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Novel architectures

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Being able to control polymer architecture is important to many of our research projects. In this strand, however, we aim to develop novel polymer architectures based around the tree-like dendritic architecture. We believe that polymers of this type will have an important role to play in the next generation of speciality polymers and biomimetic materials.

To realise this objective, different aspects of ongoing projects in the IRC are being integrated. New dendrimers are being designed, from synthesis, to characterisation and theoretical modelling and ultimately to final properties via a proper understanding of structure property relationships.

Currently our research is focussed on two themes:

Stimuli-responsive self-assembly in solution

There has been growing interest in recent years in stimuli-responsive polymers (SRP), i.e., polymers whose solubility and conformation are sensitive to environmental conditions such as temperature, pH and ionic strength. In this project, we aim to synthesise dendritic block copolymers containing SRPs and subsequently to characterise and theoretically model their self-assembly in solution.

By tuning molecular architecture, we can create dendrons that self-assemble into spherical micelles or vesicles but which can also switch on or off their self-assembly as a function of the external environment. These structures can be used as smart delivery systems (for drugs, steroids etc.) that can dispense their cargoes in response to changes in pH or temperature.

Movie The movie (above right) shows a vesicle designed to deliver drug molecules to a targeted site. The walls of the vesicles are formed from thermally sensitive dendrimers, which only aggregate to form membranes at low temperatures. On increasing the temperature, therefore, the dendrons separate, releasing the drug. Move your mouse over the movie clip to (re)start.

Lyotropic and thermotropic phases in concentrated solutions and melts

In this part of the project, we will study relatively low molecular weight dendrons that have been shown in recent years to self-assemble into thermotropic liquid crystal or quasi-crystal phases with two- and three-dimensional mesoscale periodicities. We will first explore the potential for tailoring and fine tuning mesophase structure by blending selected dendrons with other dendrons of different architectures, as well as with polar and nonpolar nondendron components.

We expect these 'molecular alloys' to exhibit novel mesophases not seen in their thermotropic counterparts. We will then investigate the potential of utilizing such structures for thermally switchable ionic conductors (using the phase transition from columnar to 3-d micellar mesophase) and as drug delivery agents (using submicron particles of dendron mesophases stabilised by non-ionic surfactants).