n (polyformaldehyde, polyoxymethylene, polycarboxane) A thermoplastic produced by the addition polymerization of a aldehyde through the carbonyl function, yielding unbranched polyoxymethylene (–O–CH2–)n chains of great length. Examples are DuPont's “Delrin” and Hoechst–Celanese's “Celcon” (acetal copolymer based on trioxane). The acetal resins are among the strongest and stiffest of all thermoplastics, and are characterized by good fatigue life, resilience, low moisture sensitivity high resistance to solvents and chemicals, and good electrical properties. They may be processed by conventional injection molding and extrusion techniques, and fabricated by welding methods used for other thermoplastics. Their main area of application is industrial and mechanical products, e.g., gears, rollers, and many automotive parts (Strong AB (2000) Plastics materials and processing. Prentice-Hall, Columbus, OH; Carley JF (ed) (1993) Whittington's dictionary of plastics. Technomic Publishing).