Question

in a copolymerization of two monomer A and B the instantaneous copolymer contains equal mol fractions of A and B when the feed composition is given by (A) = 3 (B) , while an azeotropic copolymerization occurs if (B) = 3 (A) . Show that r1=1/13 and r2=9/13 for this pair of monomers .

Answer 1

r1 and r2 are the reactivity ratios

There is an equation relating mole fractions in the monomer feed and the copolymer to the reactivity ratios

The equation is

f(1-F)/F = r2 - r1(f²/F)

where f is the mole fraction in the monomer

F is the mole fraction in the copolymer

r1 and r2 are the reactivity ratios

A plot of f(1-F)/F versus f²/F will provide r1 as the slope and r2 as the intercept

Case1

f = 1/4 = 0.25

F = 0.5

f(1-F)/F = 0.25

f²/F = 0.125

Case 2

f = 3/4 = 0.75

F = 0.5

f(1-F)/F = 0.75

f²/F = 1.125

Thus a plot is made and from the slope and intercept of the plot, we obtain r1 = 1/13 and r2 = 9/13