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Other Methods

Other Methods. Fractional Solution Soxhlet -type extraction by using mixed solvent. Reverse GPC : from low molecular weight fraction                  to high molecular weight fraction. Fractional Solution ( Soxhlet Apparatus). 1: Stirrer bar/anti-bumping granules

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Other Methods

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  1. Other Methods

  2. Fractional Solution Soxhlet-type extraction by using mixed solvent. Reverse GPC : from low molecular weight fraction                  to high molecular weight fraction

  3. Fractional Solution(Soxhlet Apparatus) 1: Stirrer bar/anti-bumping granules 2: Still pot (extraction pot) - still pot should not be overfilled and the volume of solvent in the still pot should be 3 to 4 times the volume of the soxhlet chamber. 3: Distillation path 4:Soxhlet Thimble 5: Extraction solid (residue solid) 6:Syphon arm inlet 7:Syphon arm outlet 8: Expansion adapter 9: Condenser 10: Cooling water in 11: Cooling water out

  4. Fractional Precipitation Dilute polymer solution is precipitated by variable non- solvent mixture. Precipitate is decanted or filtered Reverse fractional solution : from high molecular weight fraction to  low molecular fraction

  5. Affinity Chromatography

  6. Thin-layer Chromatography (TLC) Alumina- or silica gel coated plate. Low cost and simplicity. Preliminary screening of polymer samples or monitoring polymerization processes.

  7. Light Scattering Determination of MW Without Calibration

  8. Light scattering (determination of MW without calibration) Electromagnetic radiation • transmission: transmitted radiation passes through the medium unaltered. • absorption: energy from the incident beam is taken up, resulting in: (1)heating, (2) re-emitting at another wavelength (fluorescence, phosphorescence), (3)supporting chemical reactions. • scattering: scattering is non-specific, meaning the incident radiation is entirely re-emitted in all direction with essentially no change in wavelength. Scattering results simply from the optical inhomogeneity of the medium. • reflection: scattering at the surface of a matter (not considered here)

  9. Now we focus on the light scattering. • Application of Light Scattering for Analysis • Classical Light Scattering (CLS) or Static Light Scattering (SLS) • Dynamic Light Scattering (DLS) • CLS • Scattering center = small volumes of material that scatters light. Such as individual molecule in a gas. • Consequences of the interaction of the beam with the scattering center: depends, among other things, on the ratio of the size of the scattering center to the incident wavelength (λo). Our primary interest is the case where the radius of the scattering center, a, is much smaller than the wavelength of the incident light (a < 0.05λo, less than 5% of λo). This condition is satisfied by dissolved polymer coils of moderate molar mass radiated by VISIBLE light. When the oscillating electric field of the incident beam interacts with the scattering center, it induces a synchronous oscillating dipole, which re-emits the electromagnetic energy in all directions. Scattering under these circumstances is called Rayleigh scattering. The light which is not scattered is transmitted: , where Is and It are the intensity of the scattered and transmitted light, respectively.

  10. Oscillating electric field of incident beam interacts with scattering center, induces a synchronous oscillating dipole, which re-emits electromagnetic energy in all directions. Rayleigh scattering: (1+cos2θ), scattering centerobserver. • 1944, Debye • Rearrange: Constant, K λo, dn/dc = refractive index increment no: refractive index, π, c =[g/mL]

  11. Define “Rayleigh ratio” Rθ Iθ is inversely proportional to λo. Shorter wavelength scatters more than longer wavelength Assume: system is dilute, the net signal at the point of observation is sum of all scattering intensities from individual scatterer - no multiple scattering (scattered light from one center strike another center causing re-scattering, etc.). ? 6: What does do the osmosis pressure in here?

  12. Two ways to access the light scattering information experimentally: Turbidimetery (or spectrophotometer) Light scattering

  13. "Turbidity", = fraction of incident light which is scattered out = 1-(It/Io) •  is obtained by integrating Iθ over all angles: Substitute: 1. Turbidimeter experiment (Transmitted light intensity, It is measured) Solution is dilute, so higher order concentration terms can be ignored.

  14. Procedure: Measure at various conc.  Plot Hc/vs. c (straight line)  Determine M from intercept, 2nd virialcoeff., A2from slope

  15. 2. Light Scattering experiment(measure Iθ at certain θ and r)

  16. The slope of the plot can be either positive or negative. θ-condition

  17. (Hc)/vs. c For polydisperse sample, Turbidity (light scattering) is contributed by molecules of different MW. Define: turbidity → turbiditylight scatteringweight-average MW

  18. Rayleigh-Gans-Debye (RGD scattering) : when the scattering centers are larger than Rayleigh limit Different part of more extended domain (B) produce scattered light which interferes with that produced by other part (A) - constructive or destructive

  19. a = Q= scattering vector = (4π/λ)sin(θ/2)rg(10) Random coil Distribution is symmetrical for small particles (<λ/20). For larger particles, intensity is reduced at all angles except zero. Contributions from two scattering centers can be summed to give the net scattering intensity. The result is a net reduction of the scattered intensity Pθ = "shape factor" or "form factor" Always Pθ < 1, function of size and shape of scattering volume. Now we start seeing the angle dependence of the scattered light !

  20. p(θ) decreases with θ. • p(θ) decreases more for higher MW.

  21. Effect of MW and Chain Conformation on Pθ, and on measured MW at 90o.

  22. Random coil , Final Rayleigh equation for random coil polymer [Case 1]θ→0: Plot Kc/Rθ vs. c: Intercept=1/M, Slope=2A2 [Case 2]c→0: Plot Kc/Rθ vs. sin2(θ/2): y-=1/M, Intercept = (16π2/3Mλ2) rg2 Three information!

  23. Graphics

  24. Graphics

  25. (1) Rθ. (2) Kc/Rθ vs. c, Kc/Rθ vs. sin2(θ /2)plot. (3) θ =0c =0extrapolate. Kc/Rθ vs. sin2(θ /2) Kc/Rθ vs. c Zimm plot: : extrapolated points

  26. (Kc/Rθ) vs. c Cases 1. Small polymers: (Horizontal line) Zimm plot for PMMA in butanone λo=546 nm, 25℃, no ~1.348, dn/dc = 0.112 cm3/g Mw and A2 2. Small polymers in θ-solvent. Zimm plot of poly(2-hydroxyethyl methacrylate) in isopropanol λo=436 nm, 25℃, no ~1.391, dn/dc = 0.125 cm3/g θ-solvent: A2= 0 • Calculated values : Mw = 66,000 g/mol • A2 = 0 mol cm3/g2 • - Kc/Rθ at small angles fall mostly below the horizontal line plotted through the points from medium and large angles.

  27. 3. Larger polymers in good solvent. Zimm plot of polystyrene in toluene λo=546 nm, 25℃, no ~1.498, dn/dc = 0.110 cm3/g 4. Polymers in poor solvent: A2 Zimm plot of polybutadiene in dioxane λo=546 nm, 25℃, no ~1.422, dn/dc = 0.110 cm3/g

  28. Further Studies • Polymer Physics, M. Rubinsein and R.H. Colby. • Introduction to Physical Polymer Science , L.H. Sperling.

  29. The End

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