Quantitative size exclusion chromatography of polypropylene I: Method development

• Published in: Journal of applied polymer science 1988-03, Vol.35 (4), p.1049-1063
• Main Authors: Lew, R., Suwanda, D., Balke, S. T.
• Format: Article
• Language: English
• Subjects: Analysis and structure; Applied sciences; Exact sciences and technology; Polymer industry, paints, wood; Properties and testing; Technology of polymers
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.1988.070350418

Polypropylene was analyzed by size exclusion chromatography (SEC) at 145°C using a single‐differential refractometer detector. The objective was to provide data for characterization of polypropylene degradation during a reactive extrusion process. Two antioxidants [tetrakis(methylene(3,5‐di‐tert‐butyl‐4‐hydroxyhydrocinnamate)) methane (I) and octadecyl 3,5‐di‐tert‐butyl‐4‐hydroxyhydro cinnamate (II)] were tested for their ability to prevent thermal degradation of the polypropylene during sample preparation. The use of 0.20 wt% of (I) was effective during the 36–48 h required to completely dissolve the samples in trichlorobenzene for SEC analysis. “Reshaping” of the chromatograms by resolution correction demonstrated that, while the molecular weight averages were changed by 8% because of axial dispersion, most of the individual heights of the distributions were changed by less then 2%. Tail heights of the distributions were more affected but were also shown to be highly imprecise. Selecting individual heights of the distributions rather than molecular weight averages therefore minimized axial dispersion error and also circumvented errors in molecular weight averages originating from dilution of distribution tails below detector sensitivity limits. Various forms of distributions were examined and the equations linking the chain length distribution predicted by polymerization kinetic models to the SEC chromatogram are presented. The analytical method developed provided precise data for kinetic modeling. However, absolute accuracy requires further assessment.