MXPA96002030A - Procedure to produce copolymers in asimetri blockwise - Google Patents

Abstract

A process for producing asymmetric radial block copolymers predominantly of four branches predominantly containing, on average, two branches of copolymers of a conjugated diene and an aromatic vinyl hydrocarbon and two branches of diene copolymers or homopolymers, comprising: (a) polymerizing anionically by at least one conjugated diene monomer and at least one vinylaromatic hydrocarbon monomer to form a set of active polymer branches, (b) anionically polymerizing at least one conjugated diene monomer to form another set of active polymer branches, (c) coupling a set of active polymer branches with a coupling agent that is either a tetramethoxysilane or y-glycidoxypropyltrimethoxysilane, (d) substantially completing the coupling reaction leaving, on average, two unreacted coupling sites in the coupling agent, ( e) coupling the other set of active polymer branches to the first coupled assembly of polymer branches and (f) optionally, partially or completely hydrogenate the polymer coupling

Description

PROCEDDCI-Qiro TO PRODUCE OOPOIME-ROS Ql BLOCK ASYMETRIC RADIALS DESCRIPTION OF THE INVENTION The present invention relates to a process for preparing asymmetric radial polymers. More particularly, this invention relates to a method for producing asymmetric tadial polymers having, on average, two branches that are composed of a first type of polymer and two branches that are composed of a second type of polymer. have proposed several methods for preparing asymmetric radial polymers. As known from the prior art, radial polymers comprise three or more branches that extend outward from a core. The asymmetric radial polymers contain branches of at least two different polymers, polymers that can vary in chemical composition, structure, and / or molecular weight. A major difference in the methods that are frequently used to prepare asymmetric radial polymers resides in the selection of a coupling agent that forms the core of the radial polymer. Multifunctional coupling agents such as silicone tetrachloride have been used to form asymmetric radial polymers having three or four branches. Star-shaped radial polymers having much more branches have been formed using a polyalkenyl aromatic compound, such as divinylbenzene, as a coupling agent, for example, as described in Canadian Patent Specification No. 716,645. Before 1988, such asymmetric radial polymers were prepared by forming a mixture of the different polymer branches in the desired ratio and then adding the coupling agent to couple the branches to the coupling agent. These methods resulted in a product having, on average, the desired number of each type of branch in the asymmetric polymer. The problem associated with the production of asymmetric polymers in this way, is that the product obtained is actually a statistical distribution of all possible products, ranging from those that have all the polymer branches of a first type of polymer to those that have all the polymer branches of a second type of polymer. U.S. Patent Specification No. 5,212,249 discloses a two-reactor process for producing asymmetric radial polymers that increase the amount of polymer produced having the desired branch composition. The procedure involves separately polymerizing the monomers to separately create the two different types of branches (it was not thought possible to polymerize the branches in the same reactor and still achieve a product that is not a statistical mixture). Then one of the polymer branches is coupled to the coupling agent and when the coupling reaction is completed, the second set of polymer branches is coupled to the coupling agent. This maximizes the production of the desired species of asymmetric radial block copolymer.

The two reactor process described above is very advantageous and produces polymers which have very good properties and are useful in adhesive compositions and for a wide variety of other uses. However, when a four-branched asymmetric radial polymer containing two different branch types in a 1: 1 ratio is desired, the two reactor procedure has the disadvantage that it still produces polymers having a mixture of structures. Although the polymer will have, on average, two branches of polymers of each type, the actual product will be a mixture of asymmetric radial polymers containing three polymer branches of the first type and a polymer branch of the second type, two polymer branches of each type, and a polymer branch of the first type and three polymer branches of the second type. These polymer components will behave differently in their strength and flow properties and therefore the properties of the final product will differ according to the amount of each polymer component present. For example, a component containing three branches of polystyrene-polydiene copolymers and a homopolydiene branch will have a viscosity much greater than the desired component with two branches of polystyrene-polydiene copolymers and two homopolydiene branches. A component containing three homopolydiene branches and one polystyrene-polydiene branch will have a much lower strength than the desired component with two polystyrene-polydiene copolymer arms and two homopolymer arms. In addition, the most commonly used radial polymer coupling agent, silicon tetrachloride, is unfavorable with respect to the hydrogenation of polydiene for certain hydrogenation catalyst systems. For example, high levels of the chloride ion (produced when an active polymer chain displaces a chloride of silicon tetrachloride) have deleterious effects on certain hydrogenation catalysts, and hydrogenation catalysts that have to be extracted with aqueous acid that produces chloride ions labile during catalyst removal that promotes stress corrosion cracking in most metal containers. Therefore, it would be very advantageous to have a method that is capable of maximizing the amount of the desired four-branched polymer containing two different types of branches, for example, with two branches of copolymers and two homopolymer branches, which is produced and which does not require the use of silicon tetrachloride as a coupling agent. It would be even more advantageous to have a coupling agent that gives a higher yield of the desired species than silicon tetrachloride does. The present invention provides a process like this and produces a polymer like this. The present invention provides a process for producing a predominantly four-branched asymmetric radial block copolymer containing predominantly two branches which are copolymers of a conjugated diene and an aromatic vinyl hydrocarbon and two branches of conjugated diene copolymers or homopolymers, said method comprising: a) anionically polymerizing at least one conjugated diene manomer and at least one vinylaromatic hydrocarbon monomer to form a set of active polymer branches, (b) anionically polymerizing at least one conjugated diene monomer to form another set of polymer branches active, (c) coupling a set of active polymer branches with a coupling agent that is selected from the group consisting of tetramethoxysilane and β-glycidoxypropyltrimethoxysilane, (d) substantially completing the coupling reaction leaving, on average, two sites of unreacted coupling in the agen coupling, (e) adding the other set of active polymer branches and coupling the other set of active polymer branches to the first coupled set of polymer branches and (f) optionally, hydrogenating the partially coupled polymer, e.g. to obtain an asymmetric radial polymer with diene and hydrogenated diene branches, as a whole (to obtain an asymmetric radial polymer with hydrogenated diene branches). In a preferred embodiment, a set of polymer branches is formed by polymerizing a conjugated diene, preferably isoprene, and the other set of active polymer branches is formed by polymerizing a block of aromatic vinyl hydrocarbons, preferably styrene, and then polymerizing a block of conjugated diene, preferably a block of isoprene or butadiene, to form copolymer branches. The preferred coupling agent is tetramethoxysilane. The process of the present invention is particularly suitable for the preparation of asymmetric radial polymers from the so-called "active" polymers containing a single terminal metal ion. As is well known in the art, "active" polymers are polymers containing at least one active group such as a metal atom directly attached to a carbon atom. The "active" polymers are easily prepared by means of anionic polymerization. In general, as monomers used in the polymer branches of the polymers produced by the methods taught herein, one or more conjugated dienes containing from 4 to 12 carbon atoms can be designated such as 1,3-butadiene, isoprene, piperylene, methylpentadiene, nylbutadiene , 3, 4 -dime I-1, 3-hexadiene, and 4, 5-d? Et? -1-1, 3-octanediene, preferably those conjugated diolefins containing from 4 to 8 carbon atoms. The polymers produced by those processes may also contain branches which are copolymers of one or more of the conjugated diolefins indicated above and one or more vmyl aromatic hydrocarbon monomers, such as styrene, various alkyl-substituted styrenes, alkoxy-substituted styrenes, and vinylnaphthalene. Active polymers containing a single terminal group are, of course, well known in the art. Methods for preparing such polymers are taught, for example, in the US patent specifications Nos. 3,150,209; 3,496,154; 3,498,960; 4,145,298 and 4,238,202. Methods for preparing block copolymers such as those preferred for use in the method of the present invention are also taught, for example, in US Patent Specification Nos. 3,231,635; 3,265,765 and 3,322,856. When the polymer product is a random or tapered copolymer, the monomers are generally added at the same time, although the monomer that reacts faster can be added slowly in some cases, whereas, when the product is a block copolymer, the monomers used to form the separate blocks are added sequentially.

In general, the polymers useful as branches in the two methods of the present invention and the asymmetric radial polymer of the present invention can be prepared by contacting the monomer or monomers with an organoalkali metal compound in a suitable solvent at a temperature in the range from -150 ° C to 300 ° C, preferably at a temperature in the range of from 0 ° C to 100 ° C. Particularly effective polymerization initiators are the organolithium compounds having the general formula: RLi wherein R is an aliphatic, cycloaliphatic, alkyl-substituted, aromatic or alkyl-substituted aromatic or cycloaliphatic radical having from 1 to 20 carbon atoms. In general, polymers useful as branches in the asymmetric radial polymers of this invention may be in solution when contacted with the coupling agent. Suitable solvents include those useful in the polymerization of the polymer solution and include aliphatic, cycloaliphatic, alkyl-substituted, aromatic or alkyl-substituted aromatic or cycloaliphatic ethers and mixtures thereof. Suitable solvents, therefore, include aliphatic hydrocarbons such as butane, pentane, hexane and heptane; cycloaliphatic hydrocarbons such as cyclohexane and cycloheptane, alkyl-substituted cycloaliphatic hydrocarbons such as methylcyclohexane and methylcycloheptane; aromatic hydrocarbons such as benzene and alkyl-substituted aromatic hydrocarbons such as toluene and xylene; and ethers such as tetrahydrofuran, diethyl ether and di-n-butyl ether. As the polymers useful for preparing the asymmetric radial polymers of this invention will contain a single terminal reactive group, the polymers used in the preparation of the asymmetric radial polymers will be retained in solution after preparation without deactivating the reactive (active) site. In general, coupling agents can be added to a solution of the polymer or a solution of the polymer can be added to the coupling agent. In this invention, a set of polymer branches can be made by polymerizing at least one conjugated diene monomer to form a branch of active polymers which is then coupled. The first coupling reaction is then allowed to complete, leaving, predominantly, two coupling sites that did not react in each coupler molecule. Then, at least one conjugated diene monomer and at least one aromatic vinyl hydrocarbon monomer are polymerized to form a second set of active polymer branches. Finally, the second set of active polymer branches is coupled to the partially coupled intermediate, preferably in the presence of a polar activator to increase the particular reactivity of the last available site to react the coupling agent, to form the desired asymmetric radial block copolymer . Alternatively, the conjugated diene / vinyl aromatic branches may be reacted with the coupling agent first and the conjugated diene branches in second place. The copolymer formed is composed predominantly of the species having four branches, two of which are branches of vinyl aromatic hydrocarbon / diene copolymers and two of which are diene homo- or copolymer branches. More importantly, no species is formed that has the same four branches. By "predominantly" is meant herein that the copolymer is made of more than 50% by weight of the described species. It is preferred that the two branches are polystyrene-polydiene block copolymers (such as polystyrene-polybutadiene or polystyrene-polyisoprene or polystyrene-polybutadiene-polyisoprene where the polydienes are randomized or block polymerized) wherein the polydiene is unsaturated or either partially- or completely hydrogenated. It is preferred that two branches are polydiene (such as polybutadiene or polyisoprene or random or block copolymers of polybutadiene-polyisoprene) unsaturated or partially or completely hydrogenated. If the polydiene is polyisoprene then it is preferred to add a small polybutadiene block, preferably as a terminal block, since it is then easier to obtain a high polymer percentage of four branches in the final coupling step, - a polybutadiene block such as this is suitably less than 10% by weight of each polydiene branch, and preferably less than 5% by weight. After the first coupling reaction has been completed, it is important that, on average, two coupling sites in the coupling agent are left unreacted and available for further reaction with the second set of active polymer arms. The predominant intermediate species must have two coupling sites that did not react. "Predominant" here means the same as above. The second set of active polymer branches is coupled to the first set of polymer branches coupled via the coupling sites that did not react in the coupling agent, preferably using a coupling activator. The silicon-based coupling agent of the present invention is selected from the group consisting of tetramethoxysilane (Si (OMe) 4) and β-glycidoxypropyltri-methoxysilane. These two coupling agents produce more of the desired polymer species than silicon tetrachloride and can provide partially or completely nidogenic polymers without production of corrosive labile chloride ions. Tetramethoxysilane is preferred because it typically produces a higher level of four-branched polymers. in the final coupling step of at least 75% by weight. In general, any polar compound known to be suitable for increasing the vinyl content in diolefin polymers will be suitable for use as a coupling activator in the second coupling step of the process of this invention. Suitable polar compounds include Lewis bases. Suitable polar compounds, then, include ethers, such as diethyl ether, dibutyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, dioxane, triethylene glycol ether, 1,2-diethoxybenzene, 1,2,3-trimethoxy -benzene, 1,2,4-t rimethoxybenzene, 1, 2, 3-triethoxybenzene, 1,2,3-taxhoxybenzene and 1,2,4-trimethoxybenzene. Suitable polar compounds also include tertiary amines such as triethylamine, tributylamine and N, N, N, N-tetramethylethylenediamine. Suitable polar compounds also include tertiary amines such as triethylamine, tributylamine, and N, N, N, N-tetramethylethylene diamine. Suitable polar compounds include various pyridine and pyrolidene compounds such as dipyridinoethane, and dipyrolidinoethane. In general, the coupling activator will be used at a concentration in the range of from 10 to 1000 ppm. Preferred coupling activators are ethylene glycol diethylether, orthodimethoxybenzene, N, N, N, N-tetraethylethylenediamine, and diethyl ether, with ethylene glycol ethylether being preferred. As a general rule, in the process of the invention, the polymerization of the set of active polymer branches containing a diene and a vinylaromatic hydrocarbon or a diene can be carried out at a temperature in the range from -150 to 300 ° C, preferably from 0 to 100 ° C until the monomer has been consumed, generally within 15 to 120 minutes, preferably 30 to 60 minutes. In general, the conditions of the coupling reactions are a reaction temperature in the range of from 20 to 100 ° C, preferably 50 to 80 ° C and a reaction time in the range of from 5 to 100 minutes, preferably 15 to 60 minutes. The asymmetric radial block copolymers of the present invention may have molecular weights that vary over a wide range. In general, the molecular weights of these block copolymer branches will be in the range of from approx. 10,000 to 250,000, and the molecular weights of the polydiene branches will be in the range of from 1000 to 100,000 g / mol. The preferred block copolymer branches of the present invention fall in the molecular weight range of from 15,000 to 100,000, and the polydiene branches in the range of from 5000 to 50,000 g / mol. The molecular weights of linear polymers or non-clustered linear segmenters of polymers such as mono-, di-, triblock, etc. branches. of the star polymers before coupling are conveniently measured by gel permeation chromatography (GPC), where the GPC system has been properly calibrated. For anionically polymerized linear polymers, the polymer is essentially monodisperse (the weight average molecular weight / number average molecular weight ratio is close to unity), and it is convenient and suitably descriptive to report the "peak" molecular weight of the weight distribution observed molecular Generally, the peak value is between the average in number and in weight. The peak molecular weight is the molecular weight of the main species observed in the chromatograph. For polydisperse polymers the weight average molecular weight should be calculated from the chromatograph and used. For the materials to be used in the GPC columns, styrene-divinylbenzene gels or silica gels are commonly used and are excellent materials. Tetrahydrofuran is an excellent solvent for polymers of the type described herein. A refractive index detector can be used. The following publications reveal adequate analytical techniques: i. Modern liquid chromatography excluding size, MW Yau, JJ Kir land, DD Bly, John Wiley and Sons, New York, New York, 1979. 2. Dispersion of light from polymer solutions, MB Huglin, ed., Academic Press , New York, New York, 1972. 3. WK Kai and AJ Havlik, Applied Optics, 12, 541, (1973). 4. M. L. McConnell, American Laboratory, 63, May, 1978. The polymers prepared by the process of the present invention can be hydrogels after they are coupled. A completely hydrogenated form could be, for example, an asymmetric radial polymer of which one set of polymer branches is composed of a block copolymer of styrene and hydrogenated isoprene and / or hydrogenated butadiene and the other set of polymer branches is composed of Hydrogenated isoprene and / or hydrogenated butadiene. The polymers however can be partially hydrogenated such that one portion of each polymer is hydrogenated and another is not. For example, the styrene-butadiene branches could be coupled with isoprene branches; it is possible to selectively hydrogenate the butadiene in the styrene-butadiene branches and not significantly hydrogenate the isoprene branches. This is the preferred embodiment of the present invention. Hydrogenation can occur in a selective manner with a suitable catalyst and conditions such as those described in US reissue specification No. J7 145, US patent specification No. 4,001,199 or with a titanium catalyst such as was disclosed in U.S. Patent Specification No. 5,039,755.

The asymmetric radial polymers of this invention can be used in any of the applications for which asymmetric radial polymers having the same relative branch structure can be used. Suitable end-use applications, therefore, include modification by impact of technical thermoplastics, modification by impact of unsaturated thermoset polyesters, molded articles, adhesives, bonding layers and asphalt modification. The following is a summary of typical synthesis for the preparation of an asymmetric radial polymer of four branches in which the predominant species has a ratio of 2: 2 branches, that is, two branches of one type and two branches of the other type. The polymers are prepared by first adding approx. 2 equivalents of a first set of polymer branches to a tetrafunctional coupling agent forming a partially coupled intermediate having, on average, two polymer branches and two unreacted coupling sites. In the case of silicon tetrachloride, β-glycidoxypropyltrimethoxysilane and tetramethoxysilane, this partially coupled intermediate is actually composed of a mixture of three compounds containing one, two and three polymeric branches. In a second coupling step, two or more equivalents of a second type of polymer branch are added to the partially coupled intermediate in the presence of a polar activator (ethers such as o-dimethoxybenzene, 1,2-diethoxyethane, or 1,2-dimethoxyethane) ). As the coupling sites are very reactive with respect to the active polymer branches, the unreacted coupling agent is present after the first coupling step as evidenced by the lack of a symmetrical radial polymer containing four branches of the second type of coupling. Polymer branches in the final product mixture. In addition, since the last site of the coupling agent is much less reactive in the absence of a polar activator, a symmetrical polymer with four branches would not be produced in the first coupling step. If the molecular weights of the end product components of asymmetric radial polymer of four branches are similar, the distribution can not be determined analytically by gel permeation chromatography. In such cases, the final product distribution can be calculated from the partially coupled intermediary distribution, which is more easily determined. For example, in an asymmetric four-branched radial polymer, containing branches of styrene-butadiene diblock copolymer and polyisoprene branches, the components of the partially coupled intermediate are represented as I. and those of the final product as SB, 4 x) Ix where x is equal to the number of polysoprene branches. For the synthesis of four-branched asymmetric radial polymers with a ratio of 2: 2 branches using silicon tetrachloride couplers,? - glycoxypropionate 11-imethoxy-1-year, or tetramethoxysilane, x can be equal to 1, 2 or 3. E? The following equations, the molecular weight of the polymer branches is denoted as PM I and PM SB. The analysis of the intermediate partially coupled by gel penetration chromatography (GPC) allows the separation of the three individual components by their molecular weights. The detection of the intermediaries using a refractory index detector (I.R.) quantifies the amount of each component in the mixture. The areas of each peak, as detected by the Refractive index, are proportional to the number of repeating units that are eluted. When each repeating unit has the same mass, the% of total area for a peak as measured by I.R. it will be equal to the% percent of that component. In this way, the fraction by weight of each component in the partially coupled intermediate is determined by GPC.

The mole fraction of each intermediate is given by: Moles of Ix (l) Molar fraction of Ix = Total moles where: Mass of Ix Weight fraction of Ix (2) Moles of Ix = = PM of Ix PM of Ix for a total of 1 gram of partially coupled intermediary. The molecular weight of each component will be: MW of I "= PM I. x since the coupling agent residue, e.g. , SiCl (4-x) or Si (OMe) (4-x) does not contribute significantly to molecular weight.

The total moles will be equal to the sum of all the intermediaries - I3, I2 and I ^ Weight fraction of Ix (3) Total moles = S x = l, 2.3 PM I. x which gives the following expression for the molar fraction of each partially coupled intermediate.- / Fraction by weight of I •, x PM I. x! 4) Molar fraction of Ix = / Weight fraction of I, / S l? c = l, 2.3 PM I. x Due to the nature of the synthesis, when the final product composition is formed, the molar fraction of each component of the final product will be equal to the mole fraction of the intermediate component from which it was formed. Molar fraction (SB) (4.X) IX = Molar fraction Ix The fraction by weight of each component in the final product, (SB), 4.X) IX, can be determined from the mole fraction as follows: Mass of (SB) (4.X) IX (5) Fraction by weight of (SB) (4 X) IX = Total mass where: (6) Mass of (SB) (4.X) IX = Molar fraction of (SB) (.X) IX. [MW of (SB) (4.X) IX] = Molar fraction of Ix. [PM from (SB) (4.X) I Y- (7) PM from (SB) (4-x) Ix '= PM SB. (4-x) + PM Ix Substituting equation (7) into the equation (6) and this one in equation (5) gives: Tails. molar of I,. Mass of (SB). (4-x) + PM I.x Frac, in weight of (SB) Cotal mass The total mass is equal to the sum of all the components of the final product: .9) Cotal mass = Z Molar fraction of I ,. [PM SB. (4-x) + (PM Ix] x-1,2,3 Substituting equation (4) in equation (9) gives: Frac in weight of Ix PM I. x (10) Tocal mass r. [PM SB. (4-x) + PM Ix] • 1,2,3 Frac in weight of I -1,2,3 PM I. X J Finally, substituting equations (4) and (10) in equation (8) gives the expression for the weight fraction of each component in the final product: Ftac in I, I PM I x - - [PM SB ( 4-xl.PM I x] Fi c in peao of I, E x-til) Frac in weight of (Sb) ,,, 1. « x-, The following Examples illustrate the invention: Example 1 - Polymer 1 (PP5293) An asymmetric radial polymer was prepared by polymerization, in a first reactor, of 24.8 pounds (11.2 kg) of styrene in 242 pounds (109 , 8 kg) of cyclohexane solvent and 21.5 pounds (9.7 kg) of diethyl ether with 1050 ml of anionic polymerization initiator of sec-butyllithium at 60 ° C for 10 half-lives. After polymerization of the styrene, 62.6 pounds (28.2 kg) of butadiene was added and the butadiene was polymerized at 55 ° C for at least 10 half lives. In a separate reactor, 38.7 pounds (17.5 kg) of isoprene was polymerized into 226.45 pounds (102.7 kg) of cyclohexane using 710 ml of sec-butyl lithium at 60 ° C for at least 8 half lives . After the polymerization of the isoprene, 2 pounds (0.9 kg) of butadiene was added and the butadiene was polymerized at 60 ° C for at least 8 half-lives. To this polyisoprene, 66 ml of coupling agent tetramethoxysilane was added and the mixture was reacted for 45 min. at 60 ° C. To this partially coupled intermediate was added 285 pounds (129.3 kg) of the polystyrene-polybutadiene diblock copolymer solution in cyclohexane from the first reactor and 180 ml of 1,2-dimethoxyethylene. This mixture was reacted for 60 min. at 75 ° C to achieve the coupling of the remaining sites of the partially coupled intermediate. Any remaining active polymer branch was terminated by the addition of approx. 90 mis of methanol. The polymer was then hydrogenated under conditions that preferentially hydrogenated the polybutadiene portion of the polymer leaving the substantially unsaturated polyisoprene portion. The resulting polymer it was isolated by contacting the polymer solution with high pressure steam followed by removal of the solid polymer from the liquid phase. It was determined that the polymer product had a polystyrene molecular weight of 9,900 g / mol and a polybutadiene molecular weight of 23,700 in the diblock copolymer branches and a molecular weight of 20,300 g / mol of the homopolyisoprene branches (which contained a small terminal polybutadiene block of less than 5% by weight) by gel permeation chromatography (GPC). The polystyrene content as determined by lH NMR is 17, 4% by weight. After the selective hydrogenation, the polymer had a 60% hydrogenated gum combined with 92% of the polybutadiene and 49% of the hydrogenated polyisoprene. Polymers 2-6 Five asymmetric radial polymers were prepared in the same way as Polymer 1 except changes in the amount of solvent, reagents and coupling conditions used. Table 1 describes the polymerization and analysis of these polymers. or? l? Table 1 I NJ I Ul ro or I? u > Table 1: (continued) I NJ cp I Polymer 7; 4773 An asymmetric radial polymer was prepared by polymerization, in a first reactor, of 16.2 pounds (7.3 kg) of styrene in 259.4 pounds (117.7 kg) of cyclohexane solvent and 21.3 pounds (9, 7 kg) of diethyl ether with 1000 ml of anionic polymerization initiator of sec-butyllithium at 45 ° C for 10 half-lives. After polymerization of the styrene, 54 pounds (24.5 kg) of butadiene was added and the butadiene was polymerized at 70 ° C for at least 10 half lives. In a separate reactor, 30.3 pounds (13.7 kg) of isoprene were polymerized into 122.09 pounds (55.4 kg) of cyclohexane using 522 ml of sec-butyllithium at 55 ° C for at least 8 half-lives . To this polyisoprene, 43 ml of silicon tetrachloride coupling agent were added and the mixture was reacted for 60 min. at 25 ° C. To this partially coupled intermediate was added 219.15 pounds (99.4 kg) of the diblock copolymer solution of polystyrene-polybutadiene in cyclohexane from the first reactor and 66 ml of 1,2-dimethoxy-ethane. This mixture was reacted for 60 min. at 70 ° C to achieve the coupling of the remaining sites of the partially coupled intermediate. The polymer was then hydrogenated under conditions that preferentially hydrogenated the polybutadiene portion of the polymer leaving the substantially unsaturated polyisoprene portion. The resulting polymer was isolated by contacting the polymer solution with high pressure steam followed by removal of the solid polymer from the liquid phase. It was determined that the polymer product had a polystyrene molecular weight of 5,500 g / mol and a molecular weight of polybutadiene of 19,400 in the diblock copolymer branches and a molecular weight of 18,400 g / mol of the homopolyisoprene branches by penetration chromatography in gel (GPC). The polystyrene content as determined by lH NMR is 13.6% by weight. After selective hydrogenation, the polymer had a 50.5% hydrogenated gum combined with 90.1% of the polybutadiene and 23.3% of the hydrogenated polyisoprene. Fl-lj Polymers Four asymmetric radial polymers were prepared in the same manner as Example 7 except for changes in the amount of solvent, reagents and coupling conditions used. Table 2 describes the polymerization and analysis of these polymers.

I Iahifi-_2 I CO I Ul O Ul u.

Table 2 (continued) Polymer 12: (PP4813) An asymmetric radial polymer was prepared by polymerization, in a first reactor, of 15.6 pounds (7.1 kg) of styrene in 280.12 pounds (127.1 kg) of cyclohexane solvent with 840 ml. of initiator of anionic polymerization of sec-butyllithium at 60 ° C for 10 half lives. After polymerization of the styrene, 54.6 pounds (24.8 kg) of isoprene was added and the butadiene was polymerized at 550 ° C for 12 half-lives. In a separate reactor, 10.7 pounds (4.85 kg) of isoprene was polymerized to 42.76 pounds (19.4 kg) of cyclohexane using 435 ml of sec-butyllithium at 60 ° C for 12 half-lives. To this polyisoprene, 34 ml of silicon tetrachloride coupling agent was added and the mixture was reacted for 60 min. at 25 ° C. To this partially coupled intermediate were added 296.76 pounds (134.5 kg) of the polystyrene-polyisoprene diblock copolymer solution in cyclohexane from the first reactor and 32 ml of 1,2-dimethoxy-ethane. This mixture was reacted for 60 min. at 70 ° C to achieve the coupling of the remaining sites of the partially coupled intermediate. The polymer was then hydrogenated. The resulting polymer was isolated by contacting the polymer solution with high pressure steam followed by removal of the solid polymer from the liquid phase. It was determined that the polymer product had a polystyrene molecular weight of 6,300 g / mol and a molecular weight of polyisoprene of 22,600 in the diblock copolymer branches and a molecular weight of 9,200 g / mol of the homopolyisoprene branches by penetration chromatography in gel (GPC). The polystyrene content as determined by lH NMR is 18.4% by weight. After selective hydrogenation, the polymer had 99% 23.3% of the hydrogenated polyisoprene.

Table 4 - Polymers coupled with silicon tetrachloride * For polymer 12, the components of the final product are (SEP) 3 (EP), (SEP) 2 (EP) 2, (SEP) (EP) 3 The data presented in Tables 3 and 4 show that the coupling agent tetramethoxysilane produces much higher percentages of the components of the desired intermediate - I2 - and of the final product - (SEB) 2I2 - than the silicon tetrachloride. For the polymers coupled with tetramethoxy-silane, the I2 ranges from 63 to 83.5% by weight of the total mass of the partially coupled intermediate which gives 66.5 to 78% by weight (of the ARP polymers of four branches produced) of the final product component (SEB) 2I2 desired. For the polymers coupled with silicon tetrachloride I. it is only 25 to 51% by weight of the partially coupled intermediate distribution. This gives 18.5 to 49% of the (SEB) 2I2 (or (SEP) 2 (EP) 2) desired in the composition of the final product. In four of six polymers coupled with silicon tetrachloride, the desired four-branched ARP polymer with a ratio of 2: 2 branches does not make up the largest weight fraction of the three components of the final product. labla-_5 a Determined by chromatography and gel penetration b% asymmetric radial polymer of four branches as calculated from the distribution of partially coupled intermediates (as determined by gel permeation chromatography) using Equation 11 of the text. c Determined by NMR spectroscopy. d Measured on an Instron Model 4505 using samples cut from molded toluene plates. Calibrated length = 1 in (25.4 mm); extension ratio = 100% / min. Measured in a Brookfield Model DV-II, spindle 21.

The data in Table 5 compare the physical properties of asymmetric radial polymer coupled with silicon tetrachloride with an asymmetric radial polymer coupled with tetramethoxysilane of molecular weight and composition of similar polymer branches. The polymer coupled with silicon tetrachloride containing 50% (SEB) 3I of the total four-branched radial asymmetric polymer has a lower polymer melt flow indicating a higher melt viscosity. The highest observed resistance of the polymer coupled with tetramethoxysilane may be due to the better distribution of final product and the higher level of polydiene hydrogenation. These data show that the improved final product distribution of the polymers coupled with tetramethoxysilane results in a better performance product with more convenient properties. or in o Iahla-_fi to ether or by gel penetration chromatography. b% asymmetric radial polymer of four branches according to η was calculated from the distribution of partially coupled intermediates (as determined by gel permeation chromatography) using Equation 11 of the text. c Determined by XH NMR spectroscopy. d Measured on a Model 4505 Inßtron using samples cut from molded toluene plates. Calibrated length = 1 in (25.4 mm). extension ratio = 100% / min.

Measured in a Brookfield Model DV-II, spindle 21.

The data in Table 6 compare the physical properties of an asymmetric radial polymer coupled with silicon tetrachloride with an asymmetric radial polymer coupled with tetramethoxysilane of molecular weight and branch composition of similar polymers. The presence of a large amount of (SEB) I3 which does not form a matrix in the final product of the polymer coupled with silicon tetrachloride is balanced by the presence of high viscosity (SEB) 5I to produce an asymmetric radial polymer with melting and viscosity solution similar to the polymer coupled with tetramethoxysilane. However, the presence of this (SEB) I3 results in a much weaker polymer with significantly lower tensile strength than the polymer coupled with tetramethoxysilane despite a higher level of polydiene hydrogenation. These data show that the improved final product distribution of the tetramethoxysilane polymers results in a better performance product with more convenient properties. If the polymers indicated above have to be used in an application where they will be mixed with other ingredients, less asymmetric radial polymer coupled with tetramethoxysilane will be required to achieve an equivalent performance of the final product. Example 2 Six different coupling agents were investigated with respect to their ability to produce four branch polymers in the presence of an excess of active polybutadiene branches. In the experiments described in Table 7, more than four equivalents of active polybutadiene branches were contacted with coupling agents in the presence of 200 ppm ethylene glycol diethylether at 80 ° C for 60 minutes with stirring. In each case the polymer branch that did not react is also present as expected, due to the added excess. These data show that silicon tetrachloride, tetramethoxysilane and -y-glycidoxypropyltrimethoxysilane are effective to produce high percentages of polymers with four branches, leaving small polymers with three branches. The other three coupling agents used in these experiments, 2- (3, 4-epoxycyclohexyl) -ethyltrimethoxysilane, dimethyl adipate, and tetrakis (2-ethylbutoxy) silane produced inadequate amounts of four-branched polymers.

Ul O Ul labia--.! a Determined by gel penetration chromatography. b Calculated from the observed number of moles of polybutadiene (determined from the molecular weight of the polybutadiene) and the moles of coupling agent added to the reaction. Determined by non-linear curve fitting of gel penetration chromatograms.

Coupling agents that provide high coupling efficiency for four-branch polymers were subsequently investigated for their selectivity in a first coupling step for the synthesis of asymmetric radial polymers. In the experiments described in Table 8, two equivalents of active polyisoprene branches were contacted with the coupling agents at 60 ° C for 30 minutes with stirring. The data shows that tetramethoxysilane and β-glycidoxypropyltrimethoxysilane produce higher amounts of the partially coupled intermediates of two desired branches than silicon tetrachloride. Tetramethoxysilane is the most effective coupling agent to maximize the amount of two-branched polymer. This will give a final product that maximizes the amount of polymer with the desired structure. ro t i or i Table 6 a Determined by gel penetration chromatography. b Calculated from the observed number of moles of polybutadiene (determined from the molecular weight of the polybutadiene) and the moles of coupling agent added to the reaction. c Determined by non-linear curve adjustment of gel penetration chromatogram.

EXAMPLE 3 The influence of the polymer branch type on the selectivity of tetramethoxysilane in the first coupling step of the synthesis of asymmetric radial polymers was investigated. In the experiments detailed in Table 9 below, they were contacted approx. two equivalents of branches of 0 active polymers with tetramethoxysilane at 60 ° C for 30 minutes with stirring. The data shows that the polymers branches composed only of polyisoprene are more selective to produce higher quantities of the partially coupled two-branched intermediate comprised of 5 blocks of polyisoprene-polybutadiene. Comparing the experiment no. 9 in Table 8 above with experiment No. 10 in Table 9 below, it can be seen that even in reaction with less selective polymer branch types, tetramethoxysilane produces more of the intermediate? of two branches desired than silicon tetrachloride. As the presence of polybutadiene promotes the polymer preparation reaction to be completed, on a suitable time scale, the inclusion of polybutadiene in polyisoprene branches will yield a final product that maximizes the amount of polymer with the desired structure. ? o to Ul or Ul labla - Ü r Expert Type of Branch of Relationship Branch ?, on p. ! % in rimer- polymer polymer molar species I spec to Weight branches of 1 'of 2 Polymer molecular no .: ramac, branches (g / mol) »tetramethoxysilane 7 Poly Isoprene 8500 1.8: 1 11.7 86, 10 Po1iißoprene-4617-1112 2.1: 1 9.4 63.4 polybutadiene Determined by gel penetration chromatography. For the isoprene-butadiene branches, the first number represents the polybutadiene molecular weight, the second number represents the polybutadiene molecular weight. Calculated from the observed number of moles of polymer arms (d from the molecular weight of the polymer and the charged monomer mass) of coupling agent tetramethoxysilane added to the reaction. Determined by adjustment of non-linear curve of penetration chromatogram It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (9)

1. CLAIMS 1. A process for preparing a predominantly four-branched asymmetric radial block copolymer 3 containing predominantly two branches which are copolymers of a conjugated diene and an aromatic vinyl hydrocarbon and two branches of conjugated diene copolymers or homopolymers, characterized in that: (a) anionically polymerizing at least one conjugated diene monomer and at least one vinyl aromatic hydrocarbon monomer to form a set of active polymer branches, (b) anionically polymerizing at least one diene monomer i? 3 conjugate to form another set of branches of active polymers, (c) coupling a set of active polymer branches with a coupling agent that is selected from the group consisting of tetramethoxysilane and β-glycidoxypropyl-0-trimethoxysilane, (d) substantially completing the coupling reaction leaving, on average, two places of unreacted coupling in the coupling agent, (e) adding the other set of active polymer branches to the product of d) and coupling the other set of active polymer branches to the first coupled assembly of polymer branches and (f) optionally, partially or completely hydrogenate the coupled polymer.
2. 2. A process according to claim 1, characterized in that the coupling agent is tetramethoxysilane.
3. 3. A method according to claim 1 or claim 2, characterized in that the coupling reaction of steps (c) and (d) is performed in the absence of
4. ^ • Or a coupling activator and the coupling reaction of step (e) is carried out in the presence of a coupling activator. 4. A method according to any of claims 1 to 3, characterized in that the set of * 5 branches of polymers prepared in step (a) is composed of a block copolymer of styrene and isoprene and / or butadiene and the other set of polymer branches prepared in step (b) is composed of isoprene and / or butadiene polymerized
5. 5. A process according to claim 4, characterized in that the block polymer is hydrogenated to provide a polymer of which one set of polymer branches is composed of a block copolymer of styrene and hydrogenated isoprene and / or hydrogenated butadiene and the other The set of polymer branches is composed of hydrogenated isoprene and / or hydrogenated butadiene.
6. 6. A process according to claim 4, characterized in that the set of polymer branches prepared in step (a) is composed of a block copolymer of styrene and butadiene and the other set of polymer branches prepared in step ( b) it is polyisoprene. A process according to claim 6, characterized in that the asymmetric radial block copolymer is partially hydrogenated in step (f) to provide a polymer of which a set of polymer branches is composed of a block copolymer of styrene and hydrogenated butadiene and the other set of polymer branches is substantially unhydrogenated or partially hydrogenated polyisoprene. 8. A process according to one of claims 4 to 7, characterized in that a set of polymer branches is polyisoprene having a terminal block of polybutadiene. 9. An asymmetric radial block copolymer predominantly of four branches, characterized in that it predominantly contains two branches which are copolymers of at least one conjugated diene and at least one vinyl aromatic hydrocarbon and two homopolymer or conjugated diene copolymer branches, when Prepared by means of a process according to any of claims 1 to 8.