WO2019133338A1

WO2019133338A1 - Hybrid process for improved productivity in bulk polymerization

Info

Publication number: WO2019133338A1
Application number: PCT/US2018/066219
Authority: WO
Inventors: Timothy L. Tartamella; Joseph P. Padolewski
Original assignee: Bridgestone Corporation
Priority date: 2017-12-26
Filing date: 2018-12-18
Publication date: 2019-07-04

Abstract

Processes for carrying out a bulk polymerization are described as including the combination of an organic solvent with a polymerization mixture discharged from a polymerization vessel to extend the polymerization reaction downstream of the vessel. Organic solvent is mixed with the discharged polymerization mixture to form a diluted reaction mixture for increasing conversion of unreacted monomer discharged from the polymerization vessel. The additional organic solvent added can provide temperature control as the diluted reaction mixture is transferred. The organic solvent can be added at various introduction points downstream of the outlet of the polymerization vessel.

Description

HYBRID PROCESS FOR IMPROVED PRODUCTIVITY IN BULK

POLYMERIZATION

TECHNICAL FIELD

[001] The present disclosure relates to a method for the bulk polymerization of conjugated diene monomer, and more particularly, to selective solvent addition to a polymer mixture downstream of a reaction vessel.

BACKGROUND

[002] Polymerization of monomers can be produced by bulk or mass polymerization. Bulk polymerization is often carried out in the absence or substantial absence of any solvent, which has an effect of the monomer itself acting as a diluent and heat sink for the reaction. The lack of solvent results in the bulk polymerization involving primarily monomer and catalyst, which provides the benefit of less contaminants and reactants to remove and separate from the polymerization product downstream in the process. This benefit saves both production time and costs, and potentially a reduction in emissions from a lower solvent need.

[003] Bulk polymerization processes require careful temperature control and effective mixing since the polymerization mixture becomes very viscous. The thick mixture and cement, and lack of solvent, make temperature control difficult. As a result, a polymerization reaction can have hot spots that promote degradation, gelation or discoloration of a polymer product. Further, lack of adequate temperature control can result in run-away reactions which can be dangerous and cost prohibitive. To protect against polymer impurities or undesirable properties, conversion rates can be kept low to control temperatures, which reduces efficiency of the polymerization reaction.

[004] The many advantages provided by bulk polymerization systems make them a continued source for improvements. There is a need to enhance the temperature control of bulk polymerization reactions to improve yield, quality of product and to prevent run-away reactions. Additionally, improvements in overall conversion without having to change the operating parameters of existing bulk polymerization processes are desirable to gain efficiency and improve yield. The various configurations of polymerization vessels, for example, horizontal reactors make arriving at a solution for temperature control not trivial.

SUMMARY

[005] In a first aspect, there is a process for carrying out a bulk polymerization including mixing a diene monomer in the presence of a catalyst in an agitated reaction vessel to polymerize a portion of the diene monomer; extracting a polymerization mixture from the reaction vessel, the polymerization mixture including a polydiene and unreacted diene monomer; combining the extracted polymerization mixture with an organic solvent to form a diluted reaction mixture; polymerizing a portion of the unreacted diene monomer in the diluted reaction mixture in the presence of the combined organic solvent.

[006] In an example of aspect 1, the polymerization conversion of diene monomer in the reaction vessel is maintained below 25 percent.

[007] In another example of aspect 1, the diene monomer is selected from the group of 1 ,3- butadiene, isoprene, l,3-pentadiene, l,3-hexadiene, 2, 3-dimethyl- 1, 3-butadiene, 2-ethyl- 1,3- butadiene, 2-methyl- 1, 3 -pentadiene, 3-methyl-l,3-pentadiene, 4-methyl- l,3-pentadiene, 2,4- hexadiene and a mixture thereof.

[008] In another example of aspect 1, the catalyst is a mixture of two or more catalysts.

[009] In another example of aspect 1, the process further includes agitating the diluted reaction mixture to polymerize a portion of the unreacted diene monomer.

[0010] In another example of aspect 1, the diluted reaction mixture is maintained below 100° C during the polymerization of the portion of the unreacted diene monomer.

[0011] In another example of aspect 1, the organic solvent added to the polymerization mixture is in the range of 5 to 30 percent by weight based on the total weight of the diluted reaction mixture.

[0012] In another example of aspect 1, the polymerizing of the portion of unreacted diene monomer in the diluted reaction mixture is carried out in a transfer pipe.

[0013] In another example of aspect 1, the transfer pipe is connected to the reaction vessel.

[0014] In another example of aspect 1, the transfer pipe being equipped with a dynamic mixer. [0015] In another example of aspect 1, the polymerizing of the portion of unreacted diene monomer in the diluted reaction mixture is carried out in the absence of an open head space.

[0016] In another example of aspect 1, the conversion of unreacted diene monomer in the diluted reaction mixture is maintained below 25 percent.

[0017] In another example of aspect 1, the combined conversion of diene monomer in the reaction vessel and the unreacted diene monomer in the diluted reaction mixture is maintained below 60 percent.

[0018] In another example of aspect 1, the combined conversion of diene monomer in the reaction vessel and the unreacted diene monomer in the diluted reaction mixture is maintained below 30 percent.

[0019] In another example of aspect 1, the polymerizing of the diene monomer in the reaction vessel is carried out in a mixture that contains less than 20 percent by weight of solvent.

[0020] In another example of aspect 1, the polymerizing of the diene monomer in the reaction vessel is carried out in a mixture that contains less than 5 percent by weight of solvent.

[0021] The first aspect may be provided alone or in combination with any one or more of the examples of the first aspect discussed above.

[0022] In a second aspect, there is a process for preparing a polydiene, the process includes combining an organic solvent with a polymerization reaction mixture that is discharged from a reaction vessel, the polymerization reaction mixture includes unreacted diene monomer, catalyst and polydiene, the polydiene is less than 60 percent by weight of the total weight of the polymerization reaction mixture; polymerizing a portion of the unreacted diene monomer in the polymerization mixture in the presence of the combined organic solvent to form a polymer mixture.

[0023] In an example of aspect 2, the polymerization reaction mixture includes less than 5 weight percent of a solvent prior to the combining of the organic solvent.

[0024] In another example of aspect 2, the organic solvent is added to the polymerization reaction mixture in a discharge transfer pipe connected to the reaction vessel.

[0025] In another example of aspect 2, the organic solvent added to the polymerization reaction mixture is in the range of 5 to 30 percent by weight based on the total weight of the polymerization reaction mixture. [0026] In another example of aspect 2, the polymer mixture has a total conversion of diene monomer below 60 percent.

[0027] The second aspect may be provided alone or in combination with any one or more of the examples of the second aspect discussed above, or with any one or more of the examples of the first aspect.

[0028] It is to be understood that various features disclosed in this specification and in the drawings can be used in any and all combinations. By way of non-limiting example the various features may be combined with one another as set forth in the specification as aspects.

DETAILED DESCRIPTION

[0029] The terminology as set forth herein is for description of the embodiments only and should not be construed as limiting the invention as a whole.

[0030] Herein, when a range such as 5-25 (or 5 to 25) is given, this means preferably at least or more than 5 and, separately and independently, preferably not more than or less than 25. In an example, such a range defines independently at least 5, and separately and independently, not more than 25.

[0031] The present disclosure relates to the addition of solvent downstream of a reaction vessel, for instance, a first stage reaction vessel in a bulk polymerization process. The addition of solvent to a polymerization mixture downstream of a reaction vessel has been advantageously found to provide effective temperature control of the mixture, reduce the concentration of monomer in the mixture, reduce viscosity of the mixture and provide for additional monomer conversion in the mixture as it moves or is transferred to a next stage in a bulk polymerization process. The additional conversion is achieved without the need of a second reaction vessel or similar equipment.

[0032] Polymerization as described herein is preferably conducted within a bulk system where monomer can act as a solvent, and which generally refers to the fact that the system includes, for example, less than 50%, in other examples less than 20%, 10%, 5%, or 2% by weight organic solvent based on the total weight of the monomer, polymer, and solvent within the bulk system. In one embodiment, the bulk polymerization is carried out in the substantial absence of an organic solvent or diluent, for example, the polymerization reaction vessel contains less than 20%, 10%, 5%, or 2% by weight organic solvent based on the total weight of the monomer, polymer, and solvent within the polymerization vessel. The substantial absence of solvent can include the absence of an amount of solvent that would otherwise have an impact on the bulk polymerization conditions. In another embodiment, the bulk polymerization may be carried out in the absence of an organic solvent or diluent other than those organic solvents or diluents that are inherent to the raw materials employed. To the extent solvent is not present in any materials charged to the polymerization vessel, the polymerization system can be entirely devoid of organic solvent. In such a case, it is preferred that all recovered monomer vapor that is fed back into the reactor as recycle monomer be free of or substantially free of solvent.

[0033] The term organic solvent or diluent is used herein conventionally, for instance, to refer to organic compounds that do not polymerize or become introduced into the produced polymer product or cement. The organic solvents are generally non-reactive or inert to the catalyst composition employed in the bulk polymerization reaction. Example organic solvents can include aromatic hydrocarbons, aliphatic hydrocarbons, and cycloaliphatic hydrocarbons. Some examples of aromatic hydrocarbons include benzene, toluene, xylenes, ethylbenzene, diethylbenzene, and mesitylene; examples of aliphatic hydrocarbons include n-pentane, n- hexane, n-heptane, n-octane, n-nonane, n-decane, isopentane, isohexanes, isopentanes, isooctanes, 2,2-dimethylbutane, petroleum ether, kerosene, and petroleum spirits; and examples of cycloaliphatic hydrocarbons include cyclopentane, cyclohexane, methylcyclopentane, and methylcyclohexane. Any combination, system or mixtures of these organic solvents is also considered.

[0034] To begin the bulk polymerization process, at least unreacted monomer and catalyst, or a catalyst system, are charged to an agitated polymerization vessel. The polymerization vessel is preferably the first or primary reaction vessel in the bulk polymerization process. The polymerization may be conducted in any conventional polymerization vessel known in the art. In one or more embodiments, the polymerization can be conducted in a conventional stirred-tank reactor, for example a vertical agitated tank, which may optionally be used in conjunction with other types of reactors, such as extruders or devolatilizers. Examples of useful bulk

polymerization processes are disclosed in U.S. Pat. No. 7,351,776, which is incorporated herein by reference. In one or more embodiments, a horizontally disposed reactor can be utilized. Horizontal reactors can offer advanced shaft geometry that provides gentle kneading for minimal shear and maximum heat transfer within the polymerization reaction mixture. Horizontal reactors are suitable for solvent-free living and free-radical polymerization produced in a bulk polymerization process. Horizontal reactor equipment is known in the art and commercially available. For example, horizontal reactor equipment can be obtained from LIST (Switzerland); Coperion Wemer & Phleiderer.

[0035] The monomers that can be polymerized according to the bulk process of this disclosure can vary, for example, they can be volatile monomers and optionally non-volatile monomers. Volatile monomers can include those that are sufficiently volatile to allow heat removal by vaporization of unreacted monomer at a rate equal to the rate at which heat is generated by the polymerization reaction and at a temperature that will allow the formation of the desired polymer product. In one example, the monomers can include those that have a boiling point of at least 10° C, at least 20° C, or at least 30° C lower than the set polymerization temperature or temperature range. In one embodiment, the monomers can devoid of halogens, e.g., vinyl chloride monomers can be excluded.

[0036] Examples of monomers included in the present disclosure include conjugated diene monomers such as 1, 3-butadiene, isoprene, l,3-pentadiene, l,3-hexadiene, 2, 3 -dimethyl- 1,3- butadiene, 2-ethyl- 1,3 -butadiene, 2-methyl- 1, 3 -penta-diene, 3-methyl- l,3-pentadiene, 4-methyl- l,3-pentadiene, 2,4-hexadiene and combinations thereof. In another example, useful olefins include ethylene, propylene, 1 -butene, and l-pentene.

[0037] The catalyst employed in practicing the process of this disclosure preferably includes a coordination catalyst system. One type of coordination catalyst system includes lanthanide- based systems (e.g., neodymium-based catalyst system) and another type includes cobalt-based systems as known in the art. For example, lanthanide catalyst systems are well known in the art as described in U.S. Pat. Nos. 3,297,667, 3,541,063, 3,794,604, 4,461,883, 4,444,903, 4,525,594, 4,699,960, 5,017,539, 5,428,119, 5,064,910, and 5,844,050, which are incorporated herein by reference.

[0038] The bulk production of polymer by using catalyst systems generally employs a catalytically effective amount of a catalyst composition, for example, as mentioned above. The total catalyst concentration included in the polymerization mass depends on the interaction of variables such as material purity, polymerization temperature, polymerization rate or set conversion, desired molecular weight, etc. A specific total catalyst concentration is not disclosed but may be adjusted as known in the art, for example, the catalytically effective amounts of catalyst ingredients should be used. In one example, the amount of the catalyst used can be varied from 0.01 to 2 mmol, 0.02 to 1 mmol, or 0.05 to 0.5 mmol per 100 g of monomer, e.g., conjugated diene monomer.

[0039] Catalyst ingredients, for example those of a lanthanide system, can be charged to the polymerization vessel in a variety of techniques and order of addition. For instance, a small quantity of an organic solvent may be employed as a carrier to either dissolve or suspend the catalyst ingredients to promote catalyst delivery. In another example, monomer, such as conjugated diene monomer, can be used as a catalyst carrier.

[0040] In one or more embodiments, all of the ingredients used for the polymerization can be combined within a single vessel (e.g., a conventional stirred-tank reactor), and all steps of the polymerization process can be conducted within this vessel. In other embodiments, two or more of the ingredients can be pre-combined in one vessel and then transferred to another vessel where the polymerization of monomer (or at least a major portion thereof) may be conducted. In an example, the polymerization vessel is the first reaction vessel or first stage in a bulk

polymerization process. Further conversion of monomer or modification of polymer can be achieved downstream of the polymerization vessel, for example, after the addition of organic solvent as described in the present disclosure. In one or more embodiments, the polymerization vessel can be referred to as a primary or first-stage polymerization reaction vessel, wherein a second reactor can be present in the bulk polymerization process.

[0041] The bulk polymerization is preferably a continuous process or semi-continuous process such that the monomer and catalyst are continually fed to the vessel. However, the manner in which the monomer and catalyst system are charged may vary based upon the catalyst system employed.

[0042] In one or more embodiments, the bulk polymerization process includes a continuous polymerization process whereby catalyst and monomer are continuously fed to the

polymerization vessel or reactor and a portion of the polymerization medium or reacted polymer mixture is continuously removed from the vessel. The polymerization mixture removed from the vessel can include unreacted monomer, polymer, and residual catalyst. [0043] The reaction conditions under which the polymerization proceeds (e.g., in the vessel) may be carried out include maintaining the temperature of the polymerization mixture or diluted reaction mixture within a range from -10° C to 35° C, 0° C to 30° C, or 10° C to 25° C. In other examples, the polymerization can be carried out at a peak polymerization temperature of less than 110° C, less than 80° C, less than 50° C, less than 35° C, less than 30° C, less than 28° C, or less than 25° C. In one or more embodiments, the polymerization reaction within the polymerization vessel can be carried out under anaerobic conditions at low temperatures and at or below the vapor pressure of the monomer at the polymerization temperature. In the presence of an organic solvent, the solvent can impact the vapor pressure at which the process is conducted. Irrespective of the bulk polymerization or copolymerization process carried out, polymerization or copolymerization should be carried out at temperatures sufficiently high to ensure reasonable polymerization or copolymerization rates and avoid unduly long reactor residence times, but not so high as to result in the production of unreasonably high levels of strings and lumps due to excessively rapid polymerization or copolymerization rates.

[0044] The polymerization or copolymerization time will generally range from about 30 minutes to 60 minutes to several hours. Thus, the fresh monomer being fed to the

polymerization vessel can have an average residence time in the range of 30 minutes to 2 hours, and more preferably 30 minutes to 90 minutes before being reacted and/or exiting the vessel in a polymerization mixture.

[0045] The heat of polymerization can be removed by external cooling by a thermally controlled reactor jacket, internal cooling by evaporation and condensation of the monomer through the use of a reflux condenser connected to the reactor, or a combination of the two methods. The polymerization conditions can also be controlled to conduct the polymerization under a pressure, for example, in a range of 0.1 atmospheres to 50 atmospheres, 0.5 atmospheres to 20 atmospheres, or 1 atmosphere to 10 atmospheres. Preferably, the pressures at which the polymerizations are carried out include those that ensure that the majority of the monomer is in the liquid phase.

[0046] The bulk polymerization process is maintained at a relatively low monomer conversion, for instance, to avoid polymer gel formation. The monomer conversion in the polymerization mixture in the polymerization vessel is maintained at less than 30%, less than 25%, less than 20%, less than 15%, or less than 12% before being discharged out of the vessel. The monomer concentration within the polymerization vessel is preferably maintained at greater than 70% by weight, greater than 80% by weight, greater than 85% by weight, or greater than 88% by weight based on the total weight of the polymerization mixture within the

polymerization vessel.

[0047] At the point where a desired monomer conversion has been achieved in the polymerization vessel, a quenching agent can be added to the polymerization mixture in order to inactivate any reactive polymer chains and the catalyst or catalyst ingredients. The quenching agent can be as known in the art, for example a protic compound, which includes, but is not limited to, an alcohol, a carboxylic acid, an inorganic acid, water, or a mixture thereof. In an example, the quenching agent can include a polyhydroxy compound. An antioxidant such as 2,6-di-t-butyl-4-methylphenol may be added along with, before, or after the addition of the quenching agent. The amount of the antioxidant employed may be in the range of about 0.2% to about 1% by weight of the polymer product. The quenching agent and the antioxidant may be added as neat materials or, if necessary, dissolved in a hydrocarbon solvent or conjugated diene monomer prior to being added to the polymerization mixture. Additionally, the polymer product can be oil extended by adding an oil to the polymer, which may be in the form of a polymer cement or polymer dissolved or suspended in monomer. Conventional amounts oil may be added (e.g., 5-50 phr). Useful oils or extenders that may be employed include aromatic oils, paraffinic oils, naphthenic oils, vegetable oils other than castor oils, low PCA oils including MES, TDAE, and SRAE, and heavy naphthenic oils.

[0048] The polymerization mixture, for example as quenched in the polymerization vessel, and the various constituents of the polymerization mixture may be recovered. For example, the unreacted monomer can be recovered from the polymerization mixture such as by distilling it from the polymerization mixture by using techniques known in the art. In one or more embodiments, a devolatilizer may be employed to remove the monomer from the polymerization mixture. Once the monomer has been removed from the polymerization mixture, the monomer may be purified, stored, and/or recycled back to the polymerization process.

[0049] Prior to recovering the polymerization product from the mixture, the polymerization mixture containing at least polymer (e.g., a polydiene), unreacted monomer and catalyst is discharged or extracted from the polymerization vessel. The polymerization mixture is preferably continuously discharged from the vessel as part of the reaction mixture in the vessel that is continuously being mixed to carry out the polymerization reaction. The continuous outflow of polymerization mixture from the vessel is advantageously at a rate equal to or substantially the same as the total inlet flow to the vessel to provide an operation with a constant residence time of the polymerization reaction.

[0050] The polymerization mixture discharged from the polymerization vessel can have varying viscosity, for example, it can have the consistency of heavy oil. The continuous discharge of polymerization mixture is achieved as known in the art, for example, with a device, such as a pump, either entirely or partially integrated with the polymerization reaction vessel. In another example, the discharge device can be a gear device for drawing out the polymerization mixture or a screw positioned in the bottom of the reactor. In the instance the discharge device includes a screw, it can be a single or double screw set up. In another example, a pump can be used such as a positive displacement pump or progressive cavity pump. To control the flow rate of polymerization mixture discharge, one or more devices can be installed at the vessel outlet. The one or more devices can be connected to the polymerization vessel with a pipe or flow connection that supplies the polymerization mixture to the inlet of the device. For instance, the polymerization mixture can be discharged out of the vessel in a transfer pipe connected to an outlet port of the vessel.

[0051] As noted above, the discharged polymerization mixture can have a monomer conversion rate of 30 percent or less, and preferably less than 25 percent. The discharged polymerization mixture also can have a low solvent content as described herein, for example, less than 50%, in other examples less than 20%, 10%, 5%, or 2% by weight organic solvent based on the total weight of the polymerization mixture.

[0052] The discharged polymerization mixture is combined with an organic solvent (e.g. fresh or recycled organic solvent) to form a diluted reaction mixture containing, but not limited to, polymer, unreacted monomer, residual catalyst and organic solvent. In one or more embodiments, additional catalyst is not added to the diluted reaction mixture. Thus, the catalyst in the polymerization mixture discharged from the polymerization vessel is sufficient to catalyze further polymerization of the unreacted monomer present in the diluted reaction mixture.

[0053] The organic solvent present in the diluted reaction mixture can be a combination of the solvent being added to the discharged polymerization mixture and residual solvent already contained discharged mixture. The organic solvent is added to the polymerization mixture exiting the vessel in an amount in the range to 1 to 50, 2 to 40, 3 to 35, 4 to 30 or 5 to 25 or less than 20, 18, 15, 12, 11, 10, 9 or 8 weight percent by weight based on the total weight of the diluted mixture. The diluted reaction mixture can have less than 40 percent, less than 35 percent, less than 30 percent, less than 25 percent or less than 20 percent unreacted monomer by weight based on the total weight of the diluted mixture. The polymerization mixture can exit the polymerization vessel in the temperature range of 25° C to 120° C, 30° C to 110° C or 35° C to 100° C prior to the addition of an organic solvent.

[0054] The organic solvent can be combined with the discharged polymerization mixture at any point from the outlet in the polymerization vessel to the inlet of the next unit operation, for example, a second reactor or subsequent introduction of additional components to the

polymerization mixture. In one or more embodiments, the organic solvent is introduced into the discharged polymerization mixture prior to a discharge device or devices being used to extract polymerization mixture from the vessel. The organic solvent introduction point can be connected to a transfer pipe carrying the discharged polymerization mixture, for example, a transfer pipe that provides the flow path between the outlet of the polymerization vessel and a discharge device (e.g., a pump used for extracting mixture from the vessel). In one or more embodiments, the organic solvent can be combined with the discharged polymerization mixture with conventional techniques, for instance, by pumping, blending or injecting the solvent into the discharged polymerization mixture.

[0055] In another embodiment, the organic solvent can be combined with the discharged polymerization mixture at or near the inlet or within a discharge device. The discharge device can function to combine the solvent by mixing and dispersing the organic solvent in the polymerization mixture as it flows from the polymerization vessel. Preferably, the organic solvent is evenly mixed or dispersed into the discharged polymerization mixture to form the diluted reaction mixture. In one example, the organic solvent can be injected or forced into a pump cavity or pump inlet feed line such that the moving components or parts of the pump mix the solvent and polymerization mixture to form a diluted reaction mixture. For instance, the pump or discharge device can have an inlet pipe that is connected to an organic solvent source. The organic solvent source can be a pipe fluidly connected to the device inlet, for example, a pipe having a valve for controlling organic solvent addition to the polymerization mixture. Alternatively, the organic solvent can be combined with the polymerization mixture in a transfer pipe, e.g., downstream of a discharge device if present.

[0056] In one or more embodiments, the organic solvent can be combined with the discharged polymerization mixture by use of a mixer, for example, a static or dynamic mixing apparatus other than a discharge device if present. For example, the organic solvent and polymerization mixture can be combined together and passed through a mixer to form a diluted reaction mixture. Examples of mixing apparatuses that can be used include, but are not limited to, dynamic mixers and static mixers. Dynamic mixers can include apparatuses with moving or rotating parts (e.g., mechanical or magnetic) that promote mixing of fluids, such as a rotor-stator device or extruder-like mixer. Static mixers can include apparatuses with no moving parts, for instance a local constriction, such as a valve, an orifice, one or more baffles, or nozzle, for statically mixing the organic solvent and polymerization mixture. One or more mixers, or combination of mixers, can be used to combine the organic solvent and discharged

polymerization mixture to form the diluted reaction mixture. The mixers can be arranged in series or in parallel. In one or more embodiments, the organic solvent and discharged polymerization mixture can be passed through one or at least 2, 3, 4 or 5 mixers to form the diluted reaction mixture.

[0057] The addition of organic solvent to the polymerization mixture can provide

temperature control to the discharged polymerization mixture in that the solvent can function as a heat sink for absorbing the heat of polymerization from the diluted reaction mixture. The organic solvent can reduce the concentration of unreacted monomer in the polymerization mixture by formation of the diluted reaction mixture since the organic solvent dilutes the polymerization mixture. The polymerization reaction from the vessel can be extended into the diluted reaction mixture and the presence of the organic solvent can minimize heat build-up in the diluted reaction mixture as it flows from the polymerization vessel. In one or more embodiments, the diluted reaction mixture is formed in a closed system such that no vapor head space is present. In an example, the diluted reaction mixture is formed and located in a transfer pipe as the continued polymerization reaction takes place or until a terminator is added to halt the polymerization. Within the transfer pipe or downstream processing equipment, a terminating or coupling agent, optionally along with an antioxidant, can be added to terminate the

polymerization reaction. As described above, the transfer pipe can be equipped with discharge devices, mixing devices or a combination thereof. The polymerization reaction within the diluted reaction mixture can take place in the transfer pipe as well as in other equipment contained in the pipe or fitted with the pipe.

[0058] Termination of the polymerization mixture upon discharge from the polymerization vessel is typical to avoid high temperatures or hot spots in the mixture that can negatively affect the properties of the final polymer product. The presence of organic solvent in the diluted reaction mixture allows the polymerization reaction to continue outside of the polymerization vessel for a period of time at temperatures lower than compared to mixtures without the solvent addition. That is, the organic solvent provides additional cooling to the mixture to extend the polymerization reaction time, for example, during the transfer of the polymerization mixture to the next phase of the process or addition of a termination agent. The organic solvent can be added to the polymerization mixture at any suitable temperature, for example, in the range of 20 to 50° C, 20 to 40° C, or 20 to 30° C. In one embodiment, the organic solvent can be cooled to provide a chilled solvent stream for additional temperature control of the polymerization mixture, for example, the organic solvent can be added at the temperature range of 0 to 20° C, 5 to 15° C or 10° C.

[0059] The conversion of monomer in the polymerization mixture (i.e. prior to organic solvent addition) and in the diluted reaction mixture (i.e. after addition of organic solvent) can be maintained below 30 percent, less than 25 percent or less than 20 percent. For example, the conversion of monomer in the polymerization mixture being discharged from the reaction vessel can be below 30 percent, less than 25 percent, less than 20 percent or less than 15 percent. In one or more embodiments, the conversion of the remaining unreacted monomer in the formed diluted reaction mixture is less than 20 percent, less than 15 percent, less than 12 percent, less than 10 percent, less than 8 percent or less than 5 percent, which leads to a total monomer conversion from polymerization vessel to final conversion in the diluted reaction mixture of less than 60 percent, less than 50 percent, less than 40 percent, less than 35 percent, less than 30 percent or less than 25 percent.

[0060] The conversion rate can be determined in various ways known to those skilled in the art. For example, the conversion rate can be determined from a measurement performed on a sample of the polymerization mixture or diluted reaction mixture taken at a desirable point in the bulk polymerization process. Gas chromatography can be used to analyze the sample to determine conversion rate of monomer.

[0061] The diluted reaction mixture can be further processed as known in the art. The polymer product from the diluted reaction mixture can be recovered from the diluted reaction mixture by using techniques known in the art. For example, desolventization and drying techniques may be used (e.g., the polymer can be recovered by passing the diluted reaction mixture through a heated screw apparatus, such as a desolventizing extruder, in which the volatile substances are removed by evaporation at appropriate temperatures (100° C to 170° C) and under atmospheric or sub-atmospheric pressure). This treatment serves to remove unreacted monomer as well as any low-boiling solvent. Alternatively, the polymer can also be recovered by subjecting the diluted reaction mixture to steam desolventization, followed by drying the resulting polymer crumbs in a hot air tunnel. The polymer can also be recovered by directly drying the diluted reaction mixture on a drum dryer.

[0062] In one or more embodiments, the polymers prepared according to this disclosure can be vulcanizable. In one or more embodiments, the polymers can have a glass transition temperature (T_g) that is less than 0° C, less than -20° C, or less than -30° C. In one example, the polymers can exhibit a single glass transition temperature. In another example, the polymers may be hydrogenated or partially hydrogenated.

[0063] In one or more embodiments, the polymers of this invention may be cis-l,4- polydienes having a cis-l, 4-linkage content that is greater than 97%, greater than 97.5%, greater than 98.0%, or greater than 98.5%, where the percentages are based upon the number of diene mer units adopting the cis-l, 4-linkage versus the total number of diene mer units. The polymers can have a 1, 2-linkage content that is less than about 1.0%, less than 0.8%, less than 0.7%, or less than 0.6%, where the percentages are based upon the number of diene mer units adopting the 1, 2-linkage versus the total number of diene mer units. The balance of the diene mer units may adopt the trans-l, 4-linkage.

[0064] The number average molecular weight (M_n) of the produced polymers can be from 1,000 to 1,000,000, 5,000 to 200,000, 25,000 to 50,000, or 50,000 to 120,000, as determined by using gel permeation chromatography (GPC) calibrated with polystyrene standards and Mark- Houwink constants for the polymer in question. In one or more embodiments, the molecular weight distribution or polydispersity (M_w/M_n) of produced polymers can be less than 3.0, less than 2.9, less than 2.6, less than 2.5, less than 2.3, less than 2.1, less than 2.0, or less than 1.9.

[0065] The Mooney viscosity (ML_I+4@ 100° C) of the produced polymers can be less than 60, less than 50, less than 40, or less than 25. The gel content of the produced polymers can be less than 20% by weight, less than 10% by weight, less than 7% by weight, less than 5% by weight, less than 3% by weight, or less than 2% by weight, as determined by measuring, at room temperature, the amount of toluene-insoluble material in the polymers.

[0066] The polymers of this disclosure are particularly useful in preparing rubber

compositions that can be used to manufacture tire components. Rubber compounding techniques and the additives employed therein are generally disclosed in The Compounding and

Vulcanization of Rubber, in Rubber Technology (2^nd Ed. 1973).

[0067] All references, including but not limited to patents, patent applications, and non-patent literature are hereby incorporated by reference herein in their entirety.

[0068] While various aspects and embodiments of the compositions and methods have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the claims.

Claims

CLAIMS:

1. A process for carrying out a bulk polymerization comprising:

mixing a diene monomer in the presence of a catalyst in a reaction vessel to polymerize a portion of the diene monomer;

extracting a polymerization mixture from the reaction vessel, the polymerization mixture comprising a polydiene and unreacted diene monomer;

combining the polymerization mixture with an organic solvent to form a diluted reaction mixture;

polymerizing a portion of the unreacted diene monomer in the diluted reaction mixture in the presence of the organic solvent.

2. The process of claim 1, the polymerization conversion of diene monomer in the reaction vessel being maintained below 25 percent prior to the polymerization mixture being extracted.

3. The process of claim 1 or claim 2, the diluted reaction mixture being maintained below 100 degrees Celsius during the polymerization of the portion of the unreacted diene monomer.

4. The process of any one of claims 1-3, the organic solvent added to the polymerization mixture being in the range of 5 to 30 percent by weight based on the total weight of the diluted reaction mixture.

5. The process of any one of claims 1-4, the polymerizing of the portion of unreacted diene monomer in the diluted reaction mixture being carried out in a transfer pipe.

6. The process of claim 5, the transfer pipe being connected to the reaction vessel.

7. The process of claim 5, the transfer pipe being equipped with a mixer that agitates the diluted reaction mixture to polymerize a portion of the unreacted diene monomer.

8. The process of any one of claims 1-7, the conversion of unreacted diene monomer in the diluted reaction mixture being maintained below 25 percent.

9. The process of any one of claims 1-8, the combined conversion of diene monomer in the reaction vessel and the unreacted diene monomer in the diluted reaction mixture being maintained below 60 percent.

10. The process of any one of claims 1-9, the combined conversion of diene monomer in the reaction vessel and the unreacted diene monomer in the diluted reaction mixture being maintained below 30 percent.

11. The process of any one of claims 1-10, the polymerizing of the diene monomer in the reaction vessel being carried out in a mixture that contains less than 20 percent by weight of solvent.

12. A process for preparing a polydiene comprising:

combining an organic solvent with a polymerization reaction mixture being discharged from a reaction vessel, the polymerization reaction mixture comprising unreacted diene monomer, catalyst and polydiene, the polydiene being less than 60 percent by weight of the total weight of the polymerization reaction mixture;

polymerizing a portion of the unreacted diene monomer in the polymerization mixture in the presence of the organic solvent to form a polymer mixture.

13. The process of claim 12, the polymerization reaction mixture comprising less than 5 weight percent of a solvent prior to the combining of the organic solvent.

14. The process of claim 12 or claim 13, the organic solvent being added to the

polymerization reaction mixture in a discharge transfer pipe connected to the reaction vessel.

15. The process of any one of claims 12-14, the polymer mixture having a total conversion of diene monomer below 60 percent.