Overview
This lecture explains condensation polymers with a focus on polyesters, covering their formation, structure, key reactions, and biodegradability.
Condensation Polymers and Polyesters
- Condensation polymers are formed from monomers that combine and release small molecules, such as water.
- Polyesters are a type of condensation polymer formed using ester links.
Monomers and Polymerization Process
- Polyesters commonly use two monomers: a dicarboxylic acid (two carboxylic acid groups) and a diol (two alcohol groups).
- Monomers combine when the dicarboxylic acid loses an –OH and the diol loses a hydrogen from its –OH, forming water.
- The remaining carbon bonds directly to an oxygen, creating an ester link.
- Formation of each repeating unit releases two water molecules.
- The polymer chain is shown as a repeating unit with brackets and empty bonds at each end.
Notation and Generalization
- The letter 'n' represents the number of repeating units in the polymer.
- Water formed is shown as 2n Hâ‚‚O to indicate two molecules per unit.
- Functional requirement: each monomer must have at least two functional groups.
- There must be at least two different types of functional groups (e.g., carboxyl and alcohol).
Real-Life Example and Properties
- Ethane dioic acid and ethane diol react to form poly(ethyl ethanoate) and water.
- Polyesters are generally biodegradable, meaning microorganisms can break down the ester links.
- Addition polymers (like many plastics) are usually non-biodegradable, causing environmental persistence.
Key Terms & Definitions
- Condensation Polymer — Polymer formed when monomers join and release a small molecule (often water).
- Polyester — A condensation polymer containing ester functional groups in its backbone.
- Dicarboxylic Acid — Organic molecule with two carboxylic acid (-COOH) groups.
- Diol — Organic molecule with two alcohol (–OH) groups.
- Ester Link — The bond (-COO-) formed between an acid and an alcohol group in polyesters.
- Biodegradable — Capable of being broken down naturally by microorganisms.
Action Items / Next Steps
- Review how to draw condensation polymer formation and repeating units.
- Practice with examples: draw the polymer from given monomers.
- Read more about the differences between condensation and addition polymers.