CHAPTER 4

POLYMER STRUCTURES

LEARNING OBJECTIVES

1. Define isomerism.

2. Describe a typical polymer molecule in terms of its chain structure, and, in addition, how the molecule may be generated from repeat units.

3. Draw repeat units structures for polyethylene, poly(vinyl chloride), polytetrafluoroethylene, polypropylene, and polystyrene.

4. Distinguish between a homopolymer and a copolymer.

5. Distinguish between bifunctional and trifunctional repeat units.

6. Calculate number-average and weight-average molecular weights, and degree of polymerization for a specified homopolymer.

7. For a copolymer, given its repeat unit chemical formulas, the atomic weights of the constituent atoms, and the fraction of each repeat unit type, be able to compute the average repeat unit molecular weight.

8. Cite two features of polymer chains that restrict their ability to rotate and bend.

9. Name and briefly describe the four general types of molecular structures found in polymers.

10. Distinguish between head-to-tail and head-to-head configurations.

11. Name and briefly describe:

(a) the three types of stereoisomers,

(b) the two kinds of geometrical isomers, and

(c) the four types of copolymers.

12. Name the two classifications of polymeric materials according to their mechanical characteristics at elevated temperatures.

13. Cite the differences in behavior and molecular structure for thermoplastic and thermosetting polymers.

14. Draw repeat units for the following elastomers: polyacrylonitrile, polybutadiene, polychloroprene, poly(cis-isoprene), polyisobutylene, and polydimethylsiloxane.

15. (a) Briefly describe the crystalline state in polymeric materials

(b) Cite the main difference between the crystalline state in polymers and in metallic materials.

16. Given the density of a polymer specimen, as well as densities for totally crystalline and amorphous materials of the same polymer, be able to compute the percent crystallinity.

17. Cite how the degree of crystallinity in a polymer material is affected by polymer chemistry, by characteristics of the polymer structure, and for the various copolymers.

18. Briefly describe the structure of a chain-folded polymer crystallite.

19. Briefly describe and diagram the spherulitic structure for a semicrystalline polymer.