# Calculation of Repeating units in polymer

Assume that I want to react A with repeating units of the polymer with ratio of 1:1. That is, I want to calculate that if I have $$M_A$$ mol of A, then what grams of polymer will I need to afford $$M_A$$ mol of repeating units.

Let $$M_w$$ be average molecular weight of given polymer and $$M_u$$ be molecular weight of repeating unit. To approximately calculate that what moles of repeating units is in one mole of polymer, I divided $$M_w$$ by $$M_u$$. That is, There are approximately $$\frac{M_w}{M_u}$$ moles of repeating units in one mole of polymer.

To calculate that what moles of polymer contains $$M_A$$ moles of repeating units, I used below proportional expression.

$$\frac{M_w}{M_u}:1=M_A:x$$

Then I get $$x=\frac{M_uM_A}{M_w}$$. That is, there are $$M_A$$ moles of repeating unit in $$\frac{M_uM_A}{M_w}$$ moles of polymer. To calculate grams of polymer I need, I multipy $$x$$ by $$M_w$$, and I get the grams of polymer I need is $$M_uM_A$$. This result is a little bit weird. The grams of polymer I need is independent of average molecular weight of polymer, $$M_w$$. Is it true? Did I make some mistakes?