Polymer Structures and Synthetic Methods

The synthesis of a polymer requires the controlled coupling of a large number of monomer molecules to form the polymer chain. An obvious requirement for the monomer is that it shall be functionally capable of coupling to two other units and polymer chemists have long recognised three basic ways in which the required difunctionality can be achieved. 

The second common method of polymer synthesis involves the stepwise coupling of small molecules which are difunctional by virtue of reactive functional groups. A typical example of step-reaction polymerization would be the synthesis of polyamides by reaction of a diamine with a diacid. In these systems the chain is built up slowly by reaction of any pair of functional groups in the system and it is common for the coupling to involve elimination of a small molecule. Conventionally these polymerizations allow more control over the chain structure but difficulties in reaching very high conversions and problems of reagent purity usually lead to much shorter 

The third major method for achieving difunctionality involves the ring-opening polymerization of a cyclic monomer, typified for example by the synthesis of polyamides from cyclic lactams. Reactions of this type proceed by chain-reaction mechanisms but yield polymers more typical of step-reactions, in that they contain functional groups within the chain. 

In the search for potentially conducting conjugated polymers all of these methods have been explored. In the following sections we survey the main types of conjugated structure and briefly outline the strategies which have been adopted to prepare them. 

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