This preview shows pages 1–2. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: 1) Some basic but commonly confusing concepts: a) Is T g lower or higher than T m ? Why? b) Why is commerical polypropylene opaque while commercial polystyrene is transparent? c) Name one way which you can use to measure T g of a polymer. d) What is UCST? What is LCST? e) Why is it usually harder to mix a polymer and another polymer than to mix a polymer and a solvent? f) Can M w be smaller than M n ? g) What is x n ? How is it related to conversion in step polymerization? How can it be measured in general? h) Why is GPC strictly speaking not a method to separate molecules by mass? i) For an ideal solution of polymer in a solvent, what are the values for and Mark-Houwink constant a ? j) In the light scattering equation, is the K in Kc/ R the same as the Mark-Houwink constant K? k) What is the physical significance of the intrinsic viscosity [ ]? l) Plot melt viscosity of a polymer vs. temperature. Plot melt viscosity of a polymer vs. its molecular weight. m) A piece of ideal rubber is : [ elastic / non-elastic ] and [ linear / non-linear]. n) Name two distinct ways that we use the WLF equation. o) In the Maxwell’s model response to stress relaxation, what is the stress at t = relaxation time ? Probl e m s 2 to 7 ar e from Final Exam 2008 2) a) In a production site where PET bottles are manufactured by blow molding, a batch of bottles was found to be hazy/cloudy in appearance. There was no impurity found and there was no degradation or change in molecular weight of the PET. Provide on e po ss ibl e e xplanation for the hazy appearance and what pro ce ss c ondition can be changed to eliminate it. b) Neoprene is a synthetic rubber made via polymerization of chloroprene, which is H 2 C=C Cl-CH=CH 2 . Nam e and draw two different possible structure of the repeat units produced when this monomer is polymerized. c) The modulus of a polymer depends on temperature and the rate of deformation. Decreasing the temperature of the polymer is equivalent to (choose one): [ increasing / decreasing ] the deformation rate. Why? d) How do the following change when the mol ec ular w e ight of th e polym e r i s in c r e a s e d ? (keeping concentration [in g/L] the same if the question is about polymer solution properties) Glass transition temperature increase no change decrease Hydrodynamic radius increase no change decrease Osmotic pressure of a polymer solution increase no change decrease Intensity of scattered light from a solution increase no change decrease Boiling point of a polymer solution increase no change decrease Tensile strength increase no change decrease e) Fill in the blanks. For a polymer in a theta solvent, = _________, A 2 = _________, and Mark-Houwink constant a = ________ For a polymer in a good solvent, ___________, A 2 __________, and Mark-Houwink constant a __________ Name one unit for: tensile strength: ________; tensile toughness: __________; maximum strain ___________ 3) a) A rather brittle polymer with a T g of 100...
View Full Document