Polystyrene Repeat Unit | Polystyrene Properties

Polystyrene Repeat Unit and Properties 

Names and identification of Polymer
Polymer Class Polystyrene
General Names
Polystyrene, Polyethenylbenzene, Styrofoam®, Styron®, Fome-Cor®, Luran®, Lustrex®
Acronym PS
CAS # 9003-53-6
Repeat Unit
Identification of Monomers
Common Name Styrene
CAS # 100-42-5
Standard InChl
Standard InChlKey
SMILES C=Cc1ccccc1
Thermophysical Properties: Experimental Data
Property Unit Preferred value
Density ρ g mL-1 1.05
Molar Volume Vm mL mol-1 99.2
Glass Transition Temperature Tg K 375
Solubility Parameter δ MPa1/2 18.3
Molar Cohesive Energy Ecoh J mol-1 33300
Entanglement Molecular Weight Me g mol-1 16500
Molar Heat Capacity Cp J (mol K)-1 126
Index of Refraction n 1.6
Thermo-Physical Properties: Calculated Data
Property Unit Preferred-Value
Density ρ g mL-1 1.05
Molar Volume Vm mL mol-1 98.8
Solubility Parameter δ MPa1/2 19
Molecular Weight of Repeat unit g mol-1 104.1
Glass Transition Temperature Tg K 379
Molar Cohesive Energy Ecoh J mol-1 35800
Molar Heat Capacity Cp J (mol K)-1 129
Entanglement Molecular Weight Me g mol-1 15500

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Polystyrene Characteristics and Properties

  • Polystyrene is transparent, thanks to its lack of crystallinity.
  • Low impact strength and medium to high tensile strength.
  • Firmness in the polymer’s backbone leads to meager impact strength.
  • Polystyrene boasts good chemical resistance against diluted acids and bases. It is also an outstanding electrical insulator.
  • Weak resistance to oxygen, UV, and hydrocarbon solvents.
  • The low glass transition temperature is responsible for the low maximum temperature limit for prolonged use – (Tg = 373 K (100°C))

Polystyrene Applications 

Polystyrene, in all its forms, would be plastic or foam, is useful in several applications across many industries. The high repeating unit of polystyrene is one o the main reason for its high number of applications. Let’s have a look at them.

Industry Applications
Instrument panels, knobs, trims, energy absorbing door panels, sound dampening foams, sound protecting gears, etc.
televisions, computers, routers, printers, set-up boxes, etc.
Coolers, air-conditioners, blenders, ovens, vacuum cleaners, etc.
Building walls & roofings, refrigerators, freezers, cold storage facilities, etc
Petri dishes, test tubes, diagnostic components, culture trays, etc.
Containers, poultry trays, egg cartons, meat packaging, and foam packaging for CDs, and DVDs


Below are the frequently asked questions for repeating unit of polystyrene. Let’s dive deep and know more.

1. What is the repeat unit molecular weight for polystyrene?

Ans. 104.1 g/mol

2. What is the difference between polystyrene and expanded polystyrene?

Ans. They both have different manufacturing processes. Polystyrene is manufactured through an extrusion process. The process includes melting together the plastic resin and other ingredients. The formed liquid is then continuously extruded through a die and expands during a cooling process. That produces closed-cell rigid insulation.

Talking about expanded polystyrene is manufactured by a mold to keep small foam beads. Then heat and stem will be applied to the mold, which will cause the small beads to expand and join together.

3. What are the disadvantages of Polystyrene?


  1. The material is recyclable but very expensive
  2. Harmful to environment
  3. Susceptible to UV degradation.
  4. Weak chemical resistance to organics.
  5. High flammability.

4. What are the different types of polystyrene?

Ans. The three different types of polystyrene include polystyrene foam, polystyrene plastic, and polystyrene film. Amongst the foam, there are two types – expanded polystyrene (EPS) and extruded polystyrene (XPS).

5. Is polystyrene the same as Styrofoam?

Ans. The term Styrofoam is often used to refer to expanded polystyrene. However, it is the trademarked name for closed-cell extruded polystyrene foam made from thermal insulation.

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