6 - Polymers and Polymerization

Question 1

6.9 If a group of high # of low molecular weight molecules and a group of low # of high molecular weight have the same average molecular weight, do they have similar properties as well?

Answer 1

They may have different properties.

The fraction of low-medium-high m.w. molecules in a material has as much effect on properties as does the average mw.

Question 2

6.11 Define thermoplastic

Answer 2

Materials that under go softening and hardening due to heating and cooling.

Their weak physical bonds break and the chains slide past each other - on cooling, the bonds reform and the material hardens.

Question 3

6.12 Define thermoset

Answer 3

A polymer that does not soften on heating.

Their cross linking results in a network structure of covalently bonded atoms. The polymer becomes a single giant molecule.

Question 4

6.15 What are the three stages of Free radical polymerization (a form of addition polymerization)?

Answer 4

1. Initiation - creation of free radicals which attack double bonds on monomers
2. Propagation - Activated monomers attack double bonds of other monomers
3. Termination - materials like hydroquinone will inhibit polymerization by reacting with the free-radicals