Polymer Characterization Topics Topics Molar Mass And Molar

Polymer Characterization

Topics

Topics � Molar Mass And Molar Mass Distribution • Molecular Weight Determination • Laser Light Scattering • Chromatography Size Exclusion (GPC) • Mass Spectroscopy � Structure And Morphology • Infrared Spectroscopy • Nuclear Magnetic Resonance • X-ray Microscopy • Scanning Electron Microscopy • Atomic Force Microscopy � Dynamic Properties • Thermal Analysis

References

References

References

References

References

References

References

References

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Development of Polymers

Development of Polymers Product Synthesis Concept Design Properties Fundamentals 14

Role of Polymer Characterization Structure Synthesis Properties Characterization 15

Molecular Weight

Molecular Weight Effect on Properties Limiting Value Mechanical Property General Relationship Strength, Modulus, etc s. B = A - (BMn) DP Critical Degree of Polymerization 17

Molecular Weight Effect on Flow General Relationship [h] = K Ma K and a are constants Viscosity Mark-Houwink-Sakurada Relation Degree of Polymerization 18

Optimization of Molecular Weight Mechanical Property* Useful Range Viscosity Degree of Polymerization 19

Molecular Weight Distribution Low molecular weight molecules # of Molecules Single Value Molecular Weight Synthetic Polymers # of Molecules Broad Range of Values Molecular Weight Biological Polymers Single Value # of Molecules Molecular Weight 20

Methods of Molecular Weight Determination � Number Average Molecular Weight • End-group analysis �determine the number of end-groups in a sample of known mass • Colligative Properties �most commonly osmotic pressure, but includes boiling point elevation and freezing point depression � Weight Average Molecular Weight • Light scattering �translate the distribution of scattered light intensity created by a dissolved polymer sample into an absolute measure of weight-average MW

Methods of Molecular Weight Determination � Viscosity Average Molecular Weight • Viscometry �The viscosity of an infinitely dilute polymer solution relative to the solvent relates to molecular dimension and weight. � Molecular Weight Distribution • Gel permeation chromatography �fractionation on the basis of chain aggregate dimension in solution.

Measurement of Number Average Molecular Weight 2. 3. 1 End-group Analysis A. Molecular weight limitation up to 50, 000 B. End-group must have detectable species a. vinyl polymer : -CH=CH 2 b. ester polymer : -COOH, -OH c. amide and urethane polymer : -NH 2, -NCO d. radioactive isotopes or UV, IR, NMR detectable functional group

Measurement of Number Average Molecular Weight C. Mn = 2 x 1000 x sample wt meq COOH + meq OH D. Requirement for end group analysis 1. The method cannot be applied to branched polymers. 2. In a linear polymer there are twice as many end of the chain and groups as polymer molecules. 3. If having different end group, the number of detected end group is average molecular weight. 4. End group analysis could be applied for polymerization mechanism identified E. High solution viscosity and low solubility : Mn = 5, 000 ～ 10, 000

? 1: Find a procedure for End group Analysis for one kind of Polymer

Colligative properties Properties determined by the number of particles in solution rather than the type of particles. ØVapour pressure lowering ØFreezing point depression ØBoiling point elevation ØOsmotic pressure

How Vapor Pressure Lowering Occurs • • • Solute particles take up space in a solution. Solute particles on surface decrease number of solvent particles on the surface. Less solvent particles can evaporate which lowers the vapor pressure of a liquid.

Vapor Pressures of Pure Water and a Water Solution The vapor pressure of water over pure water is greater than the vapor pressure of water over an aqueous solution containing a nonvolatile solute. Solute particles take up surface area and lower the vapor pressure

Vapor Pressure Lowering Let component A be the solvent and B the solute B is nonvolatile Applying Raoult’s Law: where: PA= vapor pressure of the solvent in solution = vapor pressure of the solution PA*= vapor pressure of the pure solvent XA= mole fraction of the solvent

The lowering in vapor pressure, where: = mole fraction of solute

Boiling Point Elevation When a non volatile solute is added to solvent: • Vapor pressure of solvent is lowered • solution formed must be heated to higher temperature than boiling point of pure solvent to reach a vapor pressure of 1 atm. • This means that non volatile solute elevates the boiling point of the solvent which we call boiling point elevation

Boiling Point Elevation (for dilute solutions) where is the molar mass of the solvent and the molality of the solute in mol/kg

Boiling Point Elevation for dilute solutions where Kb= boiling point constant or ebullioscopic constant of the solvent

Boiling-point elevation (Ebulliometry) T ( b )C=0 = C RT 2 + A 2 C Hv. Mn Tb : boiling point elevation H v : the latent heats of vaporization We use thermistor to major temperature. (1× 10 -4℃) limitation of Mn : below 20, 000

Freezing Point Depression Addition of a nonvolatile solute to a solution lowers the freezing point of the solution relative to the pure solvent.

Freezing Point Depression (for dilute solutions) Kf= molal freezing point depression constant or cryoscopic constant

Freezing-point depression (Cryoscopy) RT 2 Tf + A 2 C ( )C=0 = Hf Mn C Tf : freezing-point depression, C : the concentration in grams per cubic centimeter R : gas constant T : freezing point Hf: the latent heats of fusion A 2 : second virial coefficient