Process for the preparation of branched polybutadiene having a high content of 1,4-cis units

Abstract

A process for the preparation of branched polybutadiene having a high content of 1,4-cis units which comprises polymerizing butadiene in the presence of at least one organic solvent, and in the presence of: a) a catalytic system prepared in situ including: (a.sub.1) at least one neodymium carboxylate, (a.sub.2) at least one alkyl compound of aluminum, (A.sub.3) at least one alkyl compound of aluminum containing at least one halogen atom, and b) at least one organic ester containing at least one halogen atom. Said branched polybutadiene having a high content of 1,4-cis units, depending on the branching degree and molecular weight distribution, can be advantageously used in various applications ranging from the modification of plastic materials [production, for example, of high impact polystyrene (HIPS)] to the production of tires, in particular the production of treads and/or of sidewalls of tires.

Claims

1. A process for the preparation of branched polybutadiene having a high content of 1,4-cis units, by the polymerization of butadiene in the presence of at least one organic solvent, and in the presence of: a) a catalytic system prepared in situ including: (a.sub.1) at least one neodymium carboxylate, (a.sub.2) at least one alkyl compound of aluminum, (a.sub.3) at least one alkyl compound of aluminum containing at least one halogen atom, and b) at least one organic ester containing at least one halogen atom, wherein the molar ratio between the at least one organic ester containing at least one halogen atom (b) and the at least one neodymium carboxylate (a.sub.1) ranges from 1/0.0005 to 1/0.0015, wherein said polymerization of said butadiene is carried out in a single reaction step and said at least one organic ester containing at least one halogen atom is directly added to the polymerization.

2. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein said butadiene is present in an amount ranging from 5% to 40% by weight with respect to the total weight of the at least one organic solvent.

3. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein the at least one organic solvent is selected from: saturated aliphatic hydrocarbons; saturated cycloaliphatic hydrocarbons; mono-olefins; halogenated hydrocarbons; or mixtures thereof.

4. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein the at least one neodymium carboxylate (a.sub.1) is neodymium versatate [Nd(versatate).sub.3].

5. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein the at least one neodymium carboxylate is used in an amount ranging from 0.1 mmoles to 10 mmoles per 1000 g of butadiene to be polymerized.

6. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein the at least one alkyl compound of aluminum (a.sub.2) is selected from compounds having general formula (I) or (II):
Al(R).sub.3  (I)
AlH(R).sub.2  (II) wherein R represents a linear or branched C.sub.1-C.sub.10 alkyl group.

7. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein the at least one alkyl compound of aluminum containing at least one halogen atom (a.sub.3) is selected from compounds having general formula (III):
AlX.sub.nR.sub.3-n  (III) wherein R represents a linear or branched C.sub.1-C.sub.10 alkyl group, X represents a halogen atom selected from chlorine, bromine, fluorine or iodine, n is 1 or 2.

8. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein the molar ratio between the at least one neodymium carboxylate (a.sub.1) and the at least one alkyl compound of aluminum (a.sub.2) ranges from 1/1 to 1/30.

9. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein the molar ratio between the at least one neodymium carboxylate (a.sub.1) and the at least one alkyl compound of aluminum containing at least one halogen atom (a.sub.3) ranges from 1/1.5 to 1/6.

10. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein the at least one alkyl compound of aluminum containing at least one halogen atom (a.sub.3) is used in such an amount that the ratio between the halogen present in said compound (a.sub.3) and the at least one alkyl compound of aluminum (a.sub.2) ranges from 0.5 to 5.

11. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein the at least one organic ester containing at least one halogen atom (b) is selected from compounds having general formula (IV): ##STR00002## wherein: R.sub.1, R.sub.2 and R.sub.3, equal to or different from each other, represent a halogen atom selected from chlorine, bromine, fluorine or iodine; linear or branched C.sub.1-C.sub.10 alkyl groups, linear or branched C.sub.2-C.sub.10 alkenyl groups, aryl groups, cycloalkyl groups, or ester groups; with the proviso that at least one of R.sub.1, R.sub.2 and R.sub.3 is a halogen atom; R.sub.4 is selected from linear or branched C.sub.1-C.sub.10 alkyl groups, linear or branched C.sub.2-C.sub.10 alkenyl groups, or aryl groups.

12. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein said process is carried out at a temperature ranging from 20° C. to 120° C.

13. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 1, wherein said process is carried out at a pressure ranging from 1 bar to 10 bar.

14. The process for the preparation of branched polybutadiene having a high content of 1,4-cis units according to claim 3, wherein said saturated aliphatic hydrocarbons are selected from butane, n-pentane, n-hexane, n-heptane, or mixtures thereof; said saturated cycloaliphatic hydrocarbons are selected from cyclohexane, cyclopentane, or mixtures thereof; said mono-olefins are selected from 1-butene, 2-butene, or mixtures thereof; and said halogenated hydrocarbons are selected from methylene chloride, chloroform, carbon tetrachloride, trichloroethylene, perchloroethylene, 1,2-dichloroethane, chlorobenzene, bromobenzene, chlorotoluene, or mixtures thereof.

15. A process for the preparation of branched polybutadiene having a high content of 1,4-cis units, by polymerizing butadiene in the presence of at least one organic solvent, and in the presence of: a) a catalytic system prepared in situ including: (a.sub.1) at least one neodymium carboxylate, (a.sub.2) at least one alkyl compound of aluminum, and (a.sub.3) at least one alkyl compound of aluminum containing at least one halogen atom, and b) at least one organic ester containing at least one halogen atom, wherein the molar ratio between the at least one organic ester containing at least one halogen atom (b) and the at least one neodymium carboxylate (a.sub.1) ranges from 1/0.0005 to 1/0.0015, wherein said polymerizing of said butadiene is carried out in a single reaction step immediately followed by recovery of the branched polybutadiene having a high content of 1,4-cis units.

Description

EXAMPLES

(1) The following characterization and analysis techniques were used.

(2) IR Analysis of the Microstructure (Content of 1,4-cis Units)

(3) The method is based on the calculation of the ratio between the intensity of the bands attributable to the isomers 1,4-trans and 1,2-vinyl and the reference band (internal standard) falling at 1312 cm.sup.−1 (more details relating to this method are described by L. J. Bellamy, “The Infrared Spectra of Complex Molecules” (1975), Vol. 1, Third Ed., Chapman and Hall). The content of 1,4-cis units was determined by the complement to 100. The preparation of the sample was carried out on a polybutadiene film obtained starting from a solution evaporated on a KBr window.

(4) Mooney Viscosity

(5) The Mooney viscosity (ML 1+4 @ 100° C.) was determined in accordance with the standard ASTM D 1646. In particular, the viscosity of the polybutadiene obtained was measured at 100° C., with a large rotor (L), by pre-heating for 1 minute and carrying out the measurement for 4 minutes.

(6) Determination of the Molecular Masses Distribution (MWD)

(7) The determination of the molecular masses distribution (MWD), from which the polydispersity index is also obtained (i.e. the M.sub.w/M.sub.n ratio), was carried out according to the method normally used via SEC (GPC) in tetrahydrofuran (THF), at 25° C., using PL-MIXED A (X4) columns and determination of the molecular masses according to the universal calibration method (k=0.000457 dl/g and α=0.693).

(8) Determination of the Weight Average Molecular Weight (M.sub.w) and Measurement of the Branching Index (g.sub.m) by Means of the SEC/MALLS Technique

(9) The weight average molecular weight (M.sub.w) and the branching index (g.sub.m) were determined according to an internal method taken from the work described in “Application Note” (1996), No. 9, Wyatt Technology and by Pavel Kratochvil, “Classical Light Scattering from Polymer Solutions” (1987), Polymer Science Library, 5, Elsevier Science Publishers B. V.

(10) By coupling a multi-angle laser light scattering detector (MALLS) with a traditional SEC/RI elution system, the absolute measurement can be contemporaneously carried out of the weight average molecular weight (M.sub.w) and of the gyration radius of the macromolecules that are separated by the chromatographic system; the amount of light scattered by a macromolecular species in solution can in fact be used directly for obtaining its weight average molecular weight (M.sub.w), whereas the angular variation in the scattering is directly correlated with its average dimensions. The fundamental relation (1) which is used is the following:

(11) $\begin{array}{cc}\frac{K*c}{R_{\theta }}=\frac{1}{M_w{P}_{\theta }}+2A_{2}c& \left(1\right)\end{array}$
wherein:
K*=optical constant which depends on the wave-length of the light used, on the refraction index (dn/dc) of the polymer, on the solvent used; M.sub.w=weight average molecular weight; c=concentration of the polymeric solution; R.sub.θ=intensity of the light scattered measured at an angle θ; P.sub.θ=function describing the variation of the light scattered with the angle at which it is measured, equal to 1 for angle θ=0.

(12) For very low concentrations (typical of a GPC system), the above fundamental relation (1) is reduced to the fundamental relation (2):

(13) $\begin{array}{cc}\frac{K*c}{R_{\theta }}=\frac{1}{M_w{P}_{\theta }}& \left(2\right)\end{array}$
and by carrying out the measurement on several angles, the extrapolation to angle null of the function K*c/R.sub.θ in relation to sen.sup.2θ/2 directly provides the weight average molecular weight (M.sub.w) from the intercept value and the gyration radius from the slope.

(14) Furthermore, as this measurement is carried out for every slice of the chromatogram, it is possible to obtain a distribution of both the weight average molecular weight (M.sub.w) and the gyration radius.

(15) The macromolecular dimensions in solution are directly correlated to their branching degree: for the same weight average molecular weight (M.sub.w), the smaller the dimensions of the macromolecule with respect to the linear correspondent, the higher the branching degree will be.

(16) Informations relating to the macrostructure of the polymer is deduced in two ways: (1) qualitatively, from the value of the parameter α, which represents the slope of the curve which correlates the gyration radius with the weight average molecular weight (M.sub.w): when, under the same analysis conditions, this value decreases with respect to a macrostructure of the linear type, there is the presence of a polymer having a branched-type macrostructure and the typical value for polybutadiene having a high content of 1,4-cis units, in tetrahydrofuran (THF), is equal to 0.58-0.60; (2) quantitatively, by estimating the branching index (g.sub.m) which is defined for each macromolecule as a ratio between the average square gyration radius of the branched macromolecule (<r.sub.2>.sub.b) and the average square gyration radius of the linear macromolecule (<r.sub.2>.sub.1), with the same molecular weight represented by the following equation (3) (M.sub.i represents the weight average molecular weight (M.sub.w) of the “ . . . th” molecule)

(17) $\begin{array}{cc}{g}_{M_i}={\left[\frac{{.Math.r_2.Math.}_b}{{.Math.r_2.Math.}_l}\right]}_{M_i}.& \left(3\right)\end{array}$

(18) The branching index (g.sub.m) represents the average of the above ratio along the molecular mass distribution and ranges from 0 to 1.

Example 1

(19) Preparation of Branched Polybutadiene Having a High Content of 1,4-cis Units

(20) 584 g of cyclohexane (d=0.78 g/ml), 68 g of 1,3-butadiene (BDE) (of Versalis spa), 0.1 ml (0.0325 mg-0.00017 mmoles) of a solution of ethyl trichloro acetate (ETA) (of VIO Chemicals) in cyclohexane 0.0014 M, 1.2 ml (145.06 mg-1.02 mmoles) of a solution of di-isobutylaluminum hydride (DIBAH) (of Akzo Nobel) in cyclohexane 0.12 M, 0.51 ml (61.49 mg-0.51 mmoles) of a solution of diethylaluminum chloride (DEAC) (purity degree of 98.5%; molar ratio Al/Cl: 1; of Albemarle) in cyclohexane 1 M, were charged into a 1.5 l reactor, equipped with a stirrer: the reactor was heated until it reached a temperature of 60° C. 0.4 ml (0.17 mmoles) of a solution of neodymium versatate [Nd(versatate).sub.3] having a molar ratio RCOOH/Nd equal to 0.3 (of Rhodia) in cyclohexane 0.6 M (molar ratios: DEAC/Nd=3, DIBAH/Nd=6, ETA/Nd=0.001), were then added.

(21) After 90 minutes, the polymerization reaction was considered complete and was interrupted: a conversion equal to 94% was measured. The polymeric solution was extracted from the reactor and a phenolic antioxidant was added (Irganox® 1520 of Ciba in an amount equal to 0.06% by weight with respect to the total weight of the polymer obtained). The polymeric solution obtained was subsequently fed to a recipient containing boiling water by the introduction of vapour and subjected to stirring thus eliminating the reaction solvent and obtaining a clot. Said clot was previously passed in a cold calendar and subsequently completely dried in a roll calendar at 80° C.

(22) The polybutadiene obtained was subjected to the characterizations indicated above, obtaining the following results:

(23) content of 1,4-cis units equal to 96%;

(24) Mooney viscosity (ML 1+4 @ 100° C.) equal to 40;

(25) branching index (g.sub.m) equal to 0.6;

(26) polydispersion index (M.sub.w/M.sub.n ratio) equal to 2.5.