WO2008064957A1

WO2008064957A1 - Process for preparing polybutene compositions having increased crystallization temperature

Info

Publication number: WO2008064957A1
Application number: PCT/EP2007/061142
Authority: WO
Inventors: Fiorella Pradella
Original assignee: Basell Poliolefine Italia S.R.L.
Priority date: 2006-12-01
Filing date: 2007-10-18
Publication date: 2008-06-05

Abstract

A process for producing a polybutene-1 composition having increased crystallization temperature TcA, comprising the step of blending the following components: A) a butene-1 polymer or polymer composition having crystallization temperature TcA equal to or higher than 50 °C; B) 5 to 3000 ppm by weight, with respect to the total weight of A) and B), of one or more metal salts of carboxylic acids containing two or more carboxylic groups bonded to a cyclic or polycyclic aliphatic or aromatic structure; said butene-1 polymer or polymer composition A) being brought to the molten state or maintained in the molten state during the blending step.

Description

"PROCESS FOR PREPARING POLYBUTENE COMPOSITIONS HAVING INCREASED CRYSTALLIZATION TEMPERATURE"

The present invention relates to a process for producing polybutene-1 compositions with increased crystallization temperature and to the compositions thus obtained.

It is known in the art that the crystallization temperature of polyolefms in general can be increased by adding nucleating agents. These nucleating agents are normally foreign materials that promote the crystallization of the polymer from the melt (heterogeneous nucleation). As a consequence of the nucleation effect, in addition to the increase of crystallization temperature, other valuable properties, in particular optical and mechanical, are enhanced. Moreover the increase of crystallization temperature makes it possible to reduce the process time in manufacturing finished articles from the molten polymer.

Thus there is a continuous effort in the art to find nucleating agents able to increase significantly the crystallization temperature of polyolefins.

In the case of polybutene-1 it is also important, as well known, to achieve a high rate of

Form II to Form I crystal transformation after solidification from the molten state, as explained for instance in US 5973076.

Many nucleating agents displaying the said effects have been already found, as disclosed in particular in the said US 5973076 and in US 4320209, US 4322503 and US 4359544.

These documents also show and explain that in the field of nucleation of polyolefins, an effective nucleating agent for one polymer may be ineffective even for a closely related polymer, thus making it very difficult to identify the nucleating agents best suited for a specific polymer, in particular for polybutene-1, which also undergoes the said crystal transformation.

For instance the nucleating agent ethyl benzoate, which is highly effective for polypropylene, is substantially ineffective in polybutene-1, even as regards the increase of crystallization temperature.

Moreover the most valuable nucleating agents for polybutene-1 should be able to further increase the crystallization temperature of polybutene-1 materials already having a high degree of crystallinity, thus a relatively high crystallization temperature even in the absence of nucleation, as the consequent enhancement of mechanical properties is highly desirable for use in the field of water pipes.

The applicant has now found that the said effects can be satisfactorily achieved by nucleating polybutene-1 with a specific class of salts of carboxylic acids.

Thus one object of the present invention is a process for producing a polybutene-1 composition having increased crystallization temperature T_c ^c, comprising the step of blending the following components:

A) a butene-1 polymer or polymer composition having crystallization temperature T_C ^A equal to or higher than 50 ⁰C, preferably equal to or higher than 55 ⁰C, selected from crystalline butene-1 homopolymers or copolymers, or their combinations, said crystallization temperature being determined by differential scanning calorimetry (DSC), according to ISO 11357, Part 3, with a heating and cooling rate of 10 °C/minute;

B) from 5 to 3000 ppm by weight, preferably from 100 to 2000 ppm by weight, more preferably from 100 to 1500 ppm by weight with respect to the total weight of A) and B), of one or more metal salts of carboxylic acids containing two or more carboxylic groups bonded to a cyclic or polycyclic aliphatic or aromatic structure; said butene-1 polymer or polymer composition A) being brought to the molten state or maintained in the molten state during the blending step.

While use of metal salts of cyclic dicarboxylic acids as nucleating agents is known for polypropylene, in particular from WO98/29494 and WO03/040230, or for polyolefm blends containing reduced amounts of butene 1 -polymers (US2006135679), no disclosure of their effectiveness in increasing the nucleation of butene-1 polymers having relatively high crystallization temperature is disclosed in the art.

Thus the process of the present invention also amounts to a new use of the salts B), in the said proportions, to increase the crystallization temperature of component A).

Preferably, in the process of the present invention the content (in the processed material) of any additional polyolefin component different from the said butene-1 polymers, if present, is of 10% by weight or less, in particular from 0.1 to 10% by weight with respect to the total weight of A) and the said additional polyolefin component. More preferably the process of the present invention is carried out in the absence of other polyolefin components (different from the said butene-1 polymers).

Another object of the present invention is a polybutene-1 composition comprising:

A) a butene-1 polymer or polymer composition selected from crystalline butene-1 homopolymers or copolymers, or their combinations;

B) from 5 to 3000 ppm by weight, preferably from 100 to 2000 ppm by weight, more preferably from 100 to 1500 ppm by weight with respect to the total weight of A) and B), of one or more metal salts of carboxylic acids containing two or more carboxylic groups bonded to a cyclic or polycyclic aliphatic or aromatic structure; said composition having a crystallization temperature T_c ^c satisfying the following relation: T_C ^C > T_C ^A + 18 where T_C ^A and T_c ^c are expressed in ⁰C, T_C ^A is the crystallization temperature of the butene-1 polymer or polymer composition A) in the absence of the metal salts B) and is equal to or higher than 50 ⁰C, preferably equal to or higher than 55 ⁰C, said crystallization temperature being determined by differential scanning calorimetry (DSC), according to ISO 11357, Part 3, with a heating and cooling rate of 10 °C/minute.

Preferably, in the compositions of the present invention the content of any additional polyolefin component (hereinafter called component A¹)) different from the said butene-1 polymers, if present, is of 10% by weight or less, in particular from 0.1 to 10% by weight with respect to the total weight of A) and the said additional polyolefin component. More preferably, in the compositions of the present invention no additional polyolefin component (different from the said butene-1 polymers) is present.

The preferred range for T_C ^A in the compositions of the invention is from 50 ⁰C or 55 ⁰C to 75 ⁰C; more preferably it is from 50 ⁰C or 55 ⁰C to 70 ⁰C.

Particularly preferred compositions according to the present invention are those having a crystallization temperature T_c ^c satisfying the following relation: T_c ^c > T_C ^A + 20.

The most preferred compositions according to the present invention are those having a crystallization temperature T_c ^c satisfying the following relation: T_c ^c > T_C ^A + 22.

By using the process of the present invention it is easy to achieve T_c ^c values of up to 40-45 ⁰C higher than the corresponding (starting) T_C ^A value.

Due to the fact that the crystallization temperatures are measured by first melting and then cooling the polymer sample (using DSC as previously said), such crystallization temperatures are attributable to the crystalline form II. In particular, the crystallization temperatures are determined after one melting cycle, followed by cooling.

Another important property for the compositions of the present invention is the rate of transformation from the said crystalline form II to the more stable crystalline form I.

Such transformation rate can be expressed as the time required to reach 80% of transformation from the form II to the form I. Such transformation time (hereinafter called tVs) can be measured with DSC by comparing the melting peak areas of the said two crystalline forms in a sufficient number of samples after increasing time from a melting and cooling cycle, and drawing a curve correlating the relative volume of form I with time. The tVs value is reached when such a relative value becomes 80%.

Preferred tVs values for the compositions of the present invention are from 48 to 100 hours, particularly for those compositions where A) comprises one or more butene-1 homoploymers.

Other preferred features of the compositions of the present invention are:

Flexural Modulus: from 400 to 550 MPa, more preferably from 450 to 550 MPa, measured after 10 days from melting and cooling to solid state; Strength at Break: from 32 to 40 N/mm², more preferably from 34 to 40 N/mm², measured after 10 days from melting and cooling to solid state; Elongation at Break: from 280 to 380%, more preferably from 280 to 350%, measured after

10 days from melting and cooling to solid state.

The butene-1 polymers preferably employed in the process and compositions of the present invention are linear homopolymers that are semicrystalline and highly isotactic (having in particular an isotacticity from 90 to 99%, preferably from 95 to 99%, measured both as mmmm pentads/total pentads using NMR and as quantity by weight of matter soluble in xylene at 0 ⁰C), typically obtained by polymerization of butene-1 with a stereospecific catalyst.

In the case when a copolymer of butene-1 is used, the isotacticity index can be expressed as the weight fraction that is insoluble in xylene, still at 0 ⁰C, and is preferably from 40% to 98%. Preferably the butene-1 polymers used in the process and compositions of the present invention have a melting point from 80 to 125 ⁰C, more preferably from 100 to 125 ⁰C, measured with the previously said DSC method, during the first heating run. Suitable copolymers of butene-1 are preferably those containing up to 5% by moles of olefinic comonomers, in particular from 0.1% to 5% by moles, more preferably from 0.1% to 3% by moles. The said comonomers are generally selected from ethylene, propylene or R- CH=CH₂ olefins where R is a C₃-Cs alkyl or cycloalkyl radical (in particular ethylene, propylene or alpha-olefms containing from 5 to 8 carbon atoms, like pentene-1, hexene-1, A- methylpentene-1 and octene-1). The said homo- and copolymers can be obtained by low- pressure Ziegler-Natta polymerization of butene-1, for example by polymerizing butene-1 (and any comonomers) with catalysts based on TiCl₃, or halogenated compounds of titanium (in particular TiCU) supported on magnesium chloride, and suitable co-catalysts (in particular alkyl compounds of aluminium). Electron-donor compounds can be added to the said catalyst components to tailor the polymer properties, like molecular weights and isotacticity. Examples of the said electron-donor compounds are the esters of carboxylic acids and alkyl alkoxysilanes.

The polymerization process can be carried out according to known techniques, for example slurry polymerization using as diluent an inert hydrocarbon solvent, or solution polymerization using for example the liquid butene-1 as a reaction medium. Moreover, it is also possible to carry out the polymerization process in the gas-phase, operating in one or more fluidized or mechanically agitated bed reactors. Solution and gas-phase processes are highly preferred.

Examples of polymerization catalysts and processes are disclosed in WO99/45043. As disclosed for instance in WO 03/042258, the butene polymers can also be prepared by polymerization in the presence of catalysts obtained by contacting a metallocene compound with an alumoxane.

While there is no particular limitation as to the molecular weight of the butene-1 polymers, it is preferred that the (co) polymers have a Melt Index'Ε" (measured according to ASTM D 1238 condition "E", at 190 °C/2.16 kg) of from 100 to 0.01, more preferably from 10 to 0.1 g/10 min.. In particular, when the polymers are to be used in the extrusion devices for the manufacture of pipes, polymers having a Melt Index in the range of from 1 to 0.1 g/10 min. and particularly from 0.3 to 0.5 g/10 min. are preferred. High values of MFR can be obtained directly in polymerization or by successive chemical treatment (chemical visbreaking) of the polymer.

The chemical visbreaking of the polymer is carried out in the presence of free radical initiators, such as the peroxides. Examples of radical initiators that can be used for this purpose are the 2,5-dimethyl-2,5-di (tert-butylperoxide)-hexane and dicumyl-peroxide. Preferred intrinsic viscosity values for the butene-1 polymers are from 1.5 to 4 dl/g, as measured in decalin at 135 ⁰C.

The molecular weight distribution (MWD) of the butene-1 polymers is not particularly critical, and can generally be comprised in a broad range. However for certain applications, like for pipes, where the process and compositions of the present invention are particularly advantageous, MWD values higher than 4, in particular higher than 6 when expressed in terms of M_w/M_n (where M_w is the weight average molecular weight and M_n is the number average molecular weight), measured by GPC analysis, are preferred.

M_w/M_n values of greater than 6 are generally considered to amount to a broad MWD.

Butene-1 polymers with a broad MWD can be obtained in several ways. One of the methods consists in using, when (co) polymerizing butene-1, a catalyst intrinsically capable of producing broad MWD polymers. Another possible method is that of mechanically blending butene-1 polymers having different enough molecular weights using the conventional mixing apparatus.

Other preferred properties of the butene-1 polymers employed in the process and compositions of the present invention are:

Flexural Modulus: from 300 to 450 MPa, more preferably from 350 to 450 MPa, measured after 10 days from melting and cooling to solid state; Strength at Break: from 32 to 40 N/mm², more preferably from 34 to 40 N/mm², measured after 10 days from melting and cooling to solid state; Elongation at Break: from 350 to 500%, more preferably from 350 to 450%, measured after

10 days from melting and cooling to solid state.

As previously said, in the process and in the compositions of the present invention it is preferred that any additional polyolefm be present in amounts of 10% by weight or less. In particular, they can be present in amounts from 0.1% to 10% by weight, more preferably from 0.1% to 5% by weight, with respect to the total weight of A) and the said additional polyolefϊn(s).

Preferred are the polyolefms known in the art as nucleating agents for butene-1 polymers, like in particular propylene polymers, both homopolymers and copolymers, and ethylene polymers.

When added in the said amounts, they substantially act as additional nucleating agents rather than as additional polymer component, as regards the resulting mechanical properties. Specific examples of propylene polymers are the isotactic homopolymers and the coplymers with reduced amounts, indicatively up to 20% by weight, of olefin comonomers, examples of which are ethylene, butene (both preferred) and the previously said R-CH=CH₂ olefins where R is a C₃-Cs alkyl or cycloalkyl radical.

The preferred values of Melt Index"L" (measured according to ASTM D 1238 condition "L", at 230 ⁰C, 2.16 kg load) for the said propylene homopolymers and copolymers are from 0.1 to lOO g/lO min..

Preferred examples of ethylene polymers are the high density polyethylene (HDPE, typically having a density from 0.940 to 0.965 g/cm ), and linear low density polyethylene (LLDPE, typically having a density from 0.900 to 0.939 g/cm³), usually obtained by low pressure polymerization, and low density polyethylene (LDPE, typically having a density from 0.917 to 0.935 g/cm³), usually obtained by high pressure polymerization. Generally the said low pressure polymerization is carried out in the presence of Ziegler-Natta catalysts, while the high pressure polymerization is carried out in the presence of radical initiators, such as peroxides.

The previously said component B) employed in the process and compositions of the present invention is selected from metal salts of carboxylic acids containing two or more carboxylic groups bonded to a cyclic or polycyclic aliphatic or aromatic structure.

Preferred metals in the said salts are those having valence from 1 to 3, in particular the metals of groups I and II of the Periodic System, Al, Fe and Cr. Particularly preferred are Li,

Na, K, Ca, Sr, Ba, Al.

Among the salts, preferred are the metal salts of carboxylic acids containing two carboxylic groups.

Particularly preferred are the metal salts of polycyclic saturated or unsaturated carboxylic acids containing two carboxylic groups.

Among the said metal salts of polycyclic carboxylic acids containing two carboxylic groups, the salts of bicyclic acids having up to 8 carbon atoms in the bicyclic structure, wherein one or more hydrogen atoms can be optionally substituted (with alkyl and/or aryl groups, optionally containing heteroatoms), are preferred. Examples of such salts and of their preparation are disclosed in the previously mentioned WO98/29494 and WO03/040230.

Particularly preferred among the said class are the salts of bicyclo [2.2.1] heptane-2,3- dicarboxylic acid, the disodium salt of which is commercially available as HPN-68 (sold by Milliken).

Other examples among the said class are the salts of bicyclo [2.2.1] hept-5-en-2,3- dicarboxylic acid and of bicyclo [2.2.2] oct-5-en-2,3-dicarboxylic acid.

Other useful salts within the definition of the present invention are the metal salts of acids wherein the carboxylic groups are bonded to aromatic cyclic structures, like the salts of phthalic acids (also substituted, as, for example, tetramethyl terephthalic acid), or to aliphatic cyclic structures, like the salts of cyclohexanedircarboxylic acids. All the said cyclic structures can contain heteroatoms, like O, N, S.

Further examples are the metal salts of acids containing more than two carboxylic groups, like benzene- 1, 2, 3 -tricarboxylic acid, benzene- 1,2,4-tricarboxylic acid, benzene-1,3,5- tricarboxylic acid, benzene- 1,2, 3, 4-tetracarboxylic acid, benzene- 1, 2,4, 5-tetracarboxylic acid.

The structure of some dimetal salts of bicyclic acids is reported below.

Disodium salt of bicyclo [2.2.1] heptane-2,3-dicarboxylic acid:

Dilithium salt of bicyclo [2.2.2] oct-5-en-2,3-dicarboxylic acid:

Also basic salts, for instance containing Al-OH groups, are included in the definition of the present invention.

All the said salts are known in the art and can be obtained by reacting the said acids with basic meal compounds, as LiOH, NaOH, or by reacting metal salts of the said acids, for instance sodium salts, with inorganic salts of other metals, like aluminum sulfate, optionally in the presence of a strong base, like NaOH.

Obviously in the process and compositions of the present invention it is also possible to add further additives commonly used in the art, such as stabilizers, antioxidants, anticorrosion agents, processing aids, and both organic and inorganic fillers.

The process of the present invention can be carried out by blending the components A) and

B) with blending techniques and apparatuses well known in the art.

Thus, one can use extruders commonly known in the art, including single-screw extruders, traditional and CoKneader (like the Buss), twin corotating screw extruders, mixers

(continuous and batch). Such blending apparatuses can be equipped with separate feeding systems for component A) and for the component B) respectively. The component B) can be added to the polymer mass inside the blending apparatus, in particular the extruder, either in the same feed port or downstream from the point at which A) is fed into the blending apparatus, so that the distance between will allow A) to have reached the form of a melted, homogeneous mass. It is also possible to premix components A) and B) before the blending step. To carry out the premixing step, any method and apparatus used in the art can be adopted, in particular medium and high speed mixers like Nauta mixer, Mixaco and

Turbomixers.

The processing temperatures during the blending step must be sufficient to bring (and keep) component A) in the molten state, or to keep component A) in the molten state if A) has been already molten when B) is added. Such temperatures preferably range from 100 ⁰C to

220 ⁰C, more preferably from 100 to 200 ⁰C, most preferably 120 to 200 ⁰C.

As previously mentioned, a preferred use for the polybutene-1 compositions of the present invention is for making pipes, in particular for water and hot fluids. In general they can be advantageously used for any application where the improved mechanical properties produced by nucleation are desirable.

The following examples are given for illustrating but not limiting purposes.

The following analytical methods have been used to determine the properties reported in the description and in the examples. Crystallization and melting temperature

The crystallization temperature (T_c ^c and T_C ^A) and the melting temperature values are determined using the following procedure according to ISO 11357 Part 3. Differential scanning calorimetric (DSC) data is obtained using a DSC QlOOO TA Instruments. Samples weighing approximately 6-8 mg are sealed in aluminum sample pans. The samples are subjected to a heating run from 5 ⁰C to 180 ⁰C with a heating rate of 10 °C/minute, and kept at 180 ⁰C under isothermal conditions for 5 minutes. The melting temperature is determined during such heating run. Then the samples are cooled from 180 ⁰C to 5 ⁰C for butene-1 homopolymers, or to -20 ⁰C for butene-1 copolymers, with a cooling rate of 10 °C/minute. The crystallization temperature is determined during the said cooling run. t'n^ determination

The t'o ₈ values are determined by first calculating the apparent melting enthalpies, based on the area of the melting peaks, of the I and II forms. Then, by dividing the apparent enthalpy of the respective melting peaks by the corresponding fusion heats of the pure crystalline phase, namely 32.5 cal/g for form I and 16 cal/g for form II, the weight, in grams, of each crystalline form present in the sample is calculated. From the weight values, the corresponding volumes (VolForm I and VolForm II) are calculated, by dividing by the corresponding densities, namely 0.95 g/cm³ for form I and 0.90 g/cm³ for form II. Then the volume percentage of form I (Vol%Form I) is calculated according to the following formula:

Vol%Form I = VolForm I x 100/(VolForm I + VolForm II).

Such analysis is carried out on various samples at increasing time after the melting and cooling cycle reported above for the determination of melting and crystallization temperatures, and the obtained Vol%Form I values are plotted versus time. From the so obtained curve the time at which the Vol%Form I is 80%, which is the tOs time, is determined.

Melt Index: ASTM D 1238 condition "E" (190 °C/2.16 kg)

Flexural Modulus: ASTM D 790, measured after 10 days from melting and cooling to solid state; Strength at Break: ASTM D 638 ISO method 527, measured after 10 days from melting and cooling to solid state; Elongation at Break: ASTM D 638 ISO method 527, measured after 10 days from melting and cooling to solid state. Determination of Solubility in Xylene at 0⁰C

2.5 g of polymer are dissolved in 250 ml of xylene, at 135°C, under agitation. After 20 minutes, the solution is cooled to 0⁰C under stirring, and then it is allowed to settle for 30 minutes. The precipitate is filtered with filter paper; the solution is evaporated under a nitrogen current, and the residue dried under vacuum at 80⁰C until constant weight. The weight percentage of polymer soluble in xylene at 0⁰C is then calculated. The percent by weight of polymer insoluble in xylene at 0⁰C is considered the isotactic index of the polymer.

Determination of Isotacticity Index by ¹³C-NMR

The measurement is carried out by preparing a 10%wt solution of the polymer in C₂Cl₄D₂ and recording the spectra at a temperature of 120⁰C with a DRX 500MHz instrument operating at 125,7 MHz under proton Waltz 16 decoupling in FT mode, with lOKhz spectral width, 90° pulse angle and 16sec. puls repetition and 3600 scans. The Isotactic index is then calculated according to: Carbon-13 NMR Spectral Assignment of Five Polyolefins Determined from the Chemical Shift Calculation and the Polymerization Mechanism, T. Asakura and others, Macromolecules 1991, 242334-2340.

MWD Determination by Gel PermeationChromatography (GPC)

Determined using a Waters 150-C ALC/GPC system equipped with a TSK column set (type GMHXL-HT) working at 135°C with 1 ,2-dichlorobenzene as solvent (ODCB) (stabilized with 0.1 vol. of 2,6-di-t-butyl p-cresole (BHT)) at flow rate of lml/min. The sample is dissolved in ODCB by stirring continuously at a temperature of 140⁰C for 1 hour. The solution is filtered through a 0.45μm Teflon membrane. The filtrate (concentration 0.08- 1.2g/l injection volume 300μl) is subjected to GPC. Monodisperse fractions of polystyrene (provided by Polymer Laboratories) were used as standard. The universal calibration for PB polymers was performed by using a linear combination of the Mark-Houwink constants for PS (K=7.11xlO^"5dl/g; α=0.743) and PB (K=1.18xlO^"4dl/g; α=0.725). Example 1 The following materials are used as components A) and B). A) Butene-1 homopolymer (PB), with Melt Index E of 0.3 g/10 min., melting point TmI, measured in the first heating run of, 124.5 ⁰C, isotacticity index of 98% and M_w/M_n of 5.5, in form of pellets.

B) Disodium salt of bicyclo [2.2.1] heptane-2,3-dicarboxylic acid. Moreover, the following additives are used.

1010 : Irganox 1010, pentaerytrityl tetrakis 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate, marketed by Ciba Geigy;

168: Irgafos 168, tris (2,4-di-tert-butylphenyl) phosphite, marketed by Ciba Geigy;

The process according to the present invention is carried out by a dry blend preparation in Turbomix and extrusion using a Leistritz 27 mm co-rotating twin screw extruder equipped with two K-Tron Loss in Weight feeders and a strand die plate having two holes of 3 mm diameter.

Running conditions: Capacity: lO kg/h; Screw speed: 220 rpm; Torque: 30%;

Die plate: 2 x 3 mm; Die pressure: 10 bar.

The temperature is 30 ⁰C at the feeding, 170 - 180 ⁰C in the rest of the extruder. The final properties of the so obtained composition are reported in Table I. For comparison purpose in the same Table I are reported, under Comparison Example 1 , the properties of the same butene-1 polymer A) used in Example 1, blended with the same additives but in the absence of component B). The extrusion conditions used to prepare the material of Comparison Example 1 are the same as in Example 1.

Table I

EXAMPLE 1 Comp. 1

PB A) (wt%) 99.5 99.6

Salt B) (wt%) 0.1 0

1010 (wt%) 0.2 0.2

168 (wt%) 0.2 0.2 τ_c ^A (⁰C) 66.5 66.5 τ_c ^c (⁰C) 90 -

Flexural Modulus (MPa) 490 410

Strength at Break (N/mm²) 36 38

Elongation at Break (%) 321 365 t'o ₈ (hours) 16 95

Claims

1. A process for producing a polybutene-1 composition having increased crystallization temperature T_c ^c, comprising the step of blending the following components:

A) a butene-1 polymer or polymer composition having crystallization temperature T_C ^A equal to or higher than 50 ⁰C, selected from crystalline butene-1 homopolymers or copolymers, or their combinations, said crystallization temperature being determined by differential scanning calorimetry (DSC), according to ISO 11357, Part 3, with a heating rate of 10 °C/minute;

B) 5 to 3000 ppm by weight, with respect to the total weight of A) and B), of one or more metal salts of carboxylic acids containing two or more carboxylic groups bonded to a cyclic or polycyclic aliphatic or aromatic structure; said butene-1 polymer or polymer composition A) being brought to the molten state or maintained in the molten state during the blending step.

2. The process of claim 1, wherein the blending step is carried out at a temperature from 100 ⁰C to 220 ⁰C.

3. The process of claim 1, wherein the metal salts B) are selected from the salts of polycyclic saturated or unsaturated carboxylic acids containing two carboxylic groups.

4. The process of claim 1, wherein the metal salts B) are selected from salts of metals of groups I and II of the Periodic System, Al, Fe and Cr.

5. Polybutene-1 compositions comprising:

B) 5 to 3000 ppm by weight, with respect to the total weight of A) and B), of one or more metal salts of carboxylic acids containing two or more carboxylic groups bonded to a cyclic or polycyclic aliphatic or aromatic structure; said composition having a crystallization temperature T_c ^c satisfying the following relation:

T_C ^C > T_C ^A + 18 where T_C ^A and T_c ^c are expressed in ⁰C, T_C ^A is the crystallization temperature of the butene-1 polymer or polymer composition A) in the absence of the metal salts B) and is equal to or higher than 50 ⁰C, said crystallization temperature being determined by differential scanning calorimetry (DSC), according to ISO 11357, Part 3, with a heating and cooling rate of 10 °C/minute.

6. Compositions according to claim 5, wherein the metal salts B) are selected from salts of metals of groups I and II of the Periodic System, Al, Fe and Cr.

7. Compositions according to claim 5, wherein the metal salts B) are selected from the salts of polycyclic saturated or unsaturated carboxylic acids containing two carboxylic groups.

8. Manufactured articles containing the compositions of claim 5.