Joining small monomer molecules into long polymer chains through repeated chemical bonding. The process that builds plastics, proteins, DNA, and cellulose.
types
addition (chain-growth) polymerization: monomers add one at a time to a growing chain via free radical, cationic, or anionic initiation. Polyethylene, polystyrene, PVC
condensation (step-growth) polymerization: monomers join with loss of a small molecule (water, HCl). Nylon, polyester, polycarbonate
copolymerization: two or more different monomers combine, tuning material properties
biological polymerization
DNA/RNA: nucleotide monomers joined by phosphodiester bonds, catalyzed by polymerase enzymes (transcription)
proteins: amino acid monomers joined by peptide bonds at ribosomes
polysaccharides: sugar monomers joined by glycosidic bonds -- cellulose, starch, chitin
cytoskeleton: actin and tubulin monomers polymerize into filaments driving mitosis and meiosis
properties
Degree of polymerization, molecular weight, branching, cross-linking, and crystallinity determine mechanical, thermal, and chemical properties. Thermoplastics soften on heating; thermosets are permanently cross-linked.
connections
cellulose is the most abundant biopolymer on Earth. fermentation products serve as monomers for bioplastics. oxidation degrades polymers (photooxidation, thermal degradation). osmosis through polymer membranes enables water purification.