Published:Journal of Chromatographic Science,
ISSN 0021-9665 Volume
45, Number 8, September 2007, pp. 524-530
Molecular Weight Distributions of Industrially-Produced
Poly-(e-Caprolactams) by Gel Permeation Chromatography
Elena Mateos[1], Vicente L. Cebolla[1], Luis
Membrado[1], Elena Piera[2], and Miguel A. Caballero[2]
[1]Instituto de Carboquímica, CSIC. P.O. Box 549, 50080
Zaragoza, Spain and
[2]NUREL, S.A., Carretera de Barcelona, km
329, Polígono de Malpica, 50016, Zaragoza, Spain
Gel permeation chromatography with differential
refractometry is used to obtain molecular weight distributions
(MWD) of poly-(e-caprolactams). Elution is carried out using
an m-cresol– chlorobenzene mixture (50:50, v/v) at 50°C.
MW values are obtained by a Hamielec-based calibration method,
using broad-MWD poly-(e-caprolactam) standards with the same
chemical nature and similar MWD to the samples. Relative errors
for the number-average MW (Mn) using this calibration method
range from 0.4% (in the low polyamide MW range) to 20% (in the
high polyamide MW range). These values are much lower than those
obtained from narrow-MWD polystyrene calibration, which range
from 39% to 78%. Similar values have been obtained for the other
usual average MW parameters. The ability to obtain repeatability
parameters for a given confidence interval and the utilization
of statistical criteria for chromatogram rejection allow this
method to be used in quality control for MWD of poly-(e-caprolactams).
Thus, production variables are related to polyamide-6 behavior
in its ulterior treatment. Typical relative standard deviation
percentages (for n = 6) of a polyamide sample range from 1.9%
(for Mn) to 3.3% (for Mz + 1).
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