Vinyl Polymer Synthesis

Self condensing vinyl polymerisation is a radical reaction process by which a polymer is formed via sequential addition of multiple monomers via polymer initiation, propagation and termination.

Poly(acrylic acid) Vinyl Polymerisation – Polymers propagate from radical initiator and grow polymer chains by sequential monomer addition

The radical is formed by a process known as inititiation, often via heating, microwaving or shining ultraviolet light on the sample. There are many different radical initiators available that are kickstarted by a range of processes and conditions but they share the common facet that they create a molecule with a highly reactive radical.

This radical can then react with the double bonds of a vinyl functional group which will rearrange, creating a new radical that can then go on to react with another monomer. This process repeats multiple times through radical propagation to form an extremely long polymer chain.

An ideal polymerisation reaction will form long polymer chains starting from the radical group at the chain end

However the reaction is not guaranteed to simply run until the available monomers have all ran out (100% conversion) as multiple radical chains can react with each other,

Polymer termination by 1) radical termination, 2) chain combination and 3) radical termination

Just three examples of chain termination are radical termination, where the chain reacts with an unreacted radical and the polymerisation ends. If the polymer chain encounters another chain also still reacting the two chains can combine. This causes a problem as the two different terminations give completely different polymer sizes, chain coupling produces one chain essentially double the size of single chains. Alternatively the reactive group can disproportionate and give you different chain ends with alkene chain ends and a double bond. If chain ends are important this is not desirable.

Due to these problems you are unlikely to produce polymer chains of the same size. This reaction will yield a distribution of polymers of different sizes, which will discuss in a future segment. There are ways to control radical polymerisation that are a hot field of polymer research and we will demonstrate some of the most common methods in a future update.