Synthetic Polymers
Objectives
- Distinguish between addition and condensation polymerization
- Know names and uses of common plastics, fibers, and rubbers
- Understand the difference between thermoplastic and thermosetting resins
Types of Polymerization
Addition polymerization: monomers with double bonds open up and link together. No by-products.
(polyethylene)
Condensation polymerization: two or more types of monomers link while losing small molecules (e.g., water).
Example: Nylon 6,6 (hexamethylenediamine + adipic acid)
Common Synthetic Polymers
| Name | Type | Polymerization | Monomer | Uses |
|---|---|---|---|---|
| Polyethylene (PE) | Thermoplastic | Addition | Ethylene | Bags, containers |
| Polypropylene (PP) | Thermoplastic | Addition | Propylene | Containers, fiber |
| PVC | Thermoplastic | Addition | Vinyl chloride | Pipes, sheets |
| Polystyrene (PS) | Thermoplastic | Addition | Styrene | Styrofoam |
| PET | Thermoplastic | Condensation | Terephthalic acid + ethylene glycol | Bottles, fiber |
| Nylon 6,6 | Thermoplastic | Condensation | Diamine + dicarboxylic acid | Fiber, gears |
| Phenol resin | Thermosetting | Condensation | Phenol + formaldehyde | Electrical parts |
Major synthetic polymers
Thermoplastic vs. Thermosetting
Thermoplastic resins: soften when heated, harden when cooled. Recyclable. Chain structure.
Thermosetting resins: once hardened, they do not soften on reheating. Cross-linked network structure.
Check Your Understanding
Q1 How is polyethylene made?
Q2 What characterizes a thermosetting resin?
Q3 What does PET stand for?
Exercises
Q1. Write the structural formula of the vinyl chloride monomer and show the polymerization reaction.
Solution
Monomer (vinyl chloride):
Polymerization:
The C=C double bond opens for addition polymerization.