Polymers can form useful platforms for delivering drugs and other therapeutic agents in the body. In the Wang laboratory, the team are developing new ways to make polymers with precise control over the sizes of those polymers and how they are distributed in the ultimate material.
Polymers are long molecules that ‘string’ chains of molecules (monomers) together. Using techniques such as atom transfer radical polymerisation (DE-ATRP), reversible fragmentation-addition chain transfer polymerisation (RAFT) and single electron transfer living radical polymerisation (SET-LRP), the group has achieved a better control over the length of the polymer chains that are formed.
Polymers are not always simply long strings of molecules, like beaded necklaces. They can also form structures such as branches, loops and cross-links. The Wang group recently made a new, 3D single cyclised polymer chain - a 'Celtic Knot' polymer -from multi-vinyl monomers. (figure 1).
The group has provided new evidence to show that it is possible to kinetically control both the overall architecture and the critical gelling point (at which a liquid becomes a gel) in the polymerisation of MVMs. It was this new, kinetically-controlled approach that allowed us to make the new 3D ‘Celtic Knot’ polymeric material.
This ability and knowledge to control the ‘intramolecular cyclisation’ in the polymerisation of MVMs will prove to be a revolutionary concept in the field of polymer science. A broad range of novel nanosize 3D-polymeric materials could be designed and produced from multi-vinyl monomers, and they will have significant applications in a wide range of different research fields and clinical applications.
And from knots to trees: over the last 20 years, it has been realised that highly branched tree-like structures – dendritic polymers - have different and very desirable properties, which can be used to revolutionise technologies ranging from molecular machines, drug/gene delivery through to photovoltaic devices.
Unfortunately, real applications of these highly branched materials are limited because of the difficulties in their preparations - including the need for specialised monomers. Our group has developed a versatile 'vinyl oligomer Combination' strategy that overcomes these difficulties and allows easy synthesis of unprecedented, highly-branched polymeric materials from easily available multi-vinyl monomers (figure 2).
This breakthrough alters the growth characteristics of polymerisation by controlling the kinetic chain length together with manipulating chain growth conditions to achieve veritable hyperbranched structures, where each monomer unit is either a branching unit or a potential branching unit (figure 3). The group has begun to apply these different novel-structured polymers on various biomedical fields in order to explore their huge potential (figure 4).