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20. 08. Sep. 19, 2008. Molecular Weight & Polymer Solutions. Chemical and Bioengineering Konkuk University. Number average and weight average moleculart weight. 몇몇 천연 고분자 (monodisperse): all polymer molecules   같은 분자량 합성 고분자 (polydisperse): - PowerPoint PPT Presentation

Text of Molecular Weight & Polymer Solutions

  • Molecular Weight & Polymer Solutions

    Chemical and BioengineeringKonkuk UniversitySep. 19, 20080820

  • (monodisperse): all polymer molecules (polydisperse): Polydisperse - a polymer that exists over a wide range of molecular massesCharacteristic of man-made polymers. ; poor mechanical property ; too tough to process ; 105~106 for vinyl polymer15,000~20,000 for polar functional group containing polymer(polyamide)Number average and weight average moleculart weight

  • (Methods to determine molecular weight)a. Absolute method : mass spectrometry, colligative propertyend group analysis, light scattering, ultracentrifugationb. Relative method : solution viscosityc. Fractionation method : GPC

  • A. number average molecular weight ( )

    B. weight average molecular weight ( ) C. z average molecular weight ( ) D. general equation of average molecular weight :

    E. > > (colligative property and end group anaylsis)(light scattering)(ultracentrifugation)( a=0 , a=1 , a=2 , )3-1-1.

  • 3-1-2. Property of Molecular weight and polymer molecular weight determines the property: the attractive force between molecular changeidentity chemical structure : chain length, surface, attractive force risemolecular weight increase polymer property increaseThreshold molecular weight: the increase rate slow , differ depend on the polymer type(structure) Polyethylene(nonpolar polymer): low attractive force, high thresholdPolyamide (H-bond polymer): high attractive force, low threshold

  • The effect of the average molecular weightthe concentration solution viscosityOver the critical molecular weight suddenly riseEntanglement molecular weight: Because of the bridging phenomenon, the viscosity suddenly rise

  • Measure of the distribution of molecular mass in a given polymer sample.

    The PDI calculated is the weight average molecular weight divided by the number average molecular weight.

    The PDI has a value always greater than 1,

    But as the polymer chains approach uniform chain length, the PDI approaches unity (1). Polydispersity index (PDI)

  • D. Polydispersity index : width of distribution

    polydispersity index (PI) = / 1 E. Example of molecular weight calculation

    a. 9 moles, molecular weight ( ) = 30,000 5 moles, molecular weight ( ) = 50,000b. 9 grams, molecular weight ( ) = 30,000 5 grams, molecular weight ( ) = 50,000

  • A. Two-step process of polymer dissolutionfirst step : the solvent diffuses into polymer masses to makea swollen polymer gelsecond step : swollen polymer gel breaks up to solution

    B. Thermodynamics of solubility : Gibb's free energy relationship G < 0 : spontaneously dissolve T and S are always positive for dissolving processConditions to be negative G,H must be negative or smaller than TS3-1-2. Polymer solution

  • C. Solubility parameter : 1, 2 = volume fractionE1/V1, E2/V2 = cohesive energy densities ( )1, 2 = solubility parameter

    if , then

  • D. Small's and Hoy's G parameter a. Small(designated G derived from Heat of vaporization)

    ex) polystyrene :

    b. Hoy(designated G based on vapor pressure measurement)

    ex) polystyrene : (d: density, M: molecular weight of unit)

  • Group molar attraction constants

  • a. polymer-polymer interactionb. solvent-solvent interactionc. polymer-solvent interactiond. polymer structure (branched or not)e. brownian motion Figure. Coil molecular shape r = end-to-end distance s = radius of gyrationE. Hydrodynamic volume of polymer molecules in solution

  • A. Molecular weight limitation up to 50,000B. End-group must have detectable speciesa. vinyl polymer : -CH=CH2b. ester polymer : -COOH, -OHc. amide and urethane polymer : -NH2, -NCOd. radioactive isotopes or UV, IR, NMR detectable functional group e. MW of linear polymerC. 3-2. Number Average Molecular Weight- Measurementn / end-group moles per 1 g(n=number of end-group)3-2-1. End-group AnalysisCOOH: end point OH: acetylation

  • 1. The method cannot be applied to branched polymers2. In a linear polymer there are twice as many end of the chain andgroups as polymer molecules3. If having different end group, the number of detected end group is average MW4. End group analysis could be applied for polymerization mechanism identified E. High solution viscosity, low solubility, steric hindrance : Mn = 5,000 ~ 10,000D. Requirement for end group analysis

  • Ex. A 0.5 g sample of an unsaturated polyester resin was reacted with excess acetic anhydride. Titration of the reaction mixture with 0.0102 M KOH required 8.17 ml to reach the end point. What is the number average molecular weight? polyester 0.5 g acetic anhydride , 0.0102 M KOH 8.17 ml KOH . Polyester ? (Acid number: mg KOH/g polymer)KOH: 56.1g/molEx. What is the DP of a sample of polyester prepared from 4-hydroxybenzoic acid if the acid number, determined with standard KOH solution, is 11.2? (CH4O2), carboxyl polymer , KOH acid number 11 DP?

  • 3-2-2. The measure of colligative property (colligative property)Colligative properties are properties of solutions that depend on the number of particles in a given volume of solvent and not on the mass of the particles.the freezing point depression, the boiling point elevation, the steam pressure depression, the osmotic pressure The mole number of polymer average molecular weight This equation show that the concentration equation of solvent was the chemcal potential difference between the solution of solvent and pure solvent

  • (1) Boiling-point elevation (Ebulliometry)

    A2 : second virial coefficient : boiling point elevation : the latent heats of vaporization

    limitation of : below 30,000 C : the concentration in grams per cubic centimeterR : gas constant(2) Freezing-point depression (Cryoscopy)

    : freezing-point depression,T : freezing point : the latent heats of fusion

  • (3) (Membrane Osmometry)According to van't Hoff equation

    limitation of : 50,000~2,000,000

    The major error arises from low-MW species diffusing through the membrane.p = r g h (cm)i. Static Osmometerii. Dynamic Osmometer

  • (4) (Vapor Pressure Osmometry) Raoult : : Raoult : Raoults law: the vapor pressure of an ideal solution is dependent on the vapor pressure of each chemical component and the mole fraction of the component present in the solutionThe equilibrium state: Solvent pressure of both sides equal, the Temperature differ

    Gap of temperature The steam pressure drop

  • The measuring vapor pressure difference of solvent and solutiondrops.

    : the heat of vaporization per gram of solvent m : molality limitation of : below 30,000 Calibration curve is needed to obtain MW of polymer sample Standard material : Benzil Vapor Pressure OsmometryMw 30,000 over: the separation osmotic pressure method Mw 30,000 under: steam osmotic pressure methodThe average molecular weight

  • A. Conventional mass spectrometer for low molecular-weight compoundenergy of electron beam : 8 -13 electron volts(eV)(5) Mass Spectrometry TOF (time-of-flight) MS The each polymers molecular ionization the condensation phase-> gas phase tranformation TOF (time-of-flight) MS: the molecular ion mass measure

  • a. matrix-assisted laser desorption ionization mass spectrometry(MALDI-MS)b. matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF)c. soft ionizationsampling: polymers are imbedded by UV laser absorbable organiccompound containing Na and K. d. , are calculated by using mass spectra.e. The price of this mass is much more than conventional mass.f. Up to = 400,000 for monodisperse polymers.B. Modified mass spectrometer for synthetic polymer

  • MS Analysis of p-Aminobenzyl Amine Conversion ProductPrnD

  • 2D SDS-PAGE and MALDI-TOF Mass AnalysisSpot expected to be PrnDMALDI-TOF MS MS fingerprinting MS sequencingPeptides identical to PrnD pQE 80L-PrnD is expressed in E. coli1231. 1329.656: QPTLVTAER

    2. 1710.910: AFYRGWVDRVASER

    3. 2021.235: AVVMDRHCSHLGANLAD

  • MALDI-TOF Mass AnalysisPoly(methyl methacrylate): 6,400

  • A. The intensity of scattered light or turbidity() is dependon following factorsa. size, b. concentration, c. polarizability, d. refractive index, e. anglef. solvent and solute interactiong. wavelength of the incident light : concentration : refractive index of the solvent : wavelength of the incident light : Avogadro's number : specific refractive increment : function of the angle, Zimm plot(after Bruno Zimm): double extrapolation of conc.and angle to zero3-3. Measurement of Weight Average Molecular Weight3-3-1. Light ScatteringB. Light sourceHigh pressure mercury lamp and laser light

    C. Limitation of molecular weight( ) : 104~107

  • When the scattering particle was smallWhen the scattering particle was largeThe light scattering of the particle

  • A. This technique is used a. for protein ( ) rather than synthetic polymersb. for determination of synthetic polymersB. Principles: under the centrifugal field, size of molecules aredistributed perpendicularly axis of rotationDistribution process: sedimentation : , 3-3-2. UltracentrifugationSedimentation( ): proportion of molecular weight,

  • 1) 5% polymer solution: too sticky to flowlow molecular weight solution: easy flow2) Viscosity: resistance of flowlong chain molecule: large friction3-4. Viscosity: the method of relative molecular weight from the assumption of the molecu

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