Question

The polydispersity index of a polymer containing $10$ molecules with molecular mass $1.0\times 10^4$ and $10$ molecules with molecular mass $1.0\times 10^5$ is approximately

• A. 1.67
• B. 0.59
• C. 1.55
• D. 0.83

Answer 1

Answer: (A)

The PDI (polydispersity index) $=\frac{M_w}{M_n}=1.67$

$M_w=$ Weight average molecular weight.

$M_n=$ Number average molecular weight.

$M_n=\frac{N_1{M}_1+N_2{M}_2}{N_1+N_2}=55,000$

$M_w=\frac{N_1{M}_1^2+N_2{M}_2^2}{N_1{M}_1+N_2{M}_2}=91818$