Chapter 11: Study Guide and Self-Assessment
This chapter deals with the principle thermal transitions that occur in polymers, crystallization, melting and the glass transition. These transitions are obviously important from various practical and end-use points of view. Is a particular polymer glassy or rubbery at a particular temperature? How does the crystallization temperature control crystallite size? At what temperature does a polymer soften or melt? This is stuff you need to know!
Objectives
Upon successfully completing this chapter you should be able to:
- Recall some basic thermodynamic concepts, particularly entropy and free energy.
- Understand the nature of crystallization, melting and the glass transition and how these transitions are accompanied by changes in properties such as specific volume.
- Realize that although crystallization is a kinetic phenomenon, thermodynamic arguments provide important insight and show that extended chain crystals have the lowest free energy.
- Recall the general features of crystallization kinetics and understand that both the rate of primary nucleation and the fold period depend upon the degree of undercooling, so that only folded chain crystals (as opposed to extended chain crystals) can form in finite time periods.
- Understand how primary crystallization also depends on undercooling and the factors that result in an inverted U-shaped dependence of the rate of crystallization on undercooling.
- Be familiar with the fact that polymers melt over a range of temperatures, understand why, and also understand the factors that affect the melting temperature (chain stiffness, intermolecular interactions, etc.).
- Understand the nature of the glass transition and the factors that affect the Tg.
Self-Assessment Questions