Among the following polymers, which one's excellent elastomeric properties are primarily due to a combination of weak intermolecular forces allowing chain flexibility AND the presence of occasional cross-links preventing permanent deformation?
Correct: C
Elastomers, like vulcanized natural rubber, are characterized by their ability to stretch and return to their original shape. This property arises from long, coiled polymer chains connected by weak intermolecular forces, allowing them to be stretched easily. The 'occasional cross-links' (introduced during vulcanization with sulfur) are crucial because they prevent the chains from slipping past each other permanently when stretched, ensuring that the material returns to its original shape once the stress is removed. Without cross-links, raw rubber would be plastic and deform permanently. PVC and Nylon 6,6 are strong, rigid plastics or fibers due to significant intermolecular forces (dipole-dipole, H-bonding) and/or high crystallinity. HDPE is a high-density, crystalline thermoplastic with limited elasticity compared to rubber.