In 1920, Hermann Staudinger, a German chemist then at the ETH Zurich, proposed — against the consensus of his colleagues — that rubbers, cellulose, proteins, and other high-molecular-weight materials were long covalent chains of small repeating units, not aggregates of small molecules held together by mysterious intermolecular forces. He was ridiculed for fifteen years and was right; the 1953 Nobel Prize finally recognized the macromolecular hypothesis. By then nylon (Carothers, DuPont, 1935), polyethylene (ICI, 1933), Teflon (Plunkett, 1938), and Kevlar (Kwolek, 1965) had transformed manufacturing. Today global plastic production exceeds 400 million tonnes per year.
A polymer is a macromolecule built from many copies of a small repeating monomer, and polymerization comes in two main flavours: addition (vinyl monomers like ethylene join without losing atoms) and condensation (each step releases water — the chemistry of nylon, PET, proteins, DNA). The mechanism matters: chain-growth propagates a single active site adding monomers one at a time; step-growth lets any two monomers or oligomers combine and only yields high molecular weight at high conversion. Structural variables determine behaviour — tacticity (the relative orientation of side groups along the chain) is the cleanest example, since isotactic polypropylene crystallises while atactic is amorphous — and cross-linking separates thermoplastics (linear, melt-and-reshape) from elastomers (lightly cross-linked, rubber) and thermosets (heavily cross-linked, no melting back). The glass transition temperature T<sub>g</sub> distinguishes glassy-and-brittle from rubbery-and-flexible behaviour; it is kinetic, not a true phase transition. The synthetic-polymer pantheon does most of the work of contemporary material life — polyethylene, polypropylene, PVC, polystyrene, PET, polyurethanes, nylons, aramids, fluoropolymers — and biological polymers do the work of life itself: proteins (amide bonds), nucleic acids (phosphodiester bonds), polysaccharides (glycosidic bonds), with cellulose the most abundant organic polymer on Earth at ~10¹¹ tonnes. Self-assembly of block copolymers, surfactants, and folding proteins underwrites much of materials science and structural biology.
Plastic-waste pollution is a major global environmental issue: of the ~9 billion tonnes of plastic ever produced, 6 billion tonnes are now waste, and microplastics (<5 mm) are found in deep-ocean sediments, Arctic ice, human blood, and breast milk. Only ~9% of all plastic ever made has been recycled; bioplastics (PLA from corn, PHA from bacteria) and chemical recycling (depolymerisation back to monomers) are the long-promised fixes still scaling toward commercial viability. High-performance polymers (Kevlar, Dyneema, polyimides) push specific strength and temperature limits; conducting polymers (Nobel 2000) drive OLED displays and organic photovoltaics; vitrimers — covalently cross-linked polymers that flow above a transition — enable recyclable thermosets.