A direct infrared estimation of cyclic oligomers in water extract of nylon 6

Abstract

Abstract Methods described in the literature for the estimation of the cyclic oligomer content (which includes cyclic dimer, trimer, etc.) of nylon 6 are indirect determinations, generally based on weight differences, and require the prior extraction of ϵ‐caprolactam (monomer) from the sample. Infrared studies show that all of the cyclic oligomers have a strong NH deformation band at 6.45 μ, whereas the monomer does not exhibit such a band. This difference in the infrared is the basis of a direct determination of the cyclic oligomer content in the presence of monomer. In the method, the residue obtained after evaporation of the water extract of nylon 6 is dissolved in tetrafluoropropanol, and the absorbance at 6.45 μ is determined by the base line method. If the per cent moisture in the original nylon 6, the per cent water extractables, and the per cent oligomers in the water extract are known, one can also estimate the monomer content of the sample.