Linear, Branched And Cross-linked Structures In Polymers

As we explained in polymer production processespolymers have long-chained molecular structures. And properties of polymers generally depend on these molecular structures. Here, we explained the molecular structure types of polymers such as; Linear branched and cross-linked structures.

Introduction to Polymers

If you are interested in the guidebook that is used for this article, click on the given link above or the ‘Shop Now’ button to check it from Amazon!

What Are The Molecular Structures Of Polymers?

Molecular structures in the polymer.

Polymers have different structures and because of this, have different properties. These molecular structures are; Linear branched and cross-linked structures.

  • Linear structure in polymer molecules: In general, linear molecular structures occur in thermoplastics. In this molecular structure, molecules have occurred in linear alignments, and there is nearly no cross-linking or branched structure.
  • Branched structure in polymer molecules: Branched structures in polymer molecules occur with the replacement of ‘H’ atoms with ‘C’ atoms in linear molecules, and because of this replacement with ‘C’, this ‘C’ makes additional and same chemical reactions with other ‘C’ atoms. Because of this phenomenon in polymer molecules, branched structures occur. Polyethylene is an example of this branched structure.
  • Cross-linked structure in polymer molecules: This structure is the main type of structure that affects the polymer properties. Cross-linking occurs in polymer structures with the same logic as the branched structure explained above. When the branches created by ‘C’ atoms are linked with each other, as shown in the illustration, a cross-linked structure occurs.

Thermosets show different levels of cross-linking structures and this affects the properties of thermosets. With the application of heat and light, cross-linking structures increases in thermoset molecular structure. A cross-linked structure makes polymer harder and brittle. Also, when the cross-linking has occurred in a polymer, there is no turn back for that material. Because polymers lose their melting ability with cross-linking structure. When you heat a cross-linked thermoset, it will not melt, just burn. Curing is the application of heat and light to create a much more cross-linked molecular structure in thermosets to be much harder and stronger. This molecular structure has very dense cross-linking is called as ‘network structure’.

Also, elastomers have cross-linked structures, but at a very low level compared with thermosets. Because of this low level of cross-linked structure, elastomers have very high ductility and resilience.


This information can be a very good summary to understand the molecular structures of polymers. Do not forget to leave your comments and questions about the molecular structures of polymers below. Your feedback is very important for us.

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button