Polyacetal trioxane

Ring opening polymerization may also occur by an addition chain reaction. For example, a ring opening reaction polymerizes trioxane to a polyacetal in the presence of an acid catalyst. Formaldehyde also produces the same polymer ... 

The effect of propagation-depropagation equilibrium on the copolymer composition is important in some cases. In extreme cases, depolymerization and equilibration of the heterochain copolymers become so important that the copolymer composition is no longer determined by the propagation reactions. Transacetalization, for example, cannot be neglected in the later stages of trioxane and DOL copolymerization111, 173. This reaction is used in the commercial production of polyacetal in which redistribution of acetal sequences increases the thermal stability of the copolymers. 

Source Methylal is a by-product in the synthesis of trioxane, an intermediate in the manufacture of polyacetal plastics (Albert et ah, 2001). 

Commercial polymers of formaldehyde are also produced using cationic polymerization. The polymer is produced by ring opening of trioxane. Since the polyacetal, POM, is not thermally stable, the hydroxyl groups are esterified (capped) by acetic anhydride (structure 5.22). These polymers are also called poly(methylene oxides). The commercial polymer is a... 

Another stable polyacetal (POM Celcon) is produced by the cationic copolymerization of a mixture of trioxane and dioxolane (structure 5.23). 

Trioxane copolymers (often called polyacetals) are used as engineering plastics in automotive, machinery, and electric industry. 

By organic chemistry formalism, polyacetals are reaction products of aldehydes with polyhydric alcohols. Polymers generated from aldehydes, however, either via cationic or anionic polymerization are generally known as polyacetals because of repeating acetal linkages. Formaldehyde polymers, which are commercially known as acetal resins, are produced by the cationic ring opening polymerization of the cyclic trimer of formaldehyde, viz., trioxane [29-30] (Fig. 1.5). 

Polyformaldehyde. Polyformaldehyde or polyacetal is made by two different processes. Delrin is made from formaldehyde by anionic polymerization catalyzed by a tertiary amine. The homopolymer is end-capped with acetic anhydride. Celcon is made from trioxane cationic copolymerization using boron trifluoride catalyst and ethylene oxide (2-3%) as the comonomer. Boron trifluoride is a Lewis acid that associates with trioxane and opens up the six-membered ring. Ethylene oxide provides the end capping. Without an end cap, polyformaldehyde is thermally unstable and loses formaldehyde units. 

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. 

Bleach resistant polyacetals consisting of 98% trioxane and 2% dioxolane was prepared by Notorgiacomo [1] and used in molding compositions. 

Another monomer that belongs to this group is cyclic trimer of formaldehyde, 1,3,5-trioxane. Cationic polymerization of 1,3,5-trioxane leading to polyoxymethylene (polyformaldehyde, polyacetal) is one of the few industrially important processes in cationic ring-opening polymerization. 

Kern and Jaacks and independently Enikolopyan ) determined the ratio kt/kp for the polymerization of 1,3,5-trioxane as being dose to 1.0. This high value is attributed to the known fact that the linear polyacetals are more basic than the cyclic ones. In these systems, the interaction of the growing spedes with the polymer segments is certainly a reversible process thus, these systems cannot be quantitatively described by the kinetic Scheme (138). Nevertheless, if reversibility is tentatively ne ected, then for [Mlo 1.0 mole 1 and [IJo = 10 4mole 1 the complete conversion of the originally formed active species would take place only after 1.4% of conversion of monomer into polymer. 

Chain growth polymerizations very often contain a double bond however, cyclic ethers will polymerize in this manner [5], POM (polyoxymethylene) made by the Celanese method shown in Figure 3.6 is an example of a cyclic ether with this method. The Celanese route for the production of polyacetal yields a more stable copolymer product via the reaction of trioxane, a cyclic trimer of formaldehyde, and a cyclic ether (e.g., ethylene oxide or 1,3 dioxalane). 

Several papers57"59 were devoted to investigating a complex process such as the cationic copolymerization of monomeric formaldehyde with dioxolane in the gas, liquid, and gas-liquid phases. It is known that polyacetal resins are industrially produced by copolymerizing cyclic acetals (trioxane, 1,3,5,7-tetraoxane), or by anionic homopolymerization of monomeric formaldehyde with subsequent modification of end groups. 

Independent determinations of microstructure and composition heterogeneity of polyacetals, which were obtained using various methods and based on different monomers (formaldehyde and trioxane to produce oxymethylene blocks, and methylene oxide and dioxolane to produce stabilized oxymethylene blocks), made it possible to reveal differences in the mechanism of the synthesis of such products. 

Hydrolysis has been the main method used for the chemical recycling of other condensation polymers, such as polyacetals and polycarbonates. Hydrolysis of polyacetals leads back to the starting monomers, formaldehyde or trioxane. Polycarbonates are polymers synthesized by the reaction of phosgene and a dihydric phenol, commonly bisphenol A. Chemical recycling of polycarbonate... 

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... 

Polyoxymethylene (polyacetal) — sometimes known as polyformaldehyde — is the polymer of formaldehyde. It is obtained either by anionic or cationic solution polymerization of formaldehyde or cationic ring-opening bulk polymerization of trioxane. Highly purified formaldehyde is polymerized in the presence of an inert solvent such as hexane at atmospheric pressure and a temperature usually in the range of -50 to 70°C. The cationic bulk polymerization of trioxane is the preferred method of production of polyoxymethylene. 

Polyacetal can also be stabilized against degradative conditions by copolymerizing trioxane with small amounts of ethylene oxide. This introduces a random distribution of -C-C- bonds in the polymer chain. Hydrolysis of the copolymer with aqueous alkali gives a product with stable hydroxyethyl end groups. The presence of these stable end groups coupled with the randomly distributed C-C bonds prevents polymer depolymerization at high temperature. 

Polyoxymethylene (polyacetal) is the polymer of formaldehyde and is obtained by polymerization of aqueous formaldehyde or ring-opening polymerization of trioxane (cyclic trimer of formaldehyde, melting point 60-60°C), the latter being the preferred method [52]. This polymerization of trioxane is conducted in bulk with cationic initiators. In contrast, highly purified formaldehyde is polymerized in solution using using either cationic or anionic initiators. 

Polyoxymethylenes or polyacetals (polymers of formaldehyde or trioxane) produce formaldehyde on heating. The chromotropic acid test for formaldehyde is positive (see Section 6.1.4). 

Acetal, (Polyacetal) Poly-oxymethylene (POM) Acetal is a polymer obtained through an addition reaction of formaldehyde — (CH2—0) . It excels in mechanical performance and is regarded as a prominent engineering polymer. It appeared in 1959 with the commercial name Delrin . A short time later a useful copolymer was also developed with a cyclic ether like ethylene oxide. The monomer formaldehyde is a gas produced mostly by oxidizing methanol, and it is very useful in thermoset polymers like phenol, urea and melamine-formaldehydes. For high purity it is initially converted to trioxane or paraformaldehyde. The polymerization is carried out by ionic mechanism, wherein the monomer is dispersed in an inert liquid (heptane). The molecular weights reach 20,000 to 110,000. 

The main chains of polyacetals consist of strictly alternating carbon-oxygen bonds of the type —CHR—O—. They are produced by polymerization of aldehydes or their cyclic trimers. The cyclic trimers and tetramers of formaldehyde are, respectively, known as trioxane and tetroxane. The formaldehyde oligomer with 6-10 monomeric units produced spontaneously in aqueous formaldehyde solutions is known as paraformaldehyde. The cyclic trimer of acetaldehyde is called paraldehyde and the cyclic tetramer is called metaldehyde. 

Poly(oxymethylene), with the monomeric unit -(rCUiO, can be produced from formaldehyde, HCHO, or its cyclic trimer, trioxane (1,3,5-trioxacyclohexane). The commerical polymer obtained from formaldehyde is also known as polyacetal homopolymer, and that from trioxane is known as polyacetal copolymer. 

Polyacetals contain (—CHR—O—) groups in the chain. Like their low-molecular-weight counterparts, they are resistant to alkalis but not to acids. Macromolecular polyacetals have been known for some time under various trivial names as modifications of the corresponding monomers, but their macromolecular nature was first recognized by H. Staudinger. Paraformaldehyde, for example, is a low-molecular-weight poly(oxy-methylene), -f-O—with n 6-100. Metaldehyde is an acetaldehyde oligomer, -(-O—CH(CH3)-)-4.6. Paraldehyde is the cyclic trimer of acetaldehyde and trioxane is the cyclic trimer of formaldehyde. 

Linear, hard, tough synthetic resins produced by the polymerisation of formaldehyde (for acetal homopolymers) or of formaldehyde with trioxane (for acetal copolymers). Acetal resins are also called as polyacetals and are used as substitutes for metals. 

Polymers with the repeat units -fCH - Of, known as polyacetals, have been known since the early 920 s. It was not until the late 1950 s, however, that research efforts resulted in high molecular weight linear, stable thermoplastic materials. Whereas these developments were directed towards homopolymers of formaldehyde at DuPont, the research at Celanese Corporation was aimed towards copolymers using trioxane, a cyclic formaldehyde trimer, as the major monomer. 

Commercial polyacetal copolymers contain 0.1 to 15 mole percent of a cyclic ether, commonly ethylene oxide or 1,3-dioxolane. Typical catalysts for this reaction are BF, or its ether complexes. In 1964, Weissermel and coworkers[5] showed that in the copolymerization of trioxane with ethylene oxide, the latter was almost completely consumed before any visible polymer was observed. During this stage of the polymerization, soluble prepolymers of ethylene oxide could be isolated [6], These prepolymers consisted primarily of oligomers with mono-, di-, and tri-ethylene oxide units. Celanese workers in 1980[7] verified also the presence of cyclic ethers, predominately 1,3-dioxolane and 1,3,5-tri-oxepane, as part of the reaction mixture. These are likely formed as reaction products of ethylene oxide and monomeric formaldehyde generated from the opening of the trioxane ring. 

Typically in the commercial manufacture of polyacetal copolymer molten trioxane, comonomer, chain transfer agent and catalyst are fed into a reactor capable of providing shear and mixing action and with the means to remove heat generated by the exothermic polymerization reaction. The solid raw polymer is removed, quenched to neutralize any traces of catalyst and washed free of unreacted monomer. The unstable chain ends are usually removed hydrolytically in a basic media. Subsequently, the polymer is washed, dried and compounded with stabilizers and other ingredients and packaged for shipment. 

Poly-1,3,5-trioxan is known to contain hemiacetal -OH groups some of these are formed because of the chain transfer to water 32, Acetylation of the -OH groups greatly enhances tKermal stability of the poly-oxymethylene polymers,and is at the base of the com -mercialization of the first polyacetal (a homopolymer of CH-O) 132a I known, in fact many years ago from the classical works of Staudinger and Kern,... 

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