A number of r e s e a r c h e s [1] have been devoted to a study of the effect of low-molecular compounds (LMC) on the p r o p e r t i e s of polyeaproamide (PCA); however, in these the effect of individual components of the LMC was not examined, particularly that of cyclic oligomers of caprolactam, which make up the main part of the LMC in PCA fibres prepared by c o n t e m p o r a r y technology [2]. In the present article we give the results of a study of the plasticizing ability of individual components of the LMC by the methods of low resolution nuclear magnetic r e s o n a n c e (NMR) and differential thermal analysis (DTA).The cyclic oligomers, which mainly consist of the cyclic dimer and t r i m e r , were obtained by the method of fractional crystallization from the dry residue of water-soluble low-molecular compounds of PCA [3]. Specimens of polymer containing additives were prepared as follows: to PCA flake, extracted and dried under manufacturing conditions, weighing 1 g, and containing no more than 0.5% LMC, was added by dusting, 3, 6, or 10% monomer or 4 or 10% of the cyclic oligomers (based on m a s s of the polymer). The specimens and additions of LMC were heated in a sealed thin-walled ampule 10 m m in diameter for 5 min. The samples containing additions of monomer were heated at 240°C. Considering that the melting point of the t r i m e r is 247~C [4] and that of the cyclic dimer is 348°C [5], the samples with additions of the cyclic oligomers were heated at 350°C. Thereupon, it was taken into account that the s h o r t -t e r m action of high t e m p e r a t u r e s does not cause any marked thermal degradation of the polymer, or, consequently, any increase in the LMC content. Thus, heating PCA for 5 rain at 280°C changes its specific viscosity by 0.01, but the increase in LMC content does not exceed 0.13% (by wt.) [6]. In this method of introducing the LMC, the possibility of nonuniform distribution of the additives in the polymer m a s s is not excluded; however, this does not prevent ascertaining their plasticizing abilit, by the NMR method.Before taking spectra, the specimens were dried to constant weight over P205. The proton resonance s p e c t r a were r e c o r d e d on a low-resolution nonseries NMR spectrometer having an autodyne sensor at a frequency of 40 MHZ, in the form of the first derivative absorption line. The glass temperature of the specimens was defined as the t e m p e r a t u r e of appearance of a narrow component [7, p. 340].To determine the plasticizing ability of individual components of the LMC in PCA, we determined the difference between the experimental, S2e, and the calculated, $2c , values of the second moment of the NMR absorption line of the investigated specimens a t -1 8 5°C :The value of $2c was calculated by the formulawhere S2PCA and S2LMC are the second moments of the absorption lines of the PCA and of the monomer or cyclic o l i g o m e r s in the PCA. In Fig. 1 we show the dependence of AS 2 on the monomer or cyclic oligomer content of the PCA. For subs...
