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Why does vulcanized rubber resist dissolving in compatible solvents?

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Vulcanized rubber resists dissolving in compatible solvents because the process of vulcanization creates a permanent, three-dimensional network of cross-links between the long-chain polymer molecules.12

In its raw state, an elastomer behaves like a viscous liquid where individual molecular chains can disentangle and flow, allowing the material to dissolve in compatible solvents. During vulcanization, sulfur or other agents react with the polymer chains to form chemical bridges (interlinks) between them.21

Because these molecules are covalently tied together into a single, continuous network, they cannot separate or disperse into a solvent. Consequently, while the rubber may absorb solvent and swell, it cannot fully dissolve, as the permanent chemical bonds prevent the chains from moving apart.2