课程名称︰高分子材料概论 课程性质︰系定必修 课程教师︰蔡丰羽 开课学院：工学院 开课系所︰材料系 考试日期（年月日）︰10/21/2008 考试时限（分钟）：180 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 :Total points=112 1. Suppose you are shopping for a plastic lunchbox that can withstand high temperatures without melting. On the shelf of supermarket, you find these 3 products: (1) PP Grade X. Price=$10 (2) PP Grade XX. Price=$30 (3) PC Grade A. Price=$50 (a) If money is not an issue and you want to get the most heat-resistant product, which one would you buy? Based on the structure of the polymers, explain why your chosen product should be the most heat-resistant. (b) It is known that the Tg of PP is -18℃. Given its low Tg, why can PP still be used to make heat-resistant lunchboxs? (c) Suppose you find out that product (1) is less heat-resistant than product (2), even though the two products are both made of PP. Based on the structure of the polymer, explain the origin of the different heat resistance. 2.(a) Draw 3 curves to qualitative show the molecular-weight distribution of a condensation polymerization at (1) short reaction time, (2) medium reaction time, (3) long reaction time (b) Draw 3 curves to qualitative show the molecular-weight distribution of a free radical polymerization at (1) short reaction time, (2) medium reaction time, (3) long reaction time (c) Draw 3 curves to qualitative show the molecular-weight distribution of a condensation polymerization at (1) low monomer concentration, (2) medium monomer concentration, and (3) high monomer concentration (d) Draw 3 curves to qualitative show the molecular-weight distribution of a free radical polymerization at (1) low monomer concentration, (2) medium monomer concentration, and (3) high monomer concentration 3.(a) Consider a condensation polymerization between 2 bi-function monomers, A-R-A and B-R'-B. If a tri-functional A monomer is added to the reaction mixture, what will its effects in terms of solubility and mechanical properties. (b) Continue from (a). With the tri-functional A monomer added, show that the branching coefficient α is given by ∞ PA PB p α= Σ [PA PB (1-p)]^n PA PB p = ─────── n=0 1- PA PB (1-p) where p is the fraction of A groups from the tri-functional monomer. (8 points) (c) Continue frim (b). Explain why the gel point is reached when α reaches 1/(f-1), where f=3 in these case. 4.(a) Give a common type of initiator (give its name and its general structure) used in anionic polymerization. Explain why this type of initiator is capable of initiating anionic polymerization. (b) Give a common monomer (give its name and its general structure) used in anionic polymerization. Explain why this monomer can be polymerized by anionic polymerization. (c) Give 3 advantages that anionic polymerization offers over free radical polymerization. 5. Consider the free-radical copolymerization of two monomers, M1 and M2. Assume that chain transfer does not occur and that initiation consumes negligible amount of M1 and M2. (a) Show that the ratio of monomer 1 to monomer 2 in the copolymer is given by 1+r1([M1]/[M2]) γ= ──────── where r1=kp11/kp12 r2=kp22/kp21 1+r2([M2]/[M1]) (b) Describe the procedure for determininf r1 and r2. (c) Derive an expression for the average sequence length in terms of the reactivity ratios and the monomer concentrations. (d) Consider that M1=styrene and M2=acrylonitrile. Given that kij =Pi Qj exp(- ei ej) with the data in the table below, determine the average sequence lengths of M1 and M2 in the copolymer first formed. Monomer Q e ======================================= Acrylonitrile 0.60 1.20 Butadiene 2.39 -1.05 p-Methoxystyrene 1.36 -1.11 p-Cyanostyrene 1.61 0.30 Methyl acrylate 0.42 0.60 Methyl methacrylate 0.74 0.40 Methyl vinyl ketine 1.0 0.7 Styrene (1.0) (-0.8) Vinyl acetate 0.026 -0.22 Vinyl chloride 0.044 0.20 (8 points) (e) How does the average sequence length affects the properties of a copolymer? --

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