Probing the Bases of Polymer Glass Transitions
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Probing the Bases of Polymer Glass Transitions
- 1. Probing the Bases of Polymer Glass Transitions Miles Ndukwe Millbrook High School Raleigh, NC
- 2. Polymers • Sustaining Life Figure 1 - DNA Figure 2 – Rubber tire • Dominating Commerce Figure 3 - Plastics Figure 4 - Clothing
- 3. Crystallinity • Crystalline – Ordered Crystalline • Amorphous Amorphous – Random • Semi-crystalline Semi-crystalline – Consists of both Figure 5 – Crystalline, amorphous, and semi-crystalline polymers
- 4. Glass Transition Temperature (Tg) • Hard, brittle Soft, rubbery Figure 6 – Visual representation of polymers’ actions at Tg.
- 5. Factors Suggested to Affect Tg 1. Conformational flexibilities of individual polymer chain backbones 2. Sizes or steric bulk of side-chains 3. Interactions between polymer chains
- 6. Review of Literature • Richardson, M. J. and Savill, N. G. “Derivation of Accurate Glass Transition Temperatures by Differential Scanning Calorimetry.” Polymer (1975). 753 • Kim, Y. W. et al. “Molecular Thermodynamic Model of the Glass Transition Temperature: Dependence on Molecular Weight.” Polymers for Advanced Technologies (2008). 944-946 • Makhiyanov, N. and Temnikova, E. V. “Glass-Transition Temperature and Microstructure of Polybutadienes.” Polymer Science (2010). 2102-2111
- 7. Statement of the Problem The focus of this research is to determine if differences in the contributions made by the three structural factors cause and explain the wide range of Tgs observed for structurally different polymers.
- 8. Research Questions 1. Why do polymers with different or even somewhat similar microstructures show different softening temperatures, sometimes ranging over several hundreds degrees Celsius? 2. Are each of the three factors (inherent conformational flexibilities of polymer chain backbones, sizes or steric bulk of side chains, and interactions between polymer chains) important in determining a polymer’s Tg?
- 9. Hypothesis If two amorphous polymers, both with nearly identical inherent conformational flexibilities of their polymer chain backbones (factor 1) and no side chains (factor 2), differ in Tg, then it is caused by differences in the interactions between polymer chains (factor 3), because the other factors have been eliminated by their commonality.
- 10. Materials and Methods Materials Production Methods • Co-polyamide Salt Preparation ‒ Mixed monomers (homopolymers) ‒ 1,6 Hexamethylenediamine ‒ Mixed monomer salts (co-polymers) ‒ Adipic Acid ‒ Sebacic Acid Monomers Melt Pre-Polymerization • Co-polyester ‒ 1,6 Hexanediol ‒ Adipic Acid Solid State Polymerization ‒ Sebacic Acid Co-Polymers
- 11. Comparison of Polymers HO OH 1,6 Adipic Acid Adipic Acid 1,6 Hexanediol Hexamethylenediamine O O Nylon 6,6 Polyester 6,6 Figure 7 – Formula of nylon 6,6 Figure 8 – Formula of polyester 6,6
- 12. Characterization of Polymers Thermal-Gravimetric Differential Scanning Analysis (TGA) Calorimetry (DSC) pH Salt Figure 10 – Perkin Elmer preparation Figure 9 – pH Pyris-1 Thermo- Figure 11 – Perkin Elmer meter Gravimetric Analyzer Diamond DSC-7 Instrument Fourier Transform Infrared Spectroscopy (FTIR) Melt pre- Solid-state polymerization polymerization Figure 12 – Nicolet Nexus 470 Spectrometer Dilute Solution Viscosity Figure 13 – Cannon-Ubbelhode Viscometer
- 13. Characterization of Polymers DSC X-Ray Diffraction (XRD) Co-polymerization Figure 14 – Philips XLF, ATPS X- Ray Diffractometer
- 14. FTIR Spectra * * H e x ame thy di a mi ne 0.3 Hexamethylenediamine Ab s 0.2 0.1 * * A d i pi c A ci d 0.4 Adipic Acid Ab s 0.2 * * N y l on 6,6 S al t 0.2 Nylon 6,6 Salt Ab s 0.1 - 0.0 * * N y l on 6-6 Nylon 6,6 0.2 Ab s 0.1 400 0 350 0 300 0 250 0 200 0 150 0 100 0 500 W av enu mber s ( c m- 1) Figure 15 – FTIR spectra of nylon 6,6 and its components
- 15. Homopolymer Melting Scans Figure 16 – DSC scans of homopolymer nylons Nylon 6,6 melting point ΔH – 53 J/g Nylon 6,10 melting point ΔH – 76 J/g
- 16. Intrinsic Viscosity and Molecular Weight Intrinsic Viscosity ([η]) and Molecular Weights of Nylon 6,10 Pre-polymers Initial production [η] Molecular weight condition (g/mol) Monomer mixture 0.125 dL/g 1,800 Atmospheric 0.266 dL/g 4,600 From pressure salts Elevated pressure 0.802 dL/g 19,000 Figure 17 – Intrinsic viscosity and molecular weight of nylon 6,10 pre-polymers
- 17. Co-Polyamide Results Figure 18– DSC scan of co-polyamide Differences in Melting Points (Tms) and ΔHs of Tms vs Ratios of the Co-polyamides Co-polyamide ratio (6,6 to Tm ( C) ΔH of melting points (J/g) 6,10) 50% - 50% 192 39 65% - 35% 220 41 80% - 20% 233 57 Figure 19– Tms and ΔHs of co-polyamide variations
- 18. Conclusion If two amorphous polymers, both with nearly identical inherent conformational flexibilities of their polymer chain backbones (factor 1) and • Inconclusive no side chains (factor 2), differ in Tg, then this is caused by different interactions between polymer chains (factor 3).
- 19. Future Directions • Use of nylon mixture (co-polyamide) • Corresponding polyesters (co-polyester) Figure 20 – DSC scan of 4 nylon mixture
- 20. Acknowledgements • God • Dr. Alan E. Tonelli, Alper Gurarslan, Jialong Shen, Kathleen Dreifus • Friends and Family • NC Project SEED • Funders: The North Carolina Local Section of the American Chemical Society, the Hamner Institute for Health Sciences, Biogen Idec, Greater Triangle Community Foundation, and the Burroughs-Wellcome Fund
Notes de l'éditeur
- Good (morning/afternoon/evening). My name is Miles Ndukwe, and I attend Millbrook High School in Raleigh, North Carolina. Over the summer, I have conducted research under the direct supervision of Dr. Alan E. Tonelli in the department of Textile Engineering, Chemistry, and Science at North Carolina State University. The research is entitled “Probing the Bases of Polymer Glass Transitions”.
- Polymers are the building blocks of many parts of our bodies and the materials we use everyday. Biopolymers, such as DNA, sustain the lives of living organisms. Various commercial products such as tires, plastics, and clothing are composed of polymers. Through this research, I plan to improve my knowledge of the softening temperature of polymers in order for industries to improve the design of polymer-based products, because their processing and use temperatures are determined by their softening temperatures.
- One of the significant characteristics of polymers is crystallinity, or the degree of structural order in a polymer. When the macromolecular chains of a polymer sample are arranged in an orderly fashion, as displayed on the top of Figure 5, it is known as a crystalline polymer. When the chains are arranged randomly and are disordered, the polymer is identified as amorphous, as seen in the middle of Figure 5. In most cases, there are no fully crystalline polymers; therefore, we have semi-crystalline polymers, which are composed of both amorphous and crystalline regions. In my research, I am studying the softening of amorphous polymers.
- The temperature at which amorphous polymers, or the amorphous regions of semi-crystalline polymers, soften from a hard and stiff state to a softer, rubbery state is known as the glass-transition temperature, which is denoted as Tg. Tgvaries with the molecular weight and the structure of a polymer. The standing red Solo cup in Figure 6 represents the stiff state of the polymer below Tg , and the melted one is an illustration of what the polymers look like above Tg. In the past, it has been revealed that there are differences in Tgs observed for structurally dissimilar polymers that can range over several hundreds degrees Celsius, and there have been many suggestions for the causes of this wide range in Tgs.
- Differences in structural factors, such as (1,2,3) have often been considered to be the leading reasons:The following sources were researched in order to provide some background information.
- -In 1975, Richardson and Savill successfully employed a method of determining Tg.-In 2008, Kim et al. discussed the relationship between Tg and the polymer’s molecular weight. -In 2010, Makhiyanov and Temnikova demonstrated that changes in the microstructure of a polymer affects Tg.With the information from these sources, in addition to other background information on this topic, the following statement of the problem was produced.
- The focus of this research is to determine if differences in the contributions made by these three structural factors cause and explain the wide range of Tgs observed for structurally different polymers. From this statement of the problem, the following research questions were formulated:
- Why do polymers with different or even somewhat similar microstructures show different softening temperatures, sometimes ranging over several hundreds degrees Celsius?Are each of the three factors (inherent conformational flexibilities of polymer chain backbones, sizes or steric bulk of side chains, and interactions between polymer chains) important in determining a polymer’s Tg?Based on these research questions, the following hypothesis was derived:
- If two amorphous polymers, both with nearly identical inherent conformational flexibilities of their polymer chain backbones and no side chains, differ in Tg, then it is caused by differences in the interactions between polymer chains because the other factors have been eliminated by their commonality, which I can then independently assess. In order to test this hypothesis, two amorphous co-polymers with structures that only cause different inter-chain interactions will be synthesized, characterized, and their Tgs will be measured and compared. The following materials and methods will be exercised in this research.
- A wholly amorphous co-polyamide was attempted to be synthesized before a structurally similar co-polyester.-Homopolymer nylons were synthesized using these production methods before the co-polyamide.-First, two salts were prepared with a mixture of two monomers, and then underwent melt pre-polymerization, so that the monomers would react.-The pre-polymers underwent solid-state polymerization to produce complete polymers of decent molecular weights.-An identical procedure was employed to synthesize the co-polyamide, but the salt consisted of a mixture of both monomer salts. Here is an example of the syntheses of a polyamide and an analogous polyester.
- Here, we have the formulas for nylon 6,6, which have amide bonds formed with HMDA, and polyester 6,6, which have ester bonds formed with hexanediol. The nylon is able to hydrogen bond, while the polyester cannot. This is the only difference in structure and would produce different interchain interactions. The following methods characterized the polymers throughout their syntheses.
- -Finding the pH of the monomer salts would confirm their formation.-Thermal-Gravimetric Analysis, or TGA, determined the maximum temperature of stability of the salts.-Differential Scanning Calorimetry, or DSC, determined the melting points of the homopolymers and their salts.This information would determine the temperature at which to maintain the salts during melt polymerization.-Fourier Transform Infrared Spectroscopy, or FTIR, analysis confirmed the nylon formation (amide bonds) of the pre-polymers. -Dilute solution viscosity was employed to compare the molecular weights of the polymers before and after solid-state polymerization.
- When characterizing the co-polymers, samples of each would undergo DSC, once again, to insure that they are amorphous and to determine their Tgs. XRD would then be employed in order to further characterize any crystallinity, or absence thereof, in the polymers, to determine if they are wholly amorphous. If the Tgs from the DSC scans differ, then I can confirm the hypothesis.
- Figure 15 displays the FTIR spectra of the nylon 6,6 polymer, its salt, and its monomer components. The amide bonds are confirmed in the nylon vibrations, such as the peak designated by the asterisk.
- Indicated by the DSC scans in Figure 16, the melting points of homopolymers nylon 6,6 and nylon 6,10 are approximately 246 and 211° C, respectively. The change in enthalpy, or ΔH, of the melting point of nylon 6,6 is around 53 J/g, and is approximately 76 J/g for nylon 6,10’s melting point. This information would confirm the nylon formation and would be applied when determining the temperature at which to maintain the polymers during solid state polymerization.
- Figure 17 displays the intrinsic viscosity and molecular weights of three samples of nylon 6,10 pre-polymers. Previous procedures did not produce products of high molecular weight. A procedure, consisting of elevated pressure, produced a pre-polymer with decent molecular weight. After undergoing an effective solid state polymerization, the molecular weight should increase even further, so that Tgs will not be affected by low molecular weights.
- In the DSC scan of the co-polyamide, the peak in the graph revealed a melting point at approximately 192° C, and this a property not found in amorphous polymers. Melting points indicate crystallinity in polymers; therefore, this method of synthesizing a wholly amorphous polymer was not effective. Other ratios of nylon 6,6 to 6,10 have been synthesized, and their melting points and ΔHs have been compared.
- The hypothesis for this research is currently inconclusive, because our method did not produce a wholly amorphous copolymer. However, melting four nylons together as well as revised bulk syntheses did, so soon I may be able to test the hypothesis.
- In the future, I would like to employ a mixture of nylon 6, 6,6, 6,10, and 11 in the synthesis of the amorphous co-polyamide. Here, I would compare DSC traces of the physical mixture of the nylons before and after heating for several hours above the temperature of the highest melting Nylon (Nylon-6,6 Tm ~ 260° C). From this scan, this method of synthesizing a wholly amorphous polymer seemed promising, indicating a change in slope, which indicates Tg of approximately 47°C. Once successful in that synthesis, the structurally analogous amorphous co-polyester will then be synthesized using a mixture of corresponding polyesters.