hs03201f10r - EMSE 201 Introduction to Materials Science...

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EMSE 201 – Introduction to Materials Science & Engineering Fall 2010 Case Western Reserve University 1 of 3 Case School of Engineering Solution to Homework #3 Explain how answers were obtained. Give appropriate units for all numerical answers. 1) (6 points) For each of the following pairs of polymers, do the following: (1) state whether or not it is possible to determine whether one polymer is more likely to crystallize than the other; (2) if it is possible, note which is the more likely and then cite reason(s) for your choice; and (3) if it is not possible to decide, then state why. (C&R problem 4.12) a) Linear and syndiotactic polypropylene; crosslinked cis-isoprene. b) Block poly(acrylonitrile-isoprene) copolymer; graft poly(chloroprene-isobutylene) copolymer. Solution (modified from the publisher’s solution manual) a) Yes, it is possible to decide for these two copolymers. The linear and syndiotactic polypropylene is more likely to crystallize than crosslinked cis-isoprene since linear polymers are more likely to crystallize than crosslinked ones. ( 3 pts ) b) Yes, it is possible to decide for these two copolymers. The block poly(acrylonitrile-isoprene) copolymer is more likely to crystallize than the graft poly(chloroprene-isobutylene) copolymer. Block copolymers crystallize more easily than graft ones, since the latter by definition are branched, and branching hinders crystallization. ( 3 pts ) 2) (6 points) For each of the following pairs of polymers, do the following: (1) state whether or not it is possible to determine whether one polymer has a higher melting temperature than the other; (2) if it is possible, note which has the higher melting temperature and then cite reason(s) for your choice; and (3) if it is not possible to decide, then state why. (C&R problem 11.26, parts a and c only) a) Branched polyethylene having a number-average molecular weight of 850,000 g/mol; linear polyethylene having a number-average molecular weight of 850,000 g/mol c) Linear and syndiotactic poly(vinyl chloride) having a number-average molecular weight of 500,000 g/mol;
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hs03201f10r - EMSE 201 Introduction to Materials Science...

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