Reduced osmotic-pressure intercept (${\lim }_{c\to 0}\Pi /c=RT/M_n$)

For polymer mass concentration $c$, the leading ideal chain pressure is $RTc/M_n$. Plotting $\Pi /c$ against $c$ and extrapolating removes the leading virial correction. The intercept has units of energy per mass; without the measurement temperature it determines $M_n/T$, not an absolute molar mass.