Polystyrene ((C₈H₈)n) — Properties, Uses & Safety

Overview

Polystyrene is a versatile vinyl polymer with the repeating unit formula (C8H8)n and a monomer molar mass of 104.15 g/mol. It is produced by the addition polymerization of styrene (vinylbenzene), a process that links styrene monomers through their carbon-carbon double bonds into long chains. At standard conditions, polystyrene is a transparent to white rigid solid, though its properties vary dramatically depending on its form. General-purpose polystyrene (GPPS) is a clear, brittle, glassy plastic used for disposable cutlery, CD cases, and laboratory Petri dishes. High-impact polystyrene (HIPS) is modified with rubber to improve toughness. Expanded polystyrene (EPS), commonly known by the brand name Styrofoam, is a lightweight foam consisting of about 95% air, widely used for insulation, packaging, and disposable coffee cups. Polystyrene is one of the most produced plastics in the world, with annual production exceeding 15 million metric tons. In its solid form, polystyrene carries no significant GHS hazard codes, though styrene monomer is a suspected carcinogen. Environmental concerns about polystyrene are significant — it is not readily biodegradable and contributes to plastic pollution in oceans and landfills. Recycling rates for polystyrene remain low compared to other plastics like PET and HDPE. For chemistry students, polystyrene is an excellent example of addition (chain-growth) polymerization, contrasting with condensation polymers like nylon. Its pendant phenyl groups prevent crystallization, making it amorphous and transparent — a direct connection between molecular structure and optical properties. The dramatic difference between rigid polystyrene and its expanded foam form illustrates how physical processing can transform material properties without changing chemical composition. Polystyrene also connects to discussions about sustainability, plastic waste, and green chemistry alternatives.

IUPAC Name

poly(1-phenylethylene)

CAS Number

9003-53-6

PubChem CID

0

Molecular Formula

(C₈H₈)n

Molar Mass

104.15 g/mol

State at STP

solid

Appearance

Transparent to white rigid solid