(Left to right): Nikos Hadjichristidis, George Zapsas and Viko Ladelta discuss the mechanism of catalyst switching in their lab at KAUST. Photo: KAUST.
(Left to right): Nikos Hadjichristidis, George Zapsas and Viko Ladelta discuss the mechanism of catalyst switching in their lab at KAUST. Photo: KAUST.

By juggling four different chemical reactions in a single flask, researchers at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia have combined four polymers to form a single multicrystalline substance. Materials that seamlessly combine multiple polymers in this way potentially merge the best aspects of each material.

The versatile new approach for creating these ‘multicrystalline multiblock polymers’, developed by a team led by Nikos Hadjichristidis at the KAUST Catalysis Center, could lead to a whole new family of advanced polymer materials. The researchers report their work in a paper in Angewandte Chemie International Edition.

Polymers are long-chain molecules made by connecting together small molecule ‘monomeric units’, like a string of identical beads on a necklace. Recently, researchers have developed ways to make ‘double-crystalline’ copolymers, in which one part of the chain is made from one kind of monomer and the other part is made from another monomer.

“Double-crystalline block copolymers have myriad applications, such as for energy storage, tissue engineering and drug delivery,” says Viko Ladelta, a member of Hadjichristidis’s team.

Adding together an even greater number of different polymer sections has the potential to produce materials with even more advanced properties. “But the synthetic procedures are very demanding,” Ladelta explains. “It was difficult to perform even the synthesis of double-crystalline block copolymers, due to the incompatibility of the monomers and catalysts.” Making materials that incorporate four different monomers in four chemically different blocks – tetra-crystalline tetrablock quarterpolymers – leads to even greater incompatibility.

To help overcome this incompatibility problem, Hadjichristidis and his team developed a novel process they call catalyst switching. Most organic catalysts used to promote a polymer-forming reaction known as ring-opening polymerization are either acids or bases. By adding one type of monomer to the polymer chain under basic conditions, then adjusting the pH and using a second catalyst to add the next monomer, Hadjichristidis and his team were able to create multiblock polymers in a single reaction pot.

“This strategy saves time and also avoids the risk of any contamination of the polymer,” Ladelta says.

Hadjichristidis’s group have previously used catalyst switching between organic catalysts to create double-crystalline and triple-crystalline polymers. Now, for the first time, the team has shown that it is possible to adjust the pH and switch from an organic catalyst to a metal catalyst to make a tetracrystalline tetrablock quarterpolymer.

“Our plan is to expand the scope of the catalyst switch strategy to other types of polymerization,” Ladelta says. “We will synthesize more complex multicrystalline polymers and collaborate with polymer physicists to understand the physical properties to guide us toward real-world applications.”

This story is adapted from material from KAUST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.