Which polymer has the larger thermal conductivity when both are linear and syndiotactic with the same degree of polymerization: PVC or polystyrene?

• A. Polystyrene
• B. PVC
• C. Both equal
• D. Cannot determine

Answer: (B)

Heat conduction in polymers is controlled by how well vibrational energy (phonons) can move along the chains and cross from one chain to another. In linear, syndiotactic polymers with the same degree of polymerization, the side groups and backbone stiffness strongly influence this transport. PVC has a chlorine substituent that makes the backbone stiffer and increases interchain attractions, improving how phonons propagate across the crystalline regions. Polystyrene, with its bulky phenyl side groups, tends to have more torsional motion and weaker effective interchain coupling, which scatters phonons more and lowers conduction. Because PVC enhances both chain rigidity and interchain cohesion, it transmits heat more efficiently than polystyrene under the same chain-length and ordering conditions.