Determination of percent ethylene in ethylene-propylene statistical copolymers

Significance of the Topic

Ethylene content in ethylene-propylene statistical copolymers directly influences mechanical strength, thermal performance and end-use properties.
A rapid, accurate and non-destructive analytical method is critical for quality assurance in polymer production and research.

Study Objectives and Overview

This work describes an FTIR-based procedure to quantify randomly distributed ethylene units in ethylene-propylene copolymers.
The approach exploits the characteristic absorption at 733 cm-1 and normalizes it against the polypropylene reference band at 1044 cm-1 to apply a Beer’s Law–type calculation.

Methodology and Instrumentation

Sample preparation involves molding representative resin samples into smooth films of 0.5–0.7 mm thickness using a heated hydraulic press (≤250 °C for up to 3 minutes), followed by inspection and selection of three defect-free replicates.
Key instrumentation:

• Agilent Cary 630 FTIR spectrometer with DialPath or TumblIR 1000 μm interface
• Equivalent portable Agilent 4500/5500 Series FTIR units
• Hydraulic press with heated platens (200 °C, 25 000 lb force)
• Optional chase mold and aluminum sheets (0.05–0.18 mm)

Main Results and Discussion

A calibration curve covering 0.3–3.5 wt % ethylene was established using standards characterized by 13C NMR.
The normalized absorbance ratio (A733/A1044) yielded a linear regression (% ethylene = M × ratio + N) with high reproducibility.
Sorbitol-based clarifier interference at 695 cm-1 was identified and requires correction for affected samples.

Method Benefits and Practical Applications

• Fast, automated analysis with minimal sample handling
• Applicable to powders and pellets
• High precision through triplicate measurements and method-driven software
• Limitations: not recommended for heavily filled or pigmented resins without adjustment

Future Trends and Potential Applications

Integrating chemometric models can enhance multi-component resolution.
Portable FTIR devices will enable on-site quality control in industrial settings.
Extending the approach to other comonomers and novel polymer blends can broaden its industrial impact.

Conclusion

The FTIR-based protocol delivers a robust, efficient and reproducible means to quantify statistical ethylene in ethylene-propylene copolymers.
Its simple sample handling and software-guided workflow support routine QA/QC and research applications.

References

• Collins W., Seelenbinder J., Higgins F. Determination of percent ethylene in ethylene-propylene statistical copolymers. Agilent Technologies; Publication 5991-0456EN, May 2012.