This patent application is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "Many high-performance materials, particularly segmented copolymers or composite structures, require controlled synthesis of polymers from functional monomers employing well defined initiators. [Macromolecular Engineering. Precise Synthesis,
"Access to well-defined block copolymers was opened by Szwarc in the 1950's [Nature 1956, 176, 1168-1169] by the development of living anionic polymerization. The biggest limitation of this technique is its sensitivity to impurities (moisture, carbon dioxide) and even mild electrophiles, which limits the process to a narrow range of monomers. The reaction medium and all components have to be extensively purified before polymerization, thus preparation of functional block copolymers or other well-defined polymeric materials in high purity can be challenging. Nevertheless, anionic polymerization, which was first implemented in an academic setting, was quickly adapted on an industrial scale and ultimately led to the mass production of several well-defined block copolymers, such as polystyrene-b-polybutadiene-b-polystyrene, performing as a thermoplastic elastomer. [Thermoplastic Elastomers, 3rd Ed.; Hanser:
"The fast industrial adaptation of such a challenging technique may be explained by the fact that anionic polymerization was the first and, indeed only example of a living polymerization process for more than three decades, that allowed for the synthesis of previously inaccessible well defined high-performance materials from a very narrow selection of vinyl monomers. Nevertheless materials based on modified block copolymers with properties that were desired in many applications, were the main driving force for scaling up anionic polymerization processes. [Ionic Polymerization and Living Polymers;
"In late 1970's to early 1990's, living carbocationic polymerization was discovered and optimized. [Adv. Polym. Sci. 1980, 37, 1-144.] However this procedure is just as sensitive to impurities as anionic polymerization and the range of polymerizable monomers for both techniques was essentially limited to non-polar vinyl monomers.
"While many earlier attempts were made to develop controlled radical polymerization (CRP) processes the critical advances were made in the mid 1990's. CRP can be applied to the polymerization of functional monomers and hence preparation of many different site specific functional (co)polymers under mild conditions became feasable. [Materials Today 2005, 8, 26-33 and Handbook of Radical Polymerization; Wiley Interscience: Hoboken, 2002.] From a commercial point of view, CRP processes can be conducted at convenient temperatures, do not require extensive purification of the monomers or solvents and can be conducted in bulk, solution, aqueous suspension, emulsion, etc. CRP allows the preparation of polymers with predetermined molecular weights, low polydispersity and controlled composition, and topology. Radical polymerization is much more tolerant of functional groups than ionic polymerization processes and a broader range of unsaturated monomers can be polymerized providing materials with site specific functionality. In addition, copolymerization reactions, which are generally challenging for ionic polymerizations due to large differences in reactivity ratios of monomers under ionic polymerization conditions, are easy to perform using radical based CRP. This provides an opportunity to synthesize polymeric materials with predetermined molecular weight (MW), low polydispersity (PDI), controlled composition, site specific functionalities, selected chain topology and composite structures that can be employed to incorporate bio- or in-organic species into the final product.
"The three most studied, and commercially promising, methods of controlling radical polymerization are nitroxide mediated polymerization (NMP), [Chemical Reviews 2001, 101, 3661-3688] atom transfer radical polymerization (ATRP), [
"The simple four component atom transfer radical polymerization (ATRP) process, shown below in Scheme 1, was discovered by Matyjaszewski at
"The catalyst is not bound to the chain end, as in coordination polymerization, and can therefore be used in a controlled/living polymerization process at sub-stoichiometric amounts relative to the initiator. Nevertheless, as a consequence of radical-radical termination reactions, proceeding with a rate=k.sub.t in Scheme 1, forming P.sub.n-P.sub.m dead chains and an excess of X-M.sub.t.sup.n+1/Ligand.
"Examples of the spectrum of new well-defined polymeric materials prepared using ATRP in the past decade include block copolymers, branched polymers, polymeric stars, brushes, and networks, each with pre-determinable site specific functionality as well as hybrids with inorganic materials or bio-conjugates. However, its widespread commercial utilization is still limited. [Chem. Rev. 2007, 107, 2270-2299.] Nevertheless, these custom fabricated materials have potential to improve the performance of a multitude of commercial products in the areas of personal care and cosmetics, detergents and surfactants, paints, pigments and coatings, adhesives, thermoplastic elastomers, biocompatible materials and drug delivery systems if a cost effective, environmentally benign, scalable process can be defined.
"The initially defined normal ATRP process requires a high catalyst concentration, often approaching 0.1 M in bulk monomer polymerization reactions, typical concentrations range from 0.5% to 1 mol % vs. monomer, [Handbook of Radical Polymerization; Wiley Interscience: Hoboken, 2002] to overcome the effects of continuous buildup of ATRP's equivalent of the persistent radical (X-M.sub.t.sup.n+1/Ligand). [
"Recent advances in ATRP by the present inventors in conjunction with one of the inventors of ATRP, K. Matyjaszewski, have been disclosed in patent applications PCT/US2006/048656 published as WO 2007/075817, hereby incorporated by reference including further incorporation of references disclosed therein to define the state of the art in ATRP and definitions for some of the language used herein. In that application it was disclosed that the concentration of the catalyst used for an ATRP can be reduced to 1-100 ppm by addition of a reducing agent, or a free radical initiator, that acts throughout the reaction to continuously regenerate the lower oxidation state activator from accumulating higher oxidation state deactivator, Scheme 2. Some suitable reducing agents listed in incorporated references include; sulfites, bisulfites, thiosulfites, mercaptans, hydroxylamines, amines, hydrazine (N.sub.2H.sub.4), phenylhydrazine (PhNHNH.sub.2), hydrazones, hydroquinone, food preservatives, flavonoids, beta carotene, vitamin A, .alpha.-tocopherols, vitamin E, propyl gallate, octyl gallate, BHA, BHT, propionic acids, ascorbic acid, sorbates, reducing sugars, sugars comprising an aldehyde group, glucose, lactose, fructose, dextrose, potassium tartrate, nitrites, nitrites, dextrin, aldehydes, glycine, and many antioxidants.
"This improvement in ATRP was called ARGET ATRP because the Activator was continuously ReGenerated by Electron Transfer. In Scheme 2 the regeneration is conducted by addition of a reducing agent but the deactivator can also be reduced by addition of a free radical initiator in a process called ICAR (Initiators for Continuous Activator Regeneration) ATRP.
"These novel initiation/catalyst reactivation procedures allow a decrease in the amount of catalyst needed to drive a controlled ATRP to high conversion from 10,000 ppm employed in classical ATRP to, in some cases, 10 ppm or less where catalyst removal or recycling would be unwarranted for many industrial applications.
"Furthermore ARGET/ICAR ATRP processes can start with the oxidatively stable, easy to handle and store Cu.sup.II species, as it is reduced in situ to the Cu.sup.I state. Furthermore, the level of control in the disclosed ICAR/ARGET ATRP processes are essentially unaffected by an excess (still small amount compared to initiator) of the reducing agent to continuously regenerate the lower oxidation state activator when/if it is oxidized in the presence of limited amounts of air. [Langmuir 2007, 23, 4528-4531.]
"Chain-end functionality in a normal ATRP may be lost by a combination of radical-radical termination reactions and by side reactions between growing radicals and the catalyst complex; Cu.sup.I (oxidation of radical to carbocation) or Cu.sup.II species (reduction of radical to carbanion). Therefore another important feature of the new ARGET/ICAR catalytic systems is the suppression/reduction of side reactions due to the use of a low concentration of the transition metal complex. Reduced catalyst-based side reactions in ICAR and ARGET ATRP allow synthesis of higher molecular weight polymers and polymers with higher chain-end functionality which may allow the preparation of pure, certainly purer, block copolymers.
"It was envisioned to be a simple robust procedure.
"In application PCT/US2006/048656 the re-activator was added to the reaction in a single addition and control was exerted over the reaction by continuous adjustment of K.sub.ATRP in the presence of excess reducing agent. Successful polymerization was achieved on the laboratory scale, 10-50 mL Schlenk flasks, for common monomers such as methyl methacrylate (MMA), butyl acrylate (nBA), styrene (St) and acrylonitrile (AN). The successful synthesis of block copolymers from common monomers such as MMA, nBA, MA and St was reported.
"The critical phrase in the above paragraph discloses the scale at which the innovative work to define the improved procedures was conducted: 10-50 mL. When the procedures disclosed in PCT/US2006/048656 were scaled up some critical process disadvantages accompanying the improvements made in application became apparent: a) slow reactions (especially for methacrylates, styrenes) b) exothermic process (especially for acrylates) requiring c) the need of precise temperature control d) limited information for scale up and automation of process.
"Procedures to overcome these limitations, particularly at larger scale, are disclosed herein. Indeed in one embodiment of the invention disclosed controlled radical polymerization processes where the rate of addition of a reducing agent/radical initiator is continuously adjusted allows conversion of monomer to polymer to exceed 80%, preferably exceed 90% and optimally exceed 95%."
In addition to the background information obtained for this patent application, NewsRx journalists also obtained the inventors' summary information for this patent application: "One embodiment of the polymerization processes of the present invention are directed to polymerizing free radically polymerizable monomers in the presence of a polymerization medium initially comprising at least one transition metal catalyst and an atom transfer radical polymerization initiator. The polymerization medium may additionally comprise a reducing agent or a radical initiator. Sufficient ligand should be added to the reaction medium to modify solubility and activity of the transition metal catalyst. The one or more reducing agents or radical initiators may be added initially or during the polymerization process in a continuous or intermittent manner or activated in an intermittent manner. The polymerization process may further comprise reacting the reducing agent with at least one of the transition metal catalyst in an oxidized state further comprising a radically transferable atom or group to form a compound that does not participate significantly in control of the polymerization process. A transition metal in the zero oxidation state can be employed as a reducing agent.
"Another embodiment of the disclosed process is directed towards continuous control over the concentration of the persistent radical in a NMP. In this embodiment the rate of decomposition of the initiator added continuously or intermittently to the reaction is selected to match the rate of radical/radical termination reactions that would otherwise build up the concentration of the stable free radical and reduce the rate of propagation.
"A further embodiment of the disclosed process concerns RAFT polymerizations. In a RAFT polymerization the rate of polymerization is controlled by the rate of decomposition of the added initiator. Normally all of the initiator is added to the reaction at the beginning of the reaction and this could lead to an increased rate of initiator decomposition if the temperature of the reaction is not well controlled throughout the polymerization vessel during each stage of the reaction. As noted for ICAR ATRP continuous addition of the initiator and monitoring of the temperature of the reaction provides information on, if and when addition of the initiator should be stopped in order to retain control over the reaction.
"Embodiments of the polymerization process of the present invention include bulk polymerization processes, polymerization processes performed in a solvent, polymerization processes conducted from solid surfaces, biphasic polymerization process including emulsion polymerization processes, mini-emulsion polymerization processes, microemulsion processes, reverse emulsion polymerization processes, and suspension polymerization processes. In such biphasic polymerization processes the polymerization processes may further comprise at least one of a suspending medium, a surfactant or reactive surfactant, and a monomer phase comprising at least a portion of the radically polymerizable monomers.
"It must be noted that, as used in this specification and the appended claims, the singular forms 'a,' 'and,' and 'the' include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to 'a polymer' may include more than one polymer or copolymers.
"Unless otherwise indicated, all numbers expressing quantities of ingredients, time, temperatures, and so forth used in the present 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 following specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. 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 invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, may inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
"It is to be understood that this invention is not limited to specific compositions, components or process steps disclosed herein, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
"This disclosed procedures provide a means to optimize and automate the polymerization processes by exercising continuous control over the ratio of activator/deactivator, concentration of persistent radical or concentration of initiator present in a CRP.
"The advantages of the disclosed 'starve feeding/activation' method include: a) use of lower amounts of catalyst and radical initiator or reducing agent, b) reduced need for precise temperature control, c) higher reaction temperature, which allows higher conversions in a shorter time with reduced amounts of solvents, d) the potential for automation of the whole process, and e) the development of safe scalable processes for exothermic polymerization reactions, although heat removal is still a requirement.
"The resulting expansion of the utilization of the proposed system for CRP will allow a reduced cost for purification of the products, a significant decrease in waste and improve safety by providing an additional means to control reaction temperature. Furthermore the rate of addition of a reducing agent/radical initiator can be continuously adjusted to allow the conversion of monomer to polymer to exceed 80%, preferably exceed 90% and optimally exceed 95% by taking into consideration the viscosity of the reaction medium and the rate of diffusion of the added reducing agent.
"In the following examples, and discussion of examples, ATRP is employed as an exemplary CRP but the disclosed procedures can be applied to NMP and RAFT as indicated above.
BRIEF DESCRIPTION OF THE FIGURES
"The following figures exemplify aspects of the disclosed process but do not limit the scope of the process to the examples discussed.
"FIG. 1. Variation of temperature inside a 1 L batch reactor during ARGET ATRP of nBA. Experimental conditions: nBA/DEBMM/CuBr.sub.2/TPMA/Sn(EH).sub.2=500/1/0.025/0.1/0.1, in bulk at 60.degree. C.
"FIG. 2. Parameters employed for the computer simulation of the polymerization of MMA under a series of reaction conditions. The purpose: to find optimal conditions for new feeding method. Results: models were built and successful simulations were performed and optimal conditions were found. Concerns: heat transfer, side reactions, catalyst stability, etc. not taken into account.
"FIG. 3A. Simulated kinetics plot.
"FIG. 3B. Simulated molecular weight and PDI vs. conversion.
"FIG. 3C. Simulated GPC trace.
"FIG. 4A. Molecular weight and PDI vs. conversion for example C1.
"FIG. 4B. GPC curves for example C1.
"FIG. 5A. Molecular weight and PDI vs. conversion for example C2.
"FIG. 5B. GPC traces for example C2.
"FIG. 6A. Molecular weight and PDI vs. conversion for example C3.
"FIG. 6B. GPC curves for example C3.
"FIG. 7A. Molecular weight and PDI vs. conversion for example C4.
"FIG. 7B. GPC curves for example C4.
"FIG. 8A. Kinetics plot for example C5.
"FIG. 8B. Molecular weight and PDI vs. conversion for example C5.
"FIG. 8C. GPC curves for example C5.
"FIG. 8D. Temperature profile for example C5.
"FIG. 9. Polymerization of MMA targeting low degree of polymerization, wherein: FIG. 9A is the kinetic plot; FIG. 9B shows the molecular weight and PDI vs. conversion; and FIG. 9C is the GPC traces for ICAR ATRP of MMA with feeding of AIBN (experiment 08-006-165). Conditions: MMA I DEBMM I CuBr.sub.2 I TPMA I AIBN=100 I 1 I 0.005 I 0.025 I-; in bulk [MMA]=8.9 mol/L, 50 ppm of Cu, T=90.degree. C. Feeding rate slow: 0.002 mol equivalent of AIBN vs. DEBMM in 1 h (AIBN in 40 ml of solvent to 850 ml of the reaction solution).
"FIG. 10. Polymerization of MMA targeting high degree of polymerization, wherein: FIG. 10A is a kinetic plot; FIG. 10B shows the molecular weight and PDI vs. conversion; and FIG. 10C is the GPC trace for ICAR ATRP of MMA with feeding of V-70 (experiment 08-006-180). Conditions: MMA I DEBMM I CuBr.sub.2 I TPMA I V-70 1000 I 1 I 0.05 10.1 I- ; in bulk [MMA]=8.9 mol/L, 50 ppm of Cu, T 80.degree. C. Feeding rate slow: 0.004 mol equivalent of V-70 vs. DEBMM in I h (V-70 in 40 ml of solvent to 850 ml of the reaction solution).
"FIG. 11. Computer simulation of polymerization of n-butyl acrylate, wherein: FIGS. 11
"FIG. 12A. Kinetics plot for example 2A.
"FIG. 12B. Molecular weight and PDI vs. conversion for example 2A.
"FIG. 12C. GPC curves for example 2A.
"FIG. 12D. Temperature profile for example 2A.
"FIG. 13A. Kinetics plot for example 2B.
"FIG. 13B. Molecular weight and PDI vs. conversion for example 2B.
"FIG. 13C. GPC curves for example 2B.
"FIG. 14. Temperature profile for run 08-006-194.
"FIG. 15. ICAR polymerization of styrene, wherein: FIG. 15A is the kinetic plot; FIG. 15B shows the molecular weight and the PDI vs. conversion; and FIG. 15C is the GPC traces for ICAR ATRP of St with feeding of AIBN (experiment 08-006-192). Conditions: St I DEBMM I CuBr.sub.2 I TPMA I AIBN 100 I 1 I 10.005 I 10.1 I 10.005; in bulk [St]=8.31 mol/L, 50 ppm of Cu, T=100.degree. C. Feeding rate slow: 0.008 mol equivalent of AIBN vs. DEBMM in 1 h (AIBN in 40 ml of solvent to 850 ml of the reaction solution).
"FIG. 16. Polymerization of St (high DP). Automation of process. ICAR ATRP of St with feeding of AIBN (experiment 08-006-193), wherein: FIG. 16A is the molecular weight and PDI vs. conversion; and FIG. 16B is the temperature profile. Conditions: St I DEBMM I CuBr.sub.2 I TPMA I AIBN 1000 I 1 I 10.05 I 10.15 I 10.025; in bulk [St]=8.31 mol/L, 50 ppm of Cu, T=100-110.degree. C. Feeding rate slow: 0.008 mol equivalent of AIBN vs. DEBMM in 1 h (AIBN in 40 ml of solvent to 850 ml of the reaction solution).
"FIG. 17. Kinetics for ICAR ATRP of St with feeding of AIBN (experiment 08-006-193) targeting high DP, wherein: FIG. 17A is the molecular weight and PDI vs. conversion; and FIG. 17B is the GPC curves. Conditions: St I DEBMM I CuBr.sub.2 I TPMA I AIBN=1000 I 1 I 0.05 I 0.15 I 0.025; in bulk [St]=8.31 mol/L, 50 ppm of Cu, T=100-110.degree. C. Feeding rate slow: 0.008 mol equivalent of AIBN vs. DEBMM in 1 h (AIBN in 40 ml of solvent to 850 ml of the reaction solution)."
URL and more information on this patent application, see: Jakubowski, Wojciech; Spanswick, James. Control over Controlled Radical Polymerization Processes. Filed
Keywords for this news article include: Legal Issues, Polymer Science, Reducing Agents,
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