Towards rapid self-healing polymer organogelators for electrophoretic type displays

Abstract

This thesis explores the development of rapid self-healing polymer organogelators that were proposed to sustain the function of an electrophoretic paper display (EPD). Two distinct topologies of the polymer gelators, prepared by atom transfer radical polymerisation (ATRP), were investigated. One was based on a linear copolymer and the second concerning a graft copolymer. Compositional differences of the copolymers established the pathways in which gelation from a non-polar organic solvent was pursued. One approach relied on the incorporation of a low molecular weight gelator (LMWG) onto a copolymer segment, whilst the other relied upon the amphilicity of diblock copolymers. In the first part of the project a linear copolymer organogelator containing the LMWG cyclo(L-aspartyl-L-phenylalanyl) (CAP) was targeted. The block copolymer composition was based on poly(lauryl methacrylate)-b-poly(2-hydroxyethyl methacrylate) (PLMA-PHEMA). Preliminary trichloroacetyl isocyanate experiments implied that the hydroxyl proton belonging to HEMA would be absent in 1H NMR spectroscopy studies following esterification. This observation was later confirmed, along with the emergence of a methylene proton signal at a chemical shift of 3.9 ppm, which strongly suggested successful synthesis of the diblock copolymer organogelator. Some of the PLMA-based graft copolymer organogelator was realised and confirmed via 1H NMR spectroscopy and gel permeation chromatography, despite evidence of poor control over the polydispersity value (PDI = 2.21). Before ATRP conditions could be optimised, the project direction was changed to a less complex method of developing a polymer organogelator. The second part of the project focused on preparing an amphiphilic linear polymer gelator based on poly(lauryl methacrylate)-b-poly(benzyl methacrylate (PLMA-PBzMA). When the PLMA degree of polymerisation (x) was fixed at 14 and the PBzMA degree of polymerisation (y) was varied, spheres (y = 34), mixed spheres and worms (y = 46) and pure worms (y = 64) in n-dodecane were observed via transmission electron microscopy (TEM). Concentrated gels (i.e., 20 wt. % PLMA-PBzMA) were formed from the mixed phase and the worms phase. Tube inversion tests of the mixed phase gel exhibited reversible de-gelation when heated to 90 °C. Dilute dispersion studies via variable-temperature 1H NMR spectroscopy and dynamic light scattering (DLS) studies showed thermo-reversibility of the nano-objects increased with decreasing lengths of y. The third part of the project followed from the success of the linear diblock copolymer gelator approach. The PLMA-PBzMA-based graft copolymers formed spherical core-shell micellar clusters in n-dodecane that were revealed by TEM. Variable-temperature 1H NMR spectroscopy showed that dilute dispersions showed thermo-reversibility irrespective of increasing lengths of y. However, variable-temperature DLS studies generally displayed kinetically frozen spheres at 90 °C. Finally, future design strategies based on the mixed phase composition were discussed towards achieving transparent gel forming organogelators. The potential for solution ATRP to prepare self-assembling copolymers for non-information display technology was also discussed.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Brian Saunders (Supervisor) & Stephen Yeates (Supervisor)