Osmotic pressure and light scattering methods are used to determine the number-average and weight-average molecular weights of polymers in solution. Polymers can be characterized as amorphous, semicrystalline, or crystalline depending on their chain structure and interactions. Thermoplastics exhibit glass transitions and/or melting points while thermosets only exhibit glass transitions.

3. In good solvents Molecules assume expanded conformations

4. In poor solvents intramolecular interactions become more significant

5. In solvents chains assume their “unperturbed dimensions” Alpha is the linear coil expansion, this is how it is related from that “equivalent radius” equation to determining what is a good/bad solvent…I think this also ‘might’ have something to do with “radius of gyration” as she mentioned in class once. Polymer Characterization FOUR ways to calculate Molecular Weight of a polymer: (look at pages starting with page 129) -Osmometry -Light Scattering -Intrinsic Viscosity -Gel-Permeation Chromatography……. (In addition to these accurate but time-consuming techniques, there are a number of secondary methods by which average molecular weight can be determined. The most important method is called gel permeation chromatography (GPC) The osmotic pressure is the additional pressure that must be imposed to keep solvent and solution sections at the same level. This static method requires a long time to reach equilibrium. Pi/c=RT/MN + RTA2c always linear. Y = C1 + C2 X A reproduction of a graph I had in my notes……: In class, she said something about this being important: -Absolute (or primary) method -Measures number average molecular weight -Lower limit is about 20,000 due to permeability of low molecular weight polymer fraction -Upper limit is about 500,000 due to inaccuracy in measuring small osmotic pressure *Important*……..maybe, study Osmotic pressure, its effect on quality Light Scattering Method: The weight average molecular weight (Mw) can be obtained directly by scattering experiments. This techniques is not used routinely used for molecular weight determination because of the difficulty and expense sample preparation. This method has these characteristics: -Absolute (or primary) method -Measures weight average molecular weight -Applicable from 10,000 to 10,000,000 -Limitation for copolymers due to difference in refractive indexes between two types of repeat units -No problems for branched polymers -Can measure radius of gyration *It would be a good idea to highlight the differences between light scattering and Osmometry* For the Zimm Method, I do not know if it will be that important since she didn’t underscore much from it, but it is def. worth a look: The most rigorous approach top determine Mw from light scattering data is a Zimm plot. A double extrapolation to both zero concentration and zero angle is used to obtain information concerning molecular weight , second virial coefficient, and chain dimensions In addition to this, from me: this procedure has the advantage that the “chain conformation” does not need to be known in advance. Also, you need to tediously measure the scattered light at many angles, which is a disadvantage because it is laborious (extra work). Intrinsic Viscosity Measurements A method widely used for routine molecular weight determination is based upon the determination of the intrinsic viscosity [], of a polymer in solution through measurements of the solution viscosity. Molecular weight is related to [] by the Mark-Houwink-Sakurada equation I think this is really important Used to find molecular weight That “n” looking symbol stands for intrinsic viscosity, The v stands for viscosity And if you know both constants a and K, you can use this equation to find Molecular Weight based on viscosity. “a” tells you how the polymer is….? (that’s what she said in class….) The intrinsic viscosity can be found by finding the y-intercept of this graph, or a graph similar that has the same xy axis And from the notes above and on other pages, I think an equation similar to this was used for this graph: π /c=RT/MN + RTA2c always linear. π /c= [n] + Kx[n]2c remember: Y=mx+b y= π /c ……m=slope= RTA2 & Kx[n]2 …… x= c ……..b=y intercept= RT/MN & [n] Chromatography/Gel Permeation Chromatography Chromatography is a separations method that relies on differences in partitioning behavior between a flowing mobile phase and a stationary phase to separate the components in a mixture. A mixture of different size solute molecules is eluted through a column of porous particles. Large molecules are swept through unhindered, while small molecules are retarded in the pores END TOPIC/CHAPTER 3 Begin Topic/Chapter 4 Solid State Properties of Polymers Recap on Thermoplastics & Thermosets… Here is stuff on this topic from last test’s notes: Thermoplastics-------amorphous---------only Tg --------semicrystalline------Tm & Tg Thermoset------amorphous-----only Tg Amorphous -random chain entanglements -most transparent resins are amorphous -greater impact strength, less shrink and warp -only Tg Spaghetti Like Semi-Crystalline -ordered crystalline structure -Crystallinity affected by processing -Exhibits both a Tc and a Tg Linear and branched polymers are thermoplastics Crosslinked network, are ultimately branched are thermoset. Polymer Morphology Morphology involves the study of the arrangement of polymer molecules into crystalline and amorphous regions. -Polymer with high crystallinity are dense, stiffer , harder, tougher and more resistant to solvents. -Amorphous domains add flexibility and promote ease of processing below the melting temperature. Presence of crystalline structure have a significant influence on the physical, thermal and mechanical properties of the polymer Example of amorphous polymer is atactic polystyrene. “as the melt is cooled, a temperature is reached at which all long-range segmental motion ceases, and this called the glass-transition temperature, Tg” In the glassy state, at T