Question

What would be the approximate molecular weight of the polyamide formed from 11-decanoamide, H2N(CH2)10CO2H, if the reaction were carried out to 98% conversion? a. 4600 g/mol b. 9200 g/mol c. 10100 g/mol d. 18,000 g/mol

Answer 1

Polyamide:

Polymer polyamide is formed by condensation polymerization.
Condensation polymerization: There is always small molecule evolved while bond formation between two monomer units.

Here in this particular polymerization, there are amine and carboxylic groups are there at monomer unit.

When amine group of one monomer approach by carboxylic group of another monomer H2O molecule evolved. So two monomer connected by one bond as a result of one H2O molecules.

According to the problem condition we have 11 such monomers so number of molecules of H2O evolved = 11-1=10

Step 1 :

First we calculated actual mass of monomer unit is converted.

Moles actually converted to product = 11 mol monomer x 98 / 100

= 10.78 mol monomer.

Moles of H2O lost from 10.78 mol monomer = 10.58 mol monomer x 10 H2O / 11 mol monomer

= 9.8 mol H2O.

Step 2 :

Total mass of polymer formed will be less than total monomers due loss of H2O molecule.

So the total mass of polymer = Mass of total monomers – mass of H2O molecule (lost )

Total mass of monomers = number of moles of monomers x molecular wt of monomers

= 10.78 mol x 201.3058 g /mol - 9.8 mol H2O x molar mass of H2O

Lets plug this value in above equation to get mass of polymer

Mass of polymer formed = (10.78 mol x 201.3058 g /mol ) – 9.8 mol H2O x 18.0148 g /mol

= 1993 g/mol

So the approximate molar mass of the polymer = 18000 g /mol