Differential Analysis in sulfenamide-based vulcanizing accelerators for rubber products by High mass Accuracy MS and Multivariate Statistical Technique

Significance of the Topic

Vulcanization accelerators based on sulfenamides play a central role in cross-linking rubber polymers to yield durable products such as tires. Small structural variations or impurities in these accelerators can alter vulcanization kinetics, material properties and safety. Reliable differentiation of closely related sulfenamide compounds from different suppliers is therefore vital for quality control and product consistency.

Study Objectives and Overview

This work aimed to distinguish five N-tert-butyl-2-benzothiazole sulfenamide (NS) and five N-cyclohexyl-2-benzothiazole sulfenamide (CZ) accelerators sourced from different manufacturers. By combining high-mass‐accuracy MSn profiling with multivariate statistical analysis, the study sought to identify characteristic components, structural analogues and manufacturing-related impurities that differentiate each sample type.

Methodology

Sample solutions (100 mg/L) in tetrahydrofuran/acetonitrile were prepared for each of the ten accelerators. Quality control mixtures of NS and CZ served to validate reproducibility. LCMS-IT-TOF was employed for full‐scan MS and MSn acquisition under electrospray positive mode. Automatic peak detection and alignment yielded matrices for statistical evaluation. Principal component analysis (PCA) using SIMCA-P+ identified sample clustering and unique features. MetID Solution and Formula Predictor software assisted structural hypothesis generation from MSn fragmentation data.

Instrumentation Used

• LCMS-IT-TOF system (Shimadzu)
• Column: Shim-pack XR-ODS, 2.0×75 mm, 2.2 µm, 40 °C
• Mobile phase A: water + 5 mmol ammonium acetate; B: acetonitrile; gradient 0–9 min 0→100 % B; 9–12 min 100 % B; re-equilibration to 15 min
• Flow rate: 0.45 mL/min; injection: 1 µL
• ESI(+): probe 4.5 kV; CDL 200 °C; Qarray 200 °C; nebulizing gas 1.5 L/min; drying gas 0.1 MPa

Main Results and Discussion

PCA score plots clearly separated each NS and CZ sample group, indicating distinct chemical profiles. Loading plots revealed unique ions responsible for discrimination. Extracted ion chromatograms confirmed characteristic peaks per manufacturer. For example, a peak at m/z 253.0831 (NS-2) was identified as a CH2-extended phenyl analogue of the NS core (C12H16N2S2), verified by successive neutral‐loss MSn fragments. A series of other analogues and by-products were similarly elucidated, highlighting both intended accelerators and minor impurities linked to synthetic routes.

Benefits and Practical Applications

Use of high‐accuracy MSn combined with multivariate techniques enables:

• Rapid quality control of accelerator batches
• Detection of structural analogues and trace impurities
• Verification of supplier consistency
• Improved understanding of vulcanization performance drivers

Future Trends and Potential Applications

Advances in real‐time high‐resolution MS and machine‐learning‐driven data analysis will further streamline accelerator profiling. Expanded compound libraries and automated structural annotation promise faster screening of new accelerator chemistries. Integration with process analytics could enable in-line monitoring of additive blending in rubber manufacture.

Conclusion

This study demonstrates that high‐mass‐accuracy MSn and multivariate statistical analysis effectively differentiate sulfenamide vulcanization accelerators from various sources. Structural analogues, minor by-products and manufacturing-specific impurities were successfully characterized, offering a powerful approach for quality assurance in rubber product development.