PROCESS FOR THE PREPARATION OF DIENE POLYMERS OR RANDOM VINYL ARENE-DIENE COPOLYMERS
20170335027 · 2017-11-23
Inventors
Cpc classification
C08F2/38
CHEMISTRY; METALLURGY
C08F2438/02
CHEMISTRY; METALLURGY
C08F2/38
CHEMISTRY; METALLURGY
International classification
Abstract
Process for the preparation of a diene polymer or a random vinyl arene-diene copolymer comprising anionically (co)polymerising at least one conjugated diene monomer, optionally in the presence of at least one vinyl arene, in the presence of at least one hydrocarbon solvent, at least one lithium-based initiator and at least one organic compound containing at least one nitroxide group having general formula (I) or (II): wherein: R.sup.1, R.sup.2, R.sup.3 and R.sup.4, mutually identical or different, represent a hydrogen atom; or are selected from C.sub.1-C.sub.20, preferably C.sub.1-C.sub.8, linear or branched alkyl groups optionally containing heteroatoms such as, for example, oxygen, nitrogen,sulphur,optionally substituted cycloalkyl groups, optionally substituted C.sub.1-C.sub.20, preferably C.sub.1-C.sub.8, linear or branched alkoxy groups, optionally substituted aryl groups; −x is an integer ranging from 0 to 7, preferably ranging from 4 to 5; −y is an integer ranging from 1 to 3, preferably ranging from 1 to 2.
##STR00001##
Claims
1. A process for the preparation of a diene polymer or a random vinyl arene-diene copolymer comprising anionically (co)polymerising at least one conjugated diene monomer, optionally in the presence of at least one vinyl arene, in the presence of at least one hydrocarbon solvent, at least one lithium-based initiator and at least one organic compound containing at least one nitroxide group having general formula (I) or (II): ##STR00003## wherein: R.sup.1, R.sup.2, R.sup.3 and R.sup.4, mutually identical or different, represent a hydrogen atom; or are selected from C.sub.1-C.sub.20, preferably C.sub.1-C.sub.8, linear or branched alkyl groups optionally containing heteroatoms selected from oxygen, nitrogen or sulfur, optionally substituted cycloalkyl groups, optionally substituted C.sub.1-C.sub.20, linear or branched alkoxy groups, optionally substituted aryl groups; x is an integer ranging from 0 to 7; y is an integer ranging from 1 to 3.
2. The process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein said conjugated diene monomer is selected from: 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene (piperylene), 2-methyl-3-ethyl-1,3-butadiene, 1,3 -octadiene, or mixtures thereof, optionally in anhydrous form.
3. The process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein said vinyl arene is selected from: styrene, a-methylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, or the alkyl derivatives thereof, or mixtures thereof, optionally in anhydrous form.
4. The process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein said anionic (co)polymerisation is carried out in the presence of: 40% by weight-100% by weight with respect to the total weight of conjugated diene monomer and optional vinyl arene, of at least one conjugated diene monomer; and 0% by weight-60% by weight with respect to the total weight of conjugated diene monomer and optional vinyl arene, of at least one vinyl arene.
5. The process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein said hydrocarbon solvent is selected from propane, n-butane, iso-butane, n-pentane, iso-pentane, n-hexane, n-heptane, n-octane, cyclohexane, cyclopentane, propene, 1-butene, iso-butene, trans-2-butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene, ethylbenzene, or mixtures thereof, optionally in anhydrous form.
6. The process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein said lithium-based initiator is selected from compounds having general formula (III):
R.sub.5(Li).sub.n (III) wherein R.sub.5 represents a C.sub.1-C.sub.20 linear or branched alkyl group, a C.sub.3-C.sub.30 cycloalkyl group, a C.sub.6-C.sub.30 aryl group; and n is an integer ranging from 1 to 4 or mixtures thereof.
7. A process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein said anionic (co)polymerisation is carried out in the presence of at least one polar modifier selected from: non-cyclic ethers; tertiary amines; cyclic ethers; chelating ethers; chelating amines; or mixtures thereof.
8. A process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein said organic compound containing at least one nitroxide group having general formula (I) or (II) is selected from: 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) or derivatives thereof or mixtures thereof; diphenylnitroxide or derivatives thereof, or mixtures thereof; 1,1,3,3 -tetraethylisoindolin-2-yl-oxyl (TEDIO); 1,1,3,3 -tetramethylisoindolin-2-yl-oxyl (TMEDIO); or mixtures thereof.
9. A process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein said organic compound containing at least one nitroxide group having general formula (I) or (II), and said lithium-based initiator are used in a molar ratio ranging from 0.1 to 20.
10. A process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein said anionic (co)polymerisation is carried out at a temperature ranging from 0° C. to 150° C.
11. A process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein said anionic (co)polymerisation is carried out for a time ranging from 5 minutes to 10 hours.
12. A process for the preparation of a diene polymer or a random vinyl arene-diene copolymer according to claim 1, wherein the resultant diene polymer or random vinyl arene-diene copolymer has a polydispersity index M.sub.w/M.sub.n ranging from 1 to 2.5.
Description
EXAMPLES
[0064] The characterisation methods below reported were used.
[0065] Microstructure Analysis (Content of 1,2-vinyl Units and Bound Styrene)
[0066] Microstructure (content of 1,2-vinyl units and bound styrene) was determined by FTIR (“Fourier Transform Infra Red”) spectroscopy by means of the absorption bands (and calculation of the relative intensity thereof) characteristic of the three types of butadiene linkage: 1,4-cis (800 cm.sup.−1 and 640 cm.sup.−1), 1,4-trans (1018 cm.sup.−1 and 937 cm.sup.−1) and 1,2 (934 cm.sup.−1 and 887 cm.sup.−1) and of bound styrene (between 715 cm.sup.−1 and 680 cm.sup.−1).
[0067] Determination of Molecular Mass Distribution (MWD)
[0068] The molecular mass distribution (MWD), which, combined with the results obtained by means of the SEC/MALLS method below reported, is also used as the basis for obtaining the polydispersity index (i.e. the ratio M.sub.w/M.sub.n), HMW (“High Molecular Weight”), W.sub.c (“Weight Coupling”) and the molecular weight corresponding to the highest peak (M.sub.p), was determined by means of Gel Permeation Chromatography (GPC) which was performed by causing a solution in tetrahydrofuran (THF) of the (co)polymer obtained to flow through a series of columns containing a solid phase composed of crosslinked polystyrene with a porosity of different sizes.
[0069] Determination of Weight-Average Molecular Weight (M.sub.w) and Measurement of Branching Index (g.sub.m) using the SEC/MALLS Method.
[0070] The weight-average molecular weight (M.sub.w) and branching index (g.sub.m) were determined according to an internal method based on 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.
[0071] By coupling a Multi-Angle Laser Light Scattering (MALLS) sensor with a conventional SEC/RI elution system, it was possible simultaneously to measure in absolute terms the weight-average molecular weight (M.sub.w) and the radius of gyration of the macromolecules which are separated by the chromatographic system; the quantity of light scattered by a macromolecular species in solution may indeed be used directly to obtain the weight-average molecular weight (M.sub.w) thereof, while the angular variation of the scattering is directly correlated with the average size thereof. The fundamental relationship (1) used is the following:
[0072] in which: [0073] K*=optical constant dependent on the wavelength of the light used, the refractive index (dn/dc) of the polymer and the solvent used; [0074] M.sub.w=weight-average molecular weight; [0075] c=concentration of the polymer solution; [0076] R.sub.θ=intensity of the scattered light measured at an angle θ; [0077] P.sub.θ=function which describes the variation of the scattered light with the angle at which it is measured, equal to 1 for angle θ=0.
[0078] For very low concentrations (typical of a GPC system), the above-stated fundamental relationship (1) is simplified to the fundamental relationship (2):
[0079] and, by carrying out measurement at a plurality of angles, extrapolation to the zero angle of the function K*c/R.sub.θ as a function of sen.sup.2θ/2 directly provides the weight-average molecular weight (M.sub.w) from the value of the intercept and the radius of gyration from the slope.
[0080] Furthermore, given that this measurement is performed for each “slice” of the chromatogram, it is possible to obtain a distribution both of the weight-average molecular weight (M.sub.w) and of the radius of gyration.
[0081] The dimensions of the macromolecules in solution are directly correlated with the degree of branching thereof: at identical weight-average molecular weight (M.sub.w), the smaller are the dimensions of the macromolecules with respect to the corresponding linear molecule, the greater is the degree of branching.
[0082] Information relating to polymer macrostructure are deduced in two ways: [0083] (1) qualitatively, from the value of the parameter a which represents the gradient of the curve which correlates the radius of gyration with the weight-average molecular weight (M.sub.w): when, under the same analysis conditions, said value falls with respect to a macrostructure of linear type, a polymer is present which has a macrostructure of branched type and the typical value for polybutadiene with a high 1,4-cis unit content, in tetrahydrofuran (THF), is equal to 0.58-0.60; [0084] (2) quantitatively by evaluating the branching index (g.sub.m) which is defined for each macromolecule as the ratio between the mean-square radius of gyration of the branched macromolecule (<r.sub.2>.sub.b) and the mean-square radius of gyration of the linear macromolecule (<r.sub.2>.sub.l), at identical molecular weight represented by the following equation (3) (M.sub.i represents the weight-average molecular weight (M.sub.w) of the “i.sup.th” molecule)
[0085] The branching index (g.sub.m) represents the mean of the above reported ratio over the molecular mass distribution and is ranging from 0 to 1.
[0086] Determination of Mooney Viscosity
[0087] Mooney viscosity was determined at 100° C. using a Monsanto MV2000E viscometer, method ASTM D1646 with L type rotor and with times 1+4 (ML.sub.1+4@100° C.).
[0088] Determination of Homopolymerisation Kinetics (K.sub.homopolymerisation)
[0089] Homopolymerisation kinetics (K.sub.homopolymerisation) were determined by analysing the UV-VIS absorption spectra recorded as below reported in Example 5.
[0090] Determination of Variation in Absorbance (Δabs)
[0091] The variation in absorbance (Δabs) was determined by analysing the UV-VIS absorption spectra recorded as below reported in Example 5.
EXAMPLE 1 (COMPARATIVE)
[0092] 600 grams of anhydrous cyclohexane (Bitolea) followed by 27 grams of freshly distilled anhydrous 1,3-butadiene (Versalis SpA) were introduced into a 1 litre stirred reactor equipped with a jacket for circulation of a temperature-control fluid. The reactor was fitted with a system for continuous measurement of the UV-VIS absorption spectra of the polymer solution which functions as described in Example 5. The temperature of the reaction mixture was thermostatically controlled to 80° C. and held constant within ±4° C. throughout the duration of the test. 0.5 mmol of n-butyllithium (Aldrich) were then introduced: the reaction conditions were maintained for 60 minutes, at the end of which ethyl alcohol (Carlo Erba) was introduced in an equimolecular quantity with respect to the quantity of n-butyllithium introduced. The polymer solution obtained was then discharged from the reactor, a phenolic antioxidant (Irganox® 1520 from Ciba in a quantity of 0.06% by weight with respect to total weight of the polymer obtained) was added and the solution was then sent for solvent removal by water stripping and subsequent drying by extrusion.
[0093] The polybutadiene obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 1.
EXAMPLE 2 (COMPARATIVE)
[0094] 600 grams of anhydrous cyclohexane (Bitolea) followed by 27 grams of freshly distilled anhydrous 1,3-butadiene (Versalis SpA) were introduced into a 1 litre stirred reactor equipped with a jacket for circulation of a temperature-control fluid. The reactor was fitted with a system for continuous measurement of the UV-VIS absorption spectra of the polymer solution which functions as described in Example 5. The temperature of the reaction mixture was thermostatically controlled to 120° C. and held constant within ±4° C. throughout the duration of the test. 0.5 mmol of n-butyllithium (Aldrich) were then introduced: the reaction conditions were maintained for 60 minutes, at the end of which ethyl alcohol (Carlo Erba) was introduced in an equimolecular quantity with respect to the quantity of n-butyllithium introduced. The polymer solution obtained was then discharged from the reactor, a phenolic antioxidant (Irganox® 1520 from Ciba in a quantity of 0.06% by weight with respect to total weight of the polymer obtained) was added and the solution was then sent for solvent removal by water stripping and subsequent drying by extrusion.
[0095] The polybutadiene obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 1.
EXAMPLE 3 (INVENTION)
[0096] 600 grams of anhydrous cyclohexane (Bitolea) followed by 27 grams of freshly distilled anhydrous 1,3-butadiene (Versalis SpA) and, subsequently, 0.5 mmol of 1,1,3,3-tetraethylisoindolin-2-yl-oxyl (TEDIO) obtained as described in American patent application US 2010/0240909 were introduced into a 1 litre stirred reactor equipped with a jacket for circulation of a temperature-control fluid. The reactor was fitted with a system for continuous measurement of the UV-VIS absorption spectra of the polymer solution which functions as described in Example 5. The temperature of the reaction mixture was thermostatically controlled to 120° C. and held constant within ±4° C. throughout the duration of the test. 0.5 mmol of n-butyllithium (Aldrich) were then introduced to obtain a molar ratio between 1,1,3,3-tetraethylisoindolin-2-yloxyl (TEDIO) and the quantity of active n-butyllithium of approx. 1:1: the reaction conditions were maintained for 60 minutes, at the end of which ethyl alcohol (Carlo Erba) was introduced in an equimolecular quantity with respect to the quantity of n-butyllithium introduced. The polymer solution obtained was then discharged from the reactor, a phenolic antioxidant (Irganox® 1520 from Ciba in a quantity of 0.06% by weight with respect to total weight of the polymer obtained) was added and the solution was then sent for solvent removal by water stripping and subsequent drying by extrusion.
[0097] The polybutadiene obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 1.
EXAMPLE 4 (INVENTION)
[0098] 600 grams of anhydrous cyclohexane (Bitolea) followed by 27 grams of freshly distilled anhydrous 1,3-butadiene (Versalis SpA) and, subsequently, 1 mmol of 1,1,3,3-tetraethylisoindolin-2-yl-oxyl (TEDIO) obtained as described above were introduced into a 1 litre stirred reactor equipped with a jacket for circulation of a temperature-control fluid. The reactor was fitted with a system for continuous measurement of the UV-VIS absorption spectra of the polymer solution which functions as described in Example 5. The temperature of the reaction mixture was thermostatically controlled to 120° C. and held constant within ±4° C. throughout the duration of the test. 0.5 mmol of n-butyllithium (Aldrich) were then introduced to obtain a molar ratio between 1,1,3,3-tetraethylisoindolin-2-yl-oxyl (TEDIO) and the quantity of active n-butyllithium of approx. 2:1: the reaction conditions were maintained for 60 minutes, at the end of which ethyl alcohol (Carlo Erba) was introduced in an equimolecular quantity with respect to the quantity of n-butyllithium introduced. The polymer solution obtained was then discharged from the reactor, a phenolic antioxidant (Irganox® 1520 from Ciba in a quantity of 0.06% by weight with respect to total weight of the polymer obtained) was added and the solution was then sent for solvent removal by water stripping and subsequent drying by extrusion.
[0099] The polybutadiene obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 1.
TABLE-US-00001 TABLE 1 Temperature HMW K.sub.homopolymerisation Example [° C.] [═N—O]/[n-butLi] D [%] [l × mol.sup.−1 × s.sup.−1] 1 (comparative) 80 0 1.08 0 — 2 (comparative) 120 0 1.28 31.4 16.5 3 (invention) 120 1.16 1.18 18.1 13 4 (invention) 120 1.75 1.11 11.0 11 D: polydispersity index M.sub.w/M.sub.n; HMW (“High Molecular Weight”): content, stated in percent by weight, of the fractions with a molecular weight which is a multiple of the molecular weight of the precursor polymer due to the presence of metalation termination reactions of the chain which lead to the formation of random branching; (K.sub.homopolymerisation): homopolymerisation rate constant.
[0100] On the basis of the data reported in Table 1, the following comments may be made. Example 1, carried out at 80° C. shows that, in the absence of the compound containing a nitroxide group (═N—O), the temperature is too low to give rise to the termination reaction and that the polymer completely lacks a high molecular weight fraction. In contrast, Example 3 and Example 4, compared with Example 2, show that the presence of the compound containing a nitroxide group ([═N—O]) significantly inhibits the formation of branching with a consequent reduction in the polydispersity index M.sub.w/M.sub.n. An appreciable reduction in the value of the homopolymerisation rate constants (K.sub.homopolymerisation) is also observed.
EXAMPLE 5 (COMPARATIVE)
[0101] 600 grams of anhydrous cyclohexane (Bitolea) followed by 27 grams of freshly distilled anhydrous butadiene (Versalis SpA) and 100 ppm of 2-methoxyethyl tetrahydrofuran (THFA-ethyl) (Thomas Swan) were introduced into a 1 litre stirred reactor equipped with a jacket for circulation of a temperature-control fluid. The reactor was fitted with a system for continuous measurement of the UV-VIS absorption spectra of the polymer solution. Said system consists of a quartz flow cell having an optical pathlength of 2 mm, connected to the reactor by means of a circuit into which an HPLC pump draws the polymer solution, passes it through the flow cell and returns it to the reactor. This enables continuous measurement of the concentration of the butadienyl living end group by application of the Lambert Beer law:
A=I ε c
[0102] in which A is absorbance, I is the optical pathlength of the measurement cell, ε is the molar absorbance coefficient (which for butadienyl in the presence of 2-methoxyethyl tetrahydrofuran is approx. 6500 l×cm.sup.−1×mol.sup.−1) and c is the molar concentration. The UV-VIS spectrum was measured using a Perkin Elmer Lambda 25 spectrophotometer in the range from 260 to 400 nm, at 2 minute intervals between one measurement and the next for the purpose of measuring the extent of the termination reaction.
[0103] The temperature of the reaction mixture was thermostatically controlled to 70° C. and held constant within ±4° C. throughout the duration of the test. 1 mmol of n-butyllithium (Aldrich) was then introduced: the reaction conditions were maintained for 30 minutes, at the end of which ethyl alcohol (Carlo Erba) was introduced in an equimolecular quantity with respect to the quantity of n-butyllithium introduced. The polymer solution obtained was then discharged from the reactor, a phenolic antioxidant (Irganox® 1520 from Ciba in a quantity of 0.06% by weight with respect to total weight of the polymer obtained) was added and the solution was then sent for solvent removal by water stripping and subsequent drying by extrusion.
[0104] The polybutadiene obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 2.
EXAMPLE 6 (INVENTION)
[0105] 600 grams of anhydrous cyclohexane (Bitolea) followed by 27 grams of freshly distilled anhydrous butadiene (Versalis SpA), 100 ppm of 2-methoxyethyl tetrahydrofuran (THFA-ethyl) (Thomas Swan) and, subsequently, 0.5 mmol of 1,1,3,3-tetraethylisoindolin-2-yl-oxyl (TEDIO) obtained as described above were introduced into a 1 litre stirred reactor equipped with a jacket for circulation of a temperature-control fluid. The reactor was fitted with a system for continuous measurement of the UV-VIS absorption spectra of the polymer solution which functions as described in Example 5. The temperature of the reaction mixture was thermostatically controlled to 70° C. and held constant within ±4° C. throughout the duration of the test. 0.5 mmol of n-butyllithium (Aldrich) were then introduced to obtain a molar ratio between 1,1,3,3-tetraethylisoindolin-2-yl-oxyl (TEDIO) and the quantity of active n-butyllithium of approx. 1:1: the reaction conditions were maintained for 30 minutes, at the end of which ethyl alcohol (Carlo Erba) was introduced in an equimolecular quantity with respect to the quantity of n-butyllithium introduced. The polymer solution obtained was then discharged from the reactor, a phenolic antioxidant (Irganox® 1520 from Ciba in a quantity of 0.06% by weight with respect to total weight of the polymer obtained) was added and the solution was then sent for solvent removal by water stripping and subsequent drying by extrusion.
[0106] The polybutadiene obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 2.
EXAMPLE 7 (INVENTION)
[0107] 600 grams of anhydrous cyclohexane (Bitolea) followed by 27 grams of freshly distilled anhydrous butadiene (Versalis SpA), 100 ppm of 2-methoxyethyl tetrahydrofuran (THFA-ethyl) (Thomas Swan) and, subsequently, 1 mmol of 1,1,3,3-tetraethylisoindolin-2-yl-oxyl (TEDIO) obtained as described above were introduced into a 1 litre stirred reactor equipped with a jacket for circulation of a temperature-control fluid. The reactor was fitted with a system for continuous measurement of the UV-VIS absorption spectra of the polymer solution which functions as described in Example 5. The temperature of the reaction mixture was thermostatically controlled to 70° C. and held constant within ±4° C. throughout the duration of the test. 0.5 mmol of n-butyllithium (Aldrich) were then introduced to obtain a molar ratio between 1,1,3,3-tetraethylisoindolin-2-yl-oxyl (TEDIO) and the quantity of active n-butyllithium of approx. 2:1: the reaction conditions were maintained for 30 minutes, at the end of which ethyl alcohol (Carlo Erba) was introduced in an equimolecular quantity with respect to the quantity of n-butyllithium introduced. The polymer solution obtained was then discharged from the reactor, a phenolic antioxidant (Irganox® 1520 from Ciba in a quantity of 0.06% by weight with respect to total weight of the polymer obtained) was added and the solution was then sent for solvent removal by water stripping and subsequent drying by extrusion.
[0108] The polybutadiene obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 2.
EXAMPLE 8 (COMPARATIVE)
[0109] 600 grams of anhydrous cyclohexane (Bitolea) followed by 9 grams of anhydrous styrene (Versalis SpA) were introduced into a 1 litre stirred reactor equipped with a jacket for circulation of a temperature-control fluid. The reactor was fitted with a system for continuous measurement of the UV-VIS absorption spectra of the polymer solution which functions as described in Example 5: in this case, the molar absorbance coefficient E for styryl in the Lambert Beer law is approx. 10000 l cm.sup.−1×mol.sup.−1. The temperature of the reaction mixture was thermostatically controlled to 80° C. and held constant within ±4° C. throughout the duration of the test. 1 mmol of n-butyllithium (Aldrich) was then introduced: the reaction conditions were maintained for 30 minutes, at the end of which ethyl alcohol (Carlo Erba) was introduced in an equimolecular quantity with respect to the quantity of n-butyllithium introduced. The polymer solution obtained was then discharged from the reactor, a phenolic antioxidant (Irganox® 1520 from Ciba in a quantity of 0.06% by weight with respect to total weight of the polymer obtained) was added and the solution was then sent for solvent removal by water stripping and subsequent drying by extrusion.
[0110] The polybutadiene obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 2.
EXAMPLE 9 (INVENTION)
[0111] 600 grams of anhydrous cyclohexane (Bitolea) followed by 9 grams of anhydrous styrene (Versalis SpA) and, subsequently, 2 mmol of 1,1,3,3-tetraethylisoindolin-2-yl-oxyl (TEDIO) obtained as described above were introduced into a 1 litre stirred reactor equipped with a jacket for circulation of a temperature-control fluid. The reactor was fitted with a system for continuous measurement of the UV-VIS absorption spectra of the polymer solution which functions as described in Example 5: in this case, the molar absorbance coefficient E for styryl in the Lambert Beer law is approx. 10000 l×cm.sup.−1×mol.sup.−1. The temperature of the reaction mixture was thermostatically controlled to 80° C. and held constant within ±4° C. throughout the duration of the test. 1 mmol of n-butyllithium (Aldrich) was then introduced to obtain a molar ratio between 1,1,3,3-tetraethylisoindolin-2-yl-oxyl (TEDIO) and the quantity of active n-butyllithium of approx. 2:1: the reaction conditions were maintained for 30 minutes, at the end of which ethyl alcohol (Carlo Erba) was introduced in an equimolecular quantity with respect to the quantity of n-butyllithium introduced. The polymer solution obtained was then discharged from the reactor, a phenolic antioxidant (Irganox® 1520 from Ciba in a quantity of 0.06% by weight with respect to total weight of the polymer obtained) was added and the solution was then sent for solvent removal by water stripping and subsequent drying by extrusion.
[0112] The polybutadiene obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 2.
TABLE-US-00002 TABLE 2 Temperature [═N—O]/ Δ abs K.sub.homopolymerisation Examples [° C.] [n-butLi] [%] [l × mol.sup.−1 × s.sup.−1] 5 (comparative) 70 0 −25 7.7 (polybutadiene) 6 (invention) 70 1.07 −17 4.5 (polybutadiene) 7 (invention) 70 1.85 −10 2.2 (polybutadiene) 8 (comparative) 80 0 −14 4.1 (polystyrene) 9 (invention) 80 1.6 −7 2.3 (polystyrene) (Δ abs): variation in the absorbance of the butadienyl end group over a time interval of 2000 seconds (Examples 5, 6 and 7) and variation in the absorbance of the styryl end group over a time interval of 3000 seconds (Examples 8 and 9), measured from when the concentration maximum of the respective end group is reached: the values are stated as a percentage variation calculated with respect to the absorbance maximum; (K.sub.homopolymerisation): homopolymerisation rate constant.
[0113] On the basis of the data reported in Table 2, it may be noted how, as the ratio between the compound containing a nitroxide group (=N—O) and the active n-butyllithium increases, the stability of the living end group increases significantly. In this case too, the homopolymerisation rate constants (K.sub.homopolymerisation) fall.
EXAMPLE 10 (COMPARATIVE)
[0114] 8000 grams of a mixture of anhydrous cyclohexane (Bitolea)/n-hexane (Bitolea) in a 9:1 ratio by weight (equal to a filling factor of 80%) and 230 ppm of 2-methoxyethyl tetrahydrofuran (THFA-ethyl) (Thomas Swan), in a molar ratio of approx. 4:1 with the quantity of n-butyllithium, and, subsequently, 300 grams of anhydrous styrene (Versalis SpA) and 900 grams of anhydrous 1,3-butadiene (Versalis SpA) were introduced into a 16 litre stirred reactor: the mixture was heated to a temperature of 40° C. with a heating jacket. 0.25 grams of n-butyllithium (Aldrich) in cyclohexane (Bitolea) (1.6 g of 15% by weight solution) were then introduced: at this point, heating with the jacket was ceased and the increase in temperature of the reaction mixture was obtained due to the exothermic nature of the reaction, up to a final temperature (peak temperature) of 80° C. 10 minutes were allowed to elapse once the peak temperature had been reached in order to eliminate any monomers which were free at the end of polymerisation, after which 0.159 g of silicon tetrachloride (SiCl.sub.4) (Aldrich), corresponding to 100% of the theoretical coupling efficiency, were introduced and a further 20 minutes were allowed to elapse for the coupling reaction to proceed to completion. The polymer solution obtained was discharged into a tank where it was stabilised with 0.7 phr of 2,6-di-t-butyl-4-methylphenol (BHT) (Great Lakes), after which 450 grams of TDAE (“treated distillate aromatic extract”) non-aromatic oil (Repsol) were added and the resultant mixture was sent for solvent removal by water stripping and subsequent drying by extrusion.
[0115] The styrene-butadiene copolymer obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 3.
EXAMPLE 11 (INVENTION)
[0116] 8000 grams of a mixture of anhydrous cyclohexane (Bitolea)/n-hexane (Bitolea) in a 9:1 ratio by weight (equal to a filling factor of 80%) and 230 ppm of 2-methoxyethyl tetrahydrofuran (THFA-ethyl) (Thomas Swan), in a molar ratio of approx. 4:1 with the quantity of n-butyllithium, and, subsequently, 300 grams of anhydrous styrene (Versalis SpA) and 900 grams of anhydrous 1,3-butadiene (Versalis SpA) were introduced into a 16 litre stirred reactor: the mixture was heated to a temperature of 40° C. with a heating jacket. 7.5 mmol of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) (Aldrich) and 3.75 mmol of n-butyllithium (Aldrich) were then introduced to obtain a molar ratio between 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and the quantity of active n-butyllithium of approx. 2:1: at this point, heating with the jacket was ceased and the increase in temperature of the reaction mixture was obtained due to the exothermic nature of the reaction, up to a final temperature (peak temperature) of 77° C. 20 minutes were allowed to elapse once the peak temperature had been reached in order to eliminate any monomers which were free at the end of polymerisation, after which 0.159 g of silicon tetrachloride (SiCl.sub.4) (Aldrich), corresponding to 100% of the theoretical coupling efficiency, were introduced and a further 20 minutes were allowed to elapse for the coupling reaction to proceed to completion. The polymer solution obtained was discharged into a tank where it was stabilised with 0.7 phr of 2,6-di-t-butyl-4-methylphenol (BHT) (Great Lakes), after which 450 grams of TDAE (“treated distillate aromatic extract”) non-aromatic oil (Repsol) were added and the resultant mixture was sent for solvent removal by water stripping and subsequent drying by extrusion.
[0117] The styrene-butadiene copolymer obtained was subjected to some of the above-mentioned characterisations: the obtained results are reported in Table 3.
TABLE-US-00003 TABLE 3 1,2- Styrene Vinyl M.sub.w AB W.sub.c M.sub.n tot M.sub.p M.sub.w tot ML ML Example [%] [%] [dalton] [%] [dalton] [dalton] [dalton] D (dry) (o.e.) 10 24.3 66.3 315000 79 857000 996000 952000 1.11 213 85.0 (comparative) 11 (invention) 25.4 63.7 330000 95 1023000 1042600 1074000 1.05 232 94.1 Styrene: styrene content in the copolymer; 1,2-vinyl: 1,2-vinyl unit content in the copolymer; M.sub.w AB: weight-average molecular weight of the copolymer; W.sub.c: “Weight Coupling” (indicates coupling efficiency); M.sub.n tot: number-average molecular weight of the copolymer after addition of the silicon tetrachloride (i.e. after the coupling reaction); M.sub.p: molecular weight of copolymer corresponding to the highest peak; M.sub.w tot: weight-average molecular weight of the copolymer after addition of the silicon tetrachloride (i.e. after the coupling reaction); D: polydispersity index M.sub.w/M.sub.n; ML: Mooney viscosity [dry = non-oil-extended (measured before addition of non-aromatic oil); o.e. = oil-extended].
[0118] On the basis of the data reported in Table 3, it may noted how using the organic compound containing a nitroxide group ([═N—O]) is capable of improving the stability of the living end group so making it possible to achieve appreciably higher coupling efficiencies.
EXAMPLE 12 (COMPARATIVE)
[0119] The polymerisation reactions were carried out in a pair of CSTR type reactors in series, each of which had a volume of 100 litres. The various reactants were introduced by means of pumps controlled by mass flow meters. The mixture of reactants, i.e. cyclohexane (Bitolea), styrene (Versalis SpA), 1,3-butadiene (Versalis SpA), 2-methoxyethyl tetrahydrofuran (THFA-ethyl) (Thomas Swan), and optional “antifouling” agent [1,2-butadiene (Bayer)], was prepared in a stirred reactor under an inert atmosphere to ensure that the composition remained constant throughout the duration of the test. The n-butyllithium (Aldrich), on the other hand, was directly introduced into the first CSTR type reactor of the series. Residence times were managed by controlling input flow rates, while the reaction temperature was determined by controlling the temperature of the solvent/monomer mixture and on the basis of the heat tonality of the reaction.
[0120] Polymerisation was performed in accordance with the above-described operating conditions, with residence times of 45 minutes for each CSTR type reactor, with introduction of a cyclohexane/monomer mixture containing 9% by weight of 1,3-butadiene and 3% by weight of styrene, together with 100 ppm di 2-methoxyethyl tetrahydrofuran (THFA-ethyl). The quantity of n-butyllithium introduced was equal to 0.028 grams per 100 grams of monomer mixture. Under these conditions, the input temperature of the first CSTR type reactor was 48° C. and the output temperature was 93° C. Once the polymer solution obtained had been deactivated by addition of ethyl alcohol (Carlo Erba) in an equimolecular quantity with respect to the quantity of n-butyllithium introduced, TDAE (“treated distillate aromatic extract”) non-aromatic oil (Repsol) was added using an in-line mixer in a quantity equal to 27.5% by weight with respect to the total weight of the finished copolymer together with a mixture of antioxidants comprising Irganox® 565 (Ciba) and Irgafos® 168 (Ciba) in a quantity such that the content in the finished copolymer was respectively 0.1% by weight and 0.4% by weight, with respect to total weight of the copolymer. The polymer solution obtained at the output from the second reactor was sent for solvent removal by water stripping and subsequent drying by extrusion.
[0121] The styrene-butadiene copolymer obtained was subjected to some of the above-mentioned characterisations: the results obtained are reported in Table 4, which also shows the residence times (r.t.) in the two CSTR type reactors.
EXAMPLE 13 (COMPARATIVE)
[0122] Polymerisation was performed in accordance with the process conditions described in Example 12 but increasing the residence times in the two CSTR type reactors to 60 minutes for each reactor, in order to reduce the quantity of free monomers present at the end of the polymerisation train.
[0123] In this connection, a cyclohexane/monomer mixture containing 9% by weight of 1,3-butadiene and 3% by weight of styrene was introduced, together with 100 ppm of 2-methoxyethyl tetrahydrofuran (THFA-ethyl). The quantity of n-butyllithium introduced was equal to 0.028 grams per 100 grams of monomer mixture. Under these conditions, the input temperature of the first CSTR type reactor was 45° C. and the output temperature was 94° C. Once the polymer solution obtained had been deactivated by addition of ethyl alcohol (Carlo Erba) in an equimolecular quantity with respect to the quantity of n-butyllithium introduced, TDAE (“treated distillate aromatic extract”) non-aromatic oil (Repsol) was added using an in-line mixer in a quantity equal to 27.5% by weight with respect to the total weight of the finished copolymer together with a mixture of antioxidants comprising Irganox® 565 (Ciba) and Irgafos® 168 (Ciba) in a quantity such that the content in the finished copolymer was respectively 0.1% by weight and 0.4% by weight, with respect to total weight of the copolymer. The polymer solution obtained at the output from the second reactor was sent for solvent removal by water stripping and subsequent drying by extrusion.
[0124] The styrene-butadiene copolymer obtained was subjected to some of the above-mentioned characterisations: the results obtained are reported in Table 4, which also shows the residence times (r.t.) in the two CSTR type reactors.
EXAMPLE 14 (INVENTION)
[0125] Polymerisation was performed in accordance with the process conditions described in Example 12 but increasing the residence times in the two CSTR type reactors to 60 minutes for each reactor, in order to reduce the quantity of free monomers present at the end of the polymerisation train.
[0126] In this connection, a cyclohexane/monomer mixture containing 9% by weight of 1,3-butadiene and 3% by weight of styrene was introduced, together with 100 ppm of 2-methoxyethyl tetrahydrofuran (THFA-ethyl) (Thomas Swan). A homogeneous mixture of n-butyllithium and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) (Aldrich) was prepared using an in-line mixer into which the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and n-butyllithium flow continuously: the conditions are adjusted to ensure a contact time between the two compounds of at least 5 minutes. The quantity of n-butyllithium which was introduced was equal to 0.112 grams per 100 grams of monomer mixture and the quantity of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) was equal to 0.82 grams per 100 grams of monomer mixture, to obtain a molar ratio between the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and the active n-butyllithium equal to 3:1. Under these conditions, the input temperature of the first CSTR type reactor was 47° C. and the output temperature was 91° C. Once the polymer solution obtained had been deactivated by addition of ethyl alcohol (Carlo Erba) in an equimolecular quantity with respect to the quantity of n-butyllithium introduced, TDAE (“treated distillate aromatic extract”) non-aromatic oil (Repsol) was added using an in-line mixer in a quantity equal to 27.5% by weight with respect to the total weight of the finished copolymer together with a mixture of antioxidants comprising Irganox® 565 (Ciba) and Irgafos® 168 (Ciba) in a quantity such that the content in the finished copolymer was respectively 0.1% by weight and 0.4% by weight, with respect to total weight of the copolymer. The polymer solution obtained at the output from the second reactor was sent for solvent removal by water stripping and subsequent drying by extrusion.
[0127] The styrene-butadiene copolymer obtained was subjected to some of the above-mentioned characterisations: the results obtained are reported in Table 4, which also shows the residence times (r.t.) in the two CSTR type reactors.
TABLE-US-00004 TABLE 4 1,2- r.t. Sty Vinyl M.sub.n M.sub.w [BDE] [Sty] Example [min] R [%] [%] [dalton] [dalton] D α [ppm] [ppm] 12 45 0 26.1 25.1 234,000 625,000 2.67 0.54 73 225 (comparative) 13 60 0 25.7 24.4 227,000 629,000 2.77 0.53 120 365 (comparative) 14 (invention) 60 3 25.8 22.9 248,000 551,000 2.22 0.58 20 58 r.t.: residence time in each reactor; R: molar ratio between the organic compound containing the nitroxide group (═N—O) and the active n-butyllithium in the polymerisation; [Sty]: content of unreacted styrene at the output from the second reactor; 1,2-vinyl: 1,2-vinyl unit content in the copolymer; M.sub.n: number-average molecular weight of the copolymer; M.sub.w: weight-average molecular weight of the copolymer; D: polydispersity index M.sub.w/M.sub.n; α: alpha MALLS index;
[0128] [BDE]: content of unreacted butadiene content at the output from the second reactor.
[0129] On the basis of the data reported in Table 4, it may be noted how in Examples 12 and 13 the value of the α MALLS index and the variation in the radius of gyration (not reported in Table 4) with respect to the molecular masses indicate that branching is concentrated in the high molecular weight (M.sub.w) fractions, whereas in the case of Example 14 the value of the α MALLS index and the variation in the radius of gyration (not reported in Table 4) with respect to the molecular masses do not reveal the presence of any significant branching. The result is confirmed by the corresponding values of the polydispersity index M.sub.w/M.sub.n. With regard to the content of free monomers measured at the output from the second reactor, it may be noted how, in the absence of the organic compound containing a nitroxide group (═N—O), the increase in residence times for each individual reactor from 45 minutes to 60 minutes is ineffective in reducing the content of free monomers at the output from a series of CSTR type reactors. Example 14 does, in contrast, show that the greater stability of the living carbanionic end groups due to the presence of the organic compound containing a nitroxide group (═N—O), makes the increase in mean residence times effective in terms of reducing the content of unreacted monomers.
EXAMPLE 15 (COMPARATIVE)
[0130] Polymerisation was performed in accordance with the process conditions described in Example 12, with the difference that the second CSTR type reactor had a volume of 50 litres. The average residence time in the first reactor was 60 minutes and that in the second reactor was 30 minutes, the concentration of 1,3-butadiene in n-hexane was 20% by weight with respect to the total weight of the solution and the temperature 135° C. The quantity of n-butyllithium introduced was equal to 0.035 g per 100 g of 1,3-butadiene. 0.015 grams of “antifouling agent” (1,2-butadiene—Bayer) per 100 g of 1,3-butadiene were also added. Under these conditions, conversion is virtually complete in the first CSTR type reactor and the polymer undergoes significant formation of long chain branching (LCB) by a thermal pathway. Once the polymer solution obtained had been deactivated by addition of ethyl alcohol (Carlo Erba) in an equimolecular quantity with respect to the quantity of n-butyllithium introduced, a mixture of antioxidants comprising Irganox® 565 (Ciba) and Irgafos® 168 (Ciba) was added using an in-line mixer in a quantity such that the content in the finished copolymer was respectively 0.1% by weight and 0.4% by weight, with respect to the total weight of the copolymer. The polymer solution obtained at the output from the second reactor was sent for solvent removal by water stripping and subsequent drying by extrusion.
[0131] The polybutadiene obtained was subjected to some of the above-mentioned characterisations: Table 5 reported the obtained results.
EXAMPLE 16 (INVENTION)
[0132] Polymerisation was performed in accordance with the process conditions described in Example 12, with the difference that the second CSTR type reactor had a volume of 50 litres. The average residence time in the first reactor was 60 minutes and that in the second reactor was 30 minutes, the concentration of 1,3-butadiene in n-hexane was 20% by weight with respect to the total weight of the solution and the temperature 135° C. 0.015 grams of “antifouling agent” (1,2-butadiene—Bayer) per 100 g of 1,3-butadiene were also added. A homogeneous mixture of n-butyllithium and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) (Aldrich) was prepared using an in-line mixer into which the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and n-butyllithium flow continuously: the conditions are adjusted to ensure a contact time between the two compounds of at least 5 minutes. The quantity of n-butyllithium which was introduced was equal to 0.105 grams per 100 grams of monomer mixture and the quantity of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) was equal to 0.513 grams per 100 grams of monomer mixture, to obtain a molar ratio between the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and the active n-butyllithium equal to 2:1. Under these conditions, conversion is virtually complete in the first CSTR type reactor. Once the polymer solution obtained had been deactivated by addition of ethyl alcohol (Carlo Erba) in an equimolecular quantity with respect to the quantity of n-butyllithium introduced, a mixture of antioxidants comprising Irganox® 565 (Ciba) and Irgafos® 168 (Ciba) was added using an in-line mixer in a quantity such that the content in the finished copolymer was respectively 0.1% by weight and 0.4% by weight, with respect to the total weight of the copolymer. The polymer solution obtained at the output from the second reactor was sent for solvent removal by water stripping and subsequent drying by extrusion.
[0133] The polybutadiene obtained was subjected to the above-described characterisations: Table 5 reported the obtained results.
TABLE-US-00005 TABLE 5 M.sub.n M.sub.w Example R [dalton] [dalton] D α 15 (comparative) 0 181,000 567,000 3.13 0.47 16 (invention) 2 189,000 425,000 2.25 0.55 R: molar ratio between the organic compound containing the nitroxide group (═N—O) and the active n-butyllithium in the polymerisation; M.sub.n: number-average molecular weight of the polymer; M.sub.w: weight-average molecular weight of the polymer; D: polydispersity index M.sub.w/M.sub.n; α: alpha MALLS index.
[0134] On the basis of the data reported in Table 5, it may be noted how the value of the α MALLS index of Example 15 indicates that branching is concentrated in the high molecular weight (M.sub.w) fractions, while in the case of Example 16 the value of the α MALLS index does not reveal the presence of any significant branching. The result is confirmed by the corresponding values of the polydispersity index (D).