It is well known that middle distillates contain alkanes which at low temperatures tend to precipitate under the form of waxes, which are linear chain paraffins having a limited solllhility and which tend to crystallize as the temperature decreases. In this way gelled structures are formed which cause the middle distillate fluidity loss. Therefore there are problems of middle distillate storage, transfer and feeding through pipes, pumps and besides plugging phenomena of the line filters and of those of the propulsor feeding ducts take place.

These problems are well known in the art and for the cold behaviour definition, middle distillates are characterized from the physical point of view by the following features determined with various standardized methods: Cloud Point (C. P.), Pour Point (P. P.), Cold Filter Plugging Point (C. F. P. P.), Wax Antisettling (W. A. S.), etc.

Various additives (CFI), also commercial, are known in the art, having selective and/or multifunctional uses able to improve the above mentioned middle distillate cold characteristics. Generally the additives have the purpose to modify the wax crystals formed at low temperatures both redu- cing the sizes and modifying the shape thereof. Indeed the cry- stals having reduced sizes give less problems of filter plugging. Another property required to the additives is that to maintain in suspension the formed crystals, i. e. to obtain the result to have a reduced settling rate. Also this effect concurs to the non filter plugging at low temperatures and specifically to reduce wax accumulation on the storage tanks bottom of middle distillates.

It is known that the additves used to overcome such disadvantages are polymeric products.

In the prior art ethylene copolymers with unsaturated esters, for example vinylacetates, maleic or fumaric acid, or unsaturated monocarboxylic acid esters, for example acrylates, are especially known. The ethylene/vinylacetate (EVA), fumarates, propionates, etc., can be mentioned. See for example USP 3,661,541, USP 4,211,534, EP 153,176, EP 153,177.

Ethylene/alpha-olefins (co) polymers suitable to the same purpose are also known in the prior art, see USP 5, 097,084, which are characterized by the substantial absence of inversions of the alpha-olefin linking, for example, propylene, as indicated by the X2 and/or X4 parameters lower than or equal to about 0.02, determined boy 1 C NMR according to the method described by J. C. Randal in"Macromolecules"11,33 (1978). The ethylene/propylene copolymers having said value of the mentioned parameters show improved CFPP values than the copolymers wherein said values are not satisfied, for example in comparison with those obtained by using vanadium-based catalysts.

The patent application WO 91/11488 describes as additives ethylene (co) polymers with alpha-olefins, in particular ethylene/propylene copolymers obtained by polymerization of ethylene with alpha-olefins in the presence of catalysts based on a) coordination organometallic compounds which are cyclopentadienyl derivatives of a metal of the Group 4b of the Periodic Table and they can be mono-, di-and tri-cyclopenta- dienes and derivatives thereof of the transition metal, with b) alumoxanes, which are the reaction products of aluminum trialkyls with water and specifically methylalumoxane. The obtained ethylene/alpha-olefin copolymers have the essential characteristic to have at least 30% of the polymeric chains with ethylene and ethylidene terminal unsaturations. These copolymers can be combined with one or more additives known in the art as CFI such as vinylacetates, fumarates, acrylates, propionates and polar compounds, for example tallowamines.

Ethylene copolymers with alpha-olefins usable as additives to increase the properties at low temperatures of the midle distillate obtainable by reaction of a bis-cyclopentadienyl derivative, characterized by having two phenoxide groups linked to the transition metal, are also known. See for example EP 848,020.

It has been surprisingly and unexpectedly found by the Applicant that mixtures of particular ethylene (co) polymers with one or more alpha-olefins as defined hereunder, show improved properties when they are used as additives to improve the middle distillate physical behaviour at low temperatures.

Specifically the invention copolymers show improved values in C. F. P. P. terms.

An object of the present invention are mixtures comprising the following components: a) ethylene copolymers (C2) with one or more of the following comonomers: -Ca: one or more linear or branched alpha-olefins, from 3 to 20 carbon atoms, and/or -CS: one or more dienes, conjugated or not, selected from: -linear from 4 to 20 carbon atoms or -cyclic wherein the ring is from 5 to 6 carbon atoms and having a total carbon atoms till 20, preferably the cyclic dienes are selected from vinylcycloalkenes or di-cyclo-pentadienes, such as vinylcyclohexene or di-cyclopentadiene- ethyliden-norbornene; -vinylaromatic monomers, such as styrene, 2,4 vinylstyrene, optionally one or more hydrogen atoms of the ring (s) of the cyclic or aromatic monomers being substituted by saturated alkyl groups from 1 to 12 carbon atoms or by unsaturated alkyl groups from 2 to 12 carbon atoms, optionally one or more carbon atoms of the ring being substituted by heteroatoms, preferably nitrogen, oxygen, sulphur; the comonomer total amount being in the range 1-50% by moles, preferably 5-25% by moles, the average molecular weight by number being in the range 300-25, 000, preferably 700-15,000; and b) ethylene copolymers with one or more comonomers mentioned in a), the comonomer total amount being in the range 1-50% by moles, preferably 5-25% by moles, the average molecular weight by number being in the range 700-15,000; the composition difference in terms of total sum of the comonomers of a) and b) being of at least 1% by moles, preferably at least 5% by moles; the a): b) ratios by weight are in the range 5: 1-1: 5.

Preferably, the composition difference in terms of total sum of the comonomers of a) and b) is at most 10-15% by moles.

The a-olefins mentioned with Ca are preferably: propylene (C3), 1-butene (C4), 1-hexene (C6), 1-octene (C8), 1-decene (C10), 1-dodecene (C12), 4-metl-1-pentene.

The Ca olefin total amount is in the range 5-25% by moles.

As C6 dienes, the conjugated dienes, for example butadie- ne, isoprene, piperylene, 1,3-hexadiene, 1,3-octadiene, 2,4- decadiene, di-cyclopentadiene; non conjugated dienes such as 1,4-hexadiene, 7-methyl-1,6-octadiene; cyclic non conjugated dienes such as norbornene, ethylidennorbornene (ENB), 4-vinyl- cyclohexene and vinylaromatic monomers such as styrene, 2,4-vi- nylstyrene, etc., can be mentioned.

The Cß diene amount is in the range 0-25% by moles, prefe- rably 1-5% by moles.

Examples of copolymers are: C2/Ca (II); C2/Cß (III); C2/Ca/CS (IV).

Examples of copolymers (II) are: ethylene/propylene (C2/C3); ethylene/propylene/butene (C2/C3/- C4); ethylene/butene/hexene (C2/C4/C6); ethylene/butene/octene (C2/C4/C8), etc.

Examples of copolymers (III) are: ethylene/ethylidennorbornene (also indicated ethylene/5- ethylidene-2-norbornene) (C2/ENB); ethylene/styrene; ethylene/ /ENB/4 vinyl-cyclohexene, etc.

Examples of copolymers (IV) are: ethylene/propylene/ethylidennorbornene (C2/C3/ENB); ethylene- <BR> <BR> <BR> <BR> <BR> <BR> /butene/ethylidennorbornene (C2/C4/ENB); ethylene/octene/ethy- lidennorbornene (C2/C8/ENB); ethylene/propylene/butadiene; <BR> <BR> <BR> <BR> <BR> <BR> ethylene/propylene/octene/ethylidennorbornene (C2/C3/C8/ENB); ethylene/butene/octene/ENB/4 vinyl-cyclohexene, etc.

The a) and b) (co) polymers are obtainable by polymeriza- tion of the monomers in the presence of catalysts comprising the reaction product between: 1) a metallocene compound with 2) a co-catalyst selected from alumoxanes and compounds of general formula: wherein (A)-is a compatible non coordinating anion, pre- ferably (D Qq) wherein Li is a neutral Lewis basis, (L1-H) + is a Bronsted acid, D is an element of the group from IIIa to VIa of the Element Periodic Table with metalloidic characteristics, preferably boron, phosphorus or arsenic with valence 3 or 5, silicon, more preferably boron with valence 3; Q, equal to or different from each other, are selected from the following groups: hydrides, halides, alkyls, aryls optionally substituted, for example with halogens, preferably F, alkoxides, aryloxides, dialkylamido, or RoCOO-wherein Ro ranges from 1 to 20 carbon atoms, with the proviso that Q is equal to halide only once; q is an integer equal to the D valence plus 1.

The metallocene compound 1) is preferably a bis-cyclo- pentadienyl derivative of general formula: (CpiCp2)-M-(L) containing groups with oxygen bound to the transition metal, in which M is a metal from the IIIb group to the IVb group or of the lanthanide series of the Element Periodic Table; Cp1 and Cp2, equal to or different from each other, represent the following groups bound to M with delocalized rr bonds, specifically with an eta 5 bond when the groups are selected from cyclopentadiene, indene, fluorene, or derivatives thereof substituted in the indene and fluorene case also with the phenilic hydrogenated ring (rings) and with substituents both in the phenil and cyclopentadienyl rings, also with hetero- atoms; or with rr bonds for example in the cyclooctatriene case; or said Cpl Cp2 groups constrained with M through a bivalent linking bridge, for example-R-type, wherein R is an alkylene, preferably from 1 to 4 carbon atoms,-Si (R') 2-wherein R'is an alkyl from 1 to 10 C atoms, preferably from 1 to 6 carbon atoms; or an aryl optionally containing heteroatoms, such as O, N, or alkylaryl or arylalkyl from 7 to 20 carbon atoms; L2 or L3, equal to or different from each other, represent a ORa group wherein Ra is an aryl group, optionally the ring carbon atoms being substituted also with heteroatoms, and optionally containing substituents for example of alkyl type from 1 to 10 carbon atoms.

See in particular EP 840,020 for the preferred 1) catalyst.

Also the metallocene compounds of patent application WO 91/11488 wherein L2 and L3 are for example halogens or alkyl groups or hydrogen, can be used. One can refer to this international patent application, herein incorporated by reference, for these metallocene catalysts.

The co-catalyst alumoxane has the general formula: (Rb-Al-O) m, in the form of cyclic compound or in the form of linear polymeric compound of formula Rb (Rb-Al-O) m A1 (Rb) 2 ; the alumoxane is generally a mixture of the two mentioned forms; Rb is an alkyl group from 1 to 5 C atoms, preferably methyl, m is an integer from 1 to 30, preferably from 4 to 20; m'is an integer from 3 to 20, preferably from 4 to 20.

The structure of invention (co) polymers was characterized by DSC (Differential Scanning Calorimetry) and 13C NMR in order to determine the % of cristalline material, the length of ethylene sequences and the amount of comonomer inversions.

The alumoxane compound of the catalytic system is prefe- rably prepared by reaction of aluminum trimethyl and water, obtaining a mixture of linear and cyclic compounds. They are generally prepared by putting into contact an aluminum trialkyl solution with water in suitable organic solvents, for example aliphatic hydrocarbons.

As known, alumoxanes are compounds containing A1-O-A1 bon- ds, having a variable molar ratio O/Al, obtainable in the art by reaction, under controlled conditions, of an aluminum alkyl, or an aluminum alkyl halide, with water and, in the case of aluminum trimethyl, also with an hydrate salt, as aluminum hexahydrate sulphate, copper pentahydrate sulphate and iron pentahydrate sulphate.

The molar ratio between Al of the 2) component alumoxane with respect to the metal amount of component 1) (metallocene) is in the range 10,000: 1-100: 1, preferably 5,000: 1-500: 1. In the case of the boron compound the ratio is in the range 0.1- 4.0: 1 and preferably 0.5-2.0: 1.

Examples of the preferred cocatalyst have the general formula: (Li-H) + (B Q4)- wherein the meanings of L1 and Q are above mentioned, B is the boron in the 3 valence state; L1 can be NH3, aniline, pyridine, quinoline, alkylamines, dialkylamines, trialkylamines with the alkyl from 1 to 8 C atoms, preferably from 1 to 4, phenylamines, etc. All these compounds can respectively form quaternary ammonium salts, pyridinium salts, quinolinium salts which represent (L,-H) . Exemplifying compounds which can be mentioned are the following: substituted trialkyl ammonium salts, for example triethylammo- nium tetraphenylborate, tripropylammonium tetraphenylborate, tris (n-butyl) ammonium tetraphenylborate, trimethylammonium te- trakis (p-tolyl) borate, tributylammonium tetrakis (pentafluoro- phenyl) borate, tripropylammonium tetrakis (2,4-dime- thylphenyl) borate, tributylammonium tetrakis (3,5-dimethylphe- nyl) borate, triethylammonium tetrakis (3,5-ditrifluoromethyl- phenyl) borate, etc.

The N, N-dialkyl anilinium salts can also be used, such as for example N, N-dimethyl anilinium tetraphenylborate, N, N-die- thyl anilinium tetraphenylborate, N, N-2,4,6-pentamethylani- linium tetraphenylborate, etc.; dialkyl ammonium salts such as di- (i-propyl) ammoniumtetrakis (pentafluorophenyl) borate, dicyclohexylammonium tetraphenylborate, etc.; triaryl phosphonium salts such as triphenylphosphfonium tetraphenylbo- rate, tri (methylphenyl) phosphonium tetrakis pentafluorophenylborate, tri (dimethylphenyl) phosphonium tetraphenylborate, etc...

Preferred non limiting examples of the 1) compound which can be used to prepare the cation complex are titanium, zirconium, vanadium, hafnium (Hf), chromium, lanthanium deri- vatives, ecc., the titanium or Zr compounds are preferred.

Examples which can be mentioned are: bis (eta 5 cyclopentadie- nyl) Zr diphenate; bis (eta 5 cyclopentadienyl) Zr of 2,3,6- trimethylphenate, bis (eta 5 cyclopentadienyl) Hf diphenate, bis tetramethylcyclopentadienyl Zr diphenate, etc.

Other metallocene catalysts which can be used are well known in the prior art, for example in EP 129,368, EP 128,046, EP 260,299, these three patents are herein incorporated by reference.

The preferred catalysts of the present invention are obt- ained for example by direct reaction of bis-cyclopentadienyl metal dialkyl, preferably dimethyl, with the corresponding phenols. See the european patent application 848,020.

The polymerization to obtain the invention copolymers can be carried out by operating in suspension, in solution or in gas phase at temperatures generally in the range 0°C-150°C at a pressure generally in the range 1-300 bar, optionally using a molecular weight regulator, for example hydrogen.

As said above, the invention (co) polymer mixtures as above defined surprisingly show improved activities as CFPP additives with respect to the single copolymers.

Specifically according to the present invention the (co- ) polymers obtained by using as catalyst the preferred 1) com- ponent in combination with the preferred 2) cocatalyst, for example boranes and/or borates as above mentioned, are pre- ferred.

The physical characteristics measurements of the middle distillates are carried out by determining the following parameters: Cloud Point (C. P.), Pour Point (P. P.) and Cold Filter Plugging Point (C. F. P. P.) as defined in the ASTM D2500- 81; ASTM D97-66 and IP 309/83 methods, respectively.

The methods for determining the invention polymer sequence distribution, specifically the X2 and X4 inversions are well known in the prior art and can be determined by 13C NMR as mentioned in the USP 5,097,084 herein incorporated by re- ference.

If desired, the percentage of terminal unsaturations of ethylidene-CRlt=CH2 type, wherein Rlt is an alkyl from 1 to 12 C atoms, or ethylene-CH=CH2 type, can be determined by IR (FT- IR) analysis (see the patent application WO 90/01503 page 26), or by iodometeric titration or 13C NMR.

The invention (co) polymers can be combined with other cold flow improvers (CFI) known in the prior art to obtain synergic effects both as regards CFPP and the filterability, and the WAS effect. As known CFIs according to the present invention, ethylvinylacetates, fumarates, acrylates, propionates are preferably used. Preferably in order to obtain an higher synergic effect, the invention polymers are combined with the above mentioned CFIs and furthermore also with a third CFI selected from the nitrogen polar compounds.

The third CFI additive, a nitrogen polar compound is gene- rally selected from aminic salts and/or amides formed by re- action of at least a molar part of a substituted hydrocarbide with a molar part of hydrocarbon acid having from 1 to 4 carboxylic acid groups and an anhydride thereof; esters/amides containing from 30 to 300, preferably from 50 to 150 total carbon atoms, can also be used. These nitrogen compounds are described in USP 4,211,534. Suitable amines are usually long chain C12-C40 primary, secondary, tertiary or quaternary amines or mixtures thereof, but shorter chains can be used if the resulting nitrogen polar compound is soluble in oil; it will usually contain from about 30 to 300 total carbon atoms. The nitrogen polar compound preferably contains at least an alkyl segment of linear C8-C24 chain.

Suitable amines comprise primary, secondary and tertiary amines, preferably secondary amines, or quaternary ammonium salts.

Examples of primary amines comprise tetradecyl amine, cocoamine, and hydrogenated tallow amine. Examples of secondary amines comprise dioctadecyl amine and methyl phenyl amine.

Amine mixtures are also suitable and many amines derived from natural materials are mixtures. A preferred amine is a secondary hydrogenated tallow amine of the HNR3R4 formula wherein R3 and R4 are alkyl groups derived from hydrogenated tallow greases composed of approximately 4% of C14,31% of C16, 59% of C18.

Examples of carboxylic acids (and anhydrides thereof) suitable for preparing these nitrogen compounds comprise cyclo- pentane-1,2 acid dicarboxylic acid and naphthalendicarboxylic acids. Generally, these acids have about 5-13 carbon atoms in the cyclic fraction. Preferred acids are benzen dicarboxylic acids such as phthalic, isophthalic and terephthalic acid. The phthalic acid or its anhydride is particularly preferred. The particularly preferred compound is the amido-amine salt formed by letting react a molar part of phthalic anhydride with two molar parts of dehydrogenated tallow amine. Another preferred compound is the diamide formed by the dehydration of this amide-amine salt. Besides, the known CFI formulations can optionally comprise other additives of fuel oils, many of which are used in the prior art or are known in the literature.

The additive concentration of the present invention, singly or in combination with the other above mentioned CFIs, to be used in the middle distillates, ranges from 10 ppm to 5,000 ppm, preferably from 50 ppm to 500 ppm, more preferably from 100 to 200 ppm. The weight ratios between the invention copolymer, the known CFI (for example EVA, fumarates, propionates, acrylates) and the nitrogen polar compound is the following: 10/1: 10/1: 10, preferably 10/1: 5/1: 5.

The present invention will be now better illustrated by the following working examples, which have a merely indicative purpose and not limitative of the scope of the invention itself.

EXAMPLES CHARACTERIZATION The molecular weight determination (both number average Mn and weight average Mw) is carried out by gel permeation chromatography (GPC-Gel Permeation Chromatography) which gives also the molecular weight distribution (MWD). See for example W. W. Yau et al"Modern Size Exclusion Liquid Chromatography", John Wiley and Sons, N. Y. 1979.

The intrinsic viscosity (dl/g) is determined according to known methods, for example in tetraline at 135°C. The Mv viscometric molecular weight can also be determined by using intrinsic viscosity methods well known in the prior art. See for example: L. H. Tung,"Fractionation of Synthetic Polymers" Ed. Marcel Dekkers Inc. N. Y. 1977, J. Polymer Sci 20,495-506, 1956; G. Moraglio, Chim. Ind. (Milano) 10 984,1959.

The molecular weight distribution is generally in the range 1.5-5, preferably 1.5-3.5.

The A and B gas oils (middle distillates) free from additives used in the tests, have the following characteristics: type A type B density (IP 160) (15°C/gxcm-3) 0.8397 0.83 I. B. P. (initial boiling point) 170.2°C 164.8°C f. b. p. (final boiling point) 355.2°C 357.1°C 90%-20% vol. 101.4°C 117.3°C f. b. p.-90% vol. 21.1°C 30.0°C C.

C. F. P. P.-8 °C-9 °C P. P.-12 °C-18 °C EXAMPLE 1 Zirconocene bisphenoxide (catalyst) synthesis In a flask containing 50 ml of toluene, 1.988 millimoles of zirconocene dimethyl have been dissolved. Subsequently 3.976 millimoles of phenol have been added under stirring. The solution develops methane according to the reaction: Cp2Zr (CH3) 2+2 C6H5OH- [C6H5O] 2 ZrCp2 +2 CH4t The process has been carried out at room temperature and is quantitative. The yields are close to 100%. After about 4 hours of stirring, the solution was evaporated and the solid characterized by 1H NMR: the spectrum shows the Cp peak and the whole series of the hydrogen peaks of the two phenyls.

Cp2Zr (O-C6H5) 2 : 1HA = 5.94 (s, 10 H, Cp), 6.75-7.29 (m, 10 H, C6H5).

EXAMPLE 2 Cocatalyst preparation tetra(perfluorophenyl)borate(BNF4)N,N'Dimethylanilinium synthesis This compound has been synthetized according to the following literature: J. A. Ewen, M. J. Elder, R. L. Jones, L. Haspeslagh, J. L. Atwood, S. G. Bott, K. Robinson, Macromol. Chem., Macromol. Symp.

48/49,253 (1991).

In a 100 ml flask 1.98 g (2.88 millimoles) of lithium tetra (perfluorophenyl) borate dissolved in 20 ml of methylene chloride are introduced. To this solution 1.05 g (6.66 millimoles) of N, N-dimethylaniline chlorhydrate dissolved in 10 ml of methylene chloride, are added. The lithium chloride precipitates, it is filtered and the solution is evaporated. A white paste is formed which is washed many times in pentane until obtaining a white solid. The yield is of about 71%.

EXAMPLE 3 (comparative) Polvmerization with the catalyst of Example 1: ethylene/uropv- lene copolymer The used reactor is a steel AISI 316 autoclave (5 1 volume) equipped with stirrer anchor shaped and able to work at a pressure f, 150 bar.

The autoclave is equipped with 4 feeding inlets, an outlet and a water circulation cooling system.

The reactor is purged many times with anhydrous and hot nitrogen and maintained under pressure at 120°C for 24 hours.

From the purification temperature the autoclave is cooled at 25°C maintaining the nitrogen pressure at 1 bar.

250 ml of distilled toluene together with 0.7 ml of triethylaluminum and, under stirring, 150 g of liquid propylene are introduced in sequence.

The mixture is heated to 70°C and when this temperature is reached, 6.5 bar of ethylene and 2 bar of hydrogen are added.

Then a 20 mg Cp2Zr (bisphenoxide) solution of Example 1 and 39.3 mg of the cocatalyst of Example 2 in 50 ml of toluene are added under an overpressure of anhydrous nitrogen.

The polymerization is carried out for 6 minutes maintaining the pressure constant by continuous feeding of ethylene.

The polymerization is quickly stopped by venting and cooling the autoclave to 25°C.

The produced polymer is precipitated using ethanol/ acetone acidified with hydrochloric acid, washed many times with ethanol/acetone and anhydrified under vacuum.

30 g of polymer containing 16% by weight of propylene (11.3% by moles) determined by IR analysis, are obtained. The viscometric molecular weight Mv is 5,700. The number average molecualr weight Mn is 2,800.

CFPP determination The obtained polymer has been used as CFPP additive for the A and B middle distillates having the above mentioned characteristics. The CFPP value has been determined by using 50 ppm of polymer.

The results are: Middle distillate CFPP (°C) A-12 B-13 EXAMPLE 4 (comparative) Polvmerization with the catalyst of Example 1: ethvlene/octene copolvmer Example 3 is repeated with the following variations: instead of propylene 100 g of octene and 5 bar of ethylene are used without employing hydrogen as molecular weight regulator and using a polymerization temperature of 80°C.

80 g of copolymer containing 30.3% by weight of octene (corresponding to 9.8% by moles) determined by 13C NMR, have been obtained.

The viscometric Mv molecular weight is 10,200. The number average Mn molecular weight is 5,000.

CFPP determination The obtained polymer has been used as CFPP additive for the B middle distillate having the above mentioned characteristics. The CFPP value has been determined by using 50 ppm of polymer.

The result was: Middle distillated CFPP (°C) B-14.

EXAMPLE 5 The CFPP has been determined in the B middle distillate by using a mixture of the polymers of Example 3 and Example 4 in a weight ratio between the two of 1: 1 according to the present invention.

The CFPP value has been determined by using 50 ppm of the mixture of the two above mentioned polymers.

The result was: Middle distillate CFPP (°C) B-17.

EXAMPLE 6 (comparative) Polymerization with the catalyst of Example 1: ethvlene/octene copolymer Example 4 is repeated with the following variations: instead of 100 g, 80 g of octene are used.

80 g of copolymer containing 24% by weight of octene (corresponding to 7.5% by moles) determined by 13C NMR, have been obtained.

The viscometric Mv molecular weight is 13,800. The number average Mn molecular weight is 6,800.

The obtained polymer has been used as CFPP additive for the B middle distillate having the above mentioned characteristics. The CFPP value has been determined by using 50 ppm of polymer.

The result was: Middle distillate (°C) B-15.

EXAMPLE 7 (comparative) Polymerization with the catalyst of Example 1 : ethylene/ propYlene/octene terpolvmer Example 3 is repeated with the following variations: 50 g of octene together with propylene, in an amount of 50 g, are also added; the polymerization temperature was of 70°C and 5 bar of ethylene without hydrogen as molecular weight regulator; 15 mg of Cp2Zr (bisphenoxide) solution of Example 1 and 29.5 mg of the cocatalyst of Example 2 in 50 ml of toluene are added under an overpressure of anhydrous nitrogen.

The polymerization is carried out for 5 minutes maintaining the pressure constant by continuous ethylene feeding.

70 g of polymer containing 16.2% by weight of propylene (12% by moles) and 11% by weight of octene (3.2% by moles) determined by 13C NMR, are obtained. The viscometric Mv molecular weight is 13,500. The number average Mn molecular weight is 6,500.

The obtained polymer has been used as CFPP additive for the A and B middle distillates having the above mentioned characteristics.

The CFPP value has been determined by using 50 ppm of polymer.

The results are: Middle distillate CFPP (°C) A-12 B-14.

EXAMPLE 8 The CFPP has been determined in the B middle distillate by using a mixture of the polymers of Examples 6 and 7 in a 1: 1 ratio by weight.

The CFPP value has been determined by using 50 ppm of the mixture of the two above mentioned products.

The result was: Middle distillate CFPP (°C) B-17.

EXAMPLE 9 (comparative) Polymerization with the catalyst of Example 1: ethvlene/ crosylene/octene terpolvmer Example 7 is repeated with the following variations: propylene in an amount of 50 g, octene 50 g.

The polymerization is carried out for 4 minutes maintaining the pressure constant by continuous ethylene feeding.

60 g of polymer containing 9.7% by weight of propylene (9.4% by moles) and 37.4% by weight of octene (13.6% by moles) determined by NMR, are obtained.

The viscometric Mv molecular weight is 14,000. The number average Mn molecular weight is 7,200.

The obtained polymer has been used as CFPP additive for the B middle distillate having the above mentioned characteristics.

The CFPP value has been determined by using 50 ppm of polymer.

The result was: Middle distillate CFPP (°C) B-14.

EXAMPLE 10 The CFPP has been determined in the B middle distillate by using a mixture of the polymers of Examples 7 and 9 in a 1: 1 ratio by weight.

The CFPP value has been determined by using 50 ppm of the mixture of the two above mentioned polymers.

The result was: Middle distillate CFPP (°C) B-18.

EX E 11 (comcarative) Polvmerization with the catalvst of Example 1: ethvlene/octene copolymer Example 3 is repeated with the following variations: instead of propylene, 100 g of octene are added; 5 bar of ethylene without using hydrogen as molecular weight regulator; 15 mg of Cp2Zr (bisphenoxide) solution of Example 1 and 29.5 mg of the cocatalyst of Example 2 in 50 ml of toluene under an overpressure of anhydrous nitrogen, are introduced.

The polymerization is carried out for 4 minutes maintaining the pressure constant by continuous ethylene feeding.

30 g of polymer containing 51% by weight of octene (20.6% by moles) determined by >3C NMR, are obtained. The viscometric Mv molecular weight is 13,100. The number average Mn molecular weight is 6,300.

The obtained polymer has been used as CFPP additive for the A middle distillate having the above mentioned characteristics.

The CFPP value has been determined by using 50 ppm of polymer.

The result was: Middle distillate CFPP (°C) A-14.

EXAMPLE 12 The CFPP has been determined in the A middle distillate by using a mixture of the polders of Examples 3 and 11 in a ratio by weight between the two respectively of 3: 1.

The CFPP value has been determined by using 50 ppm of the mixture of the two above mentioned polymers.

The result was: Middle distillate CFPP (°C) A-16.

EXAMPLE 13 The CFPP has been determined in the A middle distillate by using a mixture of the polymers of Examples 3 and 7 in a ratio by weight between the two respectively of 3: 1.

The CFPP value has been determined by using 50 ppm of the mixture of the two above mentioned polymers.

The result was: Middle distillate CFPP (°C) A-14.