Infrared Spectroscopic Determination of Alkyd Resin Components
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概要
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The infrared spectroscopic method was applied to determine alkyd resin compositions with special emphasis on the identification of polyols and cyclic monobasic carboxylic acids. The presence of polyols such as propylene glycol (PG), glycerin (G), trimethylol ethane (TME), trimethylol propane (TMP) and pentaerythritol (PE) was detectable from the characteristic absorption band in 1500-136& 1350-1040 and 1000-900 cm<SUP>-1</SUP> regions. Whether an alkyd resin was composed of polyols containing either primary OH (PG, G) or secondary OH (PE, TME, TMP) was determined from the absorption bands of primary and secondary OH groups. The former had absorptions at 1490, 1450, 1100,990 and 970 cm<SUP>-1</SUP>, and also at 1470 cm<SUP>-1</SUP> as the shoulder of the 1450 cm<SUP>-1</SUP> band, and the latter at 1470, and 970 cm<SUP>-1</SUP>, and at 1450 and 1490 cm<SUP>-1</SUP> as the shoulders of 1470 cm<SUP>-1</SUP> band. No absorption at 990 cm<SUP>-1</SUP> was observed with the latter. TMP and TME alkyds had stronger absorption at 1380 <SUP>cm-1</SUP> than at 1470 <SUP>cm-1</SUP>, with PE alkyds the situation was reversed. The PE/G weight ratio of the alkyds which were prepared from mixtures of these polyols keeping the oil length constant was proportional to the absorbance ratio D<SUB>1200</SUB>/D<SUB>1090·</SUB> The terminal OH groups had no effects on the 1100 and 1040 <SUP>cm-1</SUP> bands, while this was not the case with castor oil modified alkyd resins.<BR>Aromatic monobasic carboxylic acids such as benzoic acid and p-tert. butyl benzoic acid were detected from the absorptions of benzene ring substituents. The benzoic acid content was determined from D<SUB>710</SUB>/D<SUB>748</SUB>. In the case of soybean-oil fatty acid modified alkyd resin of 40% oil length, the benzoic acid content was obtaind from the equation, <BR>X (X) % = (1/0. 0458) X, / (D<SUB>710</SUB>-0.513D<SUB>748</SUB>)<BR>Since the extent of double bond isomerization of unsaturated fatty acid during the synthesis of alkyd resin was negligible, the geometric isomers of double bond in unsaturated fatty acid modified alkyd resin had no effects on the 990 (trans-trans conjugated) and 968 cm<SUP>-1</SUP> (isolate trans) bands, except dehydrated castor-oil modified alkyd resin.
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