Polyoxymethylene homopolymer

Polyoxymethylene glycols. See Formaldehyde Polyoxymethylene homopolymer. See Acetal... 

Poly(11 -aminoundecanoic acid)] POM Polyacetal Polyoxymethylene Homopolymer 1.42 3.1 65-70 25-75 60-120 c... 

Acetal Polyoxymethylene Homopolymer—POM PTFE Lubricated, azom.com Article ID 875. Source Plascams, Rubber and Plastics Research Association (RPRA). 

Three model polymers were subjected to Py-GC analysis in the presence of cobalt sulfate to confirm that the sequence distribntions estimated by the cyclic ethers on the pyrograms reflect those in the original polymer chain. Figure 5.17 shows the pyrograms of (a) polyoxymethylene homopolymer, (b) polyoxymethylene-1,3-dioxolane (DO) copolymer, and (c) polyoxymethylene-l,3,6-trioxocane copolymer at 400 °C in the presence of 5 wt% cobalt sulfate. 

As would be expected from the polymer structure, in the pyrogram of the polyoxymethylene homopolymer (a), formaldehyde (F) and cyclic compounds comprising only F units are observed, whereas no cyclic ether containing E unit(s) is observed. This result suggests that the formation of E unit(s) from oxymethylene sequences does not occur during the reactive pyrolysis of the polyoxymethylene homopolymer sample. 

Degradation of a polyoxymethylene homopolymer (heat and UV-stabilized) under nitrogen 450 atmosphere, detected by thermogravimetry (heating rate 10 K/min) [622]... 

Influence ofthermal-oxldatlve degradation on yield strain In polyoxymethylene homopolymer and copolymer at 130 °C In air [771]... 

Acetals. Acetal resins (qv) are polymers of formaldehyde and are usually called polyoxymethylene [9002-81-7]. Acetal homopolymer was developed at Du Pont (8). The commercial development of acetal resins required a pure monomer. The monomer is rigorously purified to remove water, formic acid, metals, and methanol, which act as chain-transfer or reaction-terminating agents. The purified formaldehyde is polymerized to form the acetal homopolymer the polymer end groups are stabilized by reaction with acetic anhydride to form acetate end groups (9). 

Acetal Resins. Acetal resins (qv) are poly (methylene oxide) or polyformaldehyde homopolymers and formaldehyde [50-00-0] copolymeri2ed with ahphatic oxides such as ethylene oxide (42). The homopolymer resin polyoxymethylene [9002-81-7] (POM) is produced by the anionic catalytic polymeri2ation of formaldehyde. For thermal stabiUty, the resin is endcapped with an acyl or alkyl function. 

The polyoxymethylenes are presently widely used in different areas. Approximatively one-third of the market is represented by homopolymers and two-thirds by copolymers. Homopolymers are produced by anionic polymerization of formaldehyde using amines, alkoxides, and other types of anionic initiators. The details of these polymerizations will not be discussed in this paper, although some of their properties will be compared to those of copolymers which are obtained by cationic copolymerization of trioxane with cyclic ethers or cyclic esters. Comprehensive reviews on general aspects of synthesis and properties of acetal resins are available [158-162],... 

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. 

The many commercially attractive properties of acetal resins are due in large part to the inherent high crystallinity of the base polymers. Values reported for percentage crystallinity (x ray, density) range from 60 to 77%. The lower values are typical of copolymer. Polyoxymethylene most commonly crystallizes in a hexagonal unit cell (9) with the polymer chains in a 9/5 helix (10,11). An orthorhombic unit cell has also been reported (9). The oxyethylene units in copolymers of tiioxane and ethylene oxide can be incorporated in the crystal lattice (12). The nominal value of the melting point of homopolymer is 17S°C, that of the copolymer is 165°C. Other thermal properties, which depend substantially on the crystallization or melting of the polymer, are listed in Table 1. See also reference 13. 

Gak et al. (100, 102) examined the nature of free radicals in polyoxymethylene. When formaldehyde homopolymer, PFA-OH was irradiated at —196° C, the initial rate of formation of the free radical — CH20- was found to be proportional to the square of the incident light intensity, which indicates the two-photon process of —CH20-radical formation. When irradiated PFA-OH was kept in the dark, some increase occurred in the concentration of -CH20- and there was a simultaneous fall in the concentration of -CH2 at temperatures above —196° C. The maximum rate was attained in the temperature range —130° C----123° C. This is caused by reaction (41). 

Fig. 19. Rates of radical production (excluding formyl radical) in polyoxymethylene materials on photolysis by 2537 A light at —196° C 1 copolymer, homopolymer, and paraformaldehyde photolyzed in vacuo 2 homopolymer and paraformaldehyde photolyzed under 10mm oxygen 3 copolymer photolyzed under 10mm oxygen, showing the great decrease In the number of radicals when the oxygen is depleted 4 copolymer photolyzed under 100 mm oxygen. [J. Polymer Sri. A-l, 7,1861 (1969),...

Polymerization of 1,3,5-trioxane (TXN) gives linear polyoxymethylene (POM), a homopolymer of formaldehyde 39). This is the only polyacetal made on the technical scale. Two methods are used for the industrial production of stable, high-molecular-weight POMs. This is either the anionic polymerization of formaldehyde or the cationic copolymerization of the cyclic trimer of formaldehyde TXN with ethylene oxide or 1,3-dioxolane (DXL) ... 

Polyoxymethylene polymers, POM, commonly known as polyacetals or Acetal resins are linear thermoplastic polymers containing predominantly the -CH -O- repeat unit in their backbone. There are two types of acetal resins available commercially (1) homopolymers made by the polymerization of formaldehyde, followed by endcapping, (2) copolymers derived from the ring opening polymerization of trioxane (a cyclic trimer of formaldehyde), and a small amount of a comonomer such as ethylene oxide. Acetal resins are... 

This chapter covers polymers in which the most important linking group is the ether moiety, which is —O—. Included in this chapter are the acetals also called polyoxymethylene (POM) or polyacetal. Acetals come in two types, homopolymer and copolymer. The third plastic type included in this chapter is polyphenylene ether (PPE) also referred to as polyphenylene oxide (PPO). 

POM Polyoxymethylene PPBC Polypropylene block copolymer PPHP Polypropylene homopolymer PPS Polyphenylene sulphide PPO Polyphenylene oxide PS Poly styrene... 

---