Which from following polymers is used to obtain oil seals?

Teflon (polytetrafluoroethylene, PTFE) is the correct material for oil seals due to its combination of chemical inertness, thermal stability, and low friction coefficient. As a synthetic fluoropolymer, it demonstrates exceptional resistance to oils, chemicals, and extreme temperatures, which are critical properties for seal integrity and durability.

While Dacron (a polyester), Nylon 6 (a polyamide), and low-density polyethylene serve various applications, none provide the superior performance required for oil seals as effectively as Teflon.

The final answer is $\boxed{A}$.