ISO 11344:2004
(Main)Rubber, raw synthetic — Determination of the molecular-mass distribution of solution polymers by gel permeation chromatography
Rubber, raw synthetic — Determination of the molecular-mass distribution of solution polymers by gel permeation chromatography
ISO 11344:2004 describes a method for the determination of the molecular mass, expressed as polystyrene, and the molecular-mass distribution of polymers produced in solution which are completely soluble in tetrahydrofuran (THF) and which have a molecular-mass range from 5 000 to 1 000 000. It is not the purpose of the standard to explain the theory of gel permeation chromatography.
Caoutchouc synthétique brut — Détermination de la répartition de la masse moléculaire pour les caoutchoucs polymérisés en solution par chromatographie par perméation de gel
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 11344
First edition
2004-04-01
Rubber, raw synthetic — Determination
of the molecular-mass distribution of
solution polymers by gel permeation
chromatography
Caoutchouc synthétique brut — Détermination de la répartition de la
masse moléculaire pour les caoutchoucs polymérisés en solution par
chromatographie par perméation de gel
Reference number
ISO 11344:2004(E)
©
ISO 2004
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ISO 11344:2004(E)
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ii © ISO 2004 – All rights reserved
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ISO 11344:2004(E)
Contents Page
Foreword. iv
1 Scope. 1
2 Normative references . 1
3 Principle . 1
4 General. 1
5 Reagents and materials. 2
6 Apparatus. 3
7 Analytical conditions . 4
8 Procedure. 4
9 Expression of results. 7
10 Precision (only for instrumental software procedure) . 8
11 Test report. 9
Annex A (informative) Molecular-mass parameters determined by instrumental software . 11
Annex B (informative) Calculation of molecular-mass parameters by manual procedure. 15
Annex C (informative) Comparison of results obtained by automatic procedure (software) and
manual procedure . 19
Annex D (informative) Guidance for using precision results. 20
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ISO 11344:2004(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 11344 was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee
SC 2, Testing and analyses.
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INTERNATIONAL STANDARD ISO 11344:2004(E)
Rubber, raw synthetic — Determination of the molecular-mass
distribution of solution polymers by gel permeation
chromatography
WARNING — Persons using this International Standard should be familiar with normal laboratory
practice. This standard 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
ensure compliance with any national regulatory conditions.
1 Scope
This International Standard describes a method for the determination of the molecular mass, expressed as
polystyrene, and the molecular-mass distribution of polymers produced in solution which are completely
3 6
soluble in tetrahydrofuran (THF) and which have a molecular-mass range from 5 × 10 to 1 × 10 .
It is not the purpose of this International Standard to explain the theory of gel permeation chromatography.
2 Normative references
The following referenced documents are indispensable for the application 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/TR 9272, Rubber and rubber products — Determination of precision for test method standards
3 Principle
The molecular components of a polymer are separated on the basis of macromolecule size on a gel
permeation column. A known quantity of a dilute solution of the polymer is injected into a stream of solvent,
which carries it through the column at a constant rate. The concentration of the separated molecular
components in the solvent stream is measured by a suitable detector. Through the use of a calibration curve,
both the number-average molecular mass (M ) and mass-average molecular mass (M ) of the material
n w
analysed can be determined from the retention time and the corresponding concentration.
4 General
4.1 Gel permeation chromatography (GPC), which is also known as size exclusion chromatography (SEC),
is a particular type of liquid chromatography which allows the separation of the various components of a
polymer based on macromolecule size.
4.2 The molecules of a polymer do not all have the same mass, but comprise a range of different masses.
For this reason, the usual concept of molecular mass is not applicable to polymeric materials. Instead,
different average molecular masses are determined as shown in Table 1.
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ISO 11344:2004(E)
Table 1 — Definitions of various kinds of molecular mass
2
Mass-average molecular mass M = Σ(N M )/Σ(N M )
w i i i I
= Σ(A M )/ΣA
i i i
Number-average molecular mass M = Σ(M N )/ΣN
n i i i
= ΣA /Σ(A /M )
i i i
3 2
z-Average molecular mass M = Σ(N M )/Σ(N M )
z i i i i
2
= Σ(A M )/Σ(A M )
i i i I
Peak molecular mass M Molecular mass at peak maximum
p
where
N is the number of moles having a molecular mass of M ;
i i
A is the area of the time-slice that corresponds to molecular mass M .
i i
The molecular-mass distribution is an important parameter in determining the properties of the polymer. It may
be represented by the polydispersity D given by:
D = M /M
w n
NOTE Polymers invariably consist of macromolecules with a range of molecular sizes. Even the so-called
monodisperse polystyrenes have a polydispersity of 1,1 compared to a value of 1,0 for a pure compound with a single
molecular mass. As the range of molecular sizes present within the polymer increases, so does the polydispersity.
5 Reagents and materials
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only
distilled water or water of equivalent purity.
5.1 Tetrahydrofuran (THF), high-purity-grade solvent.
NOTE A large stock of THF is needed to avoid frequent refills. Changes in the quantity of dissolved air or impurities
due to addition of fresh solvent cause significant variations in the refractive index and could also affect the retention time.
Air bubbles at the pump head reduce the quantity of solvent pumped (leading to errors in retention volumes and times)
and can block the pump if the volume of the air bubbles reaches excessive levels. After adding fresh solvent, it takes 2 to
3 hours to obtain a stable baseline.
5.2 Solution of o-dichlorobenzene (internal retention time standard) in THF, obtained by dilution of
3
250 mm (250 µl) of o-dichlorobenzene with 1 l of THF.
5.3 Set of certified polystyrene reference standards (minimum 10), with molecular masses in the range
2 7
5 × 10 to 1 × 10 (depending on the sample molecular-mass range) and a very narrow molecular-mass
distribution (D < 1,10) (see Table 2 for an example of such a set, available from various chemical suppliers).
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ISO 11344:2004(E)
Table 2 — Set of polystyrene standards
Actual molecular
Standard No. D (= M /M )
w n
mass M
i
1 1 030 000 1,05
2 770 000 1,04
3 336 000 1,03
4 210 000 1,03
5 156 000 1,03
6 66 000 1,03
7 30 300 1,03
8 22 000 1,03
9 11 600 1,03
10 7 000 1,04
11 5 050 1,05
6 Apparatus
Ordinary laboratory apparatus, plus the following:
6.1 Gel permeation chromatograph, consisting of the components specified in 6.1.1 to 6.1.8.
6.1.1 Solvent reservoir, of sufficient capacity to complete the analysis (see Note to 5.1) without refilling.
6.1.2 Automatic on-line degassing system or helium sparging of solvent reservoir, to stabilize the
solvent flow, mainly to prevent formation of bubbles in the solvent.
6.1.3 Pump, to ensure that the THF solvent flows at a constant rate, programmable over the range
3 3
1,7 mm /s to 165,0 mm /s with a high degree of precision.
3
6.1.4 Injector or automatic sampler, with a 100 mm (100 µl) injection loop.
6.1.5 Columns, packed with regular, rigid, porous spheres. The pore size of column packing material is
−10
expressed in Ångstrom units (1 Å = 10 m). The packing spheres are made of cross-linked polystyrene,
obtained by polymerization of styrene with divinylbenzene. The spheres shall have a nominal diameter in the
range 5 µm to 10 µm. The columns are generally 300 mm long. The pore size is selected depending on the
range of molecular masses to be analysed.
3 4 4 5
NOTE Four columns with pore sizes 10 Å, 10 Å, 10 Å and 10 Å were used when the repeatability and
reproducibility of the method described in this International Standard were determined. The solvent first enters the column
with the lowest porosity and exits from the column with the highest porosity. Other suitable columns may be used. These
types of column are available from many suppliers.
The recommended column characteristics are:
linear range: 200 to 2 000 000;
guaranteed column efficiency: > 50 000 plates/m;
column arrangement: four columns (300 mm long and 4,6 mm to 8,0 mm ID).
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ISO 11344:2004(E)
6.1.6 Detector.
Various types of detector may be used, such as differential refractometer, UV or light-scattering.
6.1.7 Integrator, capable of integrating at least 150 time-slices during the elution of the polymer being
analysed.
6.1.8 Personal computer and software, to avoid long and difficult manual calculations.
6.2 PTFE filters, having a pore size of 0,50 µm or 0,45 µm.
3 3
6.3 10 cm (10 ml) and 250 mm (250 µl) syringes.
6.4 Autocollector (optional), with glass vials.
6.5 Mixer.
7 Analytical conditions
3
Flow rate: 17 mm /s.
3
Injection volume: 100 mm (100 µl) of solution, or a quantity suitable for the volume of the column used.
Elution time of internal standard (o-dichlorobenzene): 45 min minimum.
Column temperature: (40 ± 1) °C.
8 Procedure
8.1 Solvent degassing
8.1.1 Filter the solvent (5.1) by suction through a PTFE filter (6.2).
3
8.1.2 Degas 1 dm of solvent under vacuum and/or in an ultrasonic bath for about 30 min.
To obtain a constant baseline, degassing should preferably be done 12 h before use. From time to time, the
columns should be flushed, for a period of 8 h, with THF solvent, degassed as specified in this subclause, to
remove any peroxides left in the column.
If an automatic on-line degassing system is available, the degassing operation given in this subclause can be
omitted.
8.2 Calibration
8.2.1 Use polystyrene standards (5.3) dissolved in o-dichlorobenzene solution (5.2) for calibration purposes.
To ensure constant peak size, weigh out a different amount of each individual standard as a function of its
3
molecular mass, for example 1 g/l (0,025 g in 25 cm of solution 5.2) for molecular masses around 1 000 000,
3
5 g/l (0,125 g in 25 cm of solution 5.2) for molecular masses lower than 30 000. The calibration plot shall
cover the entire range of molecular masses present in the polymer being analysed.
8.2.2 Shake the solutions gently for about 1 h.
3
8.2.3 Filter each solution through a PTFE filter (6.2) attached to a 10 cm syringe.
NOTE The reference standard solutions can be kept in a refrigerator at 6 °C to 7 °C for a maximum of 3 months.
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ISO 11344:2004(E)
8.2.4 The calibration procedure described in 8.2.4.1 to 8.2.4.6 is given by way of example.
8.2.4.1 Prepare 11 solutions of polystyrene in accordance with Table 3.
8.2.4.2 Calculate the intrinsic viscosity [η] for each standard by applying the Mark-Houwink equation
i
α
([η] = KM ) and using the known values of K (= 0,000 16) and α (= 0,700).
i i
NOTE Table 4 shows the intrinsic viscosity of the polystyrene standard solutions given in Table 3.
Table 3 — Solutions of polystyrene reference standards
Concentration
Solution No. 3 Actual molecular mass M
g in 25 cm of i
o-dichlorobenzene solution (5.2)
1 0,025 1 030 000
2 0,025 770 000
3 0,030 336 000
4 0,050 210 000
5 0,050 156 000
6 0,075 66 000
7 0,125 30 300
8 0,125 22 000
9 0,125 11 600
10 0,125 7 000
11 0,125 5 050
Table 4 — Values of [η] for the solutions in Table 3
i
Actual molecular mass M Intrinsic viscosity [η]
i i
1 030 000 2,588 8
770 000 2,111 9
336 000 1,181 8
210 000 0,850 5
156 000 0,690 7
66 000 0,378 3
30 300 0,219 3
22 000 0,175 3
11 600 0,112 0
7 000 0.078 6
5 050 0,062 6
3
8.2.4.3 When using manual injection, draw off 250 mm (250 µl) from each vial, flush the injection loop
and then inject 100 µl. Read off the retention time corresponding to the peak for each standard. With an
automatic sampler, follow the manufacturer's instructions. Repeat for a total of three times.
8.2.4.4 Average the three retention times obtained for each standard and the retention times of
o-dichlorobenzene averaged over all the runs (in this case a total of 33).
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ISO 11344:2004(E)
8.2.4.5 Plot the average retention time, in minutes, against the corresponding value of log(M [η] ) for each
i i
standard and calculate the best-fit line (see Figure 1).
8.2.4.6 The correlation coefficient shall be higher than 0,999 5. If not, repeat the calibration procedure for
the standards that are causing imperfect alignment, found by computing the difference between the certified
(actual) molecular masses and the molecular masses calculated (see Table 5) using the third-degree
polynomial representing the best-fit line in Figure 1.
For the data plotted in Figure 1, the best-fit line is given by the following third-degree polynomial:
2 3
log(M [η] ) = 26,072 144 65 – 1,746 517 348 t + 0,051 765 825 t – 0,000 585 847 t
i i i i i
For these data, the correlation coefficient is 0,999 76.
Table 5 — Calibration data corresponding to plot in Figure 1
Retention time t
i Calculated molecular
Actual molecular mass M Intrinsic viscosity [η]
i i
mass
min
1 030 000 22,08 2,588 8 1 058 592
770 000 22,89 2,111 9 749 179
336 000 25,15 1,181 8 331 816
210 000 26,15 0,850 5 206 277
156 000 27,58 0,690 7 158 756
66 000 30,18 0,378 3 69 059
30 300 32,76 0,219 3 29 520
22 000 33,68 0,175 3 21 760
11 600 35,46 0,112 0 11 344
7 000 36,64 0,078 6 7 266
5 050 37,47 0,062 6 4 998
Key
X retention time (min)
Y log(M [η] )
i i
Figure 1 — Calibration plot
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