Branched polymers prepared using multifunctional coupling agents

Abstract

Branched block copolymers derived from alkenyl aromatic hydrocarbon-1,3-diene monomer systems and branched polyisoprene homopolymers derived from isoprene can be prepared by polymerization in the presence of an anionic initiator at temperatures between 0°C and 100°C, followed by polymerization of the copolymers of formula (R 1 O)3Si-Y-Si(OR 2 )3 (R1 and R2 are independently a C1-C6 alkyl group and Y is a C2-C8 alkylene group) with a polyfunctional coupling agent. The polymer thus obtained can be used in many applications, including rubber cements with high solids content and low zero shear viscosity, and for producing aqueous latexes therefrom.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 775,624, filed December 5, 2018, and U.S. Provisional Patent Application No. 62 / 889,779, filed August 21, 2019, which are incorporated herein by reference.

[0002] The present disclosure relates to branched polymers made using multifunctional coupling agents. [Background technology]

[0003] Elastomeric block copolymers and homopolymers are synthetic materials useful for a wide range of end uses. Homopolymers and block copolymers with one or more blocks of polymerized conjugated diene blocks are examples of such materials. Examples include styrenic block copolymers, such as styrene-butadiene block copolymers, as well as polybutadiene homopolymers and polyisoprene homopolymers. Styrenic block copolymers and polyisoprene, which have relatively narrow molecular weight distributions, are commonly prepared using anionic polymerization. Synthetic polyisoprene is also produced by polymerizing isoprene using Ziegler-Natta catalysts. Polyisoprene homopolymers are synthetic, primarily stereoregular polymers that closely resemble natural rubber in properties as well as molecular structure. The polymer is first produced in an organic solution, which can then be coagulated and dried into a solid rubber or converted into an aqueous latex form. Summary of the Invention [Problem to be solved by the invention]

[0004] There is also a continuing need for new block copolymers and homopolymers with improved properties, as well as further improvements in the productivity of the processes for making these polymers and their latexes. [Means for solving the problem]

[0005] One embodiment of the present disclosure is a polymerizable compound comprising one or more polymer blocks A and one or more polymer blocks B, and having the formula (AB): m (R1O) 3-m Si-Y-Si(RO) 3-n (BA) n Each A block independently comprises at least 90 mole percent of an alkenyl aromatic hydrocarbon and has a weight average molecular weight of 9 to 15 kg / mole, and the one or more A blocks form 8 to 13 weight percent of the total weight of the block copolymer. Each B block independently comprises at least 90 mole percent of one or more 1,3-dienes and is a poly(1,3-diene) block having a weight average molecular weight of 75 to 150 kg / mole. R1 and R2 are independently H or a C1-C6 alkyl group, Y is a C2-C8 alkylene group, and m and n are independently integers having values ​​of 1 to 3. The block copolymer has a coupling efficiency (CE) of at least 40%, preferably greater than 80%.

[0006] Another aspect of the present disclosure is a compound of formula (C): m (R1O) 3-m Si-Y-Si(RO) 3-n (C) n wherein each C block is a polyisoprene block independently having a weight average molecular weight of 400-1000 kg / mol, preferably 500-700 kg / mol. R1 and R2 are independently H or a C1-C6 alkyl group, Y is a C2-C8 alkylene group, and m and n are independently integers having values ​​of 1 to 3. The homopolymer has a coupling efficiency (CE) of at least 40%, preferably greater than 80%.

[0007] Yet another aspect of the present disclosure is a method for preparing the branched block copolymer, comprising: polymerizing a first monomer comprising at least 90 mole percent of an alkenyl aromatic hydrocarbon at a temperature between 0° C. and 100° C. to form a polymer block A; adding a second monomer comprising at least 90 mole percent of one or more 1,3-dienes at a temperature between 0° C. and 100° C. to form a polymer block B; adding a polyfunctional coupling agent of formula (RO)Si-Y-Si(OR) and forming a branched block copolymer having a coupling efficiency (CE) of at least 40%.

[0008] Yet another aspect of the present disclosure is a method for preparing the branched polyisoprene homopolymer described above, comprising polymerizing isoprene in the presence of an anionic initiator at a temperature between 0° C. and 100° C. to form a polymer block C, adding a multifunctional coupling agent of formula (RO)Si-Y-Si(OR) to form a branched polyisoprene homopolymer having a coupling efficiency (CE) of at least 40%. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] As used herein, the following terms have the following meanings.

[0010] The term "active material" is used to describe a polymer chain that has a reactive carbanionic center at its growing end.

[0011] The term "coupling efficiency" (CE) is used to quantify the ratio of uncoupled polymer to coupled polymer as determined by GPC.

[0012] The term "degree of branching" refers to the average total number of polymer arms present per molecule of a branched block copolymer.

[0013] Multifunctional Coupling AgentsThe branched block copolymers and branched polyisoprene homopolymers have the general formula (I): (RO)3Si-Y-Si(RO)3(I) The polyfunctional coupling agent is prepared using a polyfunctional coupling agent represented by R1 and R2 are independently H or a C1-C6 alkyl group, and Y is a C2-C8 alkylene group. The reactive polymer chain with the carbanion chain end reacts with the two silicon centers of the coupling agent (I) to form coupled block copolymers and coupled homopolymers. Because formula (I) has six leaving groups (alkoxy groups), the coupling agent is hexafunctional, so theoretically there can be one to three polymer chains on each silicon. Any hexafunctional organosilicon compound containing formula (I) can be used as the coupling agent. In one embodiment, the preferred multifunctional coupling agent is selected from the group consisting of 1,2-bis(trimethoxysilyl)ethane (BTMSE), 1,2-bis(triethoxysilyl)ethane (BTESE), or mixtures thereof.

[0014] Branched Block Copolymers and Branched Polyisoprene Homopolymers The branched block copolymers prepared using the multifunctional coupling agent of formula (I) include one or more polymer blocks A and one or more polymer blocks B and have the general formula (II): (AB) m (R1O) 3-m Si-Y-Si(RO) 3-n (BA) n (II) It is expressed as R1, R2 and Y are as defined for formula (I), and m and n are integers that provide the degree of branching, as further described below. In some embodiments, the branched block copolymer (II) has R1 and R2 independently selected from H, methyl or ethyl, and Y is a -CH2-CH2- group.

[0015] The A block is an aromatic block composed primarily of repeat units derived from one or more alkenyl aromatic hydrocarbons. In some embodiments, the A block comprises at least 90 mole percent, 90-95 mole percent, or at least 95 mole percent of an alkenyl aromatic hydrocarbon. The weight percent of the A block in the overall block copolymer is generally less than 15 weight percent. In some embodiments, the A block forms 8-13 weight percent, alternatively 8-10 weight percent, alternatively 10-13 weight percent. The A block has a weight average molecular weight of 9-15 kg / mole. In other embodiments, the A block molecular weight is 9-12 kg / mole, alternatively 12-15 kg / mole. Any of the alkenyl aromatic hydrocarbons known in the art can be used, such as styrene, alpha-methylstyrene, para-methylstyrene, vinylnaphthalene, and the like. Styrene is the preferred monomer.

[0016] The B block is an elastomeric block composed primarily of repeat units derived from one or more conjugated dienes (1,3-dienes). In some embodiments, the B block comprises at least 90 mole percent, 90-95 mole percent, or at least 95 mole percent 1,3-dienes. Each B block has a weight average molecular weight of 75-150 kg / mole. In other embodiments, the B block molecular weight can be 75-100 kg / mole, 100-125 kg / mole, or 125-150 kg / mole. Non-limiting examples of 1,3-dienes suitable for preparing the B block include butadiene, isoprene, piperylene, cyclohexadiene, 2,3-dimethyl-1,3-butadiene, myrcene, farnesene, and the like.

[0017] The values ​​of m and n in formula (II) are independently in the range of 1 to 3. As the values ​​of m and n increase from 1 to 3, there is a corresponding increase in the amount of more highly branched copolymers in the overall copolymer. In some embodiments, the values ​​of m and n in formula (II) can be 1, 2; 1, 3; 2, 2; 2, 3; 3, 2; 3, 1 and 3, 3, respectively. When reactive polymer chains are coupled with a multifunctional coupling agent, depending on the stoichiometry and reaction conditions, it can result in a mixture of branched block copolymers having a range of m and n values ​​ranging from 1 to 3. Thus, theoretically, the overall product resulting from the coupling reaction can be characterized by an overall degree of branching, which gives the average value of m and n, as well as the degree of the total amount of branched block copolymer in the product. This in turn can affect the physical and / or chemical properties of the copolymer. In one aspect, the branched block copolymer (II) can have values ​​of m and n from 1 to 3, such that (m+n) is greater than 2 and less than or equal to 6, which can be mathematically expressed as 2<(m+n)≦6.

[0018] The branched polyisoprene homopolymer comprises one or more polymer blocks C and has the general formula (III): (C) m (R1O) 3-m Si-Y-Si(RO) 3-n (C) n (III) It is expressed as R1, R2 and Y are as defined for formula (I), and m and n are as defined for formula (II). The C block is composed primarily of repeat units derived from one or more conjugated dienes (1,3-dienes). Non-limiting examples of suitable 1,3-dienes useful for preparing the C block include butadiene, isoprene, piperylene, cyclohexadiene, 2,3-dimethyl-1,3-butadiene, myrcene, farnesene, and the like. The C block independently has a weight average molecular weight of 400 to 1000 kg / mol, preferably 500 to 700 kg / mol. The degree of branching in the branched homopolymer (III) depends on the values ​​of m and n and can vary in the same manner as described above for the branched block copolymer (II). In one embodiment, m and n have a value of 1 or 1. In another embodiment, m and n have a value of 1 to 3 such that (m+n) is greater than 2 and less than or equal to 6, which can be mathematically expressed as 2<(m+n)≦6. The value of m+n can be from 3 to 6. In some embodiments, the values ​​of m and n in formula (III) can be 1, 2; 1, 3; 2, 2; 2, 3; 3, 2; 3, 1 and 3, 3, respectively. In a preferred embodiment, R1 and R2 are independently selected from H, methyl or ethyl, and Y is a -CH2-CH2- group.

[0019] Method for producing branched copolymers: The branched block copolymer of formula (II) is obtained by first constructing a polymer block A, then a block B, followed by coupling the reactive chain ends with a polyfunctional coupling agent (I). Block A is constructed by polymerizing a first monomer, which may be one or more alkenyl aromatic hydrocarbons, containing at least 90 mole percent of alkenyl aromatic hydrocarbons, using an anionic initiator. A small amount (up to 10 mole percent) of other anionically polymerizable monomers, such as 1,3-dienes, may be present in the first monomer. A second monomer, which contains at least 90 mole percent of one or more 1,3-dienes, is then added and polymerized to obtain block B. The second monomer may contain a small amount (up to 10 mole percent) of another anionically polymerizable monomer, such as an alkenyl aromatic hydrocarbon. The reaction is carried out under an inert gas atmosphere (nitrogen or argon). The anionic initiator is generally an alkyl lithium, such as n-butyl lithium, sec-butyl lithium, n-hexyl lithium, and the like. Suitable solvents are, for example, liquid hydrocarbon solvents, such as liquid lower hydrocarbon solvents (e.g., n-pentane, cyclopentane, n-hexane, cyclohexane, n-heptane, etc.). The reaction can be carried out at temperatures between -50°C and 150°C or 20°C and 100°C. Isoprene polymerizes primarily linearly to form polyisoprene chains with "living" anionic chain ends. After the desired percent conversion of monomer is reached, the polymerization is terminated by adding a polyfunctional coupling agent of formula (I). The resulting product (II), which contains the desired branched block copolymer, can be coagulated into a solid rubber product or converted into other forms, such as an aqueous latex, if desired.

[0020] The branched polyisoprene homopolymer (III) is obtained by polymerizing isoprene using an anionic initiator under conditions similar to those described above, followed by coupling of the reactive chain ends with a polyfunctional coupling agent (I). After the desired percent conversion of the monomers is reached, the polymerization is terminated by the coupling agent (I). The resulting branched block copolymer can be coagulated into a solid rubber product or converted into other forms, such as an aqueous latex.

[0021] The rubber cement obtained above generally has a solid content of 5% by weight to 35% by weight in one embodiment, and 15% by weight to 25% by weight in another embodiment. In some embodiments, the cis content in the polyisoprene chains in the polymers (II) and (III) is in the range of 70% to 95%.

[0022] The temperature-dependent dynamic viscosity profile shows that for a given weight percent concentration, the viscosity of copolymer (II) and homopolymer (III) at comparable molecular weights is significantly lower than that of the corresponding linear copolymers and homopolymers made without coupling agents. In some embodiments, the rubber cement with polymer (II) has a cis content of 70% to 95%, a zero shear viscosity of less than 25,000 mPas, or less than 20,000 mPas, or less than 15,000 mPas, and a weight average molecular weight of 350 kg / mol to 700 kg / mol at a solids content of 15% to 25% by weight. In another embodiment, the rubber cement having polymer (III) has a cis content of 70% to 95%, a zero shear viscosity of less than 80,000 mPas, or less than 75,000 mPas, or less than 70,000 mPas, and a weight average molecular weight of 1,000 kg / mol to 3,500 kg / mol at a solids content of 15% to 25% by weight. The reduction in viscosity of the rubber cement provides a useful advantage in manufacturing set-ups, as it allows for handling of the rubber cement at up to 100% or even higher throughput without the need to oversize processing equipment.

[0023] The rubber solution of coupled polymer (II) or (III) in an organic solvent resulting from the polymerization step can be converted to an aqueous latex by mixing with an aqueous surfactant solution using a high shear mixer. The resulting emulsion is then stripped of solvent to leave less than 0.1% residual solvent. The resulting diluted aqueous latex can be concentrated to 60% rubber by weight by centrifugation or creaming.

[0024] The surfactant used in the emulsification step also stabilizes the latex once formed. The amount of surfactant used generally ranges from 0.5 to 2.0% by weight, based on the weight of the polyisoprene on a dry basis. Anionic surfactants are preferred. Examples of anionic surfactants include sodium dodecylbenzene sulfonate, other alkylaryl sulfonates, alkyl sulfonates, olefin sulfonates (e.g., Cl4 olefin sulfonate), alcohol sulfates such as sodium lauryl sulfate, optionally in combination with one or more other surfactants such as potassium caprylate, polyoxyethylene cetyl / stearyl ether, etc. In one embodiment, the surfactant may be an alkali metal salt of a rosin-type material, including rosin, dimer rosin, disproportionated rosin, and hydrogenated rosin. In another embodiment, the surfactant may also be one or more members selected from alkali metal salts of tall oil fatty acids, such as long chain fatty acids having 12 to 20 carbon atoms.

[0025] characteristics: The latexes of the branched homopolymer (II) and copolymer (III) form very good quality dipped films. The cured films formed therefrom exhibit improved properties. In some embodiments, the cured films exhibit tensile strengths of 20 MPa to 40 MPa, or at least 25 MPa, or at least 30 MPa. In some embodiments, the films also exhibit elongations of 500% to 1250%, or 750% to 1250%, or at least 750%. In some embodiments, the films also exhibit tear strengths of 15 kN / m to 35 kN / m, or at least 20 kN / m. It is also possible to form films having all three properties in the above ranges.

[0026] Use of branched polymers (II) and (III) Latexes containing polymer (II) or (III) are useful for making articles. The method involves dipping a former, free of coagulant or coated with coagulant, into an aqueous latex emulsion at least once to form a thin layer of latex film having individual particles of polyisoprene coupled to the surface of the former. Any former known in the art can be used. This technique can also be used to laminate multiple films of latex particles onto a former to make articles, such as gloves, condoms, etc., and then peel the latex film from the former. EXAMPLES

[0027] Polymer molecular weights (herein referred to as "weight average molecular weight" or "GPC molecular weight") were determined by HMW-GPC (gel permeation chromatography) using polystyrene calibration standards. The median particle size of the latex was determined by laser diffraction using a Beckman Coulter LS13320. The solids content was measured using a Sartorius MA35 moisture meter.

[0028] Coupling efficiency for reactions using multifunctional coupling agents was determined by GPC from the peak integral ratio of uncoupled polymer to higher molecular weight coupled polymer.

[0029] Coagulant solutions / dispersions were prepared by dissolving / dispersing Ca(NO3)2.4H2O (about 14%) and CaCO3 (about 5%) in water at 60°C with stirring. All latexes including the reference sample were compounded with 5 phr of a commercial masterbatch composition (containing sulfur, accelerators and antioxidants) and stabilized with a commercial surfactant. The compound was diluted with demineralized water to obtain the required 30% solids content. The pH was adjusted to 11-11.5 by addition of 1M KOH solution and the compound was stored at ambient temperature with stirring.

[0030] For the coagulant immersion runs, a metal plate was used and a standard immersion procedure was applied. Films were immersed after 1, 3 and 6 days of aging. The mechanical properties of the immersed films were determined using an Instron 3365 tensile tester equipped with a 500N load cell and a long-term extension extensometer according to ASTM D412 / ISO37 (Die C). The tensile properties are shown in Table 5.

[0031] [ Examples 1 to 5 ] Preparation of branched polyisoprene homopolymer.

[0032] Polymerizations were carried out under nitrogen atmosphere in a 10 L stainless steel reactor equipped with agitator, cooling, temperature probe, pressure probe and auxiliary equipment for addition / withdrawal of solvent, monomer and other reagents. Solvents and monomers were purified on Alcoa prior to use. The general procedure was to charge the reactor with 5 L of dry solvent and 450 g of isoprene and heated to 60° C. Dilute s-BuLi solution (0.04 M) was added to the mixture to initiate polymerization. After the required amount of monomer was converted to the required molecular weight, the reaction was stopped by adding a coupling agent (BTMSE or BTESE) in a molar ratio of living chain / coupling agent of 4 / 1. In some cases, this procedure was repeated once or twice until complete conversion of the monomer.

[0033] BTMSE and BTESE were evaluated in isoprene polymerization at different living chain concentrations, and the results are summarized in Table 1. The data show that BTMSE and BTSE have comparable coupling performance.

[0034] [Table 1]

[0035] [ Examples 6 to 8 ] Preparation of branched polyisoprene homopolymers. These were prepared as rubber cements using the procedure described above. The results are shown in Table 2. The control sample was linear (unbranched) polyisoprene made without the use of a coupling agent.

[0036] [Table 2]

[0037] [ Examples 9 to 11 ] Preparation of branched polyisoprene rubber latex. Rubber cement samples were transferred to a bench-scale latex production facility equipped with an in-line high shear mixer with dosing pumps for polymer and soap solutions, and emulsions were produced under standardized emulsification conditions from a fixed ratio of cement and aqueous disproportionated potassium rosinate salt solution. The emulsion was subsequently solvent stripped to obtain a dilute latex, which was concentrated by creaming after the addition of sodium alginate. The results are shown in Table 3. Control-2 is a reference polyisoprene rubber latex prepared from the rubber cement of Control-1 above.

[0038] [Table 3]

[0039] [Table 4]

[0040] Table 4 shows that the tensile properties of the dipped films made from branched polyisoprene made using a multifunctional coupling agent (Examples 12 and 13) are very good and comparable to those seen in the control sample film (Control-3).

[0041] [ Example 14 ] Preparation of branched styrene-isoprene block copolymers.

[0042] Polymerizations were carried out under nitrogen atmosphere in a 10 L stainless steel reactor equipped with agitator, cooling, temperature probe, pressure probe and auxiliary equipment for addition / withdrawal of solvent, monomer and other reagents. Solvents and monomers were purified on Alcoa prior to use. The reactor was charged with 5 L of dry solvent and 400 g of styrene and heated to 60° C. Dilute s-BuLi solution (0.04 M) was added to the mixture to initiate polymerization. After conversion of the styrene, 3 kg of isoprene monomer was charged. After conversion of the second monomer to the required molecular weight, the reaction was stopped by adding BTMSE coupling agent at a molar ratio of living chain / coupling agent of 4 / 1. The results are shown in Table 5. Control-4 is a commercial lot sample of polyisoprene made using GPTS (glycidylpropyltrimethoxysilane) as the coupling agent.

[0043] [Table 5]

[0044] [ Example 15 ] Preparation of branched styrene-isoprene block copolymer latexes.

[0045] The rubber cement samples from Example 14 were transferred to a bench-scale latex manufacturing facility equipped with an in-line high shear mixer with dosing pumps for the polymer and soap solutions. Emulsions were made from a fixed ratio of cement and aqueous disproportionated potassium rosin acid salt solution under standardized emulsification conditions. The emulsions were then stripped to obtain dilute latexes, which were then concentrated by creaming after the addition of sodium alginate. The results are shown in Table 6.

[0046] [Table 6]

[0047] Example 16 represents a dipped film made from the branched styrene-isoprene block copolymer latex of Example 15. Control 5 represents a dipped film made from a branched styrene-isoprene block copolymer latex derived from the block copolymer of Control 4. Table 7 shows that the tensile properties of the dipped film made from the branched styrene-isoprene block copolymer made using a multifunctional coupling agent (Example 16) are very good and comparable to those seen in the control sample film (Control-5).

[0048] [Table 7]

[0049] For the purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions and other numerical values ​​used in this specification and the appended claims are understood to be modified in all instances by the term "about". Thus, unless otherwise indicated, the numerical parameters set forth in the following specification and the appended claims are approximations that may vary depending on the desired properties sought to be obtained. It should be noted that, as used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless expressly and clearly limited to one referent. As used herein, the term "include" and its grammatical variations are intended to be non-limiting, and thus the recitation of items in a list is not intended to exclude other similar items that may be substituted or added to the listed items.

[0050] As used herein, the term "comprising" means including the elements or steps identified after the term, but any such elements or steps are not exhaustive and embodiments may include other elements or steps. Although the terms "comprising" and "including" are used herein to describe various aspects, more specific aspects of the disclosure can be and are disclosed using the terms "consisting essentially of" and "consisting of" in place of "comprising" and "including."

[0051] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed disclosure belongs. The recitation of a type of element, material or other component from which individual components or mixtures of components may be selected is intended to include all possible subtype combinations of the recited components and mixtures thereof.

[0052] The patentable scope is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the language of the claims, or if they contain equivalent structural elements that do not differ substantially from the language of the claims. To the extent not inconsistent with this specification, all citations referenced herein are incorporated by reference.

Claims

1. The polymer block comprises one or more polymer blocks A and one or more polymer blocks B, and has the formula (A-B) ｍ (R １ O) ３－ｍ Si-Y-Si(R ２ O) ３－ｎ (B-A) ｎ A branched block copolymer having the formula: each A block independently comprises at least 90 mole percent styrene, said one or more A blocks forming 8 to 13 weight percent of the total weight of said branched block copolymer; each B block comprises at least 90 mole percent isoprene; each A block independently has a weight average molecular weight of 9 to 15 kg / mole and each B block independently has a weight average molecular weight of 75 to 150 kg / mole; R １ and R ２ are independently H or C １ -C ６ is an alkyl group, and Y is C ２ -C ８ an alkylene group, m and n being independently integers having values ​​in the range of 2<(m+n)≦6; The branched block copolymer has a coupling efficiency (CE) of at least 40%. Branched block copolymers.

2. 2. The branched block copolymer of claim 1, wherein (m+n) has a value of 3 to 6.

3. Y is -CH ２ CH ２ - and R １ and R ２ 2. The branched block copolymer of claim 1, wherein is hydrogen, a methyl group, or an ethyl group.

4. Formula (C) ｍ (R １ O) ３－ｍ Si-Y-Si(R ２ O) ３－ｎ (C) ｎ A branched polyisoprene homopolymer having the formula: each C block is independently a polyisoprene block having a weight average molecular weight of 400 to 1000 kg / mol; R １ and R ２ are independently H or C １ -C ６ is an alkyl group, and Y is C ２ -C ８ an alkylene group, m and n being independently integers having values ​​in the range of 2<(m+n)≦6; The homopolymer has a coupling efficiency (CE) of at least 40%. Branched polyisoprene homopolymer.

5. 5. The branched polyisoprene homopolymer of claim 4, wherein (m+n) has a value of 3 to 6.

6. Y is -CH ２ CH ２ - and R １ and R ２ The branched polyisoprene homopolymer according to any one of claims 4 to 5, wherein is hydrogen, a methyl group, or an ethyl group.

7. 6. The branched polyisoprene homopolymer according to claim 4, wherein the C block has a weight average molecular weight of 500 to 700 kg / mol.

8. 1. A method for preparing a branched block copolymer, comprising: polymerizing a first monomer comprising at least 90 mole percent styrene at a temperature between 0° C. and 100° C. to form a polymer block A; adding a second monomer comprising at least 90 mole percent isoprene and polymerizing at a temperature between 0° C. and 100° C. to form a polymer block B; Formula (R １ O) ３ Si-Y-Si(OR ２ ) ３ adding a polyfunctional coupling agent of Formula (AB) ｍ (R １ O) ３－ｍ Si-Y-Si(R ２ O) ３－ｎ (B-A) ｎ forming a branched block copolymer having Including, each A block independently comprises at least 90 mole percent styrene, said one or more A blocks forming 8 to 13 weight percent of the total weight of said branched block copolymer; each B block comprises at least 90 mole percent isoprene; each A block independently has a weight average molecular weight of 9 to 15 kg / mole and each B block independently has a weight average molecular weight of 75 to 150 kg / mole; R １ and R ２ are independently H or C １ -C ６ is an alkyl group, and Y is C ２ -C ８ an alkylene group, m and n being independently integers having values ​​in the range of 2<(m+n)≦6; The branched block copolymer has a coupling efficiency (CE) of at least 40%. method.

9. The method of claim 8, wherein the branched block copolymer is formed as a rubber cement having a solids content of from 5% to 35% by weight.

10. The rubber cement is A cis content of 70% to 95%; and Weight average molecular weight of 350 to 700 kg / mol 10. The method of claim 9, having the following structure:

11. 1. A process for preparing a branched polyisoprene homopolymer comprising the steps of: polymerizing isoprene in the presence of an anionic initiator at a temperature between 0° C. and 100° C. to form a polymer block C; Formula (R １ O) ３ Si-Y-Si(OR ２ ) ３ adding a polyfunctional coupling agent of Formula (C) ｍ (R １ O) ３－ｍ Si-Y-Si(R ２ O) ３－ｎ (C) ｎ forming the branched polyisoprene homopolymer having Including, each C block is a polyisoprene block independently having a weight average molecular weight of 400 to 1000 kg / mol; R １ and R ２ are independently H or C １ -C ６ is an alkyl group, and Y is C ２ -C ８ an alkylene group, m and n are independently integers having a value in the range of 2<(m+n)≦6, and the homopolymer has a coupling efficiency (CE) of at least 40%; method.

12. The method of claim 11, wherein the branched polyisoprene homopolymer is formed as a rubber cement having a solids content of from 5% to 35% by weight.

13. The rubber cement is A cis content of 70% to 95%; and Weight average molecular weight of 1,000 to 3,500 kg / mol 13. The method of claim 12, comprising:

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