Processes of preparing defined monomer sequence polymers are disclosed, in which a backbone portion of the polymer is first prepared by performing one or more sequential monomeric coupling reactions with intervening membrane diafiltration purification/isolation steps, followed by a step of decorating the backbone portion with one or more side chains at predetermined positions along its length. The process represents an improvement on prior art techniques, which impose limitations on the size of the side chains that may be present. Defined monomer sequence polymers that are obtainable by the processes are also disclosed.