Quantitative 31 P NMR is used to determine the hydroxyl value (iOH in mg KOH g -1 ) of PHO-diol for the PHO-hexyl synthesis step, using Equation , where m is the sample mass in g. C and V are the concentration (in mol L -1 ) and the volume introduced (mL) of the standard solution, respectively. 𝐼 1 is the intensity of peaks between δ = 133.5 and 134.6 ppm, corresponding to primary alcohols at the end of the chain. 𝐼 2 is the intensity of peaks between δ = 135.0 and 137.0 ppm, corresponding to terminal secondary alcohols. 𝐼 𝐵𝐷𝑂 is the intensity of the peak at δ = 134.2 ppm, corresponding to residual unreacted BDO. 56.1 is the molar mass of potassium hydroxide (KOH) in g mol -1 .