Chapter 16, Problem 16.16P

Interpretation Introduction

Interpretation:

The molecular weights of all the repeat units of the polymers given in table 16.3 are to be calculated.

Concept Introduction:

The formula to calculate the molecular weight of a repeat unit is:

  ${\left(\text{MW}\right)}_{\text{repeat unit}}={\displaystyle \sum _i{a}_i{E}_i}$ ..... (1)

Here, $a_i$ is the stoichiometric number of element $E_i$ present in the repeat unit.

Answer to Problem 16.16P

The molecular weights of all the repeat units of the polymers given in table 16.3 are:

1. Polyethylene $\left(-\left[{\text{C}}_2{\text{H}}_4\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=28\text{ g/mol}$

2. Polyvinyl chloride $\left(-\left[{\text{C}}_2{\text{H}}_3\text{Cl}\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=62.5\text{ g/mol}$

3. Polypropylene $\left(-\left[{\text{C}}_3{\text{H}}_6\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=42\text{ g/mol}$

4. Polystyrene $\left(-\left[{\text{C}}_8{\text{H}}_8\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=104\text{ g/mol}$

5. Polyacrylonitrile $\left(-\left[{\text{C}}_3{\text{H}}_3\text{N}\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=53\text{ g/mol}$

6. Polymethyl methacrylate $\left(-\left[{\text{C}}_5{\text{H}}_8{\text{O}}_2\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=100\text{ g/mol}$

7. Polychlorotrifluoroethylene $\left(-\left[{\text{C}}_2{\text{F}}_3\text{Cl}\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=116.5\text{ g/mol}$

8. Polytetrafluoroethylene $\left(-\left[{\text{C}}_2{\text{F}}_4\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=100\text{ g/mol}$

Explanation of Solution

Name of all the polymers and molecular formula of their repeat units from table 16.3 are:

1. Polyethylene $\left(-\left[{\text{C}}_2{\text{H}}_4\right]-\right)$

2. Polyvinyl chloride $\left(-\left[{\text{C}}_2{\text{H}}_3\text{Cl}\right]-\right)$

3. Polypropylene $\left(-\left[{\text{C}}_3{\text{H}}_6\right]-\right)$

4. Polystyrene $\left(-\left[{\text{C}}_8{\text{H}}_8\right]-\right)$

5. Polyacrylonitrile $\left(-\left[{\text{C}}_3{\text{H}}_3\text{N}\right]-\right)$

6. Polymethyl methacrylate $\left(-\left[{\text{C}}_5{\text{H}}_8{\text{O}}_2\right]-\right)$

7. Polychlorotrifluoroethylene $\left(-\left[{\text{C}}_2{\text{F}}_3\text{Cl}\right]-\right)$

8. Polytetrafluoroethylene $\left(-\left[{\text{C}}_2{\text{F}}_4\right]-\right)$

Use equation (1) to calculate the molecular weight of the repeat unit of all the polymers as:

1. Polyethylene $\left(-\left[{\text{C}}_2{\text{H}}_4\right]-\right)$

  $\begin{array}{c}{\left(\text{MW}\right)}_{-\left[{\text{C}}_2{\text{H}}_4\right]-}=\left(2\times \text{C}\right)+\left(4\times \text{H}\right)\\ =\left(2\times \text{12}\right)+\left(4\times \text{1}\right)\\ =28\text{ g/mol}\end{array}$

2. Polyvinyl chloride $\left(-\left[{\text{C}}_2{\text{H}}_3\text{Cl}\right]-\right)$

  $\begin{array}{c}{\left(\text{MW}\right)}_{-\left[{\text{C}}_2{\text{H}}_3\text{Cl}\right]-}=\left(2\times \text{C}\right)+\left(3\times \text{H}\right)+\left(1\times \text{Cl}\right)\\ =\left(2\times \text{12}\right)+\left(3\times \text{1}\right)+\left(1\times 35.5\right)\\ =62.5\text{ g/mol}\end{array}$

3. Polypropylene $\left(-\left[{\text{C}}_3{\text{H}}_6\right]-\right)$

  $\begin{array}{c}{\left(\text{MW}\right)}_{-\left[{\text{C}}_3{\text{H}}_6\right]-}=\left(3\times \text{C}\right)+\left(6\times \text{H}\right)\\ =\left(3\times \text{12}\right)+\left(6\times \text{1}\right)\\ =42\text{ g/mol}\end{array}$

4. Polystyrene $\left(-\left[{\text{C}}_8{\text{H}}_8\right]-\right)$

  $\begin{array}{c}{\left(\text{MW}\right)}_{-\left[{\text{C}}_8{\text{H}}_8\right]-}=\left(8\times \text{C}\right)+\left(8\times \text{H}\right)\\ =\left(8\times \text{12}\right)+\left(8\times \text{1}\right)\\ =104\text{ g/mol}\end{array}$

5. Polyacrylonitrile $\left(-\left[{\text{C}}_3{\text{H}}_3\text{N}\right]-\right)$

  $\begin{array}{c}{\left(\text{MW}\right)}_{-\left[{\text{C}}_3{\text{H}}_3\text{N}\right]-}=\left(3\times \text{C}\right)+\left(3\times \text{H}\right)+\left(1\times \text{N}\right)\\ =\left(3\times \text{12}\right)+\left(3\times \text{1}\right)+\left(1\times 14\right)\\ =53\text{ g/mol}\end{array}$

6. Polymethyl methacrylate $\left(-\left[{\text{C}}_5{\text{H}}_8{\text{O}}_2\right]-\right)$

  $\begin{array}{c}{\left(\text{MW}\right)}_{-\left[{\text{C}}_5{\text{H}}_8{\text{O}}_2\right]-}=\left(5\times \text{C}\right)+\left(8\times \text{H}\right)+\left(2\times \text{O}\right)\\ =\left(5\times \text{12}\right)+\left(8\times \text{1}\right)+\left(2\times 16\right)\\ =100\text{ g/mol}\end{array}$

7. Polychlorotrifluoroethylene $\left(-\left[{\text{C}}_2{\text{F}}_3\text{Cl}\right]-\right)$

  $\begin{array}{c}{\left(\text{MW}\right)}_{-\left[{\text{C}}_2{\text{F}}_3\text{Cl}\right]-}=\left(2\times \text{C}\right)+\left(3\times \text{F}\right)+\left(1\times \text{Cl}\right)\\ =\left(2\times \text{12}\right)+\left(3\times 19\right)+\left(1\times 35.5\right)\\ \text{=116}\text{.5 g/mol}\end{array}$

8. Polytetrafluoroethylene $\left(-\left[{\text{C}}_2{\text{F}}_4\right]-\right)$

  $\begin{array}{c}{\left(\text{MW}\right)}_{-\left[{\text{C}}_2{\text{F}}_4\right]-}=\left(2\times \text{C}\right)+\left(4\times \text{F}\right)\\ =\left(2\times \text{12}\right)+\left(4\times \text{19}\right)\\ =100\text{ g/mol}\end{array}$

Conclusion

The molecular weights of all the repeat units of the polymers given in table 16.3 are:

1. Polyethylene $\left(-\left[{\text{C}}_2{\text{H}}_4\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=28\text{ g/mol}$

2. Polyvinyl chloride $\left(-\left[{\text{C}}_2{\text{H}}_3\text{Cl}\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=62.5\text{ g/mol}$

3. Polypropylene $\left(-\left[{\text{C}}_3{\text{H}}_6\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=42\text{ g/mol}$

4. Polystyrene $\left(-\left[{\text{C}}_8{\text{H}}_8\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=104\text{ g/mol}$

5. Polyacrylonitrile $\left(-\left[{\text{C}}_3{\text{H}}_3\text{N}\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=53\text{ g/mol}$

6. Polymethyl methacrylate $\left(-\left[{\text{C}}_5{\text{H}}_8{\text{O}}_2\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=100\text{ g/mol}$

7. Polychlorotrifluoroethylene $\left(-\left[{\text{C}}_2{\text{F}}_3\text{Cl}\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=116.5\text{ g/mol}$

8. Polytetrafluoroethylene $\left(-\left[{\text{C}}_2{\text{F}}_4\right]-\right)$, ${\left(\text{MW}\right)}_{\text{repeat unit}}=100\text{ g/mol}$