Epoxy titration method

Amino-terminated telechelic polybutadiene was prepared by LiAlH4 reduction of amidino end-group in polybutadiene, which was polymerised by a water-soluble initiator, 2,2 -azobis(amidinopropane)dihydrochloride. The structure was analysed by 1H- and 13C-NMR, but functionality of 2.0 was obtained by a titration method [70]. Synthesis of co-epoxy-functionalised polyisoprene was carried out by the reaction of 2-bromoethyloxirane with living polymer that was initiated with sec-butyl lithium. The functionality of the resulting polyisoprene was 1.04 by 1H-NMR and 1.00 by thin layer chromatography detected with flame ionisation detection [71]. 

Epoxy content is generally determined by wet analytical techniques. ASTM D 1652 is widely used. The most common method is based on the addition of hydrogen halide (e.g., hydrogen chloride, hydrogen bromide, or hydrogen iodide) to the epoxy group. The difference between the amount of acid added and the amount unconsumed, determined by titration with standard base, is a measure of the epoxy content. There are numerous epoxy assay methods based on this technique. The specific method used depends on the resin type being analyzed as well as on the extent to which side reactions can occur. 

Iodine and acid values obtained by standard titration methods (17.18) are given In Table I, along with approximate values of epoxy equivalent weights and oxlrane and double bond contents, for the epoxldlzed crambe and lunarla oils, and for a typical epoxldlzed commercial linseed oil. 

In addition to HPLC, elemental analysis, vapor phase osmometry. Fourier Transform Infrared Spectroscopy (FTIR), GC/MS, and NMR techniques were applied to verify the purity of the resin samples. Epoxy equivalent weights (EEW) were determined by the standard nonaqueous titration method (J ) using chloroform as the solvent. A correction for tertiary amine was obtained by conducting the titration in the absence of the quaternary halide. ... 

Epoxy resins are characterised by two or more epoxy groups in the structure. To cure an epoxy resin with a suitable hardener, accurate estimation of epoxy groups is crucial. Epoxy equivalent is defined as the amount of resin that contains one mole of epoxy. Epoxy equivalent of an epoxy sample is determined by a standard titration method [6] using hydrogen bromide solution in acetic acid. The method is briefly described next. 

Wet chemical methods determining titratable amine ate reported for products entering urethane (amine number as meq/g) or epoxy (AHEW = amine hydrogen equivalent weight) trade appHcations. For secondary amines /V-nitrosamine contaminants are reportable down to ppb using Thermoelectron Corporation thermal energy analy2er techniques. 

Another example of interest with regard to the reaction mechanism is the analysis of epoxy groups. Durbetaki60 titrated a-epoxy compounds with HBr (cf., p. 260) in glacial acetic acid with crystal violet as indicator, but the method was slow for glycidyl esters, CH2—CHCH2OOCR. As it concerns a two-step... 

Gascon and co-workers developed an analytical method suitable for the determination of 1,2-epoxy-2,4,4-trimethylpentane.<2D The epoxide was heated at 100° in a sealed tube with di-n-butylamine, and the resulting product aoetylated with acetic anhydride. Titration with perchloric arid in aoetie acid containing a suitable indicator gave the amount of tertiary amine formed. 

Solvents which are depleted of stabilizers (amine or alpha epoxide) may become acidic. The following method determines the combined effect of both alkaline (amine) and neutral (usually epoxy) stabilizers. The determination is done in two steps. First solvent is mixed with hydrochlorination reagent (0.1N HCl), then the excess is titrated with 0.1N sodium hydroxide in the presence of 0.1% bromophenyl blue as an indicator. 

Determinations of epoxy groups. Epoxy groups are usually titrated by Durbetaki s method or by Jay s derivative process In the latter, which today is the most commonly used, epoxy groups are reacted with HBr resulting from the reaction of perchloric acid with tetraethylammonium bromide. This reaction, which is stoichiometric, is carried out in the presence of crystal violet as indicator. When all epoxy groups have reacted, the excess of HBr changes the colour of the indicator. 

Amine consumption in reaction II could make it difficult to use the epoxy-carboxy reaction to prepare esters or polyesters. In fact, most of the zwitterion Z, which is formed from E and the amine, is transformed into the ester P and, at least in solution, only a small quantity of side product is formed. Moreover, titrations carried out during the reaction show that epoxy and acid groups are consumed at roughly the same rate, demonstrating that even if the contribution of reaction II to overall kinetics and mechanism is important it does not forbid the use of this method for preparation of polyesters. 

In another procedure, a halogen acid is generated by the reaction of an ionic halide salt, eg, tetraethylammoniiun bromide in acetic acid with perchloric acid with subsequent formation of a halohydrin the epoxy group is determined by back-titration with perchloric acid nsing crystal violet indicator (83). The end point can be determined visually or potentiometrically. A monograph on epoxide determinations was published in 1969 (84). This is the method adopted by ASTM and is currently used by most resin producers. 

Hydrolyzable chloride (HyCl) content of Uquid and soUd epoxy resins is determined by dehydrochlorination with potassiiun hydroxide solution imder reflux conditions and potentiometric titration of the chloride Uberated by silver nitrate. The solvent(s) employed and reflux conditions can influence the extent of dehydrochlorination and give different results. The easily hydrolyzable HyCl content, which reflects the degree of completion of the dehydrochlorination step in the epoxy resin manufacturing process, is routinely determined by a method using methanol and toluene as solvents. This is the method most commonly used to characterize LER and SER. 

Total chloride content of epoxy resins can be determined by the classical Parr bomb method in which the sample is oxidized in a Parr bomb, followed by titration with silver nitrate (78). The major disadvantage of this method is that it is time-consuming. Alternatively, X-ray fluorescence has been used successfully as a simple, nondestructive method to determine total chloride of epoxy resins. 

Comprehensive reviews of different techniques for epoxy cure monitoring are available (86,94). Wet chemical or physical analysis methods, such as solvent swell (163), titration of functional groups, IR, near IR (164), or NMR spectroscopy, are commonly used to monitor epoxy cure. 

For raw materials of reactive adhesives, the chemical equivalent values are very important to specify the reactivity, and often tested. Epoxy equivalents for epoxy resins, and functional group equivalents for hardeners are experimentally determined. Methods to measure the epoxy equivalents are described by industrial standards as follows International organization for standardization (ISO) 3001, Japan industrial standards (JIS) K 7236, and American society for testing and materials (ASTM) D 1652. For instance, JIS K 7236 indicates the methods using titration. In this process, an epoxy sample is solved with chloroform, mixed with acetic acid, tetraethylammonium bromide, and crystal violet solution. The epoxy sample solution is finally titrated with perchloric acid—acetic acid solution. If automatic titrators can be used, the epoxy... 

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