A polymer is any class of natural or synthetic substances composed of very large molecules, called macromolecules, that are multiples of simpler chemical units called monomers. Monomers are smaller molecules with two or more binding sites that can form covalent bonds with other monomers. They are the building blocks of polymers. This video discusses the unique properties polymeric materials have, because of their long, chain-like molecular structure.
When compared to water, oils, metals, salts, or other materials that we commonly interact with, polymers have very high molecular weights. Since polymer chains are very long and strand-like, they tend to entangle with each other like a bowl of spaghetti noodles. Because of this extensive entanglement, the interaction between polymer molecules is very strong. While the interaction between polymer chains is strong due to entanglement, the intermolecular bonds between polymer chains are much weaker than the covalent bonds that hold each molecule together. This allows the polymer chains to slide past each other. High molecular weight, chain entanglement, and weak intermolecular bonds give polymeric materials a very interesting property, viscoelasticity.
Viscoelastic materials exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials resist shear flow and strain linearly with time as stress is applied, whereas elastic materials will strain when stressed and quickly return to their original state once the stress is removed. Viscoelasticity gives polymeric materials the ability to absorb energy, flex, and spring back into shape without breaking.
In addition to having viscoelastic properties, polymers also exhibit non-Newtonian flow. This means that the viscosity of a molten polymer changes depending on the shear rate. This property makes thermoplastics injection-moldable, so parts like Legos, car bumpers, light switch wall plates, and many others can be mass produced.
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