Polyacetal chemical structure

Formaldehyde (anhydrous) is also the major reactant for polyacetal resins, important for engineering components. The chemical structure is essentially R0(CH20) R, with co-monomers or end-capping reagents incorporated to prevent slow reversion to formaldehyde. 

Figure A.1 General chemical structure of polyacetal resin.

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. 

The hydrolysis resistance of polyacetals depends on their chemical structure and to a lesser extent on their stabilization. POM copolymers are more resistant than POM homopolymers, because POM homopolymers contain hydrolysis-sensitive end groups. 

Ladybird beetles produce a wide variety of polyacetate or fatty acid-derived alkaloids, many of which closely resemble the ant venom alkaloids described in the previous section. The original discovery of coccinelline (75) and precoccinelline (100) (Figure 32) in blood of the European ladybird beetle, C. 1-punctata had been motivated in part by these beetles aposematic coloration and their tendency to reflex-bleed when molested. Many ladybird beetle species share these characteristics and correspondingly are chemically protected by alkaloids as well. The carbon skeletons of almost all of these alkaloids are based on simple unbranched chains. The structures, biology, and laboratory syntheses of ladybird beetle alkaloids have been reviewed previously by Daloze et al and by Glisan King and Meinwald. ... 

Outside these two families, however, no other plants have been found to produce real tetrahydro-, dihydro-, and fully aromatic isoquinoline alkaloids in a polyacetate way. Closely related, but chemically a lactam, is siamine (40) from Cassia siamea Lam. (Leguminosae) (42). The structure suggests a biogenesis from a pentaketide precursor 41 (Fig. 2), thus requiring one acetate unit less than each of the naphthyl isoquinoline alkaloid moieties. 

SEM micrographs of a polyacetal/polyur-ethane multiphase polymer are shown in Fig. 5.50. The outer surface and a fractured internal surface of this extrudate were chemically etched in order to determine the nature of the dispersed phase. The surface (Fig. 5.50A) shows a complex structure due to etching. The fracture surface after solvent extraction (Fig. 5.50B) is complex, as... 

Polyacetals prepared from formaldehyde are engineering thermoplastics, which have found use in traditional metal applications. Some trade names of these polymers are Delrin acetal homopolymer (DuPont) Celcon acetal copolymer (Celanese/Hoechst) Duracon acetal copolymer (Celanese and Diacel—joint venture) Tenac acetal homopolymer by Asahi Chemical in Japan and Ultraform acetal copolymer jointly by BASF and Degussa, in Germany. The polymers have the basic structure shown below ... 

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