Conjugated polymers are a highly promising class of materials for a diverse range of applications, from the active components of optoelectronic devices like lasers or displays, to solar cells, sensors, actuators, capacitors and bioelectronics devices. The key to their application in these areas is the ability to tune both the electronic and physical properties of the polymer. To date most approaches to manipulate such properties have relied on the copolymerisation of appropriate monomeric materials. For example the incorporation of varying amounts of electron deficient monomers into an electron rich backbone can result in significant influence on the band gap due to the hybridisation of the frontier molecular orbitals, whereas the incorporation of branched or linear sidechains can be utilised to tune polymer crystallinity and processability. However the establishment of structure-property relationships in such copolymers is complicated by the necessity to synthesise batches of varying comonomer ratios, in which it is difficult to disentangle the influence of changes in the backbone chemistry from variations in the molecular weight, end-groups and dispersities of different batches. The later are known to have a significant impact on polymer performance, and are difficult to control as comonomer ratios vary. This work will overcome these difficulties by the development of methods to directly modify the aromatic backbone of the conjugated polymer post-polymerisation, thus enabling the synthesis of libraries with consistent dispersity and length.