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Managing Editor  | May 2017

MIT researchers develop new technique for building stronger polymers

Several years ago, researchers at the Massachusetts Institute of Technology (MIT) measured the defects (loops) that formed when polymer chains bind themselves together and now that research team has developed a technique by which the number of loops is reduced and the materials made from those polymers is made stronger.



Researchers have found a new approach for reducing the number of loops (red) in a polymer.
The method could offer an easy way for manufacturers of industrially useful materials
such as plastics or gels to strengthen their materials. (MIT)


According to a report on the school’s website, the researchers changed the speed at which one component of the polymer chain was added to another. By slowing this process down, the number of loops was cut in half over a variety of polymer structures.


This could point manufacturers in the right direction for creating plastics that can make materials stronger.


The article explained, “In this paper, the researchers first focused on a type of polymer structure known as a star polymer network. This material has two different building blocks: a star with four identical arms, known as ‘B4,’ and a chain known as ‘A2.’ Each molecule of Aattaches to the end of one of the B4 arms. However, during the typical synthesis process, when everything is mixed together at once, some of the A2 chains end up binding to two of the B4 arms, forming a loop.”


It added, “The researchers found that if they added B4 very slowly to a solution of A2, each of the B4arms would quickly react with a single molecule of A2, so there was less opportunity for A2 to form loops.”


After adding the first half of the B4 solution slowly, researchers then added the second half quickly and it created cross-linked polymer networks with half the amount of loops as the standard process. It also improved the material’s strength by as much as 600 percent.


Four other polymer structures were experimented on and each time the process improved material strength, although the number of loops could not be measured.


The research was recently published in Proceedings of the National Academy of Sciences. The abstract stated:


“Controlling the molecular structure of amorphous cross-linked polymeric materials is a longstanding challenge. Herein, we disclose a general strategy for precise tuning of loop defects in covalent polymer gel networks. This ‘loop control’ is achieved through a simple semibatch monomer addition protocol that can be applied to a broad range of network-forming reactions.


“By controlling loop defects, we demonstrate that with the same set of material precursors it is possible to tune and in several cases substantially improve network connectivity and mechanical properties (e.g., ∼600% increase in shear storage modulus).


“We believe that the concept of loop control via continuous reagent addition could find broad application in the synthesis of academically and industrially important cross-linked polymeric materials, such as resins and gels.”

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