Vulcanization significantly improves the mechanical properties of natural rubber, such as elasticity and tensile strength. This process involves the introduction of cross-links between polymer chains. Which of the following statements accurately describes the chemical nature of these cross-links?
Correct: C
Vulcanization is the process of heating natural rubber (polyisoprene) with sulfur. During this process, sulfur atoms react with the double bonds in the polyisoprene chains, forming covalent sulfur bridges (-S-S-) or polysulfidic bridges (-Sₓ-) between different polymer chains. These cross-links restrict the movement of individual polymer chains, preventing them from slipping past each other permanently when stretched, which enhances the rubber's elasticity, tensile strength, and resistance to abrasion, temperature changes, and solvents. Options A, B, and D describe other types of forces or mechanisms not responsible for vulcanization's primary effect.