Polyacetal. See

Some typical properties are given in Table 11.13 in comparison with typical properties for nylon 66 (see Chapter 18) and a polyacetal (see Chapter 19) for which it has been suggested that these materials will be competitive. 

POM is usually called acetal also called polyacetal. See Acetal. 

PMMA. See Methacrylic Ester Polymers. POLYACETAL. See Acetal Resins. POLYACRYLAMIDE. See Acrylamide Polymers. 

Low density polyethylene Polyacetal (see Polyoxymethylene below) LDPE Styrene-butadiene-styrene SBS... 

Processing 353 Poly-4-methylpentene-1. see Polyolefins Polyacetal, see Polyoxymethylene Polyamide, see Metal, metal ions... 

Many thermoplastics can be considered for this application although glass fibre reinforcement provides much greater rigidity, improved strength and a higher heat distortion temperature, these materials are more brittle than the unfilled ductile polymers and have unsatisfactory impact behaviour for this application. The high-temperature creep properties of ABS are unsuitable, and polyamides not only absorb water, which affects properties, but also have poor dimensional tolerances. The three most suitable materials are therefore modified PPO, PC and polyacetal (see Chapter 7) a comparison of their properties indicates that PC is the preferred material. Furthermore, its... 

Although there is a substantial body of information in the pubHc domain concerning the preparation of polyacetals, the details of processes for manufacturiag acetal resins are kept highly confidential by the companies that practice them. Nevertheless, enough information is available that reasonably accurate overviews can be surmised. Manufacture of both homopolymer and copolymer involves critical monomer purification operations, discussion of which is outside the scope of this article (see Formaldehyde). Homopolymer and copolymer are manufactured by substantially different processes for accomplishing substantially different polymerisation chemistries. 

The major disadvantage of chemical depolymerization is that it is almost completely restricted to the recycling of condensation polymers, and is of no use for the decomposition of most addition polymers, which are the main components of the plastic waste stream. Condensation polymers are obtained by the random reaction of two molecules, which may be monomers, oligomers or higher molecular weight intermediates, which proceeds with the liberation of a small molecule as the chain bonds are formed. Chemical depolymerization takes place by promoting the reverse reaction of the polymer formation, usually through the reaction of those small molecules with the polymeric chains. Several resins widely used on a commercial scale are based on condensation polymers, such as polyesters, polyamides, polyacetals, polycarbonates, etc. However, these polymers account for less than 15% of the total plastic wastes (see Chapter 1). 

Though useful polymers can be made by these reactions, their low ceiling temperatures (see p. 599) and consequent tendency to undergo facile depolymerization by an unzipping mechanism pose serious limitations. To overcome this problem the technique of end-capping or end-blocking may be used. Thus poly-oxymethylene (polyacetal), an engineering plastic, prepared from the cyclic acetal... 

The most recent addition to the engineering polymer field is the ethylene/carbon monoxide (COPO) alternating copolymers initially introduced by Shell. The commercial polymer is highly crystalline and believed to contain small amounts of propylene to reduce the crystalline melting point to allow a broad window of process-ability. COPO should offer serious competition to polyacetal, PA, and PBT. With the favorable raw materials cost, COPO should be a successful and competitive entry. As is now expected with new polymers, intense blend patent activity accompanies the introduction. This has also occurred with COPO as is noted in various U.S. patents involving COPO blends (See Table 17.4). COPO polymers are available from Shell (Carilon ) and BP (Ketonex ). 

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