Note: polymerization reactions take many steps, they are typically of the (approximate) form
nX
X
nOr, when you have a mix of things reacting it can be something closer to
nX + nY
(XY)
n(these are not exact reaction equations, they are just signaling the general idea).
As n can take many values in the same mixture, this is not a simple equilibrium reaction. It is quite difficult to apply correctly simple LCP logic here, not understanding well why and when it works for simpler cases.