Free Radical Polymerization

Decomposition mechanism

Addition mechanism

Radical production rate

Propagation mechanism

Propagation rate

Initiator efficiency

Takes into account the fact that only some of the radicals from the initiator actually react with monomers to initiate growing chains

Mutual termination

two growing polymer chains react with each other to stop the polymerization process. Rarely occurs due to low concentration of growing polymer chains

Combination

the radicals collide and form a new covalent bond

Combination mechanism

Disproportionation

involves the transfer of a proton from one chain to another

Disproportionation mechanism

Chain transfer

An atom is transferred to the growing chain, terminating the chain and starting a new one

Chain transfer mechanism

General termination rate

Rate of polymerization

rate at which monomer is consumed

B/c Rp»Ri

Quasi-steady state assumption

the concentration of free radicals remains constant (consumed at same rate as generation)

SS monomer concentration

SS rate law

kinetic chain length equation

average number of monomers polymerized per chain radical

Kinetic chain length

equals DP for disproportionation and is twice DP for combination

Carothers theory

Assumes that the intrinsic reactivity of a functional group is independent of molecular size and is not impacted by the reaction of the other group

Increases polymerization rates

1. Temperature

2. Monomer/initator concentration

3. Solvents

Summary of mechanisms

Copolymerization

Mechanisms and reactivity ratios of

Impact monomer reactivity

1. steric hindrance

2. resonance stability at the radical site

3. double bond polarity

r1=0 and r2=0

Each comonmer prefers to react with each other resulting in alternating copolymer

r1>1 and r2>1

Each comonomer prefers to react with others of its own kind resulting in block copolymers

r1*r2=1

No preference due to chain ends resulting in random copolymer

r1>1

homopolymerization growth is preferred

r1=0

only reaction with monomer 2 will occur

Composition of monomer

Ideal copolymerization