogen sensitivity, since a larger number
 of active sites are now involved in the equilibrium of the external donor
 (MFR=7.3).
 Reference Example 4. If the situation in Example 3 is corrected by adding a
 larger amount of donor (0.3 DOP), a clearly higher DEP concentration in
 the catalyst (DEP=10.9), i.e. a more complete transesterification, is
 achieved. This leads to a slight decrease in activity as compared with
 Example 3, owing to the high DEP concentration. The high DEP concentration
 is also seen as a high isotacticity (98.0%) and also as a lower melt
 index. It can be assumed that hydrogen sensitivity decreases as a large
 amount of internal donor remains attached to the catalyst. The low MFR
 obtained in the experiment is due to this.
 Example 5. In the fifth experiment, it was investigated whether the donor
 composition could be changed by adding the DOP donor in two steps. This
 was possible, since there was still a third titanation available for the
 washing. The DOP amount added was the same as in Example 4, but it was
 added in two equal batches, to the first and the second titanation steps.
 The result showed that the DEP amount obtained by transesterification
 halved to 4.3, and the amount of DOP obtained by coordination increased to
 8.8%. This corresponded to the expectations. Washing became more
 effective, since the titanium concentration decreased 1.9%. The efficient
 TiCl.sub.3 OEt wash and the slight DEP amount increased the activity to
 38.5 kg PP/g cat. The DEP+DOP mixture which was obtained by using this
 synthesis modification proved to be effective in increasing both
 isotacticity and hydrogen sensitivity, the II % being 97.3 and the MFR
 being 7.3. The experiment showed that with this combination a sufficient
 isotacticity is achieved, but additionally the conditions are good for the
 elution of internal donor during the polymerization, whereupon an
 equilibrium interaction is achieved between the detaching donor and the
 free site, thus making hydrogen termination possible.
 Example 6. The last experiment was carried out as in Example 5, except that
 the DOP used in the second donor addition was replaced with DUP. The
 results of this experiment emphasized what had been achieved in Experiment
 5. The Ti % decreased further down to 1.5%, showing that the washing
 efficiency provided by this method was advantageous. The DEP amount also
 decreased to 3.6%, and the remaining DUP concentration was 6.5%. Thus the
 total amount of donor in this catalyst was clearly less. This was seen as
 a high activity (45.3 kg PP/g cat). The DEP-DUP donor pair additionally
 provided a very favorable isotacticity protection and made an effective
 donor equilibrium possible during polymerization, thus producing a high
 hydrogen sensitivity. Isotacticity increased to 98.2%, and MFR was 8.2.
 Trial Run Series
 After the laboratory-scale experiments 1-6, three full-scale trial run
 series were also carried out (respectively Examples A-D, F-H and J-O). In
 the laboratory, three series of catalysts were prepared, in which there
 was made a gradual shift from a donor addition in the first titanation
 (titanation I) to a donor addition in the second titanation (titanation
 II). All of the catalysts were prepared in completely inert conditions.
 First, 300 ml of TiCl.sub.4 was added to a reactor and was cooled to
 -20.degree. C. 150 ml of heptane and thereafter 25 g of MgCl.sub.2 *3EtOH
 support were fed into another reactor. This slurry was also cooled to
 -20.degree. C. The first titanation was initiated by bringing both of the
 above-mentioned cooled liquids together and by allowing them to react with
 each other.
 Thereafter the temperature was raised to +20.degree. C. and the first donor
 addition was done. Thereafter the temperature was raised to 130.degree.
 C., at which the first titanation (transesterification) was carried out in
 1.5 hours. Thereafter the titanation solution was replaced with 200 ml of
 fresh TiCl.sub.4. The second donor addition was done into the new mixture.
 The second titanation (only coordination) took place at 120.degree. C. for
 0.5 hour.
 The third titanation took place in the same manner, with the difference
 that no donor was added.
 After the TiCl.sub.4 treatment, the procatalyst was washed four times with
 400 ml of heptane, 90.degree. C., 15 minutes. The procatalyst was dried in
 a nitrogen flow. Polymerization was carried out in the same manner as in
 the preliminary experiment series.
 In the first trial series (B-D; A is a reference example), in the first
 titanation a di-2-ethyl-hexyl phthalate (DOP) donor and
 transesterification conditions were used. In the second titanation,
 diundecyl phthalate (DUP) was added in coordinating conditions. The total
 donor amount, i.e. the sum of the donor amounts of the first and second
 additions, was the same in all of the experiments. Calculated in moles,
 the donor amount was 0.3 in proportion to magnesium, i.e. the donor/Mg
 molar ratio was 0.3. The DOP, which was added in the first titanation,
 became transesterified to diethyl phthalate (DEP) owing to the high
 temperature. The DUP, added in the second titanation, did not become
 transesterified, since the temperature in the second titanation was lower
 than in the first titanation. Table 1 shows the donor addition ratios in
 the first trial series. Table 2 lists the donor compositions of the
 catalysts after the synthesis, and Table 3 lists the polymer melt indices
 (MFR.sub.2, g/10 min with a load of 2.16 kg), obtained by test
 polymerizing the catalysts in question.
 TABLE 1
 Donor amounts added in the first trial series
 DOP/Mg DUP/Mg
 Catalyst Titanation I Titanation II
 Reference example A 0.3 0.0
 B 0.25 0.05
 C 0.10 0.20
 D 0.05 0.25
 TABLE 1
 Donor amounts added in the first trial series
 DOP/Mg DUP/Mg
 Catalyst Titanation I Titanation II
 Reference example A 0.3 0.0
 B 0.25 0.05
 C 0.10 0.20
 D 0.05 0.25
 TABLE 3
 Melt indices (MFR) of the polymers
 Catalyst MFR
 Ref. A 4.7
 B 5.0
 C 6.7
 D 8.0
 The results show that a clearly increasing hydrogen sensitivity (MFR) was
 achieved in the catalysts when a shift was made from only transesterified,
 well attached internal donor to a donor mixture which also contained a
 more easily detaching internal donor. In almost all of the catalysts the
 activity was at a satisfactory level, being around 30 kg/g cat. In the
 example in which diundecyl phthalate was added to the second titanation
 (not shown in the table), an activity was observed which remained at a
 lower level. A slight decrease in isotacticity was observed, from 98% to
 slightly below 97%. However, this decrease in isotacticity is not
 significant in an industrial process.
 In the second trial series, DOP was used in both donor additions
 (transesterification and coordination). Table 4 lists the donor amounts
 added, Table 5 lists the donor compositions in the catalysts after
 synthesis, and Table 6 lists the melt indices (MFR) of the polymers.
 TABLE 4
 Donor amounts added in the second trial series
 DOP/Mg DOP/Mg
 Catalyst Activation I Activation II
 Reference example A 0.3 0.0
 F 0.2 0.1
 G 0.15 0.15
 H 0.05 0.25
 TABLE 4
 Donor amounts added in the second trial series
 DOP/Mg DOP/Mg
 Catalyst Activation I Activation II
 Reference example A 0.3 0.0
 F 0.2 0.1
 G 0.15 0.15
 H 0.05 0.25
 TABLE 4
 Donor amounts added in the second trial series
 DOP/Mg DOP/Mg
 Catalyst Activation I Activation II
 Reference example A 0.3 0.0
 F 0.2 0.1
 G 0.15 0.15
 H 0.05 0.25
 The results show that an increasing hydrogen sensitivity was achieved in
 the catalyst series when the well-attaching internal donor (DEP) was
 partly replaced with an easily detached internal donor (DOP). The
 isotacticity values in all of the polymers were very good, all being
 around 98%. The activities were of the normal level, around 30 kg/g cat.
 In an example in which DOP was added only to the second titanation, a
 decrease in activity was observed (the example is not shown in the table).
 In the third trial series, the first donor addition was maintained
 constant; the DOP(DEP)/Mg ratio in this addition was 0.15. The donor
 addition of the second activation was increased gradually from 0.0 up to
 0.3. Table 7 lists the donor additions to the synthesis, Table 8 lists the
 donor compositions of the catalysts after the synthesis, and Table 9 lists
 the polymer melt indices obtained when the catalysts of this series were
 test polymerized.
 TABLE 7
 Donor additions in the third trial series
 DOP/Mg DOP/Mg
 Catalyst Activation I Activation II
 J (reference) 0.15 0.0
 K 0.15 0.05
 L 0.15 0.10
 G 0.15 0.15
 M 0.15 0.20
 N 0.15 0.25
 O 0.15 0.30
 TABLE 8
 Donor compositions in the catalysts in the third trial series
 Catalyst DEP wt. % DEP mol. % DOP wt. % DOP mol. %
 J 5.3 0.024 1.3 0.003
 K 5.0 0.023 4.2 0.011
 L 4.7 0.021 4.8 0.012
 G 4.3 0.019 8.8 0.023
 M 3.9 0.018 9.5 0.024
 N 5.1 0.023 16.6 0.043
 O 3.8 0.017 17.2 0.044
 TABLE 8
 Donor compositions in the catalysts in the third trial series
 Catalyst DEP wt. % DEP mol. % DOP wt. % DOP mol. %
 J 5.3 0.024 1.3 0.003
 K 5.0 0.023 4.2 0.011
 L 4.7 0.021 4.8 0.012
 G 4.3 0.019 8.8 0.023
 M 3.9 0.018 9.5 0.024
 N 5.1 0.023 16.6 0.043
 O 3.8 0.017 17.2 0.044
 The results showed that also in the third trial series an increasing
 hydrogen sensitivity was achieved in the catalysts, although the change
 was not as great as in the first two trial series, owing to the constant
 DOP addition to the first activation. Isotacticity was consistently around
 97% in most of the trial series; only at the extreme points (J, O) was a
 slightly lower isotacticity (96%) obtained. The activities remained at a
 satisfactory level throughout the trial series, and were all around 30 kg
 PP/g cat.
 The experiments described above show clearly that the catalyst synthesis of
 two internal donors according to the present invention provides a catalyst
 system is obtained which yields high isotacticity values while activity
 and hydrogen sensitivity (.fwdarw.lower molecular weight, higher MFR)
 remain high.