Free-Radical Crosslinking Co Polymerization Mechanism

In suspension polymerization, the crosslinked polymer formation from mono- and poly-unsaturated monomers takes place by free-radical crosslinking of the chains (Elliott and Bowman 2002). At the beginning of (co)polymerization, only a few linear polyfunctional macromolecules (that remain dissolved in monomers) are formed. 

Radical crosslinking (co)polymerization (CRR) has several specific behaviors. The primary feature is the initiation process of the growing chains, a process that causes morphological differences in the resulting crosslinked structures. 

From the standpoint of elementary reaction steps, free-radical crosslinking (co)polymerization starts with initiation, proceeds by propagation (in which the monomers are added to the active ends of the growing chains accompanied by chain transfer), and ends with termination reactions (when the active chain ends are deactivated). 

Differences arise because of the unsaturated monomers presence. This can be incorporated into the growing chain by a single double bond. Others, that remain pendant (free), are able to participate in (co)polymerization so that, gradually, the chains are united by the pendant double bonds, and thus forming crosslinks. 

It often happens that chemical reactivity of the pendant bonds is equal to that of the polyunsaturated monomer in this case, the copolymerization scheme is identical to that of the linear binary copolymerization. 

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