Depolymerization chemistry

This strategy is used for the synthesis of three different exact-mass telechelic oligomers. GPC, NMR, and GC/MS evidence indicates that clean depolymerization chemistry occurs for all three samples. Poly( 1,4-butadiene) (38) is broken down into oligomeric units with two, three, and four repeat units using catalyst 23. Catalyst 14 is more efficient and produces even lower molecular weight oligomers, primarily one and two repeat units. When allylchlorodimethylsilane is used instead of ethylene with 14, telechelic dimers are the only product. 

Both metathesis degradation (a well documented phenomenon ) and metathesis depolymerization offer promise in issues related to chemically recycling discarded unsaturated polymers. However, it should be noted that ADMET depolymerization chemistry is distinguished from metathesis degradation chemistry by virtue of the fact that very specific products result from depolymerization and, in... 

Chemical degradation (141), whether thermally or photo-iaduced, primarily results from depolymerization, oxidations, and hydrolysis. These reactions are especially harmful ia objects made from materials that coataia ceUulose, such as wood, cottoa, and paper. The chemistry of these degradation processes is quite complex, and an important role can be played by the reaction products, such as the acidic oxidation products which can catalyze hydrolysis. 

Glycolysis is the most promising approach for the chemical recycling of polyurethanes.1 The chemistry of PUR depolymerization is complicated by the presence of other chemical groups in the polymer, such as ureas, allophanates, and biurets. 

Metathesis chemistry, histoiy of, 431-432 Metathesis depolymerization, 456-457 Metathesis polymerization, general conditions for, 440-441 Metathesis reactions, types of, 432 Methanol, 377 Methanolysis, 535... 

Nylon-6, 136, 530, 531. See also PA-6 acid-catalyzed hydrolysis of, 567-568 chemistry and catalysis of, 546 depolymerized, 532-534, 557-558 hydrolysis of, 535, 552 neutral hydrolysis of, 566-567 Nylon-6 waste, 543... 

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

Industrial Engineering Chemistry Research 40, No.2, 24th Jan.2001, p.509-14 KINETICS OF DEPOLYMERIZATION OF POLY(ETHYLENE TEREPHTHALATE) IN A POTASSIUM HYDROXIDE SOLUTION Ben-Zu Wan Chih-Yu Kao Wu-Hsun Cheng... 

While "conventional positive photoresists" are sensitive, high-resolution materials, they are essentially opaque to radiation below 300 nm. This has led researchers to examine alternate chemistry for deep-UV applications. Examples of deep-UV sensitive dissolution inhibitors include aliphatic diazoketones (61-64) and nitrobenzyl esters (65). Certain onium salts have also recently been shown to be effective inhibitors for phenolic resins (66). A novel e-beam sensitive dissolution inhibition resist was designed by Bowden, et al a (67) based on the use of a novolac resin with a poly(olefin sulfone) dissolution inhibitor. The aqueous, base-soluble novolac is rendered less soluble via addition of -10 wt % poly(2-methyl pentene-1 sulfone)(PMPS). Irradiation causes main chain scission of PMPS followed by depolymerization to volatile monomers (68). The dissolution inhibitor is thus effectively "vaporized", restoring solubility in aqueous base to the irradiated portions of the resist. Alternate resist systems based on this chemistry have also been reported (69,70). 

Interest in solution inhibition resist systems is not limited to photoresist technology. Systems that are sensitive to electron-beam irradiation have also been of active interest. While conventional positive photoresists may be used for e-beam applications (31,32), they exhibit poor sensitivity and alternatives are desirable. Bowden, et al, at AT T Bell Laboratories, developed a novel, novolac-poly(2-methyl-l-pentene sulfone) (PMPS) composite resist, NPR (Figure 9) (33,34). PMPS, which acts as a dissolution inhibitor for the novolac resin, undergoes spontaneous depolymerization upon irradiation (35). Subsequent vaporization facilitates aqueous base removal of the exposed regions. Resist systems based on this chemistry have also been reported by other workers (36,37). 

The mechanism of formation of zeolites is very complex, stemming from the diversity of chemical reactions, including various polymerization and depolymerization equilibria, nucleation and crystal growth processes. The physical and chemical nature of the reactants, which typically involve a source of aluminum and silicon along with hydroxides and salts determine the formation of zeolites. Physical effects such as aging, stirring, and temperature also play an important role. These effects lead to the complexity of zeolite formation, but are also responsible for the large number of frameworks that can be synthesized and the rich chemistry associated with this area. Cl. 21... 

Some sulfated galactans, or products of their partial depolymerization, exhibit antioxidant activity.684,685 The chemistry of radical scavenging effects is not very clear, especially taking into account the fact that several products of chemical modifications of natural polysaccharides, such as oversulfated, phosphorylated, acety-lated and phthaloylated derivatives, may demonstrate stronger antioxidant activity than the raw material.685-688... 

If there are no major disruptions, depolymerizations, or decrystallization of cell wall polymers during the reaction chemistry to modify solid wood, there are no statistical differences in mechanical properties of chemically modified wood as compared to nonmodified wood. There are so many differences in moisture levels, specific gravities, and fibers per unit cross-section in control vs. modified woods that no definitive conclusions can be made. If the reaction chemistry used to modify solid wood does result in major disruptions, depolymerizations, or decrystallization of cell wall polymers, then there are major statistical differences between control and chemically modified solid wood. Losses in mechanical properties can vary from large decreases in all properties to complete loss of cell wall structure and wood is converted to a thermoplastic film. 

Near-quantitative conversion of monomer to polymer is standard in these polymerizations, as few side reactions occur other than a small amount of cychc formation common in all polycondensation chemistry [41]. ADMET depolymerization also occurs when unsaturated olefins are exposed to pressures of ethylene gas [42,43]. In this case, the equilibriiun nature of metathesis is shifted towards low molecular weight products under saturation with ethylene. Due to the high catalytic activity of [Ru] and the abihty of [Mo] and [Ru] to create exact structures, ADMET has proven a valuable tool for production of novel polymer structures for material applications as well as model copolymer systems to help elucidate fundamental structure property relationships [5]. 

The details of the commercial preparation of acetal homo- and copolymers are discussed later. One aspect of the polymerization so pervades the chemistry7 of the resulting polymers that familiarity with it is a prerequisite for understanding the chemistry of the polymers, the often subtle differences between homo- and copolymers, and the difficulties which had to be overcome to make the polymers commercially useful. The ionic polymerizations of formaldehyde and trioxane are equilibrium reactions. Unless suitable measures are taken, polymer will begin to revert to monomeric formaldehyde at processing temperatures by depolymerization (called unzipping) which begins at chain ends. 

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