Polymerization byproducts

The. addition of mercaptans to methyl acrylate is catalyzed both by base and by sources of free radicals. The direction of addition is the same in either case, but the radical initiated reaction produces a good deal of polymeric byproduct. 

Af-Acyliminium ions are known to serve as electron-deficient 4n components and undergo [4+2] cycloaddition with alkenes and alkynes.15 The reaction has been utilized as a useftil method for the construction of heterocycles and acyclic amino alcohols. The reaction can be explained in terms of an inverse electron demand Diels-Alder type process that involves an electron-deficient hetero-diene with an electron-rich dienophile. Af-Acyliminium ions generated by the cation pool method were also found to undergo [4+2] cycloaddition reaction to give adduct 7 as shown in Scheme 7.16 The reaction with an aliphatic olefin seems to proceed by a concerted mechanism, whereas the reaction with styrene derivatives seems to proceed by a stepwise mechanism. In the latter case, significant amounts of polymeric products were obtained as byproducts. The formation of polymeric byproducts can be suppressed by micromixing. 

PET fiber is made from raw materials that are cheap and available, due to the large manufacturing infrastructure it shares with other common products, e.g. antifreeze and soda bottles. The polymerization byproducts are non-polluting, and the polymer can be recycled. 

A series of epoxides has been efficiently converted to the corresponding thiiranes using a polymer-bound quaternary ammonium thiocyanate 38. The polymeric byproduct of this transformation is the supported cyanate.56... 

Styrene reacts with arylalkanes to yield mono- and diadducts with the concomitant formation of polymeric byproducts.243 a-Methylstyrene and p-methylstyrene, in turn, give monoadducts in high yields.244,245... 

Yoshida et al. [36] have studied the effect of fast mixing of miscible systems by measuring the selectivity towards mono-alkylation in the Friedel-Crafts alkylation of aromatics. They observed a 20-fold increase in the relative selectivity of the mono-alkylate over the di-alkylated system when using a micromixer instead of a conventional batch reactor. In the cycloaddition of the N-acyHminium ion to styrene [36], 50-80% of the cycloadduct is typically lost towards polymeric byproducts. Using an interdigital micromixer, the yield to the cycloadduct increased from 20-50% to almost 80%. 

SL1414>. Octahydropyrazinol l,2-a pyrazine was obtained in an efficient manner from 1,3-dichloro-2-propanol and an A -tosylated diethylenetriamine, and the X-ray crystal structure of this fused pyrazine was obtained <04SC845>. Finally, functionalized quinoxalines and pyrazines were prepared via a microwave-assisted reaction of aryl/heteraryl 1,2-diamines and common 1,2-diketone precursors. The formation of polymeric byproducts was suppressed <04TL4873>. 

Table 1.3 summarizes the different types of polymerizations [8]. Chain-growth polymerization involves chain growth by reaction of an active polymer chain with single monomer molecules. In step-growth polymerization, polymer growth involves reactions between macromolecules. In addition, non-polymeric byproducts may be formed in both types of polymerization. However, condensative chain polymerization is very rare. Table 1.4 summarizes the differences between chain-growth polymerization and step-growth polymerization. 

The Michael addition reactions of nitro compounds such as nitromethane to CF3-containing acrylates such as ethyl (E)-ethyl 3-(trifluoromethyl)acrylate using a microflow reactor (channel width 100 pm, depth ca. 40 pm and length 80 mm flow rate 1 pi min ) has been reported. The reactions proceed smoothly in the presence of DBU as a base to afford the corresponding Michael adducts without any detectable formation of polymeric byproducts (Table 5.3) [11]. 

For example, addition of pyridine facilitates Kolbe preparations by diminishing surface blocking by polymeric byproducts which arise in some aromatic systems. 

Similarities to epoxy resin include no volatile polymerization byproducts stable B-stage resins possible low shrinkage, high adhesion and void free structures. High purity makes cyanate esters very attractive for use in electronic applications. The performance of bisphenol A dicyanate resins in printed wiring board laminates was described by Weirauch et al(4). Mobay Chemical (and Bayer) introduced products of this type for PWB applications in the United States in 1976-78. These "Triazine A resins were not commercially successful and were withdrawn from the market about 1979. 

Diazomethane reacts rapidly with unesterified fatty acids in the presence of a little methanol, which catalyses the reaction, to form methyl esters. The reagent is generally prepared as a solution in diethyl ether by the action of alkali on a nitrosamide, e.g. N-methyl-/V-nitroso-p-toluene-sulfonamide (Diazald, Aldrich Chemical Co., Milwaukee, U.S.A.). Solutions of diazomethane are stable for short periods If stored refrigerated in the dark over potassium hydroxide pellets. If they are kept too long, polymeric byproducts form which may interfere with the subsequent GC analysis. 

As had been found previously, the nature of the hydrogen donor pla) an important role in the conversion to arene adduct Thus, although consumption of enediyne was often rapid using 1,4-cyclohexadiene, optimal yields of cycloaromatization products were obtained using isopropanol, the balance of material typically composed of uncharacterized polymeric byproducts. Evidently, ring strain... 

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