Polymer MS/PhD Qualifying Exam FALL 2012 Time = 3 h Closed Books/Notes Use ONE blue book for each part.
PART-1: General Polymer Chemistry 1. Write the structural repeat units for the following polymers: (a) SAN (styrene-acrylonitrile copolymer) (b) PC (Polycarbonate) (c) SBR (styrene-butadiene rubber) (d) Nylon-4,6 (e) PET (polyethylene terephthalate) (f) Natural Rubber 2. (i) Normal poly(methylmethacrylate) is atactic. This means that (a) the methyl groups are all on the same side of the backbone. (b) the methyl groups alternate regularly back and forth along the backbone. (c) the methyl groups alternate randomly back and forth along the backbone. (d) the monomers are arranged in a head to tail arrangement along the backbone. (ii) (iii) (iv) By increasing the amount of crosslinking in a polymer you will (a) increase the upper temperature of the useful range (b) increase the amount of brittleness (c) decrease the solubility (d) all of the above (e) none of the above Use of the Mark-ouwink equation to estimate polymer molecular weight yields what average molecular weight? (a) Mn (b) Mv (c) Mw (d) Mz A graft copolymer is best described as: (a) a statistical copolymer (b) a copolymer used in biomedical engineering applications (c) a branched block copolymer (d) a cellulose based copolymer
(v) (vi) (vii) (viii) Compare two samples of polyethylene having the same molecular weight. Sample A is free of branching, while sample B contains short-chain branching. Which of the following statements is true? (a) B will have a higher T g (b) B will have a higher density (c) A will be amorphous (d) A will have a higher melting point Polyurethanes are prepared by reacting: (a) phenols and aldehydes (b) alcohols and isocyanates (c) amines and isocyanates (d) epoxides and alcohols The glass transition reflects, on a molecular scale: (a) Melting of crystals. (b) Breaking of covalent bonds. (c) Small segments of the polymer chain beginning to move relative to one another. (d) Vibration of bonds. The segment of a polypropylene chain shown below suggests that this polymer is: C 3 C 3 C 3 C 3 C 3 (a) (b) (c) (d) atactic isotactic syndiotactic highly branched 3. Suggest a reasonable explanation for each: (i) Which would be more transparent: (a) Polystyrene or (b) Isotactic polypropylene? (ii) Which will be more permeable to a gas at room temperature: (a) Isotactic polypropylene or (b) Atactic polypropylene? (iii) Which would be better polyester fiber: one made from an ester of (a) terephthalic acid, or (b) phthalic acid?
4. Draw specific volume vs. temperature curves for amorphous, semicrystalline and crystalline polymers. 5. What are thermoplastic elastomers? ow do they differ from conventional elastomers? Give one example. PART-2: Polymer Synthesis 1. Write the difference between igh Impact Polystyrene (IPS) and Transparent Impact Polystyrene (TIPS). ow is IPS prepared commercially? Describe the mechanism of the process. 2. Describe the general synthetic method for thermoplastic styrenic elastomers (e.g., styrene-butadiene-styrene copolymer), including the schematic of microphase separation. 3. The recent advent of metallocene catalysts, particularly mono-cyclopentadienyl amido complexes, better known as constrained geometry catalyst (CGC), has made possible the commercial production, for the first time, of LCBPE (a homopolymer of ethylene). This process is commonly referred to as Dow Insite technology. Describe the mechanism of formation of long chain branch in LCBPE. Compare the structure of LCBPE with LLDPE and mlldpe.
PART-3: Polymer Characterization 1.) Describe and compare the following two methods for molecular weight measurements of a polymer: GPC and LS. 2.) Describe one possible way to characterize the compatibility of a polymer blend. 3.) Draw a phase diagram for a polymer mixture. Label and describe all terms.