Within all polymers, there are structural flaws at the molecular level. In an ideal network, each polymer chain would bind only to another chain. In reality, though, many of the chains bind to themselves, forming floppy loops that can weaken the network.
A team of chemical engineers at Massachusetts Institute of Technology, Cambridge, reveal that they have developed, for the first time, a means to measure how many loops are present in a given polymer network, an advance that, they say, is the first step toward creating better, stronger materials without weak spots.
To measure the number of loops, they first designed polymer chains incorporating a chemical bond, in a specific location, that can be broken. Once the polymer crosslinks into a gel network, they treated it with a base to cleave the bond.
By knowing where the break points are, they can predict the percentages of the four different degradation products they should expect to find in an ideal, no-loop network. And, by measuring the quantity of each degradation product and comparing it with the ideal, they can determine what fraction of the polymer formed loops.
They discovered that the percentage of polymer loops ranges from about 9 percent to nearly 100 percent, depending on the concentration of polymers in the starting material and other factors.
The researchers are now looking for ways to reduce the number of loops by altering the mixture of polymers used to produce a material, as well as the reaction conditions.
