POM (copo): Polyoxymethylene (copolymer)

Short Name
POM (copo)
Polyoxymethylene (copolymer)
ETP - Engineering Thermoplastics
General Properties
Polyoxymethylene (POM), also known as acetal, polyacetal, and polyformaldehyde, is an engineering thermoplastic used in precision parts that require high stiffness, low friction and excellent dimensional stability.
Chemical Formula
Structural Formula


Glass Transition Temperature
-75 to -60 °C
Melting Temperature
140 to 175 °C
Melting Enthalpy
181 to 220 J/g
Decomposition Temperature
385 to 400 °C
Young's Modulus
2600 to 3200 MPa
Coefficient of Linear Thermal Expansion
110 to 150 *10¯6/K
Specific Heat Capacity
1.48 to 1.50 J/(g*K)
Thermal Conductivity
0.23 to 0.31 W/(m*K)
1.39 to 1.43 g/cm³
Semi-crystalline polymer
General properties
Good stiffness, toughness and stability. Low humidity absorption. Good dimensional stability. Good electrical insulation properties. Good resistance to creeping and fatigue. Good sliding properties
Injection molding, extrusion
Automobile industry. Instrument and apparatus engineering. Electrical/electronics industry. Medical engineering. Household goods. Food technology

Internet Links

NETZSCH Measurements

DSC 204 F1 Phoenix®
Sample Mass
10.55 mg
Isothermal Phase
7 min
Heating/Colling Rates
10 K/min
Al, pierced
N2 (40 ml/min)


As a semi-crystalline polymer, POM-C shows a glass transition at -71°C (both heatings, midpoints) with step heights (Δcp) of 0.09 J/(g.K) and melting peak temperatures of 170°C (1st heating, blue) and 168°C (2nd heating, green). The difference in melting temperature values is due to the better contact between the sample and crucible bottom after the first melting of the material.
The peak temperature (2nd heating, 168°C) of POM-C is 13 K lower than that of POM-H (on page 117), and the melting enthalpy differs by approx. 9% (178 J/g for POM-C, 195 J/g for POM-H). However, there is no linear relation between these
results and the actual degrees of crystallinity of the present samples, since the literature values for melting enthalpies for a crystallinity of 100% (316 to 335 J/g for POM (Homo) and 181 to 192 J/g for POM (Copo)) are strongly deviating.

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