Multiblock Copolymer Synthesis in Aqueous Heterogeneous Systems

The development of Reversible Deactivation Radical Polymerization (RDRP) techniques have revolutionized the field of polymer chemistry. These techniques provide the ease and flexibility of conventional radical polymerization, yet hold much of the control and livingness of anionic polymerization. Thus, highly organized sequence-controlled macromolecular architectures such as multiblock copolymers can now be synthesized. Synthetic chemical techniques have been implemented in homogeneous systems to achieve multiblock copolymers with time and resource efficiency, however, the synthetic procedure is limited to few monomer types, specific monomer order and low molecular weights. In order to incorporate a wider range of monomers regardless of order and to achieve high molecular weights a different synthetic approach was needed. This body of work exploits the advantages of Reversible Addition-Fragmentation Chain Transfer polymerization and heterogeneous systems to achieve multiblock copolymers of previously restricted monomer types and order, exhibiting high molecular weights. It is first demonstrated that a high degree of livingness in RAFT polymerization can be achieved in heterogeneous systems (i.e. miniemulsion) as compared to the corresponding homogeneous systems (i.e. bulk) for similar reaction conditions. The compartmentalization effect in RAFT miniemulsion polymerization results in a lower rate of bimolecular termination and thus a given DP can be achieved in a shorter time. It is also demonstrated that the high DP and high livingness can only be achieved in heterogeneous systems. This concept is subsequently experimentally confirmed by synthesizing high molecular weight triblock copolymers comprising slowly propagating monomers such as styrene and methyl methacrylate. After successful multiblock copolymer synthesis, the heterogeneous systems are further exploited to overcome the limitation of monomer order in RAFT polymerization. Multiblock copolymers irrespective of the monomer sequence are synthesized via RAFT emulsion polymerization. The inherent low monomer concentration of the monomer at reaction locus in emulsion polymerization yields a low [M]/[RAFT] ratio which results in a successful chain extension in the wrong order. The versatility of this approach is further demonstrated by synthesizing alternating pentablock copolymers comprising of butyl methacrylate, methyl methacrylate and styrene. Finally, the microphase separation of multiblock copolymers inside the particles is studied. The results demonstrate that the criteria for microphase separation in the particles is less stringent compared to the corresponding bulk system due to the orientation of the chains. The chains stretch from the particle surface to the core resulting in a multilayered structure. This work also demonstrates that the number of layers in the particles can be controlled by the number of blocks in the multiblock copolymer.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2021

Author dc:creator

• Khan, Murtaza

• Multilayered nanoparticle
• Block copolymer
• RAFT emulsion polymerization

Statement dc:rights

• open access
• CC BY-NC-ND 3.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by-nc-nd/3.0/au/

Language dc:language

EN

Identifier

https://doi.org/10.26190/unsworks/22494

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/70819