ASTM_D_4001_-_13.pdf

Designation:D400113Standard Test Method forDetermination of Weight-Average Molecular Weight ofPolymers By Light Scattering1This standard is issued under the fixed designation D4001;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This test method describes the test procedures fordetermining the weight-average molecular weight Mwof poly-mers by light scattering.It is applicable to all nonionichomopolymers(linear or branched)that dissolve completelywithout reaction or degradation to form stable solutions.Copolymers and polyelectrolytes are not within its scope.Theprocedure also allows the determination of the second virialcoefficient,A2,which is a measure of polymer-solventinteractions,and the root-mean-square radius of gyration(s2)1/2,which is a measure of the dimensions of the polymerchain.1.2 The molecular-weight range for light scattering is,tosome extent,determined by the size of the dissolved polymermolecules and the refractive indices of solvent and polymer.Arange frequently stated is 10,000 to 10,000,000,is oftenextended in either direction with suitable systems and by theuse of special techniques.1.2.1 The lower limit to molecular weight results from lowlevels of excess solution scattering over that of the solvent.Thegreater the specific refractive increment dn/dc(difference inrefractiveindicesofsolutionandsolventperunitconcentration),the greater the level of solution scattering andthe lower the molecular weight that shall be determined with agiven precision.1.2.2 The upper limit to molecular weight results from theangular dependence of the solution scattering,which is deter-mined by the molecular size.For sufficiently large molecules,measurements must be made at small scattering angles,whichare ultimately outside the range of the photometer used.1.3 The values stated in SI units are to be regarded asstandard.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE1There is no known ISO equivalent to this standard.2.Referenced Documents2.1 ASTM Standards:2IEEE/ASTM SI-10 American National Standard for Use ofthe International System of Units(SI):The Modern MetricSystem3.Terminology3.1 DefinitionsUnits,symbols,and abbreviations are inaccordance with IEEE/ASTM SI-10.4.Significance and Use4.1 The weight-average molecular weight is a fundamentalstructure parameter of polymers,which is related to manyphysical properties of the bulk material,such as its rheologicalbehavior.In addition,knowledge of the weight-average mo-lecular weight,together with knowledge of the number-average molecular weight from osmometry,provides a usefulmeasure of the breadth of the molecular-weight distribution.4.2 Other important uses of information on the weight-average molecular weight are correlation with dilute-solutionor melt-viscosity measurements and calibration of molecular-weight standards for use in liquid-exclusion(gel-permeation)chromatography.4.3 To the extent that the light-scattering photometer isappropriately calibrated,light scattering is an absolute methodand is therefore be applied to nonionic homopolymers thathave not previously been synthesized or studied.5.Apparatus5.1 Volumetric Flasks,100-mL,or other convenient size.5.2 Transfer Pipets.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Meth-ods.70.05).Current edition approved Nov.1,2013.Published November 2013.Originallyapproved in 1981.Last previous edition approved in 2006 as D4001-93(2006).DOI:10.1520/D4001-13.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.3 Photometer,whose major components,described inAppendix X1,are a light source,a projection optical system,asample-cell area,a receiver optical system,a detector system,and a recording system.Typical photometers are described andsummarized(1)3in the literature.5.4 Differential Refractometer,with sensitivity of approxi-mately 3 106refractive-index units,capable of measuringthe specific refractive increment dn/dc at the wavelength andtemperature of the scattering measurements(2).NOTE2Specific refractive increments are tabulated(2,3)for manypolymer-solvent systems.5.5 Refractome