What Are the Different Properties of Polymers?

Comprised of repeating chains of molecules, polymers are unique materials that come in an array of shapes and sizes. Every polymer has unique properties that determine its suitability for different applications. For example, polyamideimide (PAI) has exceptional tensile strength of 21,000 psi. This makes it one of the best unreinforced thermoplastics for building high-speed rotating parts for pumps, as well as ultra-durable micro moulded components used for cardiovascular surgery.

Below, we spotlight some of the different properties of polymers and why they matter.

Tensile strength

Tensile strength rates how well a polymer material withstands being stretched or placed under tension. This property is calculated by measuring how much one-directional force can be applied before the plastic breaks.

Thermal expansion

This property describes the rate at which a polymer expands or contracts when exposed to high or low temperatures. Silicone is an example of a polymer with low thermal expansion. It doesn’t expand or contract when exposed to different temperatures, making it ideal for sealing glass windows.

Thermal conductivity

How well a polymer insulates itself against heat flows is an important property used to assess materials. Polymers with high thermal conductivity are coveted when manufacturing heat transfer devices. Similarly, polystyrene foams have excellent thermal conductivity and are often used to insulate buildings and to manufacture everyday items such as coffee cups and cooler boxes.

Refractive index

Some polymers allow light to filter through while others absorb it. Polymethyl methacrylate (PMMA) is a polymer with an excellent refractive index, making it ideal for manufacturing glass substitutes. These can include skylights, shatterproof windows, optical lenses and screens used to protect spectators in ice hockey arenas.

Crystallinity

Crystallinity is a property that describes how the polymer chains are arranged. Polymers with regularly aligned chains are considered highly crystalline and are generally hard, dense and durable. That said, a polymer that’s too crystalline will be brittle and unsuitable for certain applications. HDPE used to make plastic milk bottles is an example of a crystalline polymer. It's not only durable but easy to recycle thanks to its unique properties. In comparison, polymers with irregularly aligned chains have low crystallinity. 

Permeability

Permeability describes how easily liquids, gases and other compounds can pass through a polymer material. Polyethylene, a highly impermeable polymer used to manufacture food wrappers and plastic films, is 4000 times better at preventing oxygen from seeping into products than polystyrene.

A variety of polymer analysis techniques are used to analyse these properties and determine the suitability of materials. Want to know more about analytical methods for polymer characterisation? Don’t miss our complete guide ‘Polymer Characterisation - Techniques, Types & Properties’.