Method can make a wide range of cyclic monomers

Yi Yan Yang at the A*STAR Institute of Bioengineering and Nanotechnology and co-workers have now developed a two-stage route to degradable polycarbonates that overcomes these issues.

Firstly, the team devised a two-step method to synthesise ring-shaped monomers with a wide variety of different functional groups. "These eight-membered aliphatic cyclic carbonate monomers were made from commercially-available materials that are extremely inexpensive, such as diethanolamine," explains Yang.

"We shortened the monomer synthesis route from five or six steps to two steps, which translates to lower production cost."

Secondly, the team found that a ring-opening polymerisation reaction using an organocatalyst proceeded with excellent predictability over the size of the polymers formed.
Yang was surprised by how well her team's synthetic route works.

"The formation of medium-sized rings is known to be synthetically challenging, so we didn't expect the facile formation of these rings would work without the need for special reaction conditions," she says.

In addition, polymerising such cyclic monomers can be difficult. "Therefore, it was a very nice surprise to discover that these eight-membered cyclic monomers can be polymerised well using organocatalytic ring-opening polymerisation after the reaction conditions and catalysts are optimised."

The route is suitable for use on an industrial scale, confirms Yang. "The starting materials are inexpensive, in addition, the synthetic conditions are quite mild and can be easily scaled up."

For a polycarbonate synthesised by this method, one potential application is for gene or drug delivery. The theory is that the polymer will degrade and release its cargo once it reaches the desired site in the body. Polymers can be synthesised to contain secondary amine functional groups, able to bind to DNA, for example.

"Or we could install hydrophobic functional groups to deliver hydrophobic anticancer drugs," says Yang. Functional groups that enable the polymer to work as an antimicrobial can also be easily added. Yang's group is currently working on using this platform to make polymers for various medical applications.

The method could also be used to make biodegradable polycarbonates, for uses such as packaging materials. "This inexpensive, novel robust platform could potentially be used to prepare next-generation degradable packaging materials," Yang says.