Controlling the Functionality of Amphiphilic Block Copolymers Self-assembled into Bicontinuous Nanospheres

Amphiphilic block copolymers (BCPs) can self-assemble into a variety of different aggregates in solution. Simple morphologies include spherical micelles, cylindrical micelles and vesicles (polymersomes). More complex aggregate structures include bicontinuous nanospheres which this thesis will focus on. The work in this thesis looks at thermoresponsive bicontinuous nanospheres which has an application for drug delivery.

Previously, research has demonstrated that bicontinuous nanospheres can be made from PEO-b-PODMA (poly(ethylene oxide)-block-poly(octadecyl methacrylate)) & PEO-b-PDSMA (poly(ethylene oxide)-block-poly(docosyl methacrylate)). The bicontinuous nanospheres formed are semi-crystalline due to the methacrylate block which gives a melting transition temperature (Tm). PEO-b-PODMA has a Tm of 21.8°C and PEO-b-PDSMA has a Tm of 41.3°C. This previous work showed that by copolymerising and varying wt% ratios of PODMA:DSMA that there was manipulation of the Tm which was conducted using differential scanning calorimetry (DSC). The work outlined in this thesis repeated this work but instead of copolymerising, blending block copolymers in the same varied wt% ratios of PODMA:DSMA was carried out. This was to assess whether blending polymers could manipulate the Tm in the same way. DSC analysis suggested partial mixing occurred when PEO-b-PODMA & PEO-b-PDSMA were blended.

In the hopes to achieve full blending, a series of nucleobase monomers were made which contained adenine and thymine. Adenine and thymine are base pairs where hydrogen bonding occurs between the two bases. These nucleobase monomers were then added in ATRP reactions to make random copolymers of PODMA-co-PVBT and PDSMA-co-PVBA and block copolymers of PEO-b-PODMA-co-PVBT and PEO-b-PDSMA-co-PVBA. It was the hope of the strong hydrogen bonding affect that occurs between adenine and thymine, would be enough to encourage full mixing of the polymer blends. The block copolymers were lastly self-assembled to see if bicontinuous nanospheres still formed after the nucleobases had been incorporated into the random and block copolymers.