Q $2($a$)$

$[8$ Marks$]$

A polymer blend has mass $4g.$ This is comprised of $2g$ of $C_{75}{H}_{152},1g$ of $C_{150}{H}_{302}$

and $1g$ of $C_{200}{H}_{402}.$ Calculate $M_n$ and $M_W.$

The atomic masses of $C$ and $H$ can be taken as $12\frac{g}{m}ol$ and $1\frac{g}{m}ol$ respectively.

Note:

$M_W=\frac{{\displaystyle \underset{?}{\overset{?}{}}}{N}_i{M}_i^2}{{\displaystyle \underset{?}{\overset{?}{}}}{N}_i{M}_i}$ and $M_n=\frac{{\displaystyle \underset{?}{\overset{?}{}}}{N}_i{M}_i}{{\displaystyle \underset{?}{\overset{?}{}}}{N}_i}$

where $N_i$ is the number of moles of

species i and $M_i$ is the molecular weight

of species $i.$

Q $2($b$)$

$[5$ Marks$]$

$($i$)$ Sketch the typical shape of the molecular weight distribution of a polymer

sample, showing the relative positions of the $M_n$ and $M_w$ averages.

$[3$ Marks$]$

$($ii$)$ Define the Polydispersity Index, and explain its significance.

$[2$ Marks$]$