Extrusion reaction

Example 3. Hydrolysis in an Extruder.69 PET reactive extrusion experiments were carried out on a 25-mm Berstorff ZE25 corotating twin-screw extruder with a barrel length-to-screw ratio of 28 1. The extruder consisted of six barrel sections equipped for heating, cooling, and controlling the temperature of each section of the extruder. Initially reaction extrusion of PET and water was performed with cold water at room temperature injected into the extruder. Typical operating conditions were reaction temperatures of 230-265° C, extruder speeds... 

RCM. See Ring-closing metathesis (RCM) Reaction by-products, removing, 83 Reaction extrusion, 204 Reaction index, 237 Reaction injection molding (RIM), 205 Reaction-in-mold (RIM) nylon, 149 Reaction kinetics, 76, 77 Reaction mechanisms, polyesterification, 66-69... 

Polyurethane engineering thermoplastics are also manufactured from MIDI and short-chain glycols (49). These polymers were introduced by Upjohn/Dow under the trade name Isoplast. The glycols used are 1,6-hexanediol and cydohexanedimethanol. 1,4-Butanediol is too volatile at the high processing temperatures used in the reaction extrusion process. Blends of engineering thermoplastics with TPU are also finding uses in many applications... 

The double bond in thiirene, thiirene-1-oxide, and thiirene-1,1-dioxide is expected to increase ring strain and lead, in general, to enhanced reactivity in any reactions that would lead to strain relief. Such relief would result from ringopening reactions, extrusion of S, SO, or SO2, or additions to the double bond that convert sp - to sp -carbon. Moreover, conjugation between the 7t-bond and sulfur, with its substituents, might be expected to lead to absorption of light and photochemical reactions. 

Figure 14.11. Example of reaction extrusion process. [Adapted from Narayan R, Krishnan M, Snook J B, Gupta A, DuBois P, US Patent 5,906,783, 1999.]...

Bisoxazoline is a new type of chain extender, and can couple low molecular weight PBS during polycondensation, reaction extrusion, fiber spinning, etc. Chain extension of PBS with bisoxazoline will not result in the formation of small molecules and gelling, which is promising for industrial manufacturing. Xu et al. (2007) utilized bisoxazoline as a chain extender, which improved the M from 111,700 to 189,500. 

Functionalization of PLA by grafting of maleic anhydride (MAn) by reaction extrusion in the presence of free radical initiators tert-h xiy peroxide) has also been carried out. The presence of high succinic anhydride units in the grafts was confirmed by FTIR and NMR studies. Low percentage grafting was observed in PLA due to presence of limited free radical sites [69, 70]. 

The reverse reaction, extrusion of a methylene from a metal-alkyl complex to give a species of the type M(H)(C2H4) is also known, but it is far from being systematic this is the a-H elimination (see section 5.1 and Chap. 18.5) that sometimes plays an important role in the initiation of metathesis reactions (Chap. 15). 

The sequence of Diels-Alder reactions of nonfluorinated pyrroles with hexafluorobut-2-yne followed by retro Diels-Alder reactions (extrusion of acetylene) was also used for trifluoromethylpyrrole synthesis. However, the 7-azanorbomadiene system was found to be quite thermostable [74], which undergoes cycloreversion only at very high temperature resulting in low yields of trifluoromethylated pyrroles. Hence, additional steps were necessary. For instance, the reduction of the bicyclo[2.2.1] hepta-2,5-diene 199 (formed from 198 and hexafluorobut-2-yne) to 200, followed by a cycloreversion, afforded the 3,4-bis(trifluoromethyl)pyrrole 201. Subsequent basic hydrolysis gave the target pyrrole 202. All reactions proceeded almost quantitatively to give 202 in 83 % overall yield [75]. 

C. Xiong, R. Qi, and W. Gong, The preparation and properties of wood flour/ high density polyethylene composites by in-situ reaction extrusion. Polym. for Adv. Tech. 20 (3), 273-9 (2009). 

Diazopyrazole (436) undergoes gas-phase thermal extrusion to form an azirine, probably by the mechanism shown (8lAHC(28)23i) 4-diazopyrazoles show normal diazonium-type reactions (Schemes 55 and 56) (67AHC(8)l). Analogous diazoimidazoles and diazopurines are known (67AHC(8)i). 

A similar product is obtained from the reaction of anhydro-4(5)-hydroxy-l,2,3-triazolium hydroxide (398). In this case reaction with DMAD occurred in 1 hour in boiling benzene. Extrusion of methyl isocyanate from the initial 1 1 cycloadduct (399) occurred during the reaction giving (400). 

Making just one C—C bond by radical combination is not a prominent method for preparing heterocyclics, except for those cases in which the radical pair arises from a cleavage or extrusion reaction of a heterocyclic starting material. Such cases are treated below (Section 5.03.5.2.2). 

The reaction of carbon atoms with A-unsubstituted aziridines leads to alkenes and hydrogen cyanide (72IA3455), probably via extrusion from the initially formed adduct (285). The fragmentation does not appear to be concerted, although this would be a symmetry-allowed process, since only about half the alkene formed retains the aziridine stereochemistry in the case of cM-2,3-dimethylaziridine. 

The addition of phthalimidylnitrene (374) to simple alkynes affords 1-azirines in yields of 1-15% (Scheme 10). In this reaction, which is of no real preparative value, the symmetrical 2-azirines (375) were suggested as the most plausible intermediates and unequivocal proof of the existence of such species was demonstrated from a series of 1,2,3-triazole pyrolysis reactions <71CC1518). Extrusion of nitrogen from the regioisomeric 4,5-disubstituted 1,2,3-triazoles (376) during flash vacuum pyrolysis furnished identical product mixtures which included both regioisomeric 1-azirines (377). 

A variety of 1-azirines are available (40-90%) from the thermally induced extrusion (>100 °C) of triphenylphosphine oxide from oxazaphospholines (388) (or their acyclic betaine equivalents), which are accessible through 1,3-dipolar cycloaddition of nitrile oxides (389) to alkylidenephosphoranes (390) (66AG(E)1039). Frequently, the isomeric ketenimines (391) are isolated as by-products. The presence of electron withdrawing functionality in either or both of the addition components can influence the course of the reaction. For example, addition of benzonitrile oxide to the phosphorane ester (390 = C02Et) at... 

Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

Photolysis of dlazirines to nitrogen and carbenes is a general reaction and plays a greater role in carbene chemistry than photolysis of linear diazo compounds. Whereas the latter are often obtained only under the conditions of their thermal decomposition from suitable precursors, diazirines are obtainable in a pure state in most cases. Photolysis has the further advantage to permit nitrogen extrusion at atmospheric pressure, even with low-boiling materials. 

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