Chemical structure of polymers

The chemical structure of polymers dictates a lot of their properties and includes the types of monomers and cross-links if present. For instance, the polarity of the monomer affects the hydrophilicity (i.e., water-loving) of the polymer. On the other hand, the shape of the monomer affects how easily the polymer chain bends and, hence, its stiffness.

Cross-linking is when neighboring chains stick together, affecting properties like viscosity, strength, hardness, and melting behavior. In slime, for instance, boric acid adds cross-links between chains, turning the fluid into a viscous cohesive mass. Kevlar® is another example of cross-linking: strong hydrogen bonds between neighboring chains make the chains connect like a spiderweb. This web can absorb tremendous amounts of force, explaining why we use it for bulletproof vests!

Figure 1: The chemical structure of some synthetic polymers.