ASTM D4001-93(2006)
(Test Method)Standard Test Method for Determination of Weight-Average Molecular Weight of Polymers By Light Scattering
Standard Test Method for Determination of Weight-Average Molecular Weight of Polymers By Light Scattering
SIGNIFICANCE AND USE
The weight-average molecular weight is a fundamental structure parameter of polymers, which is related to many physical properties of the bulk material, such as its rheological behavior. In addition, knowledge of the weight-average molecular weight, together with knowledge of the number-average molecular weight from osmometry, provides a useful measure of the breadth of the molecular-weight distribution.
Other important uses of information on the weight-average molecular weight are correlation with dilute-solution or melt-viscosity measurements and calibration of molecular-weight standards for use in liquid-exclusion (gel-permeation) chromatography.
To the extent that the light-scattering photometer is appropriately calibrated, light scattering is an absolute method and may therefore be applied to nonionic homopolymers that have not previously been synthesized or studied.
SCOPE
1.1 This test method describes the test procedures for determining the weight-average molecular weight Mw of polymers by light scattering. It is applicable to all nonionic homopolymers (linear or branched) that dissolve completely without reaction or degradation to form stable solutions. Copolymers and polyelectrolytes are not within its scope. The procedure also allows the determination of the second virial coefficient, A2, which is a measure of polymer-solvent interactions, and the root-mean-square radius of gyration (s2)1/2, which is a measure of the dimensions of the polymer chain.
1.2 The molecular-weight range for light scattering is, to some extent, determined by the size of the dissolved polymer molecules and the refractive indices of solvent and polymer. A range frequently stated is 10,000 to 10,000,000, but this may be extended in either direction with suitable systems and by the use of special techniques.
1.2.1 The lower limit to molecular weight results from low levels of excess solution scattering over that of the solvent. The greater the specific refractive increment dn/d c (difference in refractive indices of solution and solvent per unit concentration), the greater the level of solution scattering and the lower the molecular weight that can be determined with a given precision.
1.2.2 The upper limit to molecular weight results from the angular dependence of the solution scattering, which is determined by the molecular size. For sufficiently large molecules, measurements must be made at small scattering angles, which are ultimately outside the range of the photometer used.
1.3 The values stated in SI units are to be regarded as standard.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
There are no similar or equivalent ISO standards.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D4001 − 93(Reapproved 2006)
Standard Test Method for
Determination of Weight-Average Molecular Weight of
1
Polymers By Light Scattering
This standard is issued under the fixed designation D4001; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 This test method describes the test procedures for
determining the weight-average molecular weight M of poly-
NOTE 1—There are no similar or equivalent ISO standards.
w
mers by light scattering. It is applicable to all nonionic
2. Referenced Documents
homopolymers (linear or branched) that dissolve completely
2
without reaction or degradation to form stable solutions.
2.1 ASTM Standards:
Copolymers and polyelectrolytes are not within its scope. The
IEEE/ASTMSI-10American National Standard for Use of
procedure also allows the determination of the second virial
theInternationalSystemofUnits(SI):TheModernMetric
coefficient, A , which is a measure of polymer-solvent
2
System
interactions, and the root-mean-square radius of gyration
2 1/2
(s ) , which is a measure of the dimensions of the polymer
3. Terminology
chain.
3.1 Definitions—Units, symbols, and abbreviations are in
1.2 The molecular-weight range for light scattering is, to
accordance with IEEE/ASTMSI-10.
some extent, determined by the size of the dissolved polymer
molecules and the refractive indices of solvent and polymer.A
4. Significance and Use
rangefrequentlystatedis10,000to10,000,000,butthismaybe
4.1 The weight-average molecular weight is a fundamental
extended in either direction with suitable systems and by the
structure parameter of polymers, which is related to many
use of special techniques.
physical properties of the bulk material, such as its rheological
1.2.1 The lower limit to molecular weight results from low
behavior. In addition, knowledge of the weight-average mo-
levelsofexcesssolutionscatteringoverthatofthesolvent.The
lecular weight, together with knowledge of the number-
greater the specific refractive increment dn/dc (difference in
average molecular weight from osmometry, provides a useful
refractive indices of solution and solvent per unit
measure of the breadth of the molecular-weight distribution.
concentration), the greater the level of solution scattering and
4.2 Other important uses of information on the weight-
the lower the molecular weight that can be determined with a
average molecular weight are correlation with dilute-solution
given precision.
or melt-viscosity measurements and calibration of molecular-
1.2.2 The upper limit to molecular weight results from the
weight standards for use in liquid-exclusion (gel-permeation)
angular dependence of the solution scattering, which is deter-
chromatography.
mined by the molecular size. For sufficiently large molecules,
measurements must be made at small scattering angles, which
4.3 To the extent that the light-scattering photometer is
are ultimately outside the range of the photometer used.
appropriately calibrated, light scattering is an absolute method
and may therefore be applied to nonionic homopolymers that
1.3 The values stated in SI units are to be regarded as
have not previously been synthesized or studied.
standard.
1.4 This standard does not purport to address all of the
5. Apparatus
safety concerns, if any, associated with its use. It is the
5.1 Volumetric Flasks, 100-mL, or other convenient size.
responsibility of the user of this standard to establish appro-
5.2 Transfer Pipets.
1
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
and is the direct responsibility of Subcommittee D20.70 on Analytical Meth-
2
ods.70.05). For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved March 15, 2006. Published April 2006. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1981. Last previous edition approved in 1999 as D4001-93(1999). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D4001-93R06. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D4001 − 93 (2006)
5.3 Photometer, whose major components, described in particulate matter must be removed, sometimes with consider-
Appendix X1, are a light source, a projection optical system, a able difficulty. It should be understood that when this is done,
sample
...
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