title: Synthesis, characterisation and applications testing of polyester-block-polyolefins
Creators: name: Lykkeberg, Anna
Publisher: name: The University of Edinburgh
Year: 2025
Subjects: subject: Polyester-block-polyolefins
subject: Ring-opening polymerisation (RO(CO)P)
subject: Reversible addition-fragmentation chain transfer (RAFT) polymerisation
subject: Bifunctional systems
subject: Applications testing

description: Block copolymers (BCPs) are utilised in many industries, and there is a drive to synthesise novel copolymers with properties tailored for specific applications, and to improve the sustainability metrics of both existing and new copolymers. In particular, combining distinct polymerisation mechanisms to produce BCPs of different monomer classes, such as polyester-block-polyolefins, offers new libraries of materials. Ring-opening (co)-polymerisation (RO(CO)P) can deliver a broad variety of degradable polyesters, either through epoxide/anhydride ROCOP or the ROP of cyclic esters. Reversible addition-fragmentation chain transfer (RAFT) polymerisation offers a controlled radical polymerisation route for producing polyolefins from functionalised vinyl monomers. Designing bifunctional systems containing functionality for RO(CO)P and RAFT polymerisation is a promising route to access polyester-block-polyolefins, yet this approach remains underexplored. Overall, this thesis investigates simple and robust systems capable of delivering BCPs via RO(CO)P and RAFT, and assesses the formulations and potential applications of these copolymers. Polyesters synthesised via epoxide/anhydride ROCOP are particularly attractive, as this route offers two tuneable monomers to tailor the desired polymer characteristics. Where the limited reports of systems combining ROCOP and RAFT polymerisation often require air-sensitive conditions for the initiator synthesis and polymerisation, Chapter 2 describes the design of air-stable alternatives. Simple bifunctional alkali metal (Li, Na, K) carboxylate salts of RAFT agents were synthesised and used to prepare polyester-block-poly(vinyl acetate) BCPs by generating a macro-RAFT agent polyester. Unusually, the salts tolerate both purified and unpurified monomer feeds for ROCOP, albeit with a decrease in polymerisation control when using unpurified monomers. Successful synthesis of the target BCPs was shown, albeit with low molecular weight polyester blocks. Further investigations showed that a commercially available xanthate salt, used as the precursor to the RAFT agents used in this chapter, could be directly used as a ROCOP initiator. This generated the macro-RAFT agent polyester in fewer steps. However, in spite of the excellent activity in ROCOP, the macro-RAFT agent generated by the xanthate salt had lower end group fidelity, resulting in decreased blocking efficiency with vinyl acetate. To overcome the challenges with ROCOP in Chapter 2, Chapter 3 instead examined ROP of ε-caprolactone (CL) to prepare poly(ε-caprolactone)-poly(vinyl acetate) (PCL-PVAc) BCPs. This approach utilised a commercially available, bench-stable organocatalyst paired with a bifunctional hydroxy-capped RAFT agent acting as a ROP initiator. The target BCP was produced cleanly without unreacted polyester when using purified CL, and was an improvement over the ROCOP-RAFT approach in Chapter 2 in terms of both end group fidelity and molecular weight. While this system remained active for unpurified CL, unreacted PCL was consequently observed during BCP synthesis. This suggests that some PCL did not have the RAFT agent incorporated when produced under these conditions. Additional improvements for the PCL-block-PVAc copolymers were that either polymerisation could be performed first in a stepwise approach, and that the BCPs could be prepared in a one-step, one-pot reaction. Due to these synthetic improvements, the PCL-block-PVAc copolymers were taken forwards for application testing. In Chapter 4, the potential applications of hydrophobic-hydrophilic BCPs/polymer systems in aqueous dispersions were evaluated. The BCPs produced in Chapter 3 hydrolysed to produce PCL-block-poly(vinyl alcohol). The extent of hydrolysis and the integrity of the copolymer structures were studied by NMR spectroscopy and size exclusion chromatography. These systems were then integrated into formulations and used in detailed applications testing. The overall outlook for the thesis was summarised in Chapter 5 along with the experimental and bibliography in Chapters 6 and 7 respectively.