Copolymerization

Aims

• Statistical free radical copolymerization
• Copolymer composition

Introduction

• Polymerization of two or more monomers
• Properties of the polymer depend on monomer composition and time

Statistical copolymerization

RM1• + M1 → RM1M1	rate=k11[RM1•][M1]
RM1• + M2 → RM1M2	rate=k12[RM1•][M2]
RM2• + M1 → RM2M1	rate=k21[RM2•][M1]
RM2• + M2 → RM2M2	rate=k22[RM2•][M2]

• Monomers are consumed at different rates
• Therefore the polymer composition changes during the reaction

$F_A=\frac{r_A{f}_A^2+f_A{f}_B}{r_A{f}_A^2+2f_A{f}_B+r_B{f}_B^2}$

• Defines the polymer composition at any moment in time.
• F_A = amount of monomer A in the polymer.
• f_A = amount of monomer A in the monomer feed.
• F_A + F_B = 1
• f_A + f_B = 1

Template:Robelbox

$r_A=\frac{k_{AA}}{k_{AB}}$ and $r_B=\frac{k_{BB}}{k_{BA}}$

• Defines the relative rates of reaction.
• Ratios are set for any pair of monomers.
• No variation with solvent, concentration, temperature, etc.

r_A > 1 → HOMO propagation preferred

r_A < 1 → CROSS propagation preferred