Question

In terms of its mode of formation, how is chain growth polymerisation different from step growth polymerisation? Give an example of each.

Answer 1

Chain Growth Polymerisation: The general mechanism of addition polymerisation involves the following three steps.

1. Initiation: This step involves the formation of an active centre.
2. Propagation: In order to create dimer, trimer, etc., polymer units containing active centers, the active center attacks monomer molecules in this step.
3. Termination: This step involves the removal of the active centre from the final active polymer unit.

Step Growth Polymerisation: The condensation mechanism. First, two similar or different bi- or polyfunctional monomers condense to form a dimer during polymerization. Functional groups are present in the dimer, which can further condense with the third monomer molecule to form a trimer. Functional groups are still present in the trimer, which can condense further with the fourth monomer molecule to form a tetramer. Thus, the process continues until every monomer molecule is consumed, and a single, giant, highly molecularly weighted molecule is created.