exams3spr01 - ENSC 3313, Spring 2001 TEST3 ADs 1....

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ENSC 3313, Spring 2001 TEST3 Name ADs OiDtS each. 1. Ca culate the polydispersivity index (PDI) for a polymer given the following data: Molecular Weight Mean Mi Range (g/mol) (g/mol) Xi Wi We need Mw/Mn M =~w.M. =24650 w L., 1 1 , M =~x.M. =23500 n L., I I' 15,000-20,000 20,000-25,000 25,000-30,000 30,000-35,000 35,000--40,000 17,: 22,: 27,: 32,: 37,: 0.28 0.40 0.20 0.08 0.04 0.24 0.32 0.26 0.13 0.05 Hence Pill = -l.:.Q:1 2, Compare and contrast. a) Addition and Condensation polymerization In addition polymerization, small mers are added together, n(C2~) ~ (C2~)n, for ex~ple. Condensation polymerization involves a chemical reaction with a byproduct. The process IS not reversible, e.g., (poly)acid + (poly)alcohol ~ polyester + water. b) Thern1oplastic and thern1osetting polymers The ~ormer are chain polymers that are plastic above the glass temperature through chain segments flowIng by each other. The latter, after polymerization, is a rigid 3-dimensional network that sets. Contrast (say) polypropylene and epoxy. c) HDPE and LDPE High density polyethylene is not branched; low density polyethylene is. Accordingly, the fonner packs better, so has a higher % crystallinity and superior mechanical properties. d) Cis- and trans-polybutadiene
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exams3spr01 - ENSC 3313, Spring 2001 TEST3 ADs 1....

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