The key difference between branched and crosslinked polymers is that branched polymer molecules have side chains that are attached to the backbone of the polymer, whereas crosslinked polymer materials have linkages between major polymer molecules.
Polymers are macromolecules containing a high number of repeating units. These repeating units represent the monomers that were used to make the polymer material. There are covalent chemical bonds between monomers.
CONTENTS
1. Overview and Key Difference
2. What are Branched Polymers
3. What are Crosslinked Polymers
4. Side by Side Comparison – Branched vs Crosslinked Polymers in Tabular Form
5. Summary
What are Branched Polymers?
Branched polymers are macromolecules formed from the polymerization of monomers and have a branched structure. Branching of these polymer materials occurs via replacement of some atoms from the polymer chain with substituents. The properties of these polymers are mainly affected by the degree of branching. The substituent group is also a polymer chain composed of covalently bonded monomer units, and these side chains can be either short chains or long chains. There are different types of branched polymers such as graft polymer and comb polymer.
Figure 01: Different Types of Branched Polymers
Graft Polymer: These are branched polymers that have side chains containing different monomers to that of the main chain. In other words, it is a segmented copolymer composed of a linear backbone substituted with branches of a polymer of a different type.
Comb Polymer: These are polymers containing comb macromolecules. This means these polymers contain side chains on the same side of the backbone, and the polymer appears like a comb.
What are Crosslinked Polymers?
Crosslinked polymers are macromolecules containing linkages between polymer molecules. A crosslink is a covalent bond between two polymer chains which can be either ionic bonds or covalent bonds. These crosslinks form either during the process of polymerization or after the completion of polymerization.
Figure 02: Formation of Sulfur Crosslinks
Since crosslinks between polymer chains are stronger than normal intermolecular attractions, the polymer material formed from crosslinking is stable and stronger. These polymers occur in both synthetic forms and as naturally occurring polymers. Crosslinks are created from chemical reactions in the presence of crosslinking reagents. The most common example of crosslinked polymers is vulcanized rubber. Since natural rubber is not stiff or rigid enough, the rubber is vulcanized. There, rubber is heated with sulfur, so sulfur molecules form covalent bonds in the rubber polymer chains, connecting the chains with each other. Then the rubber becomes a stiff and rigid material which is durable.
The amount of crosslinking gives the degree of crosslinking per mole of a material. We can measure the degree of crosslinking via swelling experiment. In this experiment, the material is placed in a container with a suitable solvent. Then the change of mass or the change of volume is measured. Here, if the degree of crosslinking is low, the material swells more.
What is the Difference Between Branched and Crosslinked Polymers?
The key difference between branched and crosslinked polymers is that branched polymer molecules have side chains that are attached to the backbone of polymer, whereas crosslinked polymer materials have linkages between major polymer molecules. Moreover, branched polymers are less complicated than crosslinked polymers.
Below is a tabulation of the difference between branched and crosslinked polymers.
Summary – Branched vs Crosslinked Polymers
Branched and crosslinked polymers are macromolecular materials. The key difference between branched and crosslinked polymers is that branched polymer molecules have side chains that are attached to the backbone of polymer, whereas crosslinked polymer materials have linkages between major polymer molecules.
Reference:
1. “Emulsion Polymerization.” Principles of Polymerization, pp. 350–371., doi:10.1002/047147875x.ch4.
Image Courtesy:
1. “RAFT Architecture” By Chem538w10grp4 – Own work (Public Domain) via Commons Wikimedia
2. “Vulcanization of POLYIsoprene V.2” By Jü – Own work (CC0) via Commons Wikimedia