Molecular 'Wheels' Facilitate Development of Industrial Soft Polymers

Researchers are working on the design of novel soft polymers that can be used in industrial processes through the molecular manipulation of chemical structures in a way that could have broad application in various technologies. Scientists from Hokkaido University and other institutions in Japan worked with rotaxanes, or interlocked molecular structures, in their research to develop what are called "network polymers." Rotaxanes are composed of a linear "axle" molecule penetrating one or more cyclic "wheel" molecules, with bulky groups at the end of the axle that prevent the wheels from coming off.

The team has taken current research surrounding these structures further through the creation of macro-rotaxanes that have multicyclic wheels interlocked with several high-molecular-weight axles. These molecules are useful for the development of these novel polymers, in which ring structures more complex than simple circles hold together different strands of long polymer chains, said polymer chemist Professor Toshifumi Satoh of Hokkaido University.

“We think the multicyclic structures in these macro-rotaxanes could be useful as non-leaching additives, permanently retained in a polymer network by the way they hold onto several neighboring polymer chains,” he said.

Reviving Rotaxanes

The research reflects a renewed interest in working with rotaxanes, which initially were regarded as chemical curiosities by the scientific community. However, scientists now are exploring these for a wide range of potential applications. In addition to materials, they also could be applied to novel possibilities in molecular computing, sensor technologies, and drug delivery, the researchers said.

In terms of developing the network polymers, the 3D wheels of the rotaxanes act as unique and highly flexible forms of molecular crosslinks for the materials. This allows the wheels and the interlocked polymer strands much more freedom of movement than in conventionally cross-linked networks, the researchers reported in a paper on their work in the journal, Angewandte Chemie International Edition.

In their specific application of rotaxanes, the team worked with larger molecules than previous research groups, which achieved similar success in developing soft polymers using smaller molecular arrangements. Satoh and his team explored some of the possibilities of this new development in polymer chemistry using chemicals called polydimethylsiloxanes (PDMSs) to make the multicyclic rings.

Soft Polymer Progress

They managed to build different numbers of cyclic units with rings of different sizes that they combined with silicone polymer chains with short crosslinking agents. This caused the multicyclic units to become efficiently incorporated into a newly forming extended, mixed, and interlocked network. 

“We explored some of the potential for making modified soft materials by measuring the damping performance of the networks, which is essentially the ability of a material to absorb and reduce vibrations,” Satoh said of the research. “This revealed that our macro-rotaxanes achieved significant improvements in damping efficiency relative to conventional polymer networks.”

Moreover, structural variations should allow fine control over the properties of soft materials to make them suitable for a variety of industrial and medical applications, he said.

The researchers plan to explore their work further by creating new material possibilities based on the proof-of-concept foundations laid by their current work, Satoh said.