Midterm 1 - W 1 Name AVSV‘e/l‘ ta 2 3 MSE 450 Introduction to Polymers 4 Exam 1 10:30am—l1250 am 5 6 25 ptS 1 Styrene is almost a unique

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Unformatted text preview: W 1. Name: AVSV‘e/l‘ ta 2 . 3. MSE 450 Introduction to Polymers 4 Exam 1 February 26, 2008 ' 10:30am—l1250 am 5 6 25 ptS 1. Styrene is almost a unique monomer, in that it can be polymerized by practically 7 all methods of chain polymerization including Free radical, Anionic, Cationic, and Co-ordination (i.e., with a catalyst) A. If you needed to synthesize a set of narrow molecular weight standards (i.e., ones with a polydispersity close to 1.0), circle the method you would use. Free radical Cationic Co—ordination B. If you synthesize nearly monodisperse polystyrene with a degree of polymerization of 200, via a living polymerization, what is the theoretical polydispersity index. ' i a)0.001 PDI - 1:: N H T b) 0.996 Mn 0 n C) 1.000 W“ ‘ [la—J“ €7.00 d) l.004 [I] 6) 2.005 ’ @none ofthe above - . PVT- ‘ M709 C. An NMR analysis ofa polystyrene sample showed that it had close to 100% racemic diads. The sample would be . "x. ”\ “x a) lsotactic polystyrene \Q/n:R_/ux \W/CXKICR Q Syndiotactic polystyrene / -._‘ l“: c) Atactic polystyrene 3.; ""H H 1X ‘7, x 3., d) None Of the above uremic disc! mesa diad D. A second sample had about 50% meso diads and 50% racemic. What is the most probable tacticity of this sample? a) lsotactic polystyrene b) Syndiotactic polystyrene @Atactic polystyrene d) None of the above E. A polystyrene sample has a number average molecular weight of 100,000 and a polydispersity of5. What is the weight average molecular weight? a) 20,000 PUI= MAL b) 100,000 W (9 500,000 ., d) 100,005 0: JAIL; 6) 5,000,000 10‘" 00° l) none ofthe above 15 PtS 2. A sample of atactic polystyrene is separated into 5 fractions: Fraction + Number of Moles l Molecular Weight (g/mole)_1 W; 1 5 10,000 90,000 2 l 10 l 20,000 100,020 g 3 15 | 30,000 470,000 4 | 10 + 40,000 m, we 5 l 5 50,000 1:17.090 ZWi ‘ 0399/ m A) What is the number average molecular weight? fi“=£-N—m‘i = w ‘ 50,000 grlwle’ gm 4? B) What is the weight average molecular weight? f 950.00? ( cum) 1 ' ‘ z ' ‘ , no 4—4;». (so,ooo)+4oo,m 4 = mm 9 2w M, 5 W,m(,o_m2+mgfig( 000) on C Moo) 2’“ “3 3M“; Ilac‘omoo 2' sufium Muck C) What is the polydispersity? P01: ,2! = 5w : Lil-“6‘ Mn 30,000 12 Pts 3. Consider the following copolymers a) (BAB—B — - - B—B)-(A—A—A — - — — AflA)-(B—B — — - — B—B—B) ~5% ~90% ~5% b) A—A—A - — — - A—A—B—B — — — - B—B c) ABA-ABBAAAB—A- d) —A—B—A—B—A—B—A—B~ e) A A A -A A—A A—A I I B I B I I B B I | B B | I B B B Give the letter or letters for the polymer structures associated with each term Triblock copolymer 0* Random copolymer C Block copolymer Q1 la 8 PtS 4. In dealing with the kinetics of free radical polymerization, it is usual to assume: a) That reactivity depends on chain length. b) The concentration of radical species changes dramatically during the time a chain is being polymerized. @The concentration of radical species is constant during the time that a chain is being polymerized. d) Molecular weight is independent of the concentration of radicals during the time that a particular chain is being polymerized. e)a&c t) none ofthe above 20 PIS 5. AIBN is used to initiate the polymerization of methylmethacrylate in benzene at 60°C. [l]o = 0.02 mol/l [M]o = 2 mol/l kn: 705; kl I 50 x 10'6; kd = 0.85 x 10's, in appropriate units A) Assuming fis 1, what is the initial rate of polymerization? lb. -’ 309x 9. x ngsxiwx 0.02 ‘ M 6 82-1 M/s-L ‘y'bauo’ B) What is the degree of polymerization? Termination is by disproportionation. Assume the concentration of monomer and initiator are close to the starting values given above. 9PM: U 2 (K; Ki [1])”: 409x 1 M __ 1/2. 1 (0.99 mi” VDX lo ‘1 0.02.) .- .- '- — Liliana" 6 PtS 6. Which of the following equations is the correct expression for the number average degree of polymerization when chain transfer occurs in a free radical synthesis? , — _, a [T] "L xfi—svam B -: =ITCE‘VQ [1"] 1 [T] = = =+ —— ® m] D :1.- = ; * r: 5’3] :~: 3. [T] 14 Pts 7. Isomerism is important in determining the architecture of polymer chains. A) By NMR you determine that the diad sequence for polypropylene is ...mrrmmrrmmrrmmrrmmrrmmrrmmr... Draw a Fisher projection ofthis chain. WmmWy B) Draw Newman projections showing the trans, gauche+ and gauche- rotational isomers of polypropylene. fl xfiég trans gauche+ job‘ch (‘0? 3}” ) (or T) ...
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This test prep was uploaded on 04/07/2008 for the course MSE 450 taught by Professor Braun during the Spring '08 term at University of Illinois at Urbana–Champaign.

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Midterm 1 - W 1 Name AVSV‘e/l‘ ta 2 3 MSE 450 Introduction to Polymers 4 Exam 1 10:30am—l1250 am 5 6 25 ptS 1 Styrene is almost a unique

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