Ethylene Oxide - Polyacetal

Ethylene Oxide Containing Copolymers 7.8.1 Polyacetal - Ethylene Oxide... 

Table 7.25 Sequence distributions of polyacetal-ethylene oxide copolymers estimated by Py-GC ...

Polyacetals are among the aliphatic polyether family and are produced by the polymerization of formaldehyde. They are termed polyacetals to distinguish them from polyethers produced by polymerizing ethylene oxide, which has two -CH2- groups between the ether group. The polymerization reaction occurs in the presence of a Lewis acid and a small amount of water at room temperature. It could also be catalyzed with amines ... 

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. 

PB PBI PBMA PBO PBT(H) PBTP PC PCHMA PCTFE PDAP PDMS PE PEHD PELD PEMD PEC PEEK PEG PEI PEK PEN PEO PES PET PF PI PIB PMA PMMA PMI PMP POB POM PP PPE PPP PPPE PPQ PPS PPSU PS PSU PTFE PTMT PU PUR Poly(n.butylene) Poly(benzimidazole) Poly(n.butyl methacrylate) Poly(benzoxazole) Poly(benzthiazole) Poly(butylene glycol terephthalate) Polycarbonate Poly(cyclohexyl methacrylate) Poly(chloro-trifluoro ethylene) Poly(diallyl phthalate) Poly(dimethyl siloxane) Polyethylene High density polyethylene Low density polyethylene Medium density polyethylene Chlorinated polyethylene Poly-ether-ether ketone poly(ethylene glycol) Poly-ether-imide Poly-ether ketone Poly(ethylene-2,6-naphthalene dicarboxylate) Poly(ethylene oxide) Poly-ether sulfone Poly(ethylene terephthalate) Phenol formaldehyde resin Polyimide Polyisobutylene Poly(methyl acrylate) Poly(methyl methacrylate) Poly(methacryl imide) Poly(methylpentene) Poly(hydroxy-benzoate) Polyoxymethylene = polyacetal = polyformaldehyde Polypropylene Poly (2,6-dimethyl-l,4-phenylene ether) = Poly(phenylene oxide) Polyp araphenylene Poly(2,6-diphenyl-l,4-phenylene ether) Poly(phenyl quinoxaline) Polyphenylene sulfide, polysulfide Polyphenylene sulfone Polystyrene Polysulfone Poly(tetrafluoroethylene) Poly(tetramethylene terephthalate) Polyurethane Polyurethane rubber... 

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). 

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) ... 

Thermal stability of polyacetal is achieved by incorporating into the backbone —CH2—CH2— units, i.e., disrupting the sequence of —CH2—O— units susceptible to unzipping. This is done, by copolymerization of TXN with other cyclic ethers or acetals, preferably with 1,3-dioxolane or ethylene oxide (<5%mol)42,53). 

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... 

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. 

Polyoxymethylenes have a marked tendency to undergo thermal depolymerization with loss of formaldehyde. To prevent thermal depolymerization, polyoxymethylenes are structurally modified, the two possibilities being acetylation to block the reactivity of the end groups of co-polymerization with cyclic ethers, e.g., ethylene oxide. Polyacetals are also sensitive towards autoxidation, which invariably leads to depolymerization as a result of chain scission. The formaldehyde released by depolymerization is very likely to be oxidized to formic acid, which can catalyze further depolymerization. 

Polyacetal polyphenylene oxide are widely used as engineering thermoplastics, and epoxy resins are used in adhesive and casting application. The main uses of poly(ethylene oxide) and poly(propylene oxide) are as macroglycols in the production of polyurethanes. Polysulfone is one of the high-temperature-resistant engineering plastics. 

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. 

BAILEY, F. E and koleske, j. V., Poly(ethylene oxide). Academic Press, New York (1976) barker, s. j., and price, m. b.. Polyacetals, lliffe, London (1970)... 

There is a series of polymers having a chemical structure — [(CHR) —O— which are derived as polyacetal resins, and are known as polyalkyene oxides or polyalkylene glycols. In the above structure, the polymer with R=H and M = 1 is polyoxymethylene, which is known as Delrin. This material is a high polymer of formaldehyde, which is terminated by an ether or ester function added to stabilize the final product. Other manufactured products include copolymers with ethylene oxide or propylene oxide. The IR and Raman spectra of polyoxymethylene are shown in Reference Spectrum 55. A strong peak at 1098 cm and a doublet at 936 and 900 cm in the IR spectrum are assigned to the C—O—C stretching vibration. It is not possible to determine if the sample is a homopolymer or copolymer from this spectrum. 

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. 

The ethylene oxide contents of ethylene oxide - polyacetal copolymers were determined on the basis of cyclic ether intensities by reactive pyrolysis - gas chromatography in the presence of cobalt sulfate [135]. 

According to the authors, the cationic species present in the polymerization mixture participate in not only transacetaliza-tion but also transetherification reactions, yielding copolymers with the polyacetal and poly(ethylene oxide) blocks (see Scheme 1). These copolymers can function as the in sitM-formed suspension stabilizers adsorbed onto the surface of polyacetal particles via the polyacetal blocks and with the poly( ethylene oxide) segments providing steric stabilization. 

Scheme 1 Reaction of cationic species of 1,3,5-trioxane and 1,3-dioxoiane copoiymerization with poiy(ethylene oxide) yielding polyacetal-polyether suspension stabilizing the block copolymer.

Ishida and co-workers [14] applied reactive pyrolysis of copolymer polyacetals in the presence of cobalt sulfate incorporated into Py-GC equipped with a high-resolution capillary separation column. The method was successfully applied to study the sequence distributions in polyacetals containing low levels of copolymerised ethylene oxide units. The E contents and the distributions of E sequences up to E in polymers were evaluated on the basis of peak intensities of cyclic ethers containing E units on the pyrogram. 

Other exceptions include polymers with restricted symmetry which can, however, erystallize in a helical macroconformation because of electrostatic interactions between molecular groups of the main chain ( intrachain interactions). However, for sueh helicity to occur, the chain should exhibit a great mobility, which is the ease, for example, in the family of polyethers in the latter case, the dipole attraetion due to —groups is responsible for the stability of the crystalline state poly(ethylene oxide) (-CH2-CH2-0-) crystallizes in a I2 helix (c = 1.94 nm), whereas poly(oxymethylene) (-CH2-0-) (also called polyformaldehyde or polyacetal ) does in a 9s helix (c = 1.72 nm). In the latter case, multiple dipole interactions contribute to stiffen the chains and enhance mechanical properties of the corresponding materials. 

---