ISO 21561-1:2015

Overview

ISO 21561-1:2015 specifies laboratory procedures for the quantitative determination of the microstructure of solution‑polymerized styrene‑butadiene rubber (S‑SBR). It defines two analytical routes:

• 1H‑NMR (H‑NMR) as an absolute method for determining styrene content (mass %) and butadiene microstructure (trans, cis, vinyl expressed in mol % relative to butadiene), and
• IR spectrometry with the cast‑film method as a relative method, which can be calibrated against H‑NMR standards to give absolute values.

The standard applies only to raw (unvulcanized) S‑SBR and references ISO 1407 (solvent extraction) and ISO 1795 (sampling).

Key topics and technical requirements

• Sample preparation
  • Extract extender oils and antioxidants per ISO 1407 (ethanol‑toluene azeotrope or acetone); dry extracted rubber under vacuum at 50–60 °C.
• H‑NMR (absolute method)
  • Dissolve 15–50 mg of extracted S‑SBR in 0.5 ml CDCl3 containing 0.03 % TMS.
  • Use an FT‑NMR spectrometer with resonance frequency ≥150 MHz.
  • Measurement parameters include 15 ppm sweep width, 30° pulse, pulse repetition 4–30 s, accumulation 32–256 scans.
  • Microstructure is obtained by integrating defined spectral regions (areas A, B, C) and applying the standard’s calculation formulas.
• IR cast‑film method (relative method)
  • Dissolve 0.2 g extracted S‑SBR in 10 ml cyclohexane; cast a film on KBr plate using a 0.1 mm spacer.
  • Measure FTIR or double‑beam IR spectrum from 1 200 cm‑1 to 600 cm‑1. Target maximum absorbance 0.10–0.15 for reproducibility.
  • Calculate trans/cis/vinyl/styrene using specified peak absorbances (Hampton’s method); calibration against H‑NMR yields absolute values.
• Precision and reporting
  • The standard includes precision data, procedural notes for film preparation (Annex A), and required test report elements.

Practical applications and users

ISO 21561-1 is used where accurate characterization of S‑SBR microstructure is required:

• Rubber manufacturers for batch acceptance and process control.
• Quality control and testing laboratories performing routine composition and microstructure checks.
• Polymer R&D and formulation scientists studying structure–property relationships (e.g., glass transition, filler interactions).
• Raw material suppliers verifying styrene content and butadiene stereochemistry.
• Certification and compliance bodies requiring standardized test data.

Keywords: ISO 21561-1, styrene‑butadiene rubber, SBR microstructure determination, 1H‑NMR, IR spectrometry, cast‑film method, FTIR, raw S‑SBR.

Related standards

• ISO 21561‑2 - SBR microstructure: FTIR with ATR method (complements Part 1).
• ISO 1407 - Rubber: determination of solvent extract (sample extraction).
• ISO 1795 - Rubber sampling and preparative procedures.