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Characterizing Polymers

Characterizing Polymers. Mini-tutorial. First step in characterizing a polymer:. Use your senses (take pictures to document) What color? Does it fluoresce Transparent or opaque? Homogeneous in appearance? Solid or liquid Tacky or sticky or brittle or tough

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Characterizing Polymers

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  1. Characterizing Polymers Mini-tutorial

  2. First step in characterizing a polymer: • Use your senses (take pictures to document) • What color? Does it fluoresce • Transparent or opaque? • Homogeneous in appearance? • Solid or liquid • Tacky or sticky or brittle or tough • Mass – compare with theoretical yield

  3. Describe the material below

  4. Describe the material below

  5. Second, try and dissolve the polymer in different solvents • Water, ethanol, benzene, methylene chloride, tetrahydrofuran, acetonitrile, hexane, acetone, diethyl ether, dimethyl sulfoxide, N-methyl pyrrolidone (NMP) • Leave it at room temp overnight. Look for swelling if not dissolved. • Boil solvent for 4 hours. • If it doesn’t dissolve its probably cross-linked or really crystalline

  6. Polymer Family Tree Thermoplastics Thermosets/Elastomers Will reform when melted Will not reform Not Cross-Linked Cross-linked 90% of market 10% of market Polyethylene Epoxy 33% Melamine Formaldehyde Vinyls Phenolic 16% Polyester (unsaturated) Polypropylene Polyimide 15% Polyurethane PMMA Some are thermoplastic as well. ABS Silicone Nylon Urea Formaldehyde Polycarbonate Saturated Polyester PEEK Polyurethane Some are thermosets as well. PVC Types of Polymers & solubility Will dissolve Won’t dissolve

  7. Third, Structural Characterization of soluble polymers • 1H & 13C & 29Si Nuclear Magnetic Resonance and infrared spectroscopy • Molecular weight by gel permeation chromatography • Composition by combustion analyses • X-ray diffraction on film or powder • Viscosity of dilute solutions- shape of polymer

  8. X-ray diffraction Semi-crystalline polymer shows diffraction rings amorphous polymer shows diffuse band

  9. Or third, Structural Characterization of insoluble polymers • Harder to characterize • Solid state 1H & 13C & 29Si Nuclear Magnetic Resonance and infrared spectroscopy • Composition by combustion analyses • X-ray diffraction on film or powder

  10. Morphological Characterization of polymers • If opaque or transluscent, SEM and optical microscopy (bifringence)-crystalline or amorphous & more. • Fracture polymer and look at fracture surfaces • Look for phase separation (like immiscible block copolymers) • Look for long range order • Look for pores

  11. Thermal characterization of polymers • Thermal gravimetric analyses (TGA) – determines decomposition temperature • Differential scanning calorimetry (DSC)– detects phase changes (melting or glass transition temperatures) or chemical reactions

  12. FIGURE 5.16. Idealized differential scanning calorimetry (DSC) or differential thermal analysis (DTA) thermogram: (A) temperature of glass transition, Tg; (B) crystallization; (C) crystalline melting point, Tm; (D) crosslinking; and (E) vaporization. dΔQ/dt = electrical power difference between sample and ref- erence; ΔT = difference in temperature between sample and reference. DSC analysis

  13. Thermal gravimetric analysis

  14. Mechanical characterization of polymers • Stress-strain curves: • Young’s modulus (brittleness) • Tensile strength-pull sample appart • Flexural strength- bend until it breaks • Compressive strength-crush sample • Dynamic mechanical analyses (same info as above but with cyclic application of stress or strain. • Generate modulus temperature curves • Fatigue studies to predict failure under cyclic stress

  15. Stress-Strain Analysis Tensile strength = pull sample appart Chains in neck align along elongation direction: strengthening σ Elongation by extension of neck ε

  16. TIME DEPENDENT DEFORMATION • Data: Large drop in Er for T > Tg. • Stress relaxation test: (amorphous polystyrene) --strain to eo and hold. --observe decrease in stress with time. Adapted from Fig. 15.7, Callister 6e. (Fig. 15.7 is from A.V. Tobolsky, Properties and Structures of Polymers, John Wiley and Sons, Inc., 1960.) • Relaxation modulus: • Sample Tg(C) values: PE (low Mw) PE (high Mw) PVC PS PC -110 - 90 + 87 +100 +150 Selected values from Table 15.2, Callister 6e. 27

  17. Not every polymer needs all of these analyses, but structure is the most basic and important • Known (described in literature) polymers need less structural characterization. Often just IR and Mw from GPC. • New polymers need complete structural characterization: NMR, IR, Combustion analysis, GPC, solubility, glass transition temp and/or melting point.

  18. Morphological and Mechanical studies are dependent on research interests. • If you are interested in strong polymers, then morphological, mechanical & thermal studies are important • Other applications requiring morphological, mechanical & thermal studies would include preparation and testing of 1) membranes, 2) coatings, 3) paint, 4) polymer foams, 5) organic photovoltaics, 6) OLED’s, 7) adhesives and 8) low friction coatings

  19. Other polymer properties that are important for specialty polymers • Coatings, packaging, membranes, Photovoltaics & OLED’s; gas and water permeability should be measured. • Battery and fuel cell membranes: gas & water permeability and ion conductivity • Dielectrics, wiring insulation: dielectric and electrical conductivity • Fabrics & building materials: fire resistance • Any polymer used in sunlight or radiation or in the presence of chemicals: resistance to oxidative degradation.

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