Copolymerization

Subject classification: this is a chemistry resource.

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

Instantaneous copolymer equation $F_{A}={\frac {r_{A}f_{A}^{2}+f_{A}f_{B}}{r_{A}f_{A}^{2}+2f_{A}f_{B}+r_{B}f_{B}^{2}}}$ Defines the polymer composition at any moment in time. FA = amount of monomer A in the polymer. fA = amount of monomer A in the monomer feed. FA + FB = 1 fA + fB = 1

Reactivity ratios $r_{A}={\frac {k_{AA}}{k_{AB}}}$ 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. rA > 1 → HOMO propagation preferred rA < 1 → CROSS propagation preferred