A show of force: Novel polymer that toughens up and changes color upon mechanical stress

February 02, 2021

A fascinating and crucial ability of biological tissue, such as muscle, is self-healing and self-strengthening in response to damage caused by external forces. Most human-made polymers, on the other hand, break irreversibly under enough mechanical stress, which makes them less useful for certain critical applications like manufacturing artificial organs. But what if we could design polymers that reacted chemically to mechanical stimuli and used this energy to enhance their properties?

This goal, which has proven to be a big challenge, is under the spotlight in the field of mechanochemistry. In a recent study published in Angewandte Chemie International Edition, a team of scientists from Tokyo Tech, Yamagata University, and Sagami Chemical Research Institute, Japan, made remarkable progress with bulk self-strengthening polymers. Professor Hideyuki Otsuka, who led the study, explains their motivation: "Furthering the development of elegant bulk systems in which a force-induced reaction causes a clear change in mechanical properties would represent a game-changing advance in mechanochemistry, polymer chemistry, and materials science." They achieved this goal by focusing on difluorenylsuccinonitrile (DFSN), a 'mechanophore' or molecule that responds to mechanical stress.

The team created segmented polyurethane polymeric chains with hard as well as soft functional segments. The soft segments contain DFSN molecules acting as their "weakest link," with both of its halves joined by a single covalent bond. The soft segments also have their side chains topped off with methacryloyl units. Upon applying mechanical stress, such as simple compression or extension, on the polymer, the DFSN molecule splits into two equal cyanofluorene (CF) radicals. These CF radicals, unlike DFSN, acquire a pink color, making it easy to visually detect mechanical damage.

Most importantly, the CF radicals react with the methacryloyl units in the side chains of other polymers, causing separate polymers to chemically hook to one another in a process known as cross-linking. This phenomenon ultimately makes the overall strength of the bulk material go up as polymers become more chemically intertwined. This chemical cross-linking effect, as the scientists proved experimentally, becomes more pronounced as more compression cycles are performed on the segmented polymer samples because more DFSN molecules are split into CF radicals.

In addition, the team created a slight variant of their segmented polymer that not only turns pink but also exhibits fluorescence under ultraviolet irradiation when mechanical force is applied to it. This functionality comes in handy when trying to more accurately quantify the extent of the damage done by mechanical stress.

The attractive properties and functionalities of the developed polymers are useful, for example, for intuitive damage detection and the creation of adaptive materials. Expressing excitement for their findings, Otsuka remarks: "We successfully developed unprecedented mechanoresponsive polymers that exhibit color change, fluorescence, and self-strengthening ability, marking the first report of force-induced cross-linking reactions achieved by simply the extension or compression of a bulk film. Our findings represent a significant advance in the fundamental research of mechanochemistry and its applications in material science."

As more mechano-responsive materials with unique functions are developed, we can expect to explore their myriad applications in various industrial and engineering fields. Be sure to keep an eye out for further progress in mechanochemistry!
-end-


Tokyo Institute of Technology

Related Polymers Articles from Brightsurf:

Seeking the most effective polymers for personal protective equipment
Personal protective equipment, like face masks and gowns, is generally made of polymers.

Ultraheavy precision polymers
An environmentally friendly and sustainable synthesis of ''heavyweight'' polymers with very narrow molecular weight distributions is an important concept in modern polymer chemistry.

FSU researchers help develop sustainable polymers
Researchers at the FAMU-FSU College of Engineering have made new discoveries on the effects of temperature on sustainable polymers.

Structural colors from cellulose-based polymers
A surface displays structural colors when light is reflected by tiny, regular structural elements in a transparent material.

Growing polymers with different lengths
ETH researchers have developed a new method for producing polymers with different lengths.

Exciting new developments for polymers made from waste sulfur
Researchers at the University of Liverpool are making significant progress in the quest to develop new sulfur polymers that provide an environmentally friendly alternative to some traditional petrochemical based plastics.

Polymers can fine-tune attractions between suspended nanocubes
In new research published in EPJ E, researchers demonstrate a high level of control over a type of colloid in which the suspended particles take the form of hollow, nanoscale cubes.

Functional polymers to improve thermal stability of bioplastics
One of the key objectives for contemporary chemistry is to improve thermomechanical properties of polymers, in particular, thermostability of bioplastics.

Fluorescent technique brings aging polymers to light
Modern society relies on polymers, such as polypropylene or polyethylene plastic, for a wide range of applications, from food containers to automobile parts to medical devices.

Polymers to the rescue! Saving cells from damaging ice
Research published in the Journal of the American Chemical Society by University of Utah chemists Pavithra Naullage and Valeria Molinero provides the foundation to design efficient polymers that can prevent the growth of ice that damages cells.

Read More: Polymers News and Polymers Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.