Question

If 200 g of benzoyl peroxide are used with 38 Kg of PTFE monomer, calculate the expected molecular weight of the polymer if (i) all the termination occurs by combination (ii) all the termination occurs by disproportionation. Assume 15% efficiency for the initiator.

Answer 1

Explanation:

The molecular weight of benzoyl peroxide is 242.23 g/mol.

Therefore, number of moles present in 200 g of benzoyl peroxide are as follows.

            No. of moles = $\frac{mass}{\text{molar mass}}$

                                  = $\frac{200 g}{242.23 g/mol}$

                                  = 0.825 mol

Molecular weight of PTFE is 100 g/mol.Hence, calculate the number of moles of PTFE in 38 kg as follows.

As 1 kg = 1000 g. So, 38 kg = 38000 g.

             No. of moles = $\frac{mass}{\text{molar mass}}$

                                  = $\frac{38000 g}{100 g/mol}$

                                  = 380 mol

As it is given that the initiator is 15% active. So, actual number of moles of benzoyl peroxide are as follows.

                        $0.15 \times 0.826$

                           = 0.124 mol

For combination, 1 mol of benzoyl peroxide produces 1 chain. Therefore, degree of polymerization will be calculated as follows.

                    DP = $\frac{380 mol}{0.124 mol}$    

                          = 3065.33 mol

Average molecular weight of monomer is as follows.

       $\frac{0.124}{0.124 + 380} \times MW_{benzoyl} + \frac{380}{0.124 + 380} \times MW_{PTFE}$

       = 100.05 g/mol

Therefore, calculate the expected molecular weight of polymer as follows.

                   $3065.33 \times 100.05 g/mol$

                     = 306675.23 g/mol

Hence, for disproportion 1 mole benzoyl peroxide produces 2 chains.

                     DP = $\frac{2 \times 380}{0.124}$

                           = 6129.03

Therefore, calculate the expected polymer weight as follows.

                     $6129.03 \times 100.05$

                   = 613209.68 g/mol

Thus, we can conclude that the the expected polymer weight is 613209.68 g/mol.