Polyacetals Poly

Cationic polymerizations are not only important commercial processes, but, in some cases, are attractive laboratory techniques for preparing well-defined polymers and copolymers. Polyacetal, poly(tetramethyl-ene glycol), poly(e-caprolactam), polyaziridine, polysiloxanes, as well as butyl rubber, poly(N-vinyl carbazol), polyindenes, and poly(vinyl ether)s are synthesized commercially by cationic polymerizations. Some of these important polymers can only be prepared cationically. Living cationic polymerizations recently have been developed in which polymers with controlled molecular weights and narrow polydispersity can be prepared. 

Polyisobutylene and polybutenes Isobutylene-isoprene copolymer (Butyl rubber) Polyacetal Poly(vinyl ether)s... 

Weak links, particularly terminal weak links, can be the site of initiation of a chain unzipping reaction. A monomer or other simple molecule may be abstracted from the end of the chain in such a way that the new chain end is also unstable. The reaction repeats itself and the polymer depolymerises or otherwise degrades. This phenomenon occurs to a serious extent with polyacetals, poly(methyl methacrylate) and, it is believed, with PVC. 

As described in the previous section, under suitable reaction conditions one can prepare living polyacetals (poly-l,3-dioxolane and poly-1,3-dioxepane) in almost quantitative yields having well defined molecular weights (DPn = ([M]0 — [M]e)/[I]0), and a low content of cyclic fraction (a few percent). 

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 use of co-polymers has been alluded to above. Recent work [74] on the effect of EO sequence length on the properties of PMO/PEO copolymers has shown that optimum results are obtained with narrow, nonuniform distributions of sequence length. An alternative route [75] to the particular PEO/PMO 1 1 co-polymer is to synthesize the polyacetal, poly(l,3-dioxolane), for which the repeat unit is -CH2OCH2CH2O-, but... 

Polyacetals Poly ACN / water SUica gel NucleosU 20pl Separation according to Kruger RP, Much H, Schulz G,... 

Water-soluble or -swellable synthetic polymers, such as poly(vinyl alcohol), polyacetals, poly(acrylic acid), and polyacrylamide, are all relatively stable at neutral pH, but undergo quite rapid chain scission under acidic or basic conditions. Typical commercial polymers can be classified according to their resistance to hydrolysis (158) as follows. 

Poly(oxymethylene) polyformaldehyde polyacetal Poly(oxy-l,4-phenylene) poly(l,4-phenylene oxide)... 

Owing to vibrational and electronic couplings, UV absorption bands of polyatomic molecules in ffie condensed state are generally quite broad, with width at half-maximum commonly exceeding 60-80 nm. Even with this broadness, polymers such as polyolefins, polyacetals, poly(vinyl chloride), or polyacrylonitrile... 

Figure 8.31 Melt flow index variation with blend composition for polyacetal/poly-methyl methacrylate blend at 21(fC and 3.8-kg test load condition for MH using data from Ref. 86 (validity over 180-25(fC). (Reprinted from Ref. 78 with kind permission from Steinkopff Verlag Darmstadt.)...

Similar polyacetals were prepared by BASF scientists from CO-aldehydic aUphatic carboxyUc acids (189,190) and by the addition of poly(hydroxycarboxyhc acid)s such as tartaric acid to divinyl ethers (191) as biodegradable detergent polymers. 

There are thus no solvents at room temperature for polyethylene, polypropylene, poly-4 methylpent-l-ene, polyacetals and polytetrafluoroethylene. However, as the temperature is raised and approaches F , the FAS term becomes greater than AH and appropriate solvents become effective. Swelling will, however, occur in the amorphous zones of the polymer in the presence of solvents of similar solubility parameter, even at temperatures well below T. ... 

Some polymers such as the polyacetals (polyformaldehyde) and poly(methyl methacrylate) depolymerise to monomer on heating. At processing temperatures such monomers are in the gaseous phase and even where there is only a small amount of depolymerisation a large number of bubbles can be formed in the products. 

Gaseous monomers may also be trapped within the processing equipment and accidents have occurred as a consequence of the resulting pressure buildup. In the case of the polyacetals and poly(vinyl chloride) it is reported that at elevated temperatures these materials form a more or less explosive combination so that it is important to separate these materials rigorously at the processing stage. 

Hence at room temperature there are no solvents for polyethylene, polypropylene, poly-4-methyl-pentene-l, polyacetal or polytetrafluoroethylene, but at temperatures of about 30°C below their melting point solvents of... 

The divinylacetal of 2-furaldehyde was polymerized in vacuo with free-radical initiators at 80 °C to give low yields of the cyclic polyacetal 31132, commonly known as poly(vinylfurfural). 

Polyacetal Polyacrylamide Polyacrylonitrile Polycarbonate Polyethylene Polyethylene oxide Polyethylene terephthalate Poly isobutyl methacrylate Poly methacrylic acid Polymethyl methacrylate Polymonochlorotrifluoro ethylene Polypropylene Polystyrene... 

Poly(4-phenoxybenzoyl-1,4-phenylene) (PPBP), sulfonated, 23 718 Polyacetal, antioxidant applications, 3 121 Polyacetaldehyde, 1 103 Polyacetal fiber, 13 392 Polyacetylene, 7 514-515 26 953 conduction in, 7 527 22 208 molecular structure of, 22 211 optical band gap, 7 529t Peierls distortion in, 22 203, 208 room temperature conductivity, 7 532 synthesis of, 22 213... 

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... 

Nylon, polyacetal, polycarbonates, poly(2,6-dimethyl)phenylene oxide (PPO), polyimides, polyphenylene sulfide (PPS), polyphenylene sulfones, polyaryl sulfones, polyalkylene phthalates, and polyarylether ketones (PEEK) are stiff high-melting polymers which are classified as engineering plastics. The formulas for the repeating units of some of these engineering plastics are shown in Figure 1.15. 

Amorphous polyacetaldehyde was obtained for the first time in 1936 by Travers (9) and Letort (10) independently by cooling acetaldehyde vapor to liquid air temperature in high vacuum. The polyacetal structure of this polymer was suggested by Staudinger (//). This poly-... 

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