ISO 21561-2:2024

International
Standard
ISO 21561-2
Second edition
Styrene-butadiene rubber
2024-08
(SBR) — Determination of the
microstructure of solution-
polymerized SBR —
Part 2:
Fourier transform infrared
spectrometry (FTIR) with attenuated
total reflection (ATR) method
Caoutchouc styrène-butadiène (SBR) — Détermination de la
microstructure du SBR polymérisé en solution —
Partie 2: Méthode par spectrométrie infrarouge à transformée de
Fourier (FTIR) à réflexion totale atténuée (RTA)
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 2
6 Calibration . 2
6.1 FTIR .2
6.2 ATR .2
7 Sampling . 2
8 Procedure for measuring ATR spectrum . . 3
9 Determination of the microstructure of butadiene and the styrene content . 3
9.1 Measurement of the absorbance for each microstructure component .3
9.2 Calculation of microstructures .4
9.2.1 General .4
9.2.2 Base line correction of each absorbance peak .4
9.2.3 Ratio of absorbance .5
9.2.4 Second order terms .5
9.2.5 Styrene content and contents of three microstructure types of butadiene
portion by regression formulae .5
9.2.6 Contents of three microstructure types relative to butadiene portion in the
S-SBR .6
10 Precision . 6
11 Test report . 6
Annex A (informative) Precision results from an interlaboratory test programme . 7
Annex B (informative) Acquisition of regression formulae for microstructure .10
Annex C (informative) Determination of microstructure by NMR spectrometry .12
Bibliography .15

iii
Foreword
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bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
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Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee
SC 3, Raw materials (including latex) for use in the rubber industry.
This second edition cancels and replaces the first edition (ISO 21561-2:2016), which has been technically
revised.
The main changes are as follows:
— Clause 3 has been added;
— the units of styrene content and microstructure content of butadiene have been changed to SI units;
— the conditions of FTIR spectrum have been moved to 8.1;
— a description of regression formulae has been added in 9.2.5 and 9.2.6;
— in Table A.1, one cell has been replaced by the correct value;
— in C.3.1, the measurement conditions for C-NMR have been corrected.
A list of all parts in the ISO 21561 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
International Standard ISO 21561-2:2024(en)
Styrene-butadiene rubber (SBR) — Determination of the
microstructure of solution-polymerized SBR —
Part 2:
Fourier transform infrared spectrometry (FTIR) with
attenuated total reflection (ATR) method
WARNING 1 — Persons using this document should be familiar with normal laboratory practice. This
document does not purport to address all of the safety problems, if any, associated with its use. It is
the responsibility of the user to establish appropriate safety and health practices and to determine
the applicability of any other restrictions.
WARNING 2 — Certain procedures specified in this document can involve the use or generation of
substances, or the generation of waste, that can constitute a local environmental hazard. Reference
should be made to appropriate documentation on safe handling and disposal after use.
1 Scope
This document specifies procedures for the quantitative determination of the microstructure of the
butadiene portion and the content of styrene in solution-polymerized SBR (S-SBR) by Fourier transform
infrared spectrometry (FTIR) with attenuated total reflection (ATR) method. The styrene content is
expressed in mass fraction relative to the S-SBR. The contents of three microstructure types, i.e. vinyl, trans
and cis, are expressed in mol fraction relative to the butadiene portion in the S-SBR. This method is only
applicable to raw rubbers.
NOTE 1 Precision as shown in Annex A is not always possible to obtain for S-SBRs containing polystyrene block or
styrene content more than 45 %.
NOTE 2 Only “vinyl”, “trans” and “cis”, are used in this document. However, the expression of vinyl, trans and cis
mean as follows in general:
— vinyl: vinyl unit, vinyl bond, 1,2-unit, 1,2-bond, 1,2-vinyl-unit or 1,2-vinyl-bond;
— trans: 1,4-trans unit, 1,4-trans bond, trans-1,4 unit or trans1,4 bond;
— cis: 1,4-cis unit, 1,4-cis bond, cis-1,4 unit or cis-1,4 bond.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 1382, Rubber — Vocabulary
ISO 1795, Rubber, raw natural and raw synthetic — Sampling and further preparative procedures
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1382 apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
The IR spectrum of the S-SBR sample is measured by FTIR with ATR. The absorbances that are characteristic
of each microstructure component and styrene at the specified wave number are used to determine the
content of each component by using the specific formulae presented in this document.
5 Apparatus
5.1 FTIR, of the following specifications:
— detector: deuterium tri-glycine sulfate (DTGS) or tri-glycine sulfate (TGS);
−1
— resolution: 2 cm .
5.2 ATR, of the following specifications:
— type: single bounce ATR;
— crystal: diamond;
— angle of incidence: 45°;
— sample pressure clamp: a concave or a flat-shaped clamp which is capable of maintaining a constant
pressure on the sample. The use of a torque wrench is recommended.
6 Calibration
6.1 FTIR
Adjust the optical bench alignment of FTIR spectrometer according to the manufacturer’s instruction manual.
6.2 ATR
Set ATR in the sample chamber of FTIR and adjust the optical alignment of ATR according to the
manufacturer’s instruction manual.
7 Sampling
7.1 Prepare the test sample in accordance with ISO 1795.
NOTE The extraction of ordinary extender oils by solvent is not necessary.
7.2 Cut out a test piece from the test sample. The test piece shall have a flat surface to give good contact
with the ATR crystal and be approximately the same size as the crystal, usually a few square millimetres.

8 Procedure for measuring ATR spectrum
8.1 Set up FTIR according to the manufacturer’s instruction manual and set up the measurement
conditions as follows:
-1
— resolution: 2 cm ;
— number of scans: 32;
−1 −1
— range of wave number: 600 cm to 1 800 cm .
8.2 Set ATR with the specification in a sample chamber of FTIR.
8.3 Measure the background spectrum without sample on the ATR crystal with the conditions shown in 8.1.
8.4 Put the test piece on the ATR crystal and contact it as completely a
...