Qualitative and quantitative analysis of the polymerization of PS-b-PtBA block copolymer using picoSpin 80 NMR

Importance of the topic

Nuclear magnetic resonance spectroscopy is a fundamental tool for characterizing polymeric materials by providing insight into monomer conversion, reaction kinetics and block copolymer structure. Rapid near real-time monitoring of polymerization enables efficient optimization of reaction conditions and quality control. Low-field instruments such as the picoSpin 80 offer a cost effective solution for laboratories seeking compact, accessible NMR analysis without sacrificing essential quantitative capabilities.

Objectives and overview of the study

This application note demonstrates the use of an 82 MHz picoSpin 80 NMR spectrometer to qualitatively and quantitatively monitor the polymerization of t butyl acrylate initiated by a polystyrene RAFT reagent. The primary goals are to track the decrease of vinyl proton signals over time and to determine the degree of monomer incorporation into the final PS-b-PtBA block copolymer.

Methodology

The polymerization was carried out by combining t butyl acrylate, polystyrene reagent, AIBN radical initiator and anisole solvent in a predefined molar ratio. The mixture underwent three freeze-pump-thaw cycles for degassing and was maintained at 75 °C for twelve hours. Aliquots were withdrawn at defined time points and injected directly into the capillary cartridge with no additional workup.

Instrumentation used

• picoSpin 80 benchtop NMR spectrometer operating at 82 MHz proton frequency
• Permanent 2 tesla temperature-controlled magnet
• Disposable 40 microliter capillary cartridge and manual injection system
• Acquisition parameters: 90° excitation pulse, 750 ms acquisition time, 8 s recycle delay
• Data processed in Mnova with zero filling and phase correction

Key results and discussion

Overlay of 1H spectra collected at 0, 1, 2, 3 and 12 hours clearly shows attenuation of tBA vinyl resonances in the 5.5–6.7 ppm region accompanied by a corresponding increase of aliphatic signals at 1.4–2.8 ppm. Integration of these regions indicates a 34 percent conversion of t butyl acrylate after 12 hours, equating to an average of three tBA units incorporated per copolymer chain.

Benefits and practical applications of the method

The compact footprint and capillary injection scheme enable placement of the NMR spectrometer directly in the synthetic laboratory, allowing near continuous sampling and direct reaction feedback. This workflow reduces analysis time, simplifies sample handling and lowers operational costs compared with high-field NMR systems.

Future trends and opportunities

Advances in low-field NMR sensitivity and integration with automated flow platforms promise further improvements in throughput and data quality. Extending this approach to diverse monomer systems and copolymer architectures will broaden its impact across polymer research, process development and quality assurance.

Conclusion

The picoSpin 80 benchtop NMR spectrometer provides reliable qualitative and quantitative monitoring of RAFT polymerization in near real time. Strategic selection of resonance regions enables accurate determination of monomer conversion and block copolymer composition without extensive sample preparation. This accessible workflow streamlines polymer optimization and characterization for synthetic chemists.

References

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