Degradation of Polymers: Thermal
Course Module for ME 5XX - The Degradation of Polymers
Types of Degradation - Thermal
The breaking of chemical bonds under the influence of heat is the result
of overcoming bond dissociation energies. Organic substances such as polymers
are highly thermally sensitive due to the limited strength of the covalent
bonds that make up their structures. Scission can occur either randomly
or by a chain-end process, often referred to as an
There are many initial stages of degradation as subsets of thermal degradation. Following is a list, with brief descriptions of each.
- Random Initiation - occurs in the middle of a polymer chain, at an unspecified point.
- Terminal (end) Initiation - occurs at the end of a polymer chain, when a monomer is volatized out of the reaction medium. (ie, evaporates)
- Depropogation - occurs very similarly to terminal initiation, but the process continues and monomers keep volatizing out of the medium.
- Unimolecular Termination - A short polymer chain breaks up into products, but this rarely is accounted for in the bulk phase.
- Termination by Recombination - Two polymer radicals join together to form non-radical products.
- Termination by Disproportionation - Two polymer radicals share radicals and yield two non-radical polymers.
- Intermolecular Transfer - A polymer and a polymer radicl yield two polymers and a polymer radical.
Most of these reactions yield radicals, which are the basis of all chemical degradation.
To check out real research on thermal degradation of high-performance polymer composites, see what Oak Ridge National Labs is doing.
This page prepared by Kimberly Farrell for Professor Sisson of WPI, for use in ME XXX, Corrosion and assorted fun times.