Chapter 01 Introduction to Macromolecules
MWD = md`
Number average molecular weight
Weight average molecular weight
### Two ways to calculate the average molecular weights
#### 1 Use the formula directly
$$M_n = \frac{\sum{n_iM_i}}{\sum{n_i}}$$
$$M_w = \frac{\sum{n_iM_i^2}}{\sum{n_iM_i}}$$
#### 2 Rearange the formula and make it easier to understand
$$M_n = \sum{(\text{number fraction of one type of polymer}\times\text{molecular weight of this type of polymer})}$$
where the number fraction of one type of polymer equals the number of this type devided by the total number of all polymers.
$$M_n = \sum{(\text{weight fraction of one type of polymer}\times\text{molecular weight of this type of polymer})}$$
where the weight fraction of one type of polymer equals the weight of this type devided by the total weight of all polymers.
Use Excel to do the calculations and compare to the following results
Molecular weight distribution
Step growth polymerization
Living chain growth polymerization
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