Polystyrene (PS) — Note

Polystyrene (PS) — Comprehensive Note

1. Introduction

Polystyrene (PS) is a synthetic thermoplastic polymer obtained by the polymerisation of styrene monomer, C₆H₅CH=CH₂. It is widely used in packaging, insulation, consumer goods, and disposable products due to its lightweight, clarity, and ease of molding.

General formula: (C₈H₈)_n

2. Types of Polystyrene

Type	Description	Properties	Uses
General Purpose PS (GPPS)	Transparent, brittle	Clear, rigid, easy to mold	Disposable cups, containers, CD cases
High Impact PS (HIPS)	GPPS blended with polybutadiene	Tougher, impact-resistant	Refrigerator liners, toys, appliance housings
Expandable PS (EPS)	Contains pentane for foaming	Lightweight, insulating	Packaging materials, insulation boards
Syndiotactic PS (sPS)	Ordered polymer chain	High melting point, crystalline	Engineering applications, fibers

3. Methods of Polymerisation

Free Radical Polymerisation: Most common method; styrene monomers polymerize in bulk, solution, or suspension.
Suspension Polymerisation: Produces small, spherical beads; beads can be molded or foamed for EPS.
Emulsion Polymerisation: Produces latex for coatings and adhesives.

4. Structure

Polystyrene is a linear polymer with pendant phenyl groups (-C₆H₅) on alternate carbon atoms. Phenyl groups provide rigidity, hardness, and brittleness.

CH₂=CH–C₆H₅ → –[CH₂–CH(C₆H₅)]_n–

5. Properties

Mechanical: Rigid and brittle (GPPS); tougher (HIPS)
Thermal: Softening point 90–100°C; low thermal conductivity
Chemical: Insoluble in water; soluble in aromatic solvents
Electrical: Good insulator
Processability: Can be molded, extruded, foamed, or laminated

6. Advantages

Lightweight and easy to process
Clear (GPPS) or impact-resistant (HIPS)
Excellent insulating properties (EPS)
Cost-effective for mass production

7. Limitations

Brittle (GPPS)
Flammable; produces toxic gases on burning
Poor UV resistance unless stabilized
Not biodegradable

8. Applications

Packaging: disposable cups, trays, protective packing
Insulation: EPS boards, foam sheets
Consumer goods: toys, CD cases, appliance parts
Medical: Petri dishes, laboratory ware
Engineering: HIPS used in appliance housings and automotive components

9. Summary

Polystyrene is a versatile polymer available in transparent, impact-resistant, and expandable forms. Its lightweight, clarity, and ease of molding make it valuable for packaging, insulation, and consumer goods, while modifications such as HIPS and EPS extend its utility to tougher and insulating applications.

Polystyrene

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