Polymers

A polymer is a large molecule composed of many repeated subunits called monomers. The properties of a polymer depend on the specific monomers it is made from and the conditions under which they are combined. As a result, different polymers have different properties. Also, the same polymer can have different properties if it is manufactured using different processes.

For example, poly(ethene) is a widely used polymer. Depending on the manufacturing process used, it can have different properties. This is why both low-density and high-density poly(ethene) can be produced, each with unique properties.

  • Low-density poly(ethene) (LDPE) is flexible, soft and lightweight; It is commonly used for bags, wraps and films
  • High-density poly(ethene) (HDPE) is flexible, strong, durable and has a solid structure; It is typically used for toys, tanks, food preparation cutting boards and plumbing pipes.

The properties of a polymer can be changed by modifying the reaction temperature, reaction pressure and catalyst.

Types of Polymers

Polymers can be categorised into two types: thermosetting polymers and thermosoftening polymers.

Thermosetting Polymers

Thermosetting polymers have strong cross-links between polymer chains, which hold the structure together. As a result, these polymers are strong, rigid, and do not soften when heated. They have high melting points and tend to char and burn rather than melt when exposed to heat.

Blue blocks connected in rows by green lines and 2 per row connected vertically by orange lines. The blue blocks are labelled "monomer" and the orange line labelled "strong cross-link bonds".

Thermosoftening Polymers

Thermosoftening polymers lack covalent bonds between their chains, allowing them to melt more easily than thermosetting plastics.

Thermosoftening polymers have low melting points. When heated, the intermolecular forces break, causing the polymer chains to separate and the polymer to melt. However, these polymers can be melted and remoulded into various shapes, to make new products.

Red circles connected horizontally by green lines and connected vertically by orange squiggly lines. The orange lines are labelled "weak attractive force" and the green lines labelled " strong bonds".

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