Polymers Branch Out

July 23, 2013
Versatile synthesis approach enables higher degree of branching and yield.

A new polymerization method forms highly branched compounds from readily available multi-vinyl monomers, opening up possibilities for a range of industrial applications, say researchers at the Network of Excellence for Functional Biomaterials (NFB) at the National University of Ireland, Galway.

Taking inspiration from trees and Celtic knots, the scientists devised a method of controlling the synthesis using monomer chains that connect in an interlaced pattern. The polymers also branch and spread outward like trees. The result is a far higher degree of branching than previously obtainable, note the researchers. The team observed branch ratios of 66%, but believes this level could be extended to 70–80%.

The process, developed in collaboration with Dr. Julien Poly from the Institut de Science des Matériaux de Mulhouse, France, is called vinyl oligomer combination. The simple "one-pot" procedure could lead to easy scale-up; it's expected that these hyperbranched (HB) polymers will be cheap to produce and high in quality. More details appear in a recent article in Nature Communications.

"The versatility of our synthesis process could allow us to tailor polymer properties, such as structure, functionality, strength, size, density and degradation — with previously unimaginable ease," says NFB's Dr. Wenxin Wang, who led the research.

The work, which began in 2010, is ongoing. Making polymers into well-defined knots to study their effects is extremely difficult; Wang believes it will take several decades to fully understand and unveil the potential of these polymer structures. "By understanding better how this knot structure works, and being able to create it to order, we should be able to produce materials that exploit those architectures with greater effect," he notes.

Currently, the team is developing various functional dendritic and knot poloymers and optimizing them for different biomedical applications. "We believe that this novel synthetic approach can be applied to yield high-value dendritic and knot polymers that can have many topical applications, such as in the area of biomedical and drug delivery. … However, in reality this synthesis method could be used for a wide range of materials outside the biomedical field," says Wang.

For example, the polymers could be used to produce materials with exceptional elastic or shock-absorbing properties. Wang also notes the high branching ratio and residue vinyl groups make these knot polymers ideal for coatings.

The team plans to produce HB and knot polymers on a larger scale (at kilogram level) for hydrogel applications. Wang believes this task "is critically important to examine the scalability of our strategy towards real industrial biomedical applications." If all goes as hope, pilot production should start in two to three years.

Because their unique architectures are distinct from traditional linear polymers, the new polymer could affect proccessability, in particular, rheology. However, Wang doesn't see any issue with stability. "The produced polymers containing 30–40% vinyl groups would be significantly beneficial for further functionalization or crosslinking," he explains.

Other challenges include how to optimize the polymer's properties to match the pathway of the target disease for biomedical applications as well as regulatory approval.

The team is cooperating with Boston Scientific and Hollister Co. on further development of this technology. "Our developed strategy and polymers have attracted lots of interest from industry. …The current progress shows a really promising future for our polymer and technology," says Wang.