Polymer networks, such as rubber and nylon, consist of linked chain-like or branched molecules that almost always contain loops — structural imperfections that weaken a network's connectivity and lower the material's elasticity.

Jeremiah Johnson and his colleagues at the Massachusetts Institute of Technology in Cambridge have developed a method to count the number of the most common loops in polymeric materials. The authors broke a hydrogel, a type of polymer network that soaks up water, into quantifiable fragments that reflected the connectivity of the original network, then used mass spectrometry to count the loops. They found that too many loops prevented the gel from forming.

The researchers say they are now using their method to correlate the effects of loops on the mechanical properties of a variety of polymer networks.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1213169109 (2012)