Polyoxymethylene POM

Polyoxymethylene or polyacetal is a highly crystalline polymer. POM is most noted for its high stiffness, mechanical strength, abrasion resistance and good resistance to chemicals and solvents. It also displays good low temperature impact resistance, high dimensional stability, favourable frictional properties and low water absorption. 

The main disadvantages of the polymer are its poor resistance to acids and alkalis, and that it bums easily. It also has a restricted processing temperature range and poor UV resistance. 

Elastic modulus (MPa) (tensile with 0.2% water content) 4623 3105 8625-9660 

The first polyacetal was introduced in 1960. A problem which beset the moulders of the early polyacetal resins was that the polymer chains have to be stabilised to prevent the resin breaking down during processing at elevated temperatures. More heat-stable versions appeared in the early 1990s, incorporating new stabiUser technology that reduces mould and screw deposits. 

There are two different methods for producing polyacetals. Anionic polymerisation of formaldehyde produces homopolymers that crystallize particularly well and therefore have high stiffness and strength. The other method is cationic polymerisation of trioxane. Here the addition of small amounts of comonomers lowers the crystallinity to increase toughness. The stiffness and strength are however somewhat lower than for homopolymers. 

Polycondensation of formaldehyde was reported by Butlerov in 1859, but only in 1950 du Pont developed end-capping that prevented unzipping. POM is crystalline, thus rigid, brittle, and chemically nonreactive. Production of Delrin and Celcon started in 1959 and 1962, respectively. The world consumption of POM and its annual growth rate are 500 kt and 5 %. 

PC with PDMS Solution cast films with good properties Caird 1961 

PC and/or PEST with siloxane- For chemical, weather, and Kongo et al. 1987 

PC with poly(dimethyl siloxy Transparent, flame, and impact- Jordan and Webb 1992 

PC with siloxane/vinyl-based copolymer Thermal stability, ductility at low-T, and impact resistance Derudder and Wang 1993 

Peak Notation Assignment of Main Peaks Molecular Weight Retention Index Relative Intensity 

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Engineering polymers are often used as a replacement for wood and metals. Examples include polyamides (PA), often called nylons, polyesters (saturated and unsaturated), aromatic polycarbonates (PCs), polyoxymethylenes (POMs), polyacrylates, polyphenylene oxide (PPO), styrene copolymers, e.g., styrene/ acrylonitrile (SAN) and acrylonitrile/butadiene/styrene (ABS). Many of these polymers are produced as copolymers or used as blends and are each manufactured worldwide on the 1 million tonne scale. 

ISO 9988-1 2004 Plastics - Polyoxymethylene (POM) moulding and extrusion materials -Part 1 Designation system and basis for specifications ISO 9988-2 1999 Plastics - Polyoxymethylene (POM) moulding and extrusion materials -Part 2 Preparation of test specimens and determination of properties... 

The chains in the polymers discussed so far consist of isochains of catenated carbon atoms. However, many polymers such as the polyacetal— polyoxymethylene (POM), Delrin—have other atoms in addition to the carbon atoms in the polymer chain. As shown by the abbreviated segmental formula for the polyacetals... 

Crystalline polymers such as high-density polyethylene (hope), PP, PTFE, and polyoxymethylene (POM) exhibit somewhat higher X values than amorphous polymers such as low-density polyethylene (ldpe), atactic PS,... 

Polyoxymethylene (POM), which is called polyacetal, is a crystalline polymer of formaldehyde which has the following repeating unit ... 

Fig. 14 Creep curves of polyoxymethylene (POM) of medium molecular weight (Mw = 41 kg/mol) at 80 °C (see text for discussion)...

Figure 7.1 Spectral image for an observation line across five different polymer samples with different sizes (left to right polystyrene, PS polyoxymethylene, POM high density polyethylene, PE-HD polypropylene, PP acrylonitrile-butadiene-styrene, ABS). The left-side image shows the two-dimensional grey-scale image as delivered from the spectral imaging system, the right-hand image shows it as a three-dimensional profile plot to illustrate the spectral content.

Polyoxymethylene (POM) is, again, a crystalline polymer, with a melting point of about 180 °C. Its mechanical properties enable it to gradually replace metals in a number of applications. Many technical parts are being made from POM, such as gear wheels, bars, automotive accessories, parts of several apparatuses and machines. The polymer is used as such (e.g. Delrin ), but also as a copolymer with a small amount of ethylene oxide (e.g. Celcon and Hostaform ). 

Polyoxymethylene (POM) plastics are highly crystalline thermoplastics that are obtained by polymerization of formaldehyde and can also be in the form of trioxy-methylene oligomers (trioxane). The world-wide consumption in 1997 was 0.5 x 106 t for car parts and other articles processed by injection moulding. Polyacetals are primarily engineering materials being used to replace metals. 

Application Formaldehyde as a liquid solution of 37-52 wt% is primarily used in the production of polyoxymethylene (POM) and hexamethylenetetramine as well as synthetic resins in the wood industry. 

Formaldehyde homopolymer is composed exclusively of repeating oxymethylene units and is described by the term polyoxymethylene (POM) [9002-81-7]. Commercially significant copolymers, for example [95327-43-8], have a minor fraction (typically less than 5 mol %) of alkylidene or other units, derived from cyclic ethers or cyclic foimals, distributed along the polymer chain. The occasional break in the oxymethylene sequences has significant ramifications for polymer stabilization. 

Table 9 shows yield strength, ultimate elongation and modulus for twelve different plastics materials before treatment in supercritical carbon dioxide. Yield strength can be noted to vary in a broad range from 10.7 MPa for LDPE to 73.8 MPa for polyoxymethylene (POM). 

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