Acetals-polyoxymethylene homopolymer

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

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

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],... 

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. 

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). 

PMMA Polymethyl methacrylate (acrylic) PMMA-TToughened acrylic POM Polyoxymethylene or, acetal or, pol ormaldehyde POM-H Acetal homopolymer... 

Acetal polymers are formed from the polymerization of formaldehyde. They are also known by the name polyoxymethylenes (POM). Polymers prepared from formaldehyde were studied by Staudinger in the 1920s, but thermally stable materials were not introduced until the 1950s when DuPont developed Delrin. Homopolymers are prepared from very pure formaldehyde by anionic polymerization, as shown in Fig. 1.4. Amines and the soluble salts of alkali metals catalyze the reaction. The polymer formed is insoluble and is removed as the reaction proceeds. Thermal degradation of the acetal resin occurs by unzipping with the release of formaldhyde. The thermal stability of the polymer is increased by esterification of the hydroxyl ends with acetic anhydride. An alternative method to improve the thermal stability is copoly-... 

Acetal resin is either a homopolymer or copolymer of formaldehyde. The homopolymer is sometimes called polyoxymethylene or POM. It is made by polymerizing either anhydrous formaldehyde or its cyclic trimer triox-ane. The polymerization can he done using either acidic or basic catalysts. At least some of the end groups are hydroxyl groups and with heat, the resin... 

Copolymeiization is often used to alter the properties of homopolymers and to acUeve specific performance. For example, the flow behavior of PVC is considerably improved by incorporating vinyl acetate as comonomer. Similarly, the thermal stability of polyoxymethylene is improved considerably by incor-... 

Acetal homopolymer is a highly crystalline thermoplastic manufactured by polymerization of formaldehyde and capping the two ends of the polymer chain with acetate groups (Table 6.2). It is called polyoxymethylene (POM) and has a backbone consisted of repeating —CH2O—units. Acetal copolymers are produced by copolymerization of trioxane and small amounts of a comonomer. The comonomer randomly distributes carbon—carbon bonds in the polymer chain, which stabilizes the resin against environmental degradation. The low cost of acetals compared to other polymers with similar performance and their mechanical, chemical, and electrical properties, allows them to replace metal and other structural materials in many applications. 

Polyoxymethylene (Acetal) 20% Glass-Reinforced Homopolymer POMR... 

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