Oligomeric A2 + B3 Approach to Branched Poly(Arylene Ether Sulfone)

“One-Pot” Oligomeric A2 + B3 Approach to Branched Poly(arylene ether sulfone)s: Reactivity Ratio Controlled Polycondensation A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science By ANDREA M. ELSEN B.S., Wright State University, 2007 2009 Wright State University WRIGHT STATE UNIVERSITY SCHOOL OF GRADUATE STUDIES June 19, 2009 I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY Andrea M. Elsen ENTITLED “One-Pot” Oligomeric A2 + B3 Approach to Branched Poly(arylene ether sulfone)s: Reactivity Ratio Controlled Polycondenstation BE ACCEPTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Science. _________________________ Eric Fossum, Ph.D. Thesis Director _________________________ Kenneth Turnbull, Ph.D. Department Chair Committee on Final Examination ____________________________ Eric Fossum, Ph.D. ____________________________ Kenneth Turnbull, Ph.D. ____________________________ William A. Feld, Ph.D. ____________________________ Joseph F. Thomas, Jr., Ph.D. Dean, School of Graduate Studies Abstract Elsen, Andrea M. M.S., Department of Chemistry, Wright State University, 2009. “One-Pot” Oligomeric A2 + B3 Approach to Branched Poly(arylene ether sulfone)s: Reactivity Ratio Controlled Polycondensation The synthesis of fully soluble branched poly(arylene ether)s via an oligomeric A2 + B3 system, in which the A2 oligomers are generated in situ, is presented. This approach takes advantage of the significantly higher reactivity toward nucleophilic aromatic substitution reactions, NAS, of B2, 4-Fluorophenyl sulfone, relative to B3, tris(4-Fluorophenyl) phosphine oxide. The A2 oligomers were synthesized by reaction of Bisphenol-A and B2, in the presence of the B3 unit, at temperatures between 100 and 160 °C, followed by an increase in the reaction temperature to 180 °C at which point the branching unit was 31 incorporated. The presence of branching was confirmed via P NMR spectroscopy and the thermal properties of the polymers were evaluated utitilizing TGA and DSC analyses. iii Table of Contents 1. Introduction…………………………………………………………………………….1 Linear polymers………………………………………………………...…2 Dendrimers………………………………………………………………...5 Branched poymers………………………………………………………...9 Poly(arylene ether sulfone)s……………………………………………..14 Current project…………………………………………………………...17 2. Experimental…………………………………………………………………………..19 Synthesis of 4,4-bis-(4-methylphenoxy)diphenyl sulfone,1b……………20 Synthesis of mono-substituted tris-(4-Fluorophenyl)phosphine oxide, 3a………...………………………………………..20 Representative procedure for model reactions…………………………...20 Representative polymerization procedure………………………………..21 General procedure for reverse precipitations……………………….…....21 Preparation of GC/MS calibration curve………………………………...22 Polymerization of A2 + B2 +B2’ monomers, linear analog………………22 Synthesis of A2 capped oligomers, 2a…………………………………...22 Synthesis of branched poly(arylene ether sulfone)s, 6g…………………23 3. Results and Discussion………………………………………………………………..24 Nucleophilic aromatic substitution………………………………………24 Reactivity determination…………………………………………………24 GC/MS calibration curve………………………………………………...26 Simulation of in situ oligomeric A2 formation…………………………..30 iv Synthesis of branched poly(arylene ether sulfone)s……………………..33 Incorporation of B3 monomer……………………………………………38 Estimation of degree of branching, DB…………………………………..39 Thermal Analysis………………………………………………………...44 Conclusions………………………………………………………………47 4. References……………………………………………………………………………..48 vList of Figures I. Introduction: Figure 1. Chain Entanglements……………………………………………………...…....1 Figure 2. Intrinsic or inherent viscosity versus Mn for a generic linear polymer……...…2 Figure 3. Young’s Modulus versus temperature plot for a generic linear polymer…........3 Figure 4. Poly(amido amine)……………………………..………………………….…...6 Figure 5. Generic scheme of a branched polymer…………...…………………………...9 Figure 6. Comparison of mechanical properties versus degree of branching for linear, dendritic and branched polymers………………………………………………………...10 Figure 7a. Comparison of linear, dendritic and branched polymer viscosity versus degree of branching……………………………………………………………………………...11 Figure 7b. Comparison of linear, dendritic and branched polymer viscosity versus Mw………………………………………………………………………………………..11 II. “One-Pot” Oligomeric A2 + B3 Polymerization of Poly(arylene ether sulfone)s: Reactivity Ratio Controlled Polycondensation Figure 8. 4-Fluorophenyl sulfone, tris-(4-Fluorophenyl)phosphine oxide and bis-(4- Fluorophenyl)phenyl phosphine oxide…………………………………………………..25 Figure 9. The 300 MHz 1H NMR spectrum (CDCl3) of 1b……………………………..27 Figure 10. The 75 MHz 13C NMR (CDCl3) spectrum of 1b…………………………….28 Figure 11. The 121 MHz 31P NMR (CDCl3) spectrum of 3a mixture…………………..30 Figure 12. GPC overlay of 6b and 6b1…………………………………………………..34 Figure 13. Overlay of “one-pot” polymers, 6a-f………………………………………..35 Figure 14. Overlay of MeOH soluble, insoluble and crude polymer……………………36 vi Figure 15. Overlay of 6d, 6f and 6g……………………………………………………..38 Figure 16. The 300 MHz 1H NMR spectrum (CDCl3) of 6c……………………………39 Figure 17. Potential B3 structural units…………………………………………………40 Figure 18. The 121 MHz 31P NMR (CDCl3) spectrum of 6d mixture…………………..41 Figure 19. Overlay of 31P NMR spectra of 6a-h………………………………………...43 Figure20 Overlay of TGA traces under N2………………………………...……………45 Figure 21. Overlay of DSC spectra for samples 6a-h…………………………………...46 vii List of Schemes I. Introduction: Scheme 1. Divergent and convergent methods for synthesis of dendrimers…………....8 Scheme 2. Various syntheses of hyperbranched polymers...............................................13 Scheme 3. Generic synthesis of polysulfones…………...………………………………15 Scheme 4. Generic synthesis of the oligomeric A2 + B3 system………………………...16 Scheme 5. Synthesis of branched PAES via the oligomeric A2 + B3 system……………17 II. “One-Pot” Oligomeric A2 + B3 Polymerization of Poly(arylene ether sulfone)s: Reactivity Ratio Controlled Polycondensation Scheme 6. NAS mechanism……………………………………………………………..34 Scheme 7. Synthesis of 1b……………………………………………………………….27 Scheme 8. Synthesis of phosphoryl based compounds 3a-c…………………………….29 Scheme 9. Model Reaction Scheme……………………………………………………..31 Scheme 10. Conversion of 3 to 2a as an AB2 oligomer………………………………...32 Scheme 11. Branched PAEs polymer synthesis…………………………………………33 Scheme 12. Synthesis of PAEs via “two-pot” literature method………………………..37 Scheme 13. Synthesis of 6h……………………………………………………………...37 viii List of Tables I. “One-Pot” Oligomeric A2 + B3 Polymerization of Poly(arylene ether sulfone)s: Reactivity Ratio Controlled Polycondensation Table 1. Reactivity data of 4-Fluorophenyl sulfone, tris(4-Fluorophenyl)phosphine oxide and bis-(4-Fluorophenyl)phenylphosphine oxide……………………………………….26 Table 2. GC/MS data of model reactions………………………………………………..32 Table 3. Reaction conditions utilized for the preparation of branched PAEs…………...33 Table 4. Mn and PDI values of PAEs…………………………………………………...44 Table 5. Incorporation of B3 monomer………………………………………………….39 Table 6. Degree of branching values…………………………………………………….42 Table 7. TGA and DSC data for 6a-h…………………………………………………...45 ix Acknowledgements I would first like to thank Dr. Eric Fossum for his guidance, support and encouragement throughout my career at Wright State University as well as the faculty and staff of the Chemistry department. Also, many thanks to my husband, Nick, my parents, Jack and Donna, and to my sister, Laura. This could not have been accomplished without their endless love and support. xINTRODUCTION Linear Polymers Linear polymers are the most basic of polymers, consisting of only a simple back bone with two end groups. While linear polymers all have the same global structure, their individual structure will influence the conformation they exhibit. For example, poly (pphenylene terephthalamide) will exhibit a rigid-rod like structure.1 This means the polymer is in a defined rod-like shape and very little movement is allowed. On the other hand, polymers with a structure which has flexible bonds, as in poly(ether)s, will allow for random coil behavior, meaning there is no defined pattern within the structure of the polymer. While movement in rigid rod polymers is restricted, random coil polymers can participate in chain entanglements, where the chains become intertwined with one another or themselves (Figure 1). Specifically, these chain entanglements bestow mechanical properties to the polymer. Figure 1. Chain Entanglements. Intermolecular forces can also play a role in the ability of polymers to participate in chain entanglements. While the structure of the polymer may not be rigid on its own, 1when enough time is allowed, the polymer chains can align their intermolecular forces to form a crystalline material. For example, poly(ethylene terephthalate) can either be amorphous or crystalline depending on the time allotted for cooling. If cooled slowly, crystallites will form and the polymer’s amorphous material will be “tied down” by the crystalline material until the crystallites melt. In this semi-crystalline material, only the small portions between crystallites can have chain entanglements, significantly reducing the total number of chain entanglements within the polymer and therefore also changing the mechanical properties. While many factors influence the ability of a polymer to participate in chain entanglements, the number-average molecular weight (Mn) of the polymer is the most important. The lowest Mn value a polymer can have and still participate in chain entanglements is known as the Critical Point of Entanglement (Mc). The Mc for a specific polymer can be found by plotting viscosity versus Mn (Figure 2). Mc Mn Figure 2. Intrinsic or Inherent viscosity versus Mn for a generic linear polymer. 2 Below Mc, the viscosity is determined through Equation 1 where KL is a constant for low degree of polymerization and Z is the number of monomer units in the polymer backbone. Within this range the viscosity scales with Mn to the 1.0 power. η = KLZ1.0 (1) Above Mc the viscosity is determined through Equation 2. Again, Z is the number of monomer units in the polymer backbone, while KH represents a constant for high degree of polymerization. Also note the difference in power with which viscosity scales with Mn, changing from 1.0 to 3.4. This was derived using scaling concepts by de Gennes.1 η = KHZ3.4 (2) An example of a mechanical property is viscoelasticity behavior, which is the ability to relieve various stresses through the capacity of these chain entanglements to adopt different conformations. The viscoelastic behavior of a polymer can be described by Young’s Modulus. Figure 3. Young’s Modulus versus temperature plot for a generic linear polymer. 3 Young’s Modulus measures a polymer’s response to an applied stress. This is described in Equation 3 as the stress on the polymer over the strain by the polymer and is simply a way to measure the stiffness of the polymer. E = ε/σ (3) For a typical amorphous or semi-crystalline polymer there are five regions within Young’s Modulus (Figure 3). Region 1 is the Glassy Region, which is found at low temperatures where polymers exhibit high modulus. High modulus means the material is very hard and brittle. Throughout this region, movement within the polymer is restricted to vibrations and very small rotations. As the temperature is increased, the polymer goes through the Glass Transition (Tg), which is shown as region 2. At this point the polymer gains enough energy to show signs of cooperative motion in the backbone resulting in a considerable drop in the modulus of the polymer. Next, the modulus flattens as the polymer continues to warm and enters region 3, the Rubbery Plateau. Within this region the polymer exhibits elastic behavior. The material has enough energy that it may be stretched out, causing the chains to straighten. When the stress is removed, the chains relax back into entropically favorable positions. Region 4, called the Rubbery Flow Region acts similarly to region 3 when the stress is applied on a short time scale, however, if the stress is applied over long periods of time, the polymer will not be able to snap back to its original shape like it would in region three. The final region is the Liquid Flow Region. Here, at very high temperatures, the polymer has enough energy that the chains can move relatively quickly past one another allowing for a liquid-like behavior.1 While the physical properties of linear polymers are very attractive for many applications, most do have one quality that is undesirable: high viscosity. Typically, the 4viscosity of linear polymers is very high and this becomes a major problem when trying to process the polymer after synthesis. Often, the polymer must be diluted with solvent to obtain a processable material; therefore, it is sought-after to find a similar material that maintains the physical properties, but with a lower viscosity than traditional linear polymers. Dendrimers A second class of polymers, dendrimers, differs significantly from linear polymers. Dendrimers are unique because at every monomer unit they are perfectly branched. The structure of dendrimers consists only of dendritic units and chain ends which affords their globular, spherical shape.2 The first dendrimer, Polyamidoamine (PAMAM), was synthesized by Dow in 1986 (Figure 4).3 Dendrimers are typically prepared by either a divergent or convergent approach. As used in the synthesis to produce PAMAM, the divergent method grows the dendrimer outward by starting with a core molecule and adding a “layer” of monomer with each reaction to every functional group at the current chain ends. While this method has proven to be very successful in the production of many dendrimers including poly(amidoamines)4, polyethers5, and poly(arylamines)6 there are several downfalls with the method. For example, late in the synthesis, the number of functional groups on the dendrimer required to react with the monomer for proper generation growth is quite high.7 It becomes quite difficult to ensure that all reactions have occurred, creating an imperfect dendrimer. 5NH2 O H2N NH2 <ul style="display: flex;"><li style="flex:1">NH2 </li><li style="flex:1">H2N </li></ul>NH2 ON HN NH O NH HN O NH OO<ul style="display: flex;"><li style="flex:1">O</li><li style="flex:1">NH </li></ul>N O N HN NH N<ul style="display: flex;"><li style="flex:1">O</li><li style="flex:1">N</li></ul>O O HN NH <ul style="display: flex;"><li style="flex:1">NH2 </li><li style="flex:1">N</li></ul>H H2N OHN N OHN N H2N OHN NH NO N NH2 O ONH O O O HN NH N N N H NNH O O NH2 O O O HN HN NH H2N HN N O<ul style="display: flex;"><li style="flex:1">N</li><li style="flex:1">H2N </li></ul>Chain End HN H2N O HN ODendritic Unit NH2 NH2 Figure 4. Poly(amidoamine). An alternative approach, the convergent method, was first introduced by Fréchet and Hawker in 1990.8-10 It begins with the chain ends and works inward toward the center 6of the molecule to finally attach all “dendritic wedges” to a core molecule forming the completed dendrimer. This method often requires only two reactions for each generation growth7 thus allowing for a cleaner synthesis and, potentially, a more perfect structure.8, 11, 12 Unfortunately, this method limits the number of generations for the dendrimer as the focal point of the reaction becomes sterically crowded. However, regardless of which method is used to synthesize dendrimers, it is a very tedious process as both require several steps as well as extensive purification after each generation is formed (Scheme 1).13 7<ul style="display: flex;"><li style="flex:1">Divergent </li><li style="flex:1">Convergent </li></ul>2x 6x Scheme 1. Divergent and convergent methods for synthesis of dendrimers 8 Due to the dense surfaces of dendrimers, they cannot have chain entanglements with other dendritic molecules. Therefore, dendritic materials generally exhibit poor mechanical properties and engineering applications are often limited to blending agents while biological applications range from molecular delivery agents to unimolecular micelles.14 An interesting characteristic of dendrimers is their intrinsic viscosity. Unlike linear polymers, whose viscosity continues to rise with increasing molecular weight, a dendrimer’s viscosity typically goes through a maximum as the density of the surface increases and is always lower than its linear counterpart.15 Branched Polymers Branched polymers, are a hybrid of linear and dendritic polymers, both structurally and physically. In Figure 5 a generic structure of a branched polymer is shown and it is evident that these polymers consist of linear, dendritic and teminal units. Terminal Unit Linear Unit Dendritic Unit Figure 5. Generic representation of a branched polymer 9Branched polymers are unique because their properties are directly related to the degree of branching (DB). The degree of branching, DB is defined by the number of linear ( L), terminal ( T<ul style="display: flex;"><li style="flex:1">), and dendritic ( </li><li style="flex:1">D) units present in each polymer (Equation 5). </li></ul>D + T DB = (5) D + T + L So by changing the number of branching units within the polymer the physical properties should also change. Figure 6 depicts the relationship between mechanical properties and DB. Linear polymers have no branching (DB = 0) and their mechanical properties are very good. On the other hand, dendrimers have perfect branching (DB = 1) while their mechanical properties are very poor. Branched polymers are unique in that they can be prepared with varying DB values, thus, it should be possible to tailor their mechanical properties. For example, if a highly branched polymer is made, it should exhibit more dendritic-like qualities, while a very lightly branched polymer should exhibit qualities closer to those of linear polymers.

Oligomeric A2 + B3 Approach to Branched Poly(Arylene Ether Sulfone)

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