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exam3fall2000

# exam3fall2000 - ENSC 3313 Fall 2000.1.nswer I alll O...

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ENSC 3313, Fall 2000 Name ..1 .nswer alll O Questions. 2 Doints each. I. Calculate the polydispersivity index (Pill) for a polymer given the following data: Molecular Weight Mean Mi Range (f!1mol) (g/mol) Xi Wi 15,000-20,000 17,500 0.22 0.20 20,000-25,000 22,500 0.48 0.39 25,000-30,000 27,500 0.20 0.26 30,000-35,000 32,500 0.08 0.13 35,000-40,000 37,500 0.02 0.02 Hence pm = -LQ4 2. How many kg of S are needed to cross link 4% of the sites in 3000 kg of polyisoprene? Assume the S is 30% efficient. Isoprene is CSH8. The amu of S = 32. To completely cross link, 2 of S link 2 mers of isoprene. Isoprene is CsHgo Hence, need 32 kg of S to com~letely cross link 68 kg of isoprene at 100% efficiency. Thus, need ~x32xOo04 kg ofS to cross link 4% of the sites of3000 kg of isoprene -~kg. 68 But, s is 30% efficient, so need ~ -ill kg. 0.3 3 b) condensation With reference to polymers, explain the terms a) glass transition temperature, polymerization, c) HDPE and LDPE, d) degree of polymerisation. a) The glass transition temperature is that temperature below which thermoplastic polymers become brittle because there is not enough thermal energy available for chain segments to slide by one another. b) Condensation polymerization, in contrast to addition polymerization, does not occur by adding small molecules together, rather by a specific chemical reaction involving a by-product. Thus, the process is not reversible. For example: (poly) acid + (poly) alcohol ~ polyester + water

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exam3fall2000 - ENSC 3313 Fall 2000.1.nswer I alll O...

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