Question

Define the number average molecular masses of a polymer.

Answer 1

If a polymer is made of n₁ moles of molecular mass M₁, n₂ moles of molecular mass M₂, n₃ moles of molecular mass M₃, .... and so on, the number average molecular mass `(bar M_n)` is defined as 

`bar M_n =  (n_1M_1 + n_2M_2 + n_3M_3 + .....)/(n_1 + n_2 + n_3 + .....)`

= `(sum n_i M_i)/(sum n_i)`

where n_i is the number of moles having molecular mass M_i.