Q.Explain in detail free radical mechanism involved during preparation of addition polymer.

Step 1 (Chain initiation). An initiator/catalyst such as benzoyl peroxide, acetyl peroxide or tert-butyl peroxide decomposes to generate a free radical; for example, acetyl peroxide, CH3-CO-O-O-CO-CH3, decomposes to give 2 CH3-CO-O* radicals, which further lose CO2 to give methyl radicals, CH3*. This free radical (call it R*) then adds across the C=C double bond of a vinyl monomer, CH2=CHY, giving a new, bigger radical, R-CH2-CHY*, made up of the attached initiator fragment plus the monomer unit.

Step 2 (Chain propagation). This new radical reacts with another molecule of vinyl monomer, forming a still bigger radical, which in turn reacts with yet another monomer molecule; this sequence, R-CH2-CHY* + n CH2=CHY -> R-(CH2-CHY)n-CH2-CHY*, repeats very rapidly, quickly building a high molecular mass radical chain.

Step 3 (Chain termination). Eventually chain growth stops. The most common termination mode is combination: two separate growing chain radicals join together at their radical ends, 2 R-(CH2-CHY)n-CH2-CHY* -> R-(CH2-CHY)n+1-(CHY-CH2)n+1-R, using up both radical centres and giving one finished, non-reactive polymer molecule. …

Present the three named mechanistic steps of free-radical addition polymerization in order, with the initiator example (acetyl/be …

• Omitting the initiator's own decomposition step and starting the explanation directly from 'a radical adds to the monomer'. …