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How does cross-linking affect the properties of polymers?
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polymer
Industrial polymers are synthesized from simple compounds joined together to form long chains. For example, polyvinyl chloride is an industrial homopolymer synthesized from repeating units of vinyl chloride.
Cross-linking, also known as interlinking, is a chemical process that fundamentally alters the physical behavior of polymers by creating a permanent network of molecules.12
The primary effects of cross-linking include:
- Prevention of Flow: By tying polymer chains together, cross-linking prevents molecules from flowing past one another. This transforms viscous liquids or soft materials into stable, elastic solids that maintain their shape even when heated.12
- Enhanced Elasticity: In elastomers, cross-links allow the material to be stretched under tension while ensuring it reverts to its original configuration once the tension is released.2
- Improved Thermal and Solvent Resistance: Because the molecules are chemically bonded into a network, cross-linked polymers do not dissolve in compatible solvents; they may only swell. Additionally, these materials—often called thermosets—cannot be remolded upon reheating, as they have become infusible and insoluble.13
- Crystallization Control: Cross-linking can disrupt the regularity of polymer chains, which helps prevent the material from hardening or becoming brittle at low temperatures.1
In industrial applications, this process is frequently referred to as vulcanization, particularly when using sulfur to treat rubber.12