1、Designation: D4001 93 (Reapproved 2006)D4001 13Standard 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
2、, 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 Scope*1.1 This test method describes the test procedures for determining the weigh
3、t-average molecular weight Mw of polymers by lightscattering. It is applicable to all nonionic homopolymers (linear or branched) that dissolve completely without reaction ordegradation to form stable solutions. Copolymers and polyelectrolytes are not within its scope. The procedure also allows thede
4、termination of the second virial coefficient, A2, which is a measure of polymer-solvent interactions, and the root-mean-squareradius 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 th
5、e size of the dissolved polymermolecules and the refractive indices of solvent and polymer. A range frequently stated is 10,000 to 10,000,000, but this may beis often extended in either direction with suitable systems and by the use of special techniques.1.2.1 The lower limit to molecular weight res
6、ults from low levels of excess solution scattering over that of the solvent. Thegreater the specific refractive increment dn/dc (difference in refractive indices of solution and solvent per unit concentration), thegreater the level of solution scattering and the lower the molecular weight that cansh
7、all 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 determinedby the molecular size. For sufficiently large molecules, measurements must be made at small scattering angles, which are ultimatelyout
8、side the range of the photometer used.1.3 The values stated in SI units are to be regarded as standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and h
9、ealth practices and determine the applicability of regulatorylimitations prior to use.NOTE 1There areis no similar or equivalent ISO standards.known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2IEEE/ASTM SI-10 American National Standard for Use of the International Syst
10、em of Units (SI): The Modern Metric System3. Terminology3.1 DefinitionsUnits, symbols, and abbreviations are in accordance with IEEE/ASTM SI-10.4. Significance and Use4.1 The weight-average molecular weight is a fundamental structure parameter of polymers, which is related to many physicalproperties
11、 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 ofthe molecular-weight distribution.4.2 Other important uses
12、of information on the weight-average molecular weight are correlation with dilute-solution ormelt-viscosity measurements and calibration of molecular-weight standards for use in liquid-exclusion (gel-permeation)chromatography.1 This test method is under the jurisdiction of ASTM Committee D20 on Plas
13、tics and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.70.05).Current edition approved March 15, 2006Nov. 1, 2013. Published April 2006November 2013. Originally approved in 1981. Last previous edition approved in 19992006as D4001-93 (1999).-93 (2006). DOI: 10.1520/D4001-9
14、3R06.10.1520/D4001-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard a
15、nd is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only
16、 the current versionof the standard as published by ASTM is to be considered the official document.*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 States14.3 To the extent that
17、 the light-scattering photometer is appropriately calibrated, light scattering is an absolute method and mayistherefore be applied to nonionic homopolymers that have not previously been synthesized or studied.5. Apparatus5.1 Volumetric Flasks, 100-mL, or other convenient size.5.2 Transfer Pipets.5.3
18、 Photometer, whose major components, described in Appendix 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)3 in the literature.5.4 Differential Refractomet
19、er, with sensitivity of approximately 3 106 refractive-index units, capable of measuring thespecific refractive increment dn/dc at the wavelength and temperature of the scattering measurements (2).NOTE 2Specific refractive increments are tabulated (2,3) for many polymer-solvent systems.5.5 Refractom
20、eter, Abb type or equivalent, capable of measuring the refractive indices of solvents and solutions at thewavelength and temperature of the scattering measurements.5.6 Spectrophotometer, capable of measuring the absorbance of solutions at the wavelength of the scattering measurements.5.7 Laminar-Flo
21、w Clean-Air Station, to provide a dust-free area for preparing and cleaning solutions and filling the scatteringcell.5.8 Filters and Filter Holders, for cleaning solvents and solutions. Membrane filters with pore sizes from 0.10 to 0.45 m, usedin glass or plastic filter holders, are recommended.5.8.
22、1 For water and aqueous solutions, and for organic solvents that do not attack the material, the use of polycarbonate(Nucleopore) filters is recommended. These filters have the advantages of high flow rate without the use of gas pressure, minimalretention of solute on the filter, and efficient clean
23、ing action. For other solvents, the use of cellulosic filters (Millipore or equivalent)is recommended.NOTE 3Sintered-glass filters may beis sometimes used, but these are relatively expensive and difficult to clean between uses. Centrifugation may beissometimes used, but this step requires special ca
24、re and techniques, or special scattering cell design, to be satisfactory.6. Reagents and Materials6.1 Solvents, as required. Since dn/dc is a function of composition, solvents shouldshall be of high purity. Significant errors inmolecular weight, which depends on the square of d n/dc, maywill be incu
25、rred if literature values of dn/dc are employed and theactual value of this quantity is different because of impurities in the solvent.6.2 12-Tungstosilicic Acid, as standard for calibration of photometer.7. Sample7.1 The sample must be homogeneous, and must be thoroughly free of all foreign impurit
26、ies. If at all possible, samples to beused for light-scattering measurements must be specially treated from synthesis on to minimize exposure to or contamination withparticulate impurities. Gels, which may Gels that consist of very high-molecular-weight particles, are sometimes formed duringsynthesi
27、s and will interfere with the analysis.All such particulate matter must be removed, sometimes with considerable difficulty.It should be understood that when this is done, the remaining sample is no longer truly representative of the entire polymer. Theextent of the difference from the original sampl
28、e will depend on the removal techniques employed.NOTE 4Reduction of sample particle size in a clean Spex or Wiley mill speeds solution and, with slow-dissolving materials, may be is essential ifthe measurements are to be made in a reasonable time. Overheating with consequent sample degradation must
29、be avoided during the milling process.Hard, tough samples or those with low melting points can be are handled by mixing with clean dry ice, milling the mixture, and then allowing the dryice to sublime. Clean dry ice may be obtained by opening a tank of carbon dioxide to the atmosphere. Commercial dr
30、y ice is usually has often been shownto be contaminated.8. Preparation of Dust-Free Cell and Contents8.1 Clean all glassware, including the scattering cell, with a suitable detergent to remove grease and other contaminants. Useof an ultrasonic cleaning bath is recommended. Rinse glassware at least f
31、our times with distilled water to remove all traces ofdetergent, and dry in a clean, dust-free drying oven.NOTE 5A laminar-flow clean-air station is recommended for providing a dust-free area for solution preparation and filtration. If a clean-air stationis not used, a closed area in a location free
32、 of drafts and of sufficient size to hold the filter unit, scattering cell, and other glassware shouldshall be provided.used.3 The boldface numbers in parentheses refer to the list of references at the end of this test method.D4001 1328.2 Filter solvent directly into the scattering cell. First rinse
33、 the cell several times with 5 to 10 mL of filtered solvent each, toremove dust particles. Be sure upper Upper surfaces of the interior of the cell are shall be well washed down. Close the cell witha cap similarly rinsed with filtered solvent. After rinsing, fill the cell with the minimum amount of
34、solvent required to bring theliquid level above the point where the light beam in the photometer passes through the cell.NOTE 6Use of a small filter holder fitting between a hypodermic syringe and needle is convenient where only small quantities of liquids need be arefiltered. A cell cap, with a hol
35、e just large enough to insert the needle, may conveniently be is used.8.3 Place the scattering cell in the photometer, or in an equivalent strong light beam, and examine it in the dark, viewing at smallscattering angles. Bright specks of dust shouldmust not be visible; if they are, the cell was not
36、rinsed completely or the filtrationprocedure is inadequate.8.4 Subsequent use of the clean cell for adding increments of filtered solution or for replacing solvent with solution requiresno further rinsing, except to ensure that residual solvent remaining, after the cell is emptied, is removed and re
37、placed with solution.9. Procedure9.1 Calibrate the light-scattering photometer. This calibration is required to convert measurements of scattered light intensityfrom arbitrary to absolute values, an essential step in the calculation of molecular weight. The calibration procedure, which islengthy and
38、 requires great care to obtain accurate results, is given in Appendix X2. The calibration constant of most photometersremains stable for long periods of time, however, so thatmaking the calibration procedure need be carried out onlyinfrequently.infrequent.9.2 Prepare a stock solution of polymer, not
39、ing the precautions of Sections 7 and 8, at a concentration estimated as follows: Fora polymer of Mw = 100,000 in a solventsuch that dn/d c 0.2 mL/g (for example, polystyrene in 2-butanone), the stock solution shouldshall be in the range from 10 to20 g/L. Since scattered intensity is proportional to
40、 Mw and to the square of dn/dc, estimates of the stock-solution concentrationrequired for other samples and systems can be is made. Prepare no more stock solution than is required by the following procedure.9.3 Select one of the following measurement schemes:9.3.1 Where the volume of liquid required
41、 for measurement in the photometer can be is varied by at least a factor of two, it isrecommended that the scattering from the minimum volume of solvent be measured first, followed by measurement of solutionsprepared in the cell by the addition of weighed or volumetrically measured aliquots of filte
42、red stock solution. From four to six suchsolutions shouldshall be measured, the most concentrated consisting of approximately equal volumes of solvent and stock solutionif its concentration is selected in accordance with 9.2, and the least concentrated being about one fourth this concentration. Aspe
43、cific example is given in Appendix X3.9.3.2 If the volume of liquid in the scattering cell cannot be varied as in 9.3.1, it will be is necessary to prepare and filter intothe cell from four to six separate solutions covering the range suggested in 9.3.1.9.3.3 A further alternative, which alternative
44、 is felt to be unduly complicated, is to to measure the most concentrated solutionfirst (for this purpose, the stock solution concentration estimated in 9.3.1 shouldshall be reduced by a factor of two), followed bysuccessive dilutions with solvent.The scattering from the pure solvent must be measure
45、d in a separate step, and it may be necessaryto step. If necessary, start dilution sequences at two or more concentration levels to obtain the range specified in 9.3.1.9.4 Measure the scattering of the pure solvent, filtered into the cell as described in Section 8, and of each of the series of filte
46、redsolutions described in 9.3, following the instructions provided with the photometer or in the literature (4), being sure that thefollowing steps are included. (This procedure is based on the scheme of 9.3.1.)9.4.1 Instrument CheckSee that the photometer is prepared for measurement, with the lamp
47、lit, high voltage supplied to thephotomultiplier detector, and all components fully warmed up and stabilized.9.4.2 Solvent PreparationFill the cleaned scattering cell with filtered solvent as described in Section 8, insert it in theinstrument, and align it as required.9.4.3 Intensity LevelSelect the
48、 wavelength-isolating filter to be used. Turn the detector to the specified angle and set the levelof high voltage, or adjust the slit openings, as called for to provide an appropriate solvent reading. In subsequent steps, do notreadjust these variables, but change amplifier gain by known factors or
49、 insert neutral filters of known transmittance as required tomaintain readings on scale.9.4.4 Solvent MeasurementAfter the cell has remained undisturbed in the photometer for 10 to 15 min to allow residual dustto settle out, read and record the scattered intensity at angles of 30, 90, 150, and at least three pairs between, symmetricallyplaced with respect to 90, as available on the photometer used.9.4.5 ReferenceTurn the phototube to the specified reference angle, adjust amplifier gain or insert neutral filters as required,insert the reference standard, and re
