Polyoxymethylene (POM), also known as acetal,[4] polyacetal, and polyformaldehyde, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability.

POM is intrinsically opaque white because of its high crystalline composition but can be produced in a variety of colors.

[5] Typical applications for injection-molded POM include high-performance engineering components such as small gear wheels, eyeglass frames, ball bearings, ski bindings, fasteners, gun parts, knife handles, and lock systems.

[11] Patents by MacDonald and coworkers describe the preparation of high-molecular-weight hemiacetal-terminated (~O−CH2OH) POM,[12] but these lack sufficient thermal stability to be commercially viable.

In 1960, DuPont completed construction of a plant to produce its own version of acetal resin, named Delrin, at Parkersburg, United States.

Shortly thereafter, in a limited partnership with the Frankfurt firm Hoechst AG, a factory was built in Kelsterbach, Hessen; from there, Celcon was produced starting in 1962,[15] with Hostaform joining it a year later.

The formaldehyde is then polymerized by anionic catalysis, and the resulting polymer stabilized by reaction with acetic anhydride.

The polymerization can take place in a non-polar solvent (in which case the polymer forms as a slurry) or in neat trioxane (e.g. in an extruder).

After polymerization, the acidic catalyst must be deactivated and the polymer stabilized by melt or solution hydrolysis to remove unstable end groups.

Stable polymer is melt-compounded, adding thermal and oxidative stabilizers and optionally lubricants and miscellaneous fillers.

[citation needed] Typical applications for injection-molded POM include high-performance engineering components (e.g. gear wheels, ski bindings, yoyos, fasteners, lock systems).

When supplied as extruded bar or sheet, POM may be machined using traditional methods such as turning, milling, drilling etc.

Because the material lacks the rigidity of most metals, care should be taken to use light clamping forces and sufficient support for the work piece.

As can be the case with many polymers, machined POM can be dimensionally unstable, especially with parts that have large variations in wall thicknesses.

Typically these processes involve surface etching, flame treatment, using a specific primer/adhesive system, or mechanical abrasion.

DuPont uses a patented process for treating acetal homopolymer called satinizing that creates a surface roughness sufficient for micromechanical interlocking.

As the polymer is sensitive to both chlorine and acid hydrolysis, it may perform very poorly when exposed to the reactive gases, particularly hydrogen chloride (HCl).

Failures in this latter instance can occur with seemingly unimportant exposures from well sealed joints and do so without warning and rapidly (the component will split or fall apart).