ISO 21561-2:2016

Overview

ISO 21561-2:2016 specifies a standardized laboratory method for quantitative determination of the microstructure of solution‑polymerized styrene‑butadiene rubber (S‑SBR) using Fourier Transform Infrared Spectrometry (FTIR) with an Attenuated Total Reflection (ATR) accessory. The method reports styrene content as mass % of the whole polymer and butadiene microstructures (vinyl, trans, cis) as mol % relative to the butadiene fraction. It applies only to raw rubbers and is intended for industrial quality control, R&D and material characterization.

Key topics and technical requirements

• Principle: Measure ATR‑FTIR absorbances at characteristic wavenumbers and calculate component contents using regression formulae derived from reference S‑SBR samples.
• Sampling: Prepare test pieces in accordance with ISO 1795 (raw rubber sampling and preparative procedures).
• Apparatus:
  • FTIR with DTGS or TGS detector, typically 32 scans, 2 cm−1 resolution, spectral range about 600–1 800 cm−1.
  • Single‑bounce ATR (diamond crystal), 45° incidence, and a sample pressure clamp (preferably torque‑controlled).
• Measurement:
  • Record background and sample ATR spectra under consistent atmospheric conditions to avoid CO2 interference.
  • Measure absorbance peaks for styrene, cis, vinyl and trans at specified wavenumber ranges (examples: styrene ~695–761 cm−1; vinyl ~905–996 cm−1; trans ~962–967 cm−1; baseline at 1 200 cm−1). Note: cis peaks can be weak or hidden when styrene content is high.
• Calculations:
  • Apply baseline corrections and compute normalized absorbance ratios.
  • Use specified regression equations to obtain styrene and microstructure contents in mass %. Convert vinyl/trans/cis to mol % of butadiene using the provided formulae.
• Limitations: Precision shown in Annex A may not be achieved for S‑SBRs containing polystyrene blocks or with styrene > ~45 mass %.
• Reporting: Test report must include sample details, reference to ISO 21561‑2, number of test pieces, results (rounded to one decimal %), test procedures used and test dates.

Applications and users

• Polymer producers: incoming quality control of S‑SBR batches and process monitoring.
• Tire and rubber product manufacturers: verifying polymer microstructure for performance (wear, wet grip, hysteresis).
• Analytical laboratories and R&D: routine characterization and comparative studies of S‑SBR formulation and synthesis routes.
• Regulatory/standards labs: ensuring traceable, repeatable microstructure data for material specifications.

Related standards

• ISO 21561‑1 - Part 1: H‑NMR and FTIR with cast‑film method (alternative microstructure determination methods).
• ISO 1795 - Sampling and preparative procedures for raw rubber.
• See Annex A and B of ISO 21561‑2 for precision data and regression equation acquisition details.

Keywords: ISO 21561‑2:2016, SBR microstructure, solution‑polymerized SBR, FTIR ATR method, styrene content, vinyl cis trans, raw rubber testing, polymer characterization.