Addition Polymerization

Three ways of addition polymerization

1. Head to tail type
2. Head to head type
3. Random type

Mechanisms:

1. Free radical polymerization #

1. Initiation
   1. Spontaneous decomposition of an initiator into free radicals R*
   2. Addition of the radical from 1. to the monomer to form primary radical/initiator radical M* to initiate the chain.
2. Propagation: M*+M
3. Termination: by
   1. Collision between two growing chains
   2. growing chain+M*
   3. growing chain+inhibitors
   4. Happens rarely: disproportionation of an H atom from one radical to another: 1 unsaturated+1 saturated polymers

2. Ionic #

Instead of free radicals, here the unstable intermediates are: cations or anions Consists of the same steps:

1. Initiation
   1. Cationic mechanism: Lewis acids like AlCl₃, BF₃, H₂SO₄
2. Propagaion
3. Termination
   1. In cationic mechanism: terminator=anion
   2. In anionic mechanism: terminator=cation

Polymerization of olefins with metallic sodium, sodium ethoxide takes place via Anionic addition polymerization.

3. Coordination #

Also called Ziegler-Natta polymerization Transition metal halides with organometallic compounds, polymerization of olefins leads to stereospecific polymerization.

1. Initiation with Cat R’
2. Propagation
3. Termination with HX

Helps to form HDPE (High density polyethylene)