Other meanings of Polymer
MATERIALS SCIENCE
A polymer is a substance composed of very large molecules, or macromolecules, built from repeating structural units linked by covalent bonds. Polymers include natural materials such as cellulose, proteins, and DNA as well as synthetic materials such as polyethylene, nylon, and epoxy resins. Their properties depend not only on chemical composition but also on chain length, branching, molecular arrangement, crystallinity, and processing history.
Polymers are macromolecules made from repeating units joined into chains or networks. The repeating unit is not necessarily identical to the starting monomer: polymerization can rearrange atoms or eliminate small molecules such as water. IUPAC distinguishes a polymer molecule from a polymeric material, which may also contain additives, fillers, solvents, or multiple polymer species.1
Some polymers are linear, while others are branched, cross-linked, or networked. These architectures strongly influence mobility and strength. A high molecular mass alone does not determine performance; the distribution of chain lengths, the spacing of branches, and the strength of intermolecular forces are equally significant. Proteins and nucleic acids are sequence-defined biological polymers, whereas many industrial polymers have statistically varying sequences and architectures.
Polymerization is commonly grouped into chain-growth and step-growth processes. Chain-growth reactions add monomers to an active site, as in the production of polyethylene from ethylene; step-growth reactions join molecules bearing reactive functional groups and often produce small-molecule by-products. Ring-opening polymerization provides another important route, especially for polyesters and other specialty materials.2
Thermoplastics soften when heated and can generally be reshaped, while thermosets develop permanent cross-linked networks. Elastomers combine flexible chains with enough cross-linking to recover their shape after deformation. Copolymers contain two or more monomer types; block, graft, alternating, and random arrangements allow chemists to tune toughness, adhesion, permeability, or compatibility. Cellulose, starch, natural rubber, collagen, and DNA demonstrate that polymer chemistry is not confined to manufactured plastics.
Polymer performance arises from chain motion, crystallinity, and interactions between chains. Amorphous regions can undergo a glass transition, changing from a hard, glassy state to a softer, rubbery state; semicrystalline polymers combine ordered crystallites with disordered regions. Orientation produced by drawing can increase strength in one direction, while plasticizers, fillers, fibers, and stabilizers alter flexibility, stiffness, durability, or resistance to heat and light.
These effects support a wide application range: packaging films, pipes, textiles, paints, adhesives, medical devices, electronic insulation, aerospace composites, and ion-conducting membranes. Advanced polymers include hydrogels, conducting polymers, polymer electrolytes, and high-performance aromatic materials. In medicine, biodegradable polymers can serve as sutures, drug-delivery carriers, and temporary scaffolds, although biological response depends on chemistry, degradation products, surface properties, and implant design.
Polymer properties can change substantially after manufacture because chains slowly rearrange, relax, oxidize, or absorb moisture. This time dependence, called viscoelasticity, explains creep under a constant load and stress relaxation under fixed deformation. A polymer may therefore meet a short-term strength test yet fail after years of service. Recycling is also chemically diverse: mechanical recycling preserves polymer molecules but can reduce quality through heat and contamination, whereas chemical recycling attempts to recover monomers or useful feedstocks.3
Not all polymers are plastics, and not all plastics are single polymers: commercial objects frequently contain blends, coatings, pigments, reinforcing fibers, and stabilizers. Microplastics can arise from the breakdown of larger articles or be released directly from products and textiles; their environmental behavior depends on size, shape, density, and surface chemistry.4 Polymer science consequently spans chemistry, physics, engineering, biology, and environmental research.
Terminology follows IUPAC usage; polymer properties are reported broadly because particular values depend on composition, molecular architecture, additives, processing, and test conditions.
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