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The mechanism of acid curing of epoxy resins catalyzed with tertiary amines was investigated by using model systems composed of phenylglycidyl ether and benzoic acid or acetic acid anhydrides in the presence of benzyldimethylamine. The reaction was studied by NMR spectrometry, liquid chromatography, and ozone absorption. The main findings are that (1) the tert‐amine is bound chemically and irreversibly during the reaction under the formation of a quaternary ammonium salt magnified image and (2) 1‐phenyloxypropanediol‐2,3‐dibenzoate or diacetate is the main reaction product. The suggested reaction mechanism involves initiation in which the tertiary amine reacts with the epoxy group, giving rise to a zwitterion that contains a quaternary nitrogen atom and an alkoxide anion; the latter immediately reacts with the anhydride and quaternary salt is formed. In a later stage the carboxy anion of the quaternary salt reacts first with the epoxy group, then with the anhydride. By this reaction diester is formed and the carboxy anion is regenerated.

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It was found that three crystalline forms of ethylene glycol dibenzoate can be prepared. Infrared and Raman spectra of these three forms, as well as of the glassy and liquid states, were measured. From 3JHH coupling constants obtained by analysis of the 13C satellite band of the -CH2- group in 1H NMR spectra, and from the 3JCH coupling constants of the -CO.O.CH2- fragment obtained by analysis of the carbonyl band in 13C NMR spectra it was found that in the liquid state the -CH2-CH2- group exists predominantly in the gauche conformational structure, and the bonds C-O-C-C assume predominantly a trans orientation. The results of the analysis of NMR and vibrational spectra were used for the structural interpretation of conformationally sensitive bands in vibrational spectra of ethylene glycol dibenzoate.

Infrared and Raman spectra of ethyl benzoate and diethyl terephthalate were measured in their crystalline forms, in the glassy state and in the melt. With liquid samples, the NMR coupling constants 3 J CH of the group -CO.O.CH2-were also measured. By analysis of these measurements it was found that in the liquid state of ethyl benioate the following conformers are present: forms with a fully planar structure; forms with the methyl group twisted out of the aromatic and ester group plane by rotation about the O-C2HS bond; and forms with non-planar mutual , orientation of the ester group and the aromatic ring, formed by rotation about the Car-CO or CO-O bonds. The first two forms are aJso present in the crystalline modifications of ethyl benzoate. Diethyl terephthalate in the liquid state is present in forms analogous to those of ethyl benzoate; in addition, it contains isomers differing by the mutual orientation of the two ester groups on the aromatic ring.As part of our studies of the conformational structure of poly(ethylene terephthalate) model • compounds, in our previous paper! we have investigated the relation between conformational structure and vibrational spectra of methyl benzoate and dimethyl terephthalate; we have discussed the problem of conformer generation in these molecules by rotation about the bonds Car-C; CO-O, and of the mutual cis-trans isomerism of the ester groups of dimethyl terephthalate. In ethyl benzoate and diethyl terephthalate, additional rotations are possible about the O-C2HS bond. Complete infrared and Raman spectra of ethyl benzoate have so far been measured in the liquid state 2 -6; only in the range of lattice vibrations (10-200 cm -!), Raman spectra have also been measured in the crystalline state 7 . Infrared and Raman spectra of diethyl terephthalate have only been measured in the crystalline state S ,6,S. These spectra have been interpreted partly on the basis of analogy with the spectra of similar molecules 2 -4 ,6,s, partly by comparison of the experimental band frequencies with the normal vibrations calculated from secular equations s . The influence of conformational structure upon vibrational spectra has not been analyzed so far. By X-ray analysis it was found 9 that diethyl terephthalate in the crystalline state contains molecules which are essentially planar, with a trans mutual orientation of the two ester groups on the aromatic ring. Measuremen~s of dipole moments! 0 have indicated that diethyl terephthalate in benzene solution contains approximately equal populations of molecules with cis and trans mutual orientation of ester groups; for ethyl benzoate a structure with the ester group twisted ou' t of the plane of the aromatic ring!! has been proposed.