Write notes on different types molecular masses of polymers .

Explanation

The molecular mass of the polymer doesnot remian constant as the case of simple chemical substances . So the molecular weight of a polymer us expressed in terms of " average value " .The average molecular masses of polymers expressed in different ways . The following are the important among them.
i) Number average molecular mass `(barM_(n))`, ii) Weight average molecular mass `(barM_(w))`
i) Number average molecular mass `(barM_(n))` : If a polymer sample contains `N_(1)` particles of mass `M_(1)` each and `N_(2)` particles of mass `M_(2)` each and so on .
The number average molecular weight `(barM_(n))` of the polymer `=(overset(oo)underset(n_(i)=1)(sum)N_iMi)/(overset(oo)underset(n_(i)=1)(sum)N_(i)`
`(bar(M_(n))` can be determined by end group analysis method (or) physical methods based on calculated by multiplying the molecular weight of each type of particle with contribution of the species to the total weight of the sample .
Weight average molecylar weight `(barM_(w))`of the polymer `=(overset(oo)underset(n_(i)=1)sumN_(i)M_(i)^2)/(overset(oo)underset(n_(i)=1)sumN_(i)M_(i)`