Section 28 mixed bonding 51 give three examples of

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Unformatted text preview: to ammonia, you get NH4 . If this material is introduced to Cl , what is the nature and strength of the bond formed? (This sort of bond occurs in a type of material called an ionomer.) 46. Predict which member of each pair of materials below has a higher melting temperature. a. C2 F4 or C2 H2 F2 b. CH4 or NH3 (predict the higher vaporization temperature) c. C14 H30 or C5 H12 47. Secondary bonds are present and extremely important in polymer behavior. Natural polymers are either animal- or vegetable-based. Animal fibers contain @ NH bonds. Vegetable fibers contain @ OH bonds. Do you expect natural polymers to be moisture sensitive, i.e., capable of bonding with H2 O? 48. What binds one molecule to another in a molten mass of polymer? 49. Which chemical group is capable of larger secondary bonding forces, one that contains C N groups or one that contains CH3 groups? 50. Secondary bonding involves electronic attraction of dipoles, or partial charges. Primary bonding also involves electronic interactions, but of whole charges. Estimate the relative magnitude of secondary bonding forces and compare them with primary bond strengths. In so doing you have estimated how much stronger a polymer can be when all the covalent bonds are aligned in one direction, such as in some fibers, and how weak they are normal to that direction. SECTION 2.8 Mixed Bonding 51. Give three examples of materials that exhibit mixed bonding at the primary bond level and three examples of materials that exhibit both primary and secondary bonding. 52. Suppose a material is partly ionic and partly covalently bonded. If an external environment can shift the balance of charge sharing and charge transfer, how will this affect electrical conductivity? If the material were partly covalent and partly metallic, how would your answer change? Of what use would such a material be? 53. Some covalently bonded materials can be doped with electron acceptors, allowing charge to jump from the covalent bond to the acceptor and back, perhaps into another covalent bond. How will the presence of dopant affect electrical conductivity. 54. Ni3 Al is an intermetallic that retains good mechanical properties at high temperature. This characteristic is typically ascribed to ionic solids. Is this material at least partially ionic? SECTION 2.9 The Structure of Polymer Molecules 55. Human hair is not a thermoplastic material but rather a thermoset material. Much as in the case of vulcanized rubber, the crosslinks are sulfur bridges. Crosslinks give hair molecules a memory...
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