What do thermodynamic quantities such as ΔHf, S°, ΔGf mean for polymers as opposed to single molecules - e.g. are they just large molecules and these thermodynamic quantities will vary depending on chain length, or do we treat them differently from molecules and there is only one enthalpy change of formation at 298.15 K, arbitrary of chain length, for, say, poly(ethene)? How about the reaction enthalpy, entropy or Gibbs' free energy for the production of the polymer - does it refer to, say, one mole of the polymer being formed, and that too only one specific number of units?