Quantitative Analysis of a Water-soluble Polymer Using the i-Raman EX Spectrometer

Importance of the Topic

Vibrational spectroscopy, encompassing infrared and Raman techniques, offers detailed molecular fingerprints essential for polymer characterization. Raman spectroscopy, in particular, excels at probing nonpolar functional groups and aromatic structures while being largely insensitive to water, making it an ideal approach for quantifying the degree of functionalization in water-soluble polymers.

Objectives and Study Overview

The primary goal was to develop a robust, user-friendly Raman-based method to determine the extent of polystyrene functionalization to a water-soluble polymer. A two-step analytical workflow was designed: first, a classification model confirms sampling of the aqueous polymer layer; second, a quantitative PLS1 model predicts the percentage of functionalization. The workflow targets routine use in a plant QC laboratory via push-button operation.

Methodology

Sample preparation involved transferring aqueous polymer solutions (10–20 weight percent solids) into borosilicate vials. Data analysis comprised two chemometric methods:

• Phase classification using PCA-MD: Kennard-Stone partitioning, mean centering, max-value normalization, PCA with Mahalanobis distance, 3 principal components over 650–1700 cm⁻¹.
• Quantitative determination of % functionalization via PLS1: autoscaling, Savitzky-Golay second derivative (3rd order, window size 5), 6 latent variables, spectral region 995–1200 cm⁻¹, model export in CMML.

Used Instrumentation

Hardware:

• i-Raman EX spectrometer with 1064 nm excitation, ~495 mW laser power, 180° backscatter geometry, spectral range 250–2500 cm⁻¹, resolution ~9.5 cm⁻¹; thermoelectrically cooled 512-element InGaAs detector.
• Fiber-optic probe interfaced to enclosed cuvette/vial holder adapter (BWT-840000287) and 15 mm borosilicate screw-cap vials.

Software:

• BWSpec v4.04 for data acquisition (dark subtraction, 500 ms exposure, 264 scans, total ~5 minutes per sample).
• BWIQ version 3.0.6 for chemometric model development (classification and regression tools including PCA-MD and PLS1).

Main Results and Discussion

Phase classification achieved 100% accuracy on training and validation sets for distinguishing aqueous polymer from the organic phase. Raman spectra of low, medium, and highly functionalized polymers showed distinct aromatic peaks at ~1002 cm⁻¹ (initial) and ~1132 cm⁻¹ (functionalized).

A simple univariate band-ratio method (If/(Ii+If)) displayed excellent linear correlation with 1H NMR reference data, validating spectral quality. The PLS1 quantitative model (29 calibration and 31 validation samples) yielded:

• Calibration R² = 0.95, validation R² = 0.87
• RMSEC = 1.22%, RMSEP = 1.43%
• Single-day precision 0.49% RSD, external lot RMSE 1.31–1.43%

These statistics confirm strong predictive performance and reproducibility of the Raman method.

Benefits and Practical Applications

The developed Raman approach offers rapid measurement of aqueous polymer samples without interference from water, delivering reliable quantification of functionalization in under five minutes per analysis. Its user-friendly, push-button workflow and robust chemometric models make it suitable for multiuser plant QC environments, facilitating real-time quality assurance and process monitoring.

Future Trends and Potential Applications

Emerging directions include extending this Raman workflow to other polymer systems, in situ process analytical technology for real-time reaction monitoring, integration with process control systems, adoption of advanced machine learning classifiers (e.g., SVM), and further miniaturization of portable Raman probes for field or manufacturing-floor analysis.

Conclusion

A compact i-Raman EX system combined with tailored chemometric models enables accurate, precise, and rapid quantification of polymer functionalization in aqueous media. The method’s simplicity and reliability have established it as a routine QC tool in an industrial setting.

References

1. N J Everall, J M Chalmers, P R Griffiths Vibrational Spectroscopy of Polymers Principles and Practice John Wiley & Sons Chichester 2007
2. J L Koenig Spectroscopy of Polymers American Chemical Society Washington DC 1991
3. P J Larkin Infrared and Raman Spectroscopy Principles and Spectral Interpretation Second Edition Elsevier Cambridge MA 2018
4. M Otto Chemometrics Statistics and Computer Application in Analytical Chemistry Wiley-VCH Weinheim 2017