MatSE 443

Introduction to the Materials Science of Polymers

Penn State University

Introduction to the Materials Science of Polymers

Penn State University

PC Painter and MM Coleman Essentials of Polymer Science(DEStech Publications) |

## Chapter 5 (pgs. 113-120 only)

**Concepts that you must know:**

- Definition of 'extend of reaction' (p), also as a probability.
- Statistics of Polycondensation: average molecular weights (Mn, Mw) as a function of the 'extend of reaction' (p), polydispersity as function of p
- Mole fraction & Weight fraction of x-mers in polycondensation
- Know how to apply simple Equations [e.g. eq.5.15 (also in Fig.5.9), eq. in Fig.5.10, and eq.5.17(typo)]. That is, given the p, or the concentrations (initial and concentration at p) of functional groups to calculate x
_{n}, x_{w}, and polydispersity (x_{w}/ x_{n}).

**Exercises:**

- *Go through the derivations of x
_{n}(p) (pg. 115, eq.5.3), and x_{n}(p,r) (pg. 116, eq.5.9) - *Go through the derivation of the Mole fraction & Weight fraction (pg. 117-119)

**Interactive Module:**

You need the Flash Player (v.6 or later) plugin (which can be obtained

*free*from here)

The files are extremely small (typically half a minute with a modem) and can be run directly from this web-page.

- Start by showing one curve (mole/weight fraction) at a time and observe how each curve changes with p (move the slider). Plot both curves and compare their shapes and positions. (can you connect it back to the definitions of Mn and Mw from chapter 2?)
- Comment on how the values of Mw, Mn, and d depend on the "extend of the reaction" (p).
- Which molecule size has the largest
**mole fraction**at any instant in the reaction (p)? Which molecule size has the largest**weight fraction**at any instant in the reaction (p)? Comment on the two!