Patent Application
20080058482
For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in the specification
The term “unmodified polymer chain end” of this disclosure is defined as a polymer chain end derived from an initiator plus a monomer, wherein the initiator reacts with the monomer to polymerize the monomer resulting in the formation of a polymer chain, where the polymer chain end does not include the addition of a subsequent moiety, or modification of the polymer chain end. Schematically, the “unmodified polymer chain end” can be further defined as:
A+Z-I---->I-(A)n-A−Z+
where A is the monomer; Z-I is the initiator; and I-(A)n-A−Z+ is the unmodified polymer chain end.
The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).
Unless otherwise indicated, all numbers expressing quantities or ingredients, measurement of properties and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, their numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains errors necessarily resulting from the standard deviations found in their respective testing measurements.
The method of this disclosure describes making a copolymer with controlled molecular weight and narrow polydispersity in a plug flow manner comprising, in a tubular reactor, polymerizing an anionically polymerizable monomer to form unmodified polymer chain ends, and further reacting the polymer chain ends with at least one (meth)acrylate monomer without synthetically modifying the polymer chain ends in a living anionic polymerization. The method further describes living anionic copolymerization in a stirred tubular reactor with temperature controlled sections.
In a further aspect of this disclosure, “living anionic polymerization” refers to a chain polymerization that proceeds via an anionic mechanism without chain termination or chain transfer. Further discussion of this topic can be found in Anionic Polymerization Principles and Applications, H. L. Hsieh, R. P. Quirk, Marcel Dekker, NY, N.Y., 1996, pages 72-127.
A copolymer of this disclosure is further described, wherein anionically polymerizable monomers are polymerized forming unmodified polymer chain ends, and sequentially polymerizing (meth)acrylate monomers from the polymer chain ends. The copolymerization occurs in a plug flow reactor or tubular reactor having one or more temperature controlled sections.
A copolymer of this disclosure having a formula: I-(A)x-(B)y is described, where I is the initiator, A is an anionically polymerizable monomer, and B is the (meth)acrylate monomer sequentially polymerized by a living anionic polymerization mechanism in a plug flow reactor having one or more temperature controlled sections. The unmodified polymer chain ends of A are unmodified without the addition of a subsequent moiety, thus providing an initiating species for the (meth)acrylate monomer (B). A controlled process for continuously making controlled structure copolymers via anionic polymerization is described. Multi-block copolymers can be contemplated from the disclosure.
In an exemplary embodiment, I is an initiator for polymerizing A as a first block, and B is sequentially polymerized as a second block of the copolymer from the polymer chain ends of A without modification. The unmodified polymer chain ends of A initiate B, and further polymerize B to form a copolymer.
In an exemplary embodiment, no subsequent moiety is added to the polymer chain ends of A prior to initiation, and polymerization of monomer B.
The present disclosure provides for a copolymer with a controlled structure. The process is controlled by a number of factors which include temperature or temperature profile in the reactor, the molar ratio of monomers to initiators, and monomer addition sequence. These factors affect the molecular weight, polydispersity, and structure of the final polymerized organic material, or copolymer.
In another aspect of this disclosure, temperature control, percent solids, rate of monomer addition, and time of mixing in a continuous stirred reactor provide for reproducing the copolymers with a similar molecular weight having a narrower polydispersity index than that obtained without temperature control. In a stirred tubular reactor, the exothermic nature of anionic polymerizations can be controlled, thus reducing the complications of side reactions and solution phenomena commonly often associated with the production of copolymers containing polar monomers.
The average molecular weight of the resultant polymeric material is established by controlling the monomer to initiator ratio. This ratio is established by controlling the respective monomer and initiator flow rates. Narrow molecular weight distributions can be further achieved by controlling the temperature of the reaction mixture. Avoiding high temperatures minimizes unwanted side reactions that can result in polymer chains having differing molecular weight averages.
Polydispersity can be influenced by the reaction kinetics of the reaction mixture and the minimization of side reactions, especially when temperature sensitive monomers are present. Maintaining optimum temperatures in each zone of the reactor can positively influence reaction kinetics. Maintaining optimum temperatures can also positively affect the solution viscosity, and the solubility of the reactants.
The structure of the polymerized copolymer is determined by the sequence of monomer addition(s). Homopolymers are formed when only one monomer is polymerized, and random copolymers are formed when more that one monomer type is introduced simultaneously. Segmented block copolymers are formed when more than one monomer is polymerized, where a first monomer is polymerized to form a first block, and a second monomer is sequentially polymerized from the first block.
In an exemplary embodiment of this disclosure, the anionically polymerizable monomer is polymerized to form a first block having unmodified polymer chain ends, where the polymer chain ends initiate the polymerization of the (meth)acrylate monomers to form a second block of the copolymer.
In an exemplary embodiment of this disclosure, the temperature profile of the reactor can be controllable over time, and that the reaction mixture be impelled in a relatively plug flow manner through a tubular or plug flow reactor. This allows the reaction mixture in the reactor at a given location to be subjected to the same reaction conditions as those encountered by previous and subsequent reaction mixture portions as they pass by the same location.
Maintaining temperature control and movement of the reaction mixture in a substantially plug flow manner are complicated by the exothermic nature of the type of reaction being performed, i.e., anionic polymerizations. The use of anionic polymerization methods for the production of block copolymers containing polar monomers may be complicated by side reactions and solution phenomena. Proper mixing and temperature control promote the ability to reproduce the same materials, such as having a similar average molecular weight, and having a narrower polydispersity index (PDI) than those obtained without proper temperature control. The PDI of the copolymers of this disclosure can be less than 3, more preferably can be less than 2, and most preferably can be less than 1.5.
One suitable plug-flow, temperature-controlled reactor is a plug flow reactor (hereinafter “PFR”) or tubular reactor. In one aspect, the tubular reaction can be a stirred tubular reactor. Any type of reactor, or combination of reactors, in which a reaction mixture can move through in a substantially plug flow manner is also suitable. In an aspect of the disclosure, “plug flow manner” refers to a reactor where the fluid moves in a coherent fashion, and the residence time can be substantially the same for all fluid components. Combinations of PFRs, including combinations with extruders, are also suitable. Regardless of the type of reactor chosen, the temperature or temperature profile of the reactor is suitably controllable to the extent that a plug of the reaction mixture in a particular location within the reaction zone (i.e., the portion of the reaction system where the bulk of polymerization occurs) at time t1 will have substantially the same temperature, or temperature profile as another plug of the reaction mixture at that same location at some other time t2. The reaction zone can include more than one temperature-controlled zone of the reactor. PFRs can provide for substantially plug flow movement of the reaction mixture, and can be configured such that good temperature control can be attained, and are therefore useful in getting the average molecular weight of the polymer product to remain close to a target value, i.e., have a narrow polydispersity range.
In one aspect, the term “residence time” refers to the time necessary for a theoretical plug of reaction mixture to pass completely through a reactor.
In a continuous polymerization process of the present disclosure, at least one anionically polymerizable monomer, and an initiator are present in the reaction mixture. The function of the initiator is to generate anions in the presence of an anionically polymerizable monomer, which further polymerizes, and forms unmodified polymer chain ends. The polymer chain ends, without synthetic modification, react with the (meth)acrylate monomers to form a second block of a copolymer in a living polymerization.
Anionically-polymerizable monomers are those that generally have a terminal unsaturated carbon-carbon bond. Examples include styrenics, dienes (e.g., aliphatic dienes, cycloaliphatic dienes, and combinations thereof), [n]metallocenophanes, and combinations thereof, as well as anionically-polymerizable polar monomers. Suitable vinyl aromatic monomers further include, but are not limited to, for example, styrene, p-methylstyrene, methyl-3-styrene, ethyl-4-styrene, dimethyl-3,4-styrene, trimethyl-2,4,6-trimethylstyrene, tert-butyl-3-styrene, dichloro-2-6-styrene, vinyl naphthalene, vinyl anthracene, and combinations thereof. Polymerizable dienes include, but are not limited to, for example, isoprene, isoprene-derivatives, butadiene, 1,3-pentadiene, cyclohexadiene, and combinations thereof.
In an exemplary embodiment of this disclosure, isoprene is an anionically polymerizable monomer for forming the first block of the copolymer with unmodified polymer chain ends.
In an exemplary embodiment of this disclosure, styrene is an anionically polymerizable monomer for forming the first block of the copolymer with unmodified polymer chain ends.
Suitable monomers include those that have multiple reaction sites. For example, some monomers may have at least two anionically-polymerizable sites. Another example is a monomer that has at least one functionality that is not anionically-polymerizable in addition to at least one anionically polymerizable site. Such functionalities are known in the art and include those that are reactive by the following mechanisms: condensation, ring opening, nucleophilic displacement, free radical coupling, photolytic coupling, and hydrosilylation.
Initiators particularly useful with specific monomers are well known in the art. Initiators compatible with the exemplary monomer systems discussed herein are summarized in Hsieh et al., Anionic Polymerization: Principles and Practical Applications, Ch. 5, and 23 (Marcel Dekker, New York, 1996). Typical initiators for anionically polymerizable monomers include alkyl and aryl lithiums. These initiators may include, but are not limited to, for example, n-butyl lithium, sec-butyl lithium, tert-butyl lithium, fluorenyl lithium, naphthyllithium, phenyllithium, p-tolyllithium, and combinations thereof.
In an exemplary embodiment of this disclosure, sec-butyl lithium is an initiator for an anionically polymerizable monomer creating unmodified polymer chain ends.
In an exemplary embodiment, the living copolymerization of (meth)acrylates provides for (meth)acrylate monomers, which are polymerized by the unmodified polymer chain ends of a first block to form the second block of the copolymer. In this disclosure, the reactivity of the unmodified polymer chain ends in a plug flow reactor provides for reduced reactivity prior to the addition of (meth)acrylate monomer. The reduced reactivity of the unmodified polymer chain ends reduces the propensity of the anionic polymer chain end to react with the ester carbonyl group of the (meth)acrylate monomers.
In order to reduce the propensity for side reactions during the anionic polymerization of (meth)acrylates, which offer dual functionalities, typically, the basicity of the initiator or polymer chain end is reduced. The anionically polymerizable monomers are substantially consumed prior to the addition of monomers for the formation of a sequential block of the copolymer. For copolymers having (meth)acrylate monomers as the sequential block of a copolymer, the polymer chain ends are typically reacted with a subsequent moiety or reagent, such as α-methylstyrene or 1,1-diphenylethylene, to reduce the anionic polymer chain end reactivity. Typically, α-methylstyrene, or 1,1-diphenylethylene are added to the polymer chain ends, wherein the reagent lacks the propensity to self propagate or polymerize, thus resulting in a chain end containing from 1 to 2 reagent units prior to the addition of the (meth)acrylate monomer. The moiety can be reacted with the growing polymer chain end prior to the initiation and polymerization of (meth)acrylates.
Anionically-polymerizable polar monomers, such as alkyl(meth)acrylates, alkylfluoro(meth)acrylates, branched (meth)acrylates, cyclic (meth)acrylates, and aromatic (meth)acrylates are generally temperature sensitive. In one aspect, t-butyl acrylate is an anionically polymerizable polar monomer. These monomers tend to undergo a significant number of side reactions under adiabatic polymerization conditions, where the initial temperature of the reaction mixture is relatively low, typically well below 40° C., and more commonly below 0° C., and even more commonly at −78° C. Temperature sensitive monomers are susceptible to significant side reactions of the living polymer chain ends with reactive sites, such as ester carbonyl groups, with chain transfer, back-biting, and termination occurring on the same, or a different, polymer chain as the reaction temperature rises. Without a temperature-controlled system, the initial temperature typically must be low to avoid having the exothermic reaction result in a temperature so high that it causes significant side reactions. These side reactions generally result in an undesirable broadening of the polydispersity and lack of molecular weight control for the copolymer that is formed.
More specifically, (meth)acrylate polar monomers include, but are not limited to, for example, tert-butyl(meth)acrylate, methyl(meth)acrylate, isodecyl(meth)acrylate, n-C12H25 (meth)acrylate, n-C18H37(meth)acrylate, allyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, isostearyl(meth)acrylate, isobornyl(meth)acrylate, cyclohexyl(meth)acrylate, phenoxyethyl (meth)acrylate, benzyl(meth)acrylate, and combinations thereof.
In another embodiment, two or more meth(acrylate) monomers may form a triblock copolymer. In one aspect, a first (meth)acrylate monomer is selected from the group comprising tert-butyl(meth)acrylate, methyl(meth)acrylate, isodecyl(meth)acrylate, n-C12H25 (meth)acrylate, n-C18H37(meth)acrylate, allyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, isostearyl(meth)acrylate, isobornyl(meth)acrylate, cyclohexyl (meth)acrylate, phenoxyethyl(meth)acrylate, and benzyl(meth)acrylate, which can self propagate (e.g., polymerize) with the unmodified polymer chain ends, followed by the addition of a second (meth)acrylate resulting in a A-B-C triblock structure. In a further aspect, a second meth(acrylate) monomer can include monomers such as glycidyl (meth)acrylate, dimethylaminoethyl(meth)acrylate, N-methyl (perfluorobutanesulfonamido)ethyl(meth)acrylate, and combinations thereof, achieving an A-B-(C/D) triblock copolymer structure, wherein C/D is a random copolymer.
In another embodiment, C/D can be a mixture of monomers selected from the group comprising tert-butyl(meth)acrylate, methyl(meth)acrylate, isodecyl(meth)acrylate, n-C12H25 (meth)acrylate, n-C18H37(meth)acrylate, allyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, isostearyl(meth)acrylate, isobornyl(meth)acrylate, cyclohexyl (meth)acrylate, phenoxyethyl(meth)acrylate, benzyl(meth)acrylate, glycidyl(meth)acrylate, dimethylaminoethyl(meth)acrylate, and N-methyl(perfluorobutanesulfonamido)ethyl (meth)acrylate.
In an exemplary embodiment of this disclosure, methyl(meth)acrylate is polymerized with the unmodified polymer chain ends of the first block of the copolymer.
In an exemplary embodiment of this disclosure, t-butyl(meth)acrylate is polymerized with the unmodified polymer chain ends of the first block of the copolymer.
Controlled architecture polymer structures formed by the process of the present disclosure include those made with temperature sensitive monomers, resulting in narrow polydispersities at temperatures preferably between −78° C. and 250° C., more preferably −40° C. to +120° C., and most preferably, between −40° C. and 50° C. Because the present disclosure allows for temperature control of the system in a tubular reactor, the initial temperature of the reaction mixture can be maintained at or near the desired temperature throughout the reaction. The reaction mixture can initially be at room temperature or at another desired temperature instead of starting at a low temperature and ending at a high temperature after the exothermic reaction. Further, in a living polymerization for making a copolymer, factors such as temperature of the sections or zones, percent monomer solids in the reactor, rate of addition of the monomers and initiators to the reactor, and mixing of the reaction components within the PFR need to be considered.
The copolymer of the present disclosure can be formed from temperature sensitive monomers, non-temperature sensitive monomers, or a combination of one or more types of temperature sensitive monomers, and one or more types of non-temperature sensitive monomers. In this disclosure, the temperature sensitive monomers can be sequentially polymerized from the polymer chain ends of a first block, which has not been synthetically modified. The temperature sensitive polar monomers can be anionically polymerized sequentially from the first block of the copolymer.
The ratio of monomer to initiator determines the average molecular weight of the resulting polymer. Because the polymerized monomers of the present disclosure have “living” ends, subsequent monomers may be added, without additional initiators when a block copolymer is being made. In this embodiment, it has been found that unmodified polymer chain ends can be used to sequentially initiate and polymerize a second block of a copolymer, more specifically (meth)acrylate monomers in a tubular reactor.
In an exemplary embodiment of this disclosure, the polymer chain ends of the anionically polymerizable monomers are unmodified.
In another aspect, the anionic initiating species of the unmodified polymer chain ends generates an intermediate species, without modification by 1,1-diphenylethylene or α-methyl styrene, to typically achieve a lower pKa, which initiates the (meth)acrylate monomer to form the second block of the copolymer. Other reactive moieties may be considered to lower the pKa of the polymer chain end.
The term pKa is the negative logarithm of the acid dissociation constant, Ka, where pKa=−log10Ka. Ka is obtained from the activity ratio of the conjugate base and the conjugate acid multiplied with the proton activity.
In order to form a copolymer having a subsequent (meth)acrylate containing block, the conjugate acid pKa value of the initiating species may be substantially the same or smaller than the pKa of the conjugate acids corresponding to the initiating carbanionic polymer chain ends of the anionically polymerizable monomer as described in Quirk, R. P., Applications of Anionic Polymerization Research, ACS Symposium Series #696, 1998, pages 6-19.
The continuous copolymerization of (meth)acrylates of this disclosure can be described with at least one or more controlled temperature zones. Temperature control and flow of the reaction mixture in a plug flow reactor, and subsequent addition of (meth)acrylate monomer is accomplished without synthetic modification, to influence the pKa of the carbanionic polymer chain ends of the first block of the copolymer. Controlled molecular weight, and polydispersity of the copolymer can be accomplished with the unmodified initiating species of the polymer chain ends of the first block.
This disclosure provides for the synthesis of, random and blocks copolymers, star-branched random and block copolymers, and end-functionalized polymers via living anionic solution polymerizations. In an additional aspect, tri-block and multiblock copolymers can be synthesized in a living polymerization.
In living systems, polymerization can be initiated by reaction of an anionic source (e.g., initiator), with anionically polymerizable monomers. These reactions are typically highly exothermic and air/moisture sensitive reactions. These reactions may proceed until nearly all of the residual monomer is consumed. Upon nearly complete or complete monomer consumption, the “living” and hence reactive chains may be terminated or treated with the same or other anionically polymerizable monomers at a later point along the reactor profile to form higher average molecular weight polymers. These anionically produced “living” chains can also serve as precursors to a number of different polymer structures.
An example of a living system in a plug flow or tubular reactor comprises mixing an alkyl lithium reagent as an anionic initiating source with anionically polymerizable monomers, such as styrene or isoprene, in the first zone of reactor 40 of
In another embodiment of this disclosure, mixing different types of monomers in the first zone of reactor 40 can produce random copolymers, formed by random initiation and propagation of the constituent monomers.
Star or hyperbranched materials can be synthesized by addition of difunctional reagents to living anionic polymerizations. The difunctional monomers can couple polymer chains resulting in branching. Alternatively, living anionically produced chains can be coupled by multifunctional or multisite terminating agents to produce starbranched materials. Suitable difunctional reagents include divinyl benzene (DVB), vinylbenzyl chloride and di(meth)acrylic monomers such as hexanediol di(meth)acrylate (HDDMA), which may be used as comonomers for the production of starbranched materials.
In another embodiment, the reaction mixture comprises a solvent. The function of the solvent is to facilitate mobility of the monomers, initiator, and the polymer produced as well as serving as a partial heat sink.
Solvents compatible with specific monomers are well known in the art. Solvents compatible with the exemplary monomer systems of this disclosure are summarized in Hsieh et al., Anionic Polymerization: Principles and Practical Applications, Ch. 5, and 23 (Marcel Dekker, New York, 1996). One or more solvents can be used as a reaction solvent system. In an exemplary embodiment, the amount of solvent is sufficient to solubilize the reaction components (including additional monomer added downstream) and the resulting product. In an exemplary embodiment, the total monomer concentration in a solvent is from 10 to 80 weight percent. In an exemplary embodiment, the (meth)acrylate monomer concentration ranges from 1 to 50 weight percent. With polar monomers, typical solvents include, but are not limited to, for example, benzene, ethylbenzene, cyclohexane, toluene, tetrahydrofuran and xylene. Co-solvents such as dialkyl ethers, (diethyl ether, dibutyl ether), tetrahydrofuran, or tetramethylene diamine may also be used for both polar and nonpolar monomer systems.
Anionically polymerized polymers can be terminated by adding reagents for terminating a “living” anionic polymerization. Suitable terminating agents include oxygen, water, hydrogen, steam, alcohols, ketones, esters, amines, hindered phenols, and combinations thereof.
Anionic polymerizations are not readily amenable to the polymerization of monomers containing relatively acidic, proton donating groups such as amino, hydroxyl, thiol, carboxyl or acetylene functional groups. Methodologies to include such functional groups typically involve the use of protected terminating agents (Afn), derived by the use of suitable protecting groups that are stable to the conditions of anionic polymerization and can be readily removed by post polymerization treatments. Such suitable terminating agents include, but are not limited to, for example, chloroorganosilyalkenes, chlorosilanes (ClSiMe2NMe2, ClSiMe2OR, ClSiMe2H), 1,3-bis(trimethylsilyl)carbodiimmide, 1-(3-bromopropyl)-2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentane, (3-bromopropoxy)-tert-butyldimethylsilane, 2-(3-brompropoxy)tetrahydro-2H-pyran, and combinations thereof.
Protected terminating agents with multiple reactive sites may be used to couple two living polymer chains thereby increasing the average molecular weight. Suitable multifunctional or multisite protected terminating agents include, but are not limited to, for example, dimethyl phthalate, phosphorus trichloride, methyltrichlorsilane, silicon tetrachloride, hexachlorodisilane, and 1,2,3-tris(chloromethyl)benzene, dichlorodimethylsilane, dibromo-p-xylene, dichloro-p-xylene, bischloromethylether, methylene iodide, 1-4-dibromo-2-butene, 4-diiodo-2-butene, and 1,2-dibromoethane.
In another embodiment, the protected terminating agent becomes attached to the polymerizing end of a said chain, and may be multifunctional in nature. The multifunctional terminating agent is capable of terminating multiple chains, thereby producing a star-like macromolecule.
In one aspect of the present disclosure, a continuous process for producing anionically polymerized copolymers having controlled structures, includes, for example, random and block copolymers, star-branched random and block copolymers, and end-functionalized copolymers.
The continuous process for making a copolymer of this disclosure in a plug flow manner of the stirred tubular reactor is described. The reaction mixture flows through the reactor, where the anionically polymerizable monomer reacts with an initiator, followed by polymerization of the monomer to form a first block. Consumption of the monomer yields unmodified polymer chain ends. The unmodified polymer chains ends are used for the subsequent initiation of temperature sensitive polar monomers. The unmodified polymer chain ends initiate the polymerization of at least one (meth)acrylate monomer to form a copolymer.
In one embodiment of this disclosure, as illustrated in
As illustrated in
As illustrated in
In addition to temperature control of the sections or zones, reactor 40 has the capability to impel, from the input end of the reactor 40 to its output end, in a substantially plug flow manner the reaction mixture. The reaction mixture can be impelled through reactor 40 by an external means such as a pressure feed, or by an internal means.
An exemplary embodiment of a continuous stirred tubular reactor is illustrated in
Referring again to
Optionally, any or all of the flanges may be further equipped with a flange inlet port 106, that is in fluid communication with the reaction chamber. A flange inlet port 106 may provide an opportunity to add components to the reaction mixture. The flange may also have an analytical port 107 as an optional port for the removal of an aliquot or reaction mixture for subsequent analysis, other types of monitoring of the reaction mixture at various points in the reaction chamber, or both. In one aspect of this disclosure, the flange inlet port 106 may be designed as to allow for substantial radial mixing with a feedblock of
In another embodiment of this disclosure, the feedblock 200 as illustrated in
As illustrated in
In one aspect of the disclosure, purification methods include sparging the monomer(s) with an inert gas (e.g., N2), and passing the combined stream of the monomer(s) and any solvent to be used in the initiator solutions through one or more purification columns. Such columns are packed with particles that selectively remove dissolved deactivating species. For example, molecular sieves and a variety of desiccants can remove H2O while activated copper can remove O2 from fluids coming into contact therewith. Those skilled in the art are aware of the importance of removal of H2O and O2 from reaction mixture components as well as numerous ways of accomplishing the same. Low water and oxygen concentrations, i.e., below 10 ppm, ensure that very little initiator or “living” polymer chain is deactivated. Polymerization inhibitors may be removed from monomers by treatment with basic alumina (Al2O3) chromatographic materials, as is known in the art. Initiator(s), monomer(s), and solvent(s) are then mixed at the inlet of reactor 40, or are introduced through separate inlets and mixed at some point downstream from the inlet end of reactor 40.
In one embodiment illustrated in
In an embodiment, a branching agent can be a multifunctional anionically polymerizable monomer or multifunctional terminating or coupling agent, where the addition of monomer results in the formation of a star-branched polymer.
Although a pressure feed (i.e., a pressurized tank with a control valve) can be used for each component, the components typically are impelled by pump mechanisms, though this is not essential. A wide variety of pump designs can be useful in the present disclosure as long as the pump seal is sufficient to exclude oxygen, water, and other initiator deactivating materials from feed supply units 12a-12g. Examples of potentially useful pumps include gear pumps, diaphragm pumps, centrifugal pumps, piston pumps, and peristaltic pumps. Selection of a suitable pump for a particular system is within the knowledge of one or ordinary skill in the art.
Some initiator systems are delivered to reactor 40 in the form of a slurry, i.e., a suspension of small particles in a solvent. For example, s-butyl lithium can be mixed in cyclohexane for use with diene and vinyl aromatic monomers. Such slurry initiator systems can settle in feed supply unit 12f and in pump 16f unless care is taken. A mechanism to keep the initiator system well mixed in feed supply unit 12f can be used. Examples of such mechanisms include multiple agitator blades and a pump-around loop. Additionally, such initiator systems can be impelled to reactor 40 by a pump 16f, that can easily handle slurries. Examples of suitable pumps include peristaltic and diaphragm pumps. Tubing used to transport the reaction mixture components to reactor 40 from 12a-g must be capable of handling high pressure and of substantially excluding materials capable of deactivating the initiator being used, e.g., water and oxygen. Useful tubing materials include stainless steel, polypropylene, polyethylene, and polytetrafluoroethylene. When a peristaltic pump is used as one of pumps 16a-16g, the tubing can be a fluoroelastomer.
In an exemplary embodiment, the rate at which pumps 16a-16g impel the reaction mixture components to reactor 40 illustrated in
In one embodiment, the residence time of the copolymer made by the process can range from 30 seconds to 12 minutes per section. The residence times of the reaction mixture and (meth)acrylate monomers can vary as a function of the number of sections and the size of the reactor.
Reactor 40 can be any type of reactor or reactor design that allows for substantially plug flow of a reaction mixture having a total monomer concentration of 10 to 80 weight percent, as well as allowing proper temperature control of the reaction mixture. The reactor can have multiple downstream feed stream injection points. PFRs are further described in U.S. Pat. Nos. 6,448,353; 6,969,491; 6,716,935; 6,969,490; and 7,022,780, herein incorporated by reference.
In a further embodiment of this disclosure, the ability to add reagents at numerous points along the reaction pathway in a PFR makes the PFR well suited for living polymerizations, and functionalizing the end group structure of a polymer. Shorter residence times can result in less waste during changeover (e.g., a change in the type(s) of monomer(s), solvent(s) or initiator(s) being used, the ratio of monomers, the amount(s) of initiator(s), the targeted average molecular weight) and a substantially reduced response time to process condition changes.
In an exemplary embodiment, the reactor has one or more independently temperature controlled zones. A reactor with a single temperature-controlled zone may be used but, if fewer than about two zones are used, the molecular weight and molecular weight distribution of the resulting copolymer tend to be broader than desired. Notwithstanding the foregoing, when the copolymer of this disclosure is being made, the reactor can have at least one independently temperature controlled zone with or without the addition of pre-heaters.
Prior to being used in the process of the present disclosure, reactor 40 may be pretreated. Commonly pretreating is accomplished by filling reactor 40 with a dilute solution of initiator and allowing it to stand for, e.g., about 24 hours. Thereafter, a gaseous sparge and suitable anhydrous solvent can be used to remove the pretreating mixture.
Reaction mixture components can be delivered from purification unit 14 and the initiator feed storage unit 12g to reactor 40 by means of pressure created by pumps 16a-16g. Before reaching reactor 40, the reaction mixture components optionally can pass through heat exchanger 30.
In an embodiment, optional heat exchanger 30 can be used when reactor 40 is to be run at a temperature above or below the temperature of the reaction mixture components prior to being introduced into reactor 40. For example, where the first section of reactor 40 is maintained at or near a temperature of 50° C., the reaction mixture preferably enters the first section of reactor 40 at or near 50° C. Where the reaction mixture components are individually maintained near room temperature (e.g., approximately 25° C.), optional heat exchanger 30 can be a preheater that raises the temperature of the combined reaction mixture components to approximately that of the first section of reactor 40. The monomer may be initially at room temperature or less than room temperature prior to entering the reactor.
Reactor 40 can be surrounded by a jacket containing a circulating heat transfer fluid (e.g., water, steam, liquid nitrogen), which serves as the means to remove heat from or add heat to reactor 40 and the contents thereof. To aid in temperature control, temperature sensing devices (e.g., thermometers and/or thermocouples) can extend into reactor 40 to measure the temperature of the reaction mixture passing thereby. Based on the output of the temperature sensing devices, the temperature and circulation rate of the heat transfer fluid contained in the jacket can be adjusted manually or automatically (e.g., by means of a computer controlled mechanism).
By dividing reactor 40 into sections and individually controlling the temperature of each section, the reaction mixture can be made to encounter a temperature profile. For example, each section of reactor 40 can be maintained at the same (or nearly the same) set temperature, thus ensuring that the reaction mixture encounters a steady temperature profile. This can be accomplished by having separate jackets around each section, or having some other means to independently control the temperature of each section. Cyclic temperature profiles also are possible. Alternatively, each successive section of reactor 40 can be maintained at a temperature higher (or lower) that the previous section, thus ensuring that the reaction mixture encounters a rising (or falling) temperature profile.
The temperatures at which the zones are maintained will depend on the materials being used and the reaction desired, but in general, the system can be operated at temperatures between −78° C. and 250° C., more preferably −40° C. to +120° C., and most preferably, between −40° C. and 50° C. In one aspect, the temperature zones of the system can be operated from −78° C. to 60° C. when used with polar monomers. For a given reaction, the temperature of the reaction mixture can be usually maintained within a range narrower than these operating ranges. The objective of controlling the temperature of each section can be to ensure that the temperature of the reaction mixture can be at a temperature that can be conducive to the desired reaction and will not promote unwanted side reactions. If a reactor were long enough it can be possible that the reaction mixture temperature could be adequately controlled with a single jacketed zone; however, such a system would be not be particularly efficient.
If desired, during the course of an ongoing polymerization, the temperature profile can be changed by changing the temperature of one or more of the sections. Changing the temperature profile can be one way to affect the molecular weight distribution of an organic material for which the polymerization behavior of the monomers can be altered by temperature. Such monomers include (meth)acrylates as described herein. For example, when a reaction is exothermic, side reactions result in polymers with varying molecular weights which can be limited by controlling the temperature of the reaction mixture. Typically, the temperature of the reaction mixture will increase whenever monomer is added and polymerization takes place. Therefore, an exothermic reaction may occur when a first monomer is initially fed into the reactor. Another exothermic reaction may occur downstream when a second monomer is added after the first monomer is partially or fully converted and the mixture may have cooled from the initial reaction.
In an exemplary embodiment, the temperature of the temperature controlled section for polymerizing the (meth)acrylate monomer is lower than the section for polymerizing the anionically polymerizable monomer.
In addition to temperature control, another feature of reactor 40 is the capability to impel, from the input end of reactor 40 to its output end, in a substantially plug flow manner, the reaction mixture contained therein. This means that a given segment of a reaction mixture continues down the length of reactor 40 with about the same velocity profile as a segment traveling there through either earlier or later. The manner in which a reaction mixture can be impelled through reactor 40 can be by an external means such as a pressure feed (e.g., a pump) or by an internal means (e.g., a screw in an extruder). Plug flow can be assisted by lateral mixing means (e.g., radial paddles in a PFR).
In one aspect, the reaction mixture has a total monomers (anionically polymerizable monomer(s) and (meth)acrylate monomer(s)) concentration of 10 to 80 weight percent, and more typically has a concentration of 25 to 60 weight percent. These concentrations allow the reaction mixture to be more easily impelled downstream as polymer forms and increase the viscosity of the reaction mixture.
In an embodiment, reactor 40 can be a stirred tubular reactor (PFR), which may consist of a series of cylinders joined together to form a tube as illustrated in
The shaft can be made from a variety of inert metals, one example being stainless steel. Where a corrosive initiator such as alkyllithium can be used in the PFR, the shaft can be made from a corrosion resistant stainless steel (e.g., 316 L stainless steel).
Where the shaft can be hollow, it can be cooled (if desired). This can be accomplished by running a heat transfer fluid, such as water, through it.
To assist in maintaining substantially plug flow through a PFR, the paddles can be designed so as to minimize reaction mixture build-up on the paddles and shaft. Build-up often occurs in stagnant regions, which are normally located on the walls of the tube or on the downstream surfaces of paddles, and can result in reduced heat transfer and plugging of the PFR. PFRs are cleaned less frequently than batch reactors (and because long term continuous operation can be desirable), build-up can result in a loss of residence time. Having to rid a PFR of build-up can result in a loss of production time and the introduction of solvents into the PFR can deactivate catalyst during future runs. Build-up and the problems resulting therefrom can be minimized by proper paddle design.
Optimization of paddle design can involve the use of cylindrical and/or streamlined designs as well as providing for narrower wall clearances toward the outer end of the PFR. Use of paddles with flexible tips (e.g., made from an elastomer such as polytetrafluoroethylene) can assist in scraping the walls of the tube. Alternatively, build-up can be minimized by periodically alternating the direction of paddle rotation. Direction can be alternated every few seconds or minutes (or whatever time frame seems to best inhibit build-up with a particular reaction mixture).
Where a gaseous monomer can be used, the PFR tube can be made from a very strong material (e.g., stainless steel) that can withstand the elevated pressure necessary to assure solubility of the gaseous monomer.
PFR s and combinations of PFR s have been mentioned as examples of useful designs for reactor 40. They are meant to be merely illustrative. One skilled in the art will recognize, using the teachings of the present disclosure that, other designs (e.g., those that allow for substantially plug flow and temperature control of a mixture with a total monomer concentration of 10 to 80 weight percent solids) are within the scope of the present disclosure when used as reactor 40.
Where a PFR can be used alone as reactor 40, a terminating agent solution may be added to the reaction mixture soon after it exits reactor 40. This can be accomplished by blending the reaction mixture and terminating agent and protected terminating agent feeds (not shown) through a simple T-pipe arrangement. To ensure thorough mixing of the two feeds, the combined feed can be fed into another mixer (e.g., a static mixer).
Those skilled in the art will recognize that a wide variety of materials can be used to terminate various initiator systems, which include, for example, oxygen, water, steam, alcohols, ketones, esters, amines and hindered phenols.
The polymer and/or the reaction mixture can be to be processed at elevated temperatures (e.g., high temperature devolatilization of the reaction mixture or hot-melt coating of the polymer), with the addition of a thermal stabilizer. A variety of thermal stabilizers, including hindered phenols and phosphites, are widely used in the industry. A stabilizer can be used, where it is soluble in the monomer and polymer; otherwise, a solvent will be necessary as a delivery mechanism.
In the instance where a hindered phenol has been used as the terminating agent, addition of a separate thermal stabilizer may be unnecessary.
Where the polymer product can be to be used in pure form, unreacted monomer can be stripped out of the reaction mixture by optional devolatization mechanism 50. A variety of known devolatilization processes are possible. These include, but are not limited to, vacuum tray drying on, for example, silicone-lined sheets; wiped film and thin film evaporators (when the average molecular weight of the polymer can be not too high); steam stripping; extrusion through a spinneret; and air drying.
In an exemplary embodiment, the devolatilization mechanism 50 can be a DISCOTHERM B high viscosity processor (List AG; Acton, Mass.). Other manufacturers such as Krauss-Maffei Corp. (Florence, Ky.) and Hosokawa-Bepex (Minneapolis, Minn.) make similar processors. These types of processors have been found to be efficient in separating polymer product from the remainder of the terminated reaction mixture. If desired, such processors can be maintained at below ambient pressures so that reduced temperatures can be used. Use of reduced pressures permits the recapture of very volatile components without extensive degradation of the polymer.
The remaining components of the reaction mixture (e.g., solvents, and any terminating agent solution) that were used may be condensed and separated from each other. Commonly, these materials can be removed by means of distillation; e.g., solvents(s) with boiling points that differ significantly from those of the terminating agent. Recycled solvent passes through purification unit 14 prior to being reintroduced into reactor 40.
Once the polymer product has been isolated from the remainder of the reaction mixture, it can be discharged from the reactor 40, and collected directly from outlet 60 in a desired container.
Exemplary embodiments of this disclosure are further illustrated by the following examples. The particular materials and amounts thereof, as well as other conditions and details, recited in these examples should not be used to unduly limit this disclosure.
The average molecular weight and polydispersity of a sample was determined by Gel Permeation Chromatography (GPC) analysis. Approximately 25 mg of a sample was dissolved in 10 milliliters (mL) of tetrahydrofuran (THF) to form a mixture. The mixture was filtered using a 0.2 micron polytetrafluoroethylene (PTFE) syringe filter. Then about 150 microliters (μL) of the filtered solution was injected into a Plgel-Mixed B column (Polymer Laboratories, Amherst, Mass.) that was part of a GPC system also having a Waters® 717 Autosampler and a Waters® 590 Pump (Waters Corporation, Milford, Mass.). The system operated at room temperature, with a THF eluent that moved at a flow rate of approximately 0.95 mL/min. An Erma ERC-7525A Refractive Index Detector (JM Science Inc. Grand Island, N.Y.) was used to detect changes in concentration. Number average molecular weight (Mn) and polydispersity index (PDI) calculations were based on a calibration mode that used narrow polydispersity polystyrene controls ranging in molecular weight from 580 g/mole to 7.5×106 g/mole. The actual calculations were made with PL Caliber® software (Polymer Laboratories, Amherst, Mass.).
The concentration of different blocks in a block copolymer was determined by Nuclear Magnetic Resonance (NMR) spectroscopy analysis. A sample was dissolved in deuterated chloroform to a concentration of about 10 weight % solids, and placed in a Unity® 500 MHz NMR Spectrometer (Varian Inc., Palo Alto, Calif.). Block concentrations were calculated from relative areas of characteristic block component spectra.
The 1 L PFR had a reaction zone capacity of 0.94 L and consisted of five jacketed (shell-in-tube) glass sections (Pyrex® cylinders). The tube had an inner diameter of 3.01 cm and an outer diameter of 3.81 cm. The shell had a diameter of 6.4 cm. All five sections, corresponding to zones 1-5, were 25.4 cm long. The sections were joined together by stainless steel coupling disks. The coupling disks were equipped with individual temperature sensing thermocouples extending into the interior of the cylindrical sections. These thermocouples permitted the temperature of the reaction mixture in each section to be monitored and adjusted up or down (as necessary) to a set point by varying the temperature of the heat transfer fluid flowing through the jacketed sections. The coupling disks also contained various single inlet ports through which monomer or solvent could be added into the reaction mixture.
Extending through the center of the joined cylinders was a stainless steel shaft with a length 154.9 cm and a diameter of 0.95 cm. The shaft was suspended along the cylinder axis by shaft alignment pins. The shaft was split into two sections, one section for the first four zones and the other section for the fifth zone. The second section of the shaft butted into a Teflon plug in the first section of the shaft. This allowed the two sections of the shaft to be stirred at two different rates and two different directions in the same reactor. Thirty detachable stainless steel paddles with approximately 2.1 cm between each paddle were affixed to the shaft. The rectangular paddles were 1.6 mm thick, 1.91 cm wide and 2.54 cm long. Each section contained six paddles. Each end of the shaft was attached to a variable speed, ¼ hp Baldor industrial gear motor. The stir rate from either end could be controlled from 1 rpm to 314 rpm.
Heat transfer was accomplished by attaching recirculators to the jackets. All zones were heated or cooled with water. They were all independently heated or cooled except zones 4 and 5, which were heated or cooled in series from the same recirculator. Zone 1 was heated or cooled in a co-current manner while the other four zones were heated or cooled in a countercurrent fashion.
Temperatures in the reactor were monitored and recorded through use of a thermocouple temperature recorder (OCTTEMP 8-channel recorder, Omega Engineering, Inc. Stamford, Conn.) and accompanying software interfaced with a personal computer. Thermocouples (type J; Omega Engineering, Inc. Stamford, Conn.) were positioned in each of the stainless steel coupling pieces to provide zone batch temperatures during polymerizations.
The 10 L stirred tubular reactor (PFR) had a capacity of 10 liters and consisted of five jacketed (shell-in-tube) glass sections (Pyrex cylinders). Each tube section had an outside diameter of 7.62 cm, an inside diameter of 6.99 cm, and a length of 57.2 cm. The jackets had an outside diameter of 11.63 cm, an inside diameter of 10.99 cm, and a length of 52.1 cm. The tube sections were joined together with stainless steel coupling flanges, each 3.18 cm thick. The coupling flanges were equipped with individual temperature sensing thermocouples extending into the interior of the tube sections. These thermocouples permitted the temperature of the reaction mixture in each section to be monitored and adjusted up or down, as necessary, to a set point by varying the temperature of the heat transfer fluid flowing through the jacketed sections. Additionally, this reactor was equipped with a preheater to allow for heating of the inlet raw materials prior to initiation. The coupling flanges also contained various inlet ports through which material could be added into the reaction mixture. The PFR was closed off at both ends with stainless steel flanges.
Extending through the center of the joined cylinders was a 1.27 cm diameter stainless steel shaft suspended along the center of the cylinder axis by three shaft alignment pins extending from each of the coupling flanges. Thirty-eight detachable stainless steel paddles with approximately 4.5 cm between each paddle were attached to the shaft. The rectangular paddles in the first four zones were 0.24 cm thick, 4.5 cm wide and 5.1 cm long. The rectangular paddles in the fifth zone were 0.24 cm thick, 5.1 cm wide and 5.7 cm long. The number of paddles in this configuration was as follows: 7 paddles in Zone 1, 8 paddles in Zone 2, 8 paddles in Zone 3, 8 paddles in Zone 4, and 7 paddles in Zone 5. The shaft was attached to a 2.2 kW variable speed motor.
Temperature control for zones 1 and 2 were controlled with recirculating water pumps. Temperature control for zones 3-5 was maintained using HFE 7100 (3M Company, St. Paul, Minn.) cooling fluid, which recirculated through a ½ inch stainless steel coil immersed in a bath consisting of dry-ice/Isopar L (Exxon Mobil Company, Fairfax, Va.).
An initiator solution was prepared by mixing 65 g of 1.4 M sec-butyllithium in cyclohexane with 3000 g of oxygen-free cyclohexane. Table 1 lists chemicals used in this disclosure. Styrene monomer was fed at a rate of 16.5 g/min through a 1″ diameter×3′ long packed column of basic alumina oxide followed by a 1″ diameter×3′ long column of 3 Å molecular sieves and into zone 1 of the PFR. Toluene was fed at a rate of 31.0 g/min through two packed columns, 1″ diameter×3′ long, 3 Å molecular sieves and into zone 1. The s-BuLi solution was fed into zone 1 at a feed rate of 5.5 g/min. A color change from clear to red was observed in zone 1 when the initiator solution contacted the monomer, and an exotherm resulted. The reaction temperature was kept at about 100° C. by adjusting the jacket temperature of zone 1 to 80° C. The temperature of the jackets in each of the 5 zones of the PFR was individually maintained at: #1=80° C., #2=70° C., #3=50° C., #4=5° C., and #5=5° C.
The materials flowed through the first four zones, facilitated by stirring paddles along the reaction path. Polymerization of the polystyrene continued to substantially 100% completion by the end of zone 4, thereby forming a “living” polystyrene solution. The t-BMA was fed at a rate of 1.5 g/min through a 1″ diameter×3′ long packed column of basic alumina oxide followed by a 1″ diameter×3′ long packed column of 3 Å molecular sieves and into zone 5. The resulting poly(styrene-t-BMA) block copolymer was terminated with isopropanol and samples were collected for analysis. The total residence time for this reaction was about 15.2 minutes.
GPC and NMR analysis was done on the block copolymer to verify the reaction proceeded to completion. The block copolymer was determined to have a Mn=7.3×104 with a polydispersity index of 1.5 and 7.7 mol % t-BMA polymer. NMR determined the polymer to be 99% block copolymer. Neither styrene nor t-BMA monomer was detected.
Additional chromatography was done to confirm that the styrene/t-BMA ratio was constant throughout all polymer chains. This was accomplished by comparing the RI (refractive index) trace (corresponding to both styrene and t-BMA) with the uv 280 nm trace (corresponding to the presence of the styrene ring). If the peaks from both traces overlap and display the same shape, then presumably the styrene and (meth)acrylate are distributed in the same ratio throughout all chain lengths. The shapes were consistent with a constant ratio throughout all polymer chains.
The polymerization for Examples 2a and 2b was done in the same manner as Example 1 except that a poly(isoprene-b-methyl(meth)acrylate) block copolymer was synthesized. An initiator solution was prepared by mixing 225 g of 1.4 M sec-butyllithium in cyclohexane with 3000 g of oxygen-free cyclohexane. Example 2a was polymerized with DPE, while 2b did not use DPE. The feed rates into the reactor as well as reactor feed locations are shown in Table 2. In this example, THF was used as a co-solvent to increase the kinetics of the isoprene polymerization. The jacket temperature profile was #1=60° C., #2=60° C., #3=−70° C., #4=−70° C., and #5=−70° C.
Three samples of Example 2a and three samples of 2b were taken to determine if MMA could be polymerized from living polyisoprene chain ends without the use of DPE. GPC and NMR were performed on the samples and the data is presented in Table 3. The data shows the ability to polymerize block copolymers containing MMA anionically without the use of DPE.
The polymerization for Examples 3A and 3B was done in a similar manner as Example 1, except that the 10 L PFR was used rather than the 1 L PFR. An initiator slurry was prepared by 1845 g of 1.4M s-BuLi to 8000 g of oxygen-free cyclohexane. The feed rates into the reactor as well as reactor feed locations are shown in Table 4. Toluene was fed via reciprocating piston pump and all other flows were fed via pressure-feeding through control valves. The total reactor residence time was 7.0 minutes and the polymerization was carried out at 32.7% solids. The preheater and jacket temperature profile was: preheater=40° C. #1=50° C., #2=20° C., #3=−60° C., #4=−60° C., and #5=−60° C.
The samples from Example 3 were taken throughout the course of the experiment. Diblock copolymers were formed throughout the experiment without a chain modifier, such as DPE, and product stability was demonstrated. GPC and NMR data is shown in Table 5.
