In this blog post, we’ll explore what polymers are, where they come from, how they’re synthesized, and why they’ve established themselves as a core material in modern industry.
There are countless polymers all around us. Not only natural polymers—such as rice, which is made of starch; wood, which is made of cellulose; and biopolymers like proteins—but also fibers like polyester, as well as numerous synthetic plastics such as Styrofoam and PVC, are all polymeric materials. In other words, almost everything we eat and wear, along with countless other items we use—such as cell phones, watches, computers, and pens—are made of polymers. So what exactly are these polymers—which are indispensable in modern society—where did they originate, and how are they made?
Polymers generally refer to substances with very high molecular weights formed by the repetitive linking of one or more types of unit molecules. The unit molecules that make up a polymer are called monomers. Although people have been discovering and using polymers empirically for a long time, it was not until the mid-19th century that humans began to design and synthesize them directly. In 1846, German chemist Christian Friedrich Schönbein chemically modified cellulose, a natural polymer, to create the substances that form the basis of nitrocellulose and celluloid. Subsequently, in 1907, Leo Baekeland developed Bakelite using phenol and formaldehyde—a material with excellent insulating properties that retains its shape once hardened. Furthermore, in the 1930s, Wallace Carothers developed nylon, which achieved great success as it was used in a variety of products such as stockings, underwear, and shoe soles. Over the next 100 years or so, research into creating new polymers continued steadily, leading to the development of a wide variety of polymer materials.
Polymers exhibit specific physical properties as monomers bond together in long chains or cross-linked networks. Just as the shape and feel of a beaded necklace vary depending on how the beads are arranged, the application, elasticity, strength, and heat resistance of a polymer depend on the sequence of monomer arrangement and the synthesis method. For example, when glucose serves as the monomer, the hydroxyl groups (–OH) of different glucose molecules react to form an ether bond, and the two molecules bond as water is released. Among the various hydroxyl groups on glucose, connections primarily occur at specific positions; when the bonded glucose molecules are arranged in a long chain in the same direction, they form cellulose, and when they form a helical structure, they form starch. Therefore, although the starch in rice and the cellulose in wood both use glucose as their starting material, their arrangement and structure differ, resulting in significantly different properties.
So, how can monomers be linked to form polymers? The polymerization reactions that create polymers from monomers are broadly classified into three types.
The first is condensation polymerization. This refers to a reaction in which new bonds are formed while small molecules, such as water, are released during the bonding process—similar to how starch and cellulose are formed, as described earlier. Polymers produced by condensation polymerization can form various structures; typical examples include polyesters, polyamides (nylon), and phenolic resins.
Second is addition polymerization. This type occurs when monomers have double or triple bonds. As the electrons involved in the multiple bonds rearrange, new single bonds form between the monomers, and this process repeats to create a long-chain structure. This can be likened to a group of people holding hands; when a new person joins, they release part of the existing chain to join hands with the newcomer. Polymers formed by addition polymerization generally take on a long-chain shape; examples include polyvinyl chloride (PVC), polyethylene (PE), and polystyrene (PS).
The third type is ring-opening polymerization. When a monomer has a ring structure, the bond within the ring opens to form highly reactive species, which then link together continuously to form a polymer. This is similar to untying small, interlocked rings and connecting them to one another. Typical examples include polycaprolactone (PCL), polylactide (PLA), and polyethylene oxide (PEO), which have recently been widely used in the production of biodegradable polymers.
We have briefly reviewed the history and synthesis methods of polymers. Polymer engineering—which produces materials with entirely different properties depending on the starting materials and arrangement methods—has established itself as a core field in today’s high-tech industries. Recently, the scope of applications has continued to expand to include organic semiconductor materials used in nanometer-scale electronic devices and flexible displays, biodegradable polymers used in eco-friendly packaging, and medical polymers utilized for tissue regeneration and drug delivery. In just over 100 years, polymers have significantly transformed modern society, and they are expected to continue playing a vital role as a key field driving the development of sustainable materials and advanced technologies.
