To answer this question, I have to assume that (HEMA) is to react with specific polyurethane, e.g., the one made from 1,4- butanediol & 1,4-butylenediisocyanate.

HEMA has the formula C6H10O3 (i.e. the molar mass= 130 g/mole) while the repeating unit of the polyurethane has the formula C10H8N2O3 (i.e. the molar mass of the unit = 214 g/mole). In grams, the polyurethane amount will be 1.08 x 214= 231.12 while the amount of HEMA will be 1x 130= 130 g. Therefore, if you use 23.1 g. PU versus 13 g. HEMA then you are following the given molar ratio. Of course, take care not to have any traces of water when the reaction is done unless there is need to obtain spongy product.