Controlling polymer microstructure using multiblock copolymers via reversible addition-fragmentation chain transfer polymerization

Reversible addition fragmentation chain transfer (RAFT) polymerization is a very versatile way to generate synthetic polymeric materials. Multiblock copolymers have received enormous scientific interest recently due to the ability to mimic the sequence-regulated microstructure of biopolymers. The objective of this thesis was to investigate RAFT polymerization and explore its potential in the synthesis of sequence-controlled multiblock polymeric chains, and their use to tune the micro-structure of the polymers, engineer single chain polymeric nanoparticles, and fabricate functional polymeric nanomaterials. This work firstly addresses the investigation of the enormous ability of sequence-controlled multiblock copolymer to tune the physical properties by altering their microstructure. A series of sequence controlled multiblock copolymers were synthesized by RAFT polymerization using ethylene glycol methyl ether acrylate and tert-butyl acrylate as monomers. These block copolymers were synthesized with an alternating order of the two monomers with a similar total degree of polymerization. The number of blocks was varied by decreasing the length of each block while keeping the ratio of monomers constant. Their microphase separation was studied by investigating the glass transition temperature utilizing differential scanning calorimetry analysis. Small angel X-ray scattering analysis was also applied to investigate the transition of the microphase separation with the variation of the segmentations of these multiblock copolymers. The study found the microstructure was significantly affected by the number of segments of the polymer chain whilst keeping the total length constant. Having demonstrated the enormous potential of sequence controlled multiblock copolymers to access defined microstructures, further studies were focused on mimicking the controlled folding process of the peptide chain to a secondary and tertiary structure using sequence controlled multiblock copolymers. RAFT polymerization was used to produce multiblock copolymers, which are decorated with pendant cross-linkable groups in foldable sections, separated by non-functional spacer blocks in between. An external cross linker was then used to cause the folding of the specific domains. A chain extension-folding sequence was applied to create polymer chains having individual folded subdomains. In order to achieve a further step on the way to copy nature’s ability to synthesize highly defined bio-macromolecules with a distinct three dimensional structure, linear diblock copolymer precursors were synthesized by RAFT polymerization. One block of the precursor with pendant functional groups was folded using an external cross-linker to form tadpole-like single chain nanoparticles (SCNPs). These tadpole-like SCNPs could then self-assemble into a more complex stimuli responsive 3D structure by adaptation to environmental pH changes. The stimuli responsive assemblies were found to be able to dissociate responding to low pH or exposure to glucose