Catalyst switch strategy is the key step in the production of a four-component crystalline tetrablock quarterpolymer.
By juggling four
different chemical reactions in a single flask, researchers at KAUST have
combined four polymers to form a single multicrystalline substance. Materials
that seamlessly combine multiple polymers potentially merge the best aspects of
The versatile new
approach for creating these “multicrystalline multiblock polymers,” developed
by Nikos Hadjichristidis from the KAUST
Catalysis Center and his team, in collaboration with Yves
Gnanou, could lead to a whole new family of advanced polymer materials.
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.
“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 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.
his team have developed a trick, called catalyst switching, to help overcome
the incompatibility problem. Most organic catalysts that are used for a
polymer-forming reaction, called 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, it is possible 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.
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 it is possible to adjust the pH, then switch from an
organic to a metal catalyst, to make a tetracrystalline tetrablock
“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
Ladelta, V., Zapsas, G., Abou-hamad, E., Gnanou, Y. & Hadjichristidis, N. Tetracrystalline tetrablock quarterpolymers: Four different crystallites under the same roof. Angewandte Chemie International Edition advance online publication, 26 August 2019.| article
Sandra Ramirez Cherbuy