1、Designation: D 6579 06Standard Practice forMolecular Weight Averages and Molecular WeightDistribution of Hydrocarbon and Terpene Resins by Size-Exclusion Chromatography1This standard is issued under the fixed designation D 6579; the number immediately following the designation indicates the year ofo
2、riginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers the determination of apparentmolecula
3、r weight (MW) averages and molecular weight distri-butions (MWD) for THF-soluble hydrocarbon and terpeneresins by size-exclusion chromatography (SEC). This tech-nique is not absolute; it requires calibration with standards ofknown molecular weight. This practice is applicable to resinscontaining mol
4、ecular-weight components that have elutionvolumes falling within the elution volume range defined bypolystyrene standards.NOTE 1SEC is also known as gel permeation chromatography (GPC).1.2 SEC systems employ low-volume liquid chromatogra-phy components and columns packed with relatively small(genera
5、lly 3 to 20 m) microporous particles. High-performance liquid chromatography instrumentation and auto-mated data handling systems for data acquisition and process-ing are also required.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for inform
6、ationonly.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.2. Re
7、ferenced Documents2.1 ASTM Standards:2D 804 Terminology Relating to Naval Stores, Including TallOil and Related ProductsD 3016 Practice for Use of Liquid Exclusion Chromatogra-phy Terms and RelationshipsD 6440 Terminology Relating to Hydrocarbon Resins3. Terminology3.1 For definitions of size-exclus
8、ion chromatography terms,see Practice D 3016.3.2 For definition of terpene resin, see Terminology D 804.3.3 For definitions of resin terms, see Terminology D 6440.4. Summary of Practice4.1 In this practice, a dilute solution of a hydrocarbon orterpene resin sample is injected into a liquid mobile ph
9、asecontaining the same solvent used to prepare the resin solution.The mobile phase transports the resin into and through achromatography column (or set of columns connected inseries) packed with a rigid or semirigid, porous substrate thatseparates the molecules according to their size in solution. A
10、detector monitors the eluate as a function of elution volume (ortime). Upon emerging from the column(s), the fractions ofsize-separated molecules are detected and their elution vol-umes (or times) and (usually) concentrations recorded.Through calibration, the elution volumes (or times) are con-verte
11、d to apparent molecular weights, and various molecularweight parameters for the sample resin are calculated from themolecular weight/concentration data.5. Significance and Use5.1 The MW averages and the MWD are important charac-teristics of a resin. They may be used for a variety ofcorrelations for
12、fundamental studies, processing, or productapplications. The MW and MWD values may also be used forproduction quality control of resins.5.2 LimitationsComparison of SEC molecular weight val-ues should be made only if the data were obtained underidentical chromatographic conditions.6. Apparatus6.1 So
13、lvent ReservoirThe solvent reservoir must holdsufficient solvent to ensure consistency of composition for anumber of analyses. The reservoir should isolate the solvent1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications and is the d
14、irect responsibility ofSubcommittee D01.38 on Hydrocarbon Resins.Current edition approved Nov. 1, 2006. Published November 2006. Originallyapproved in 2000. Last previous edition approved in 2000 as D 6579 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Custom
15、er Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,
16、PA 19428-2959, United States.from the atmosphere, permit control of the environment incontact with the solvent, and be inert to the solvent employed.Some means of agitation (for example, magnetic stirring) isrecommended to ensure uniform composition.6.2 Solvent Pumping SystemThe principal requiremen
17、t ofthe pumping system is production of a relatively constant andpulseless flow of solvent through the columns. In general, therate of flow should be adjustable between 0.1 and 5.0 mL/min,and back pressures should not exceed limits specified by thecolumn manufacturer. If the elution volume is not be
18、ingmeasured directly or corrected for systematic changes, theprecision in the flow rate must be at least 60.3 % under theconditions and over the time interval required for running atypical analysis.6.3 Sample InjectorThe purpose of an injection system isto generate a sharply defined zone of solution
19、 containing theresin when introducing the resin into the flow stream. Avalve-and-loop assembly or any of a number of commerciallyavailable high-performance liquid chromatography automaticinjection systems can be used for this purpose. It is requiredthat contribution to band spreading be minimal and
20、that theinjector be able to operate at the back pressure generated by thecolumns.6.4 ColumnsStainless steel columns with uniform andhighly polished inside walls should be used. Columns withlengths ranging from 15 to 50 cm, plus special end fittings,frits, and connectors designed to minimize dead vol
21、ume andback-mixing are recommended. Micro-particulate, semirigidorganic gels, and rigid, solid, porous packing materials areused for SEC. Generally, the packing materials have narrowparticle size distributions, with particle sizes in the range from3 to 20 m. Packing materials are available in a vari
22、ety ofshapes and pore sizes. Columns may be packed with particlesof relatively uniform pore size or with a “mixed bed” ofparticles to produce a broad range of pore sizes for polymerseparation. If a set of columns is used, it is recommended thatthe columns be connected, starting from the injector out
23、let,from columns having the smallest to those having the largestpacking pore size.NOTE 2Select the number of columns and pore sizes based on themolecular weight range of the resins being analyzed, and on the degree ofresolution required.6.5 DetectorsThe purpose of the detector is to continu-ously mo
24、nitor the concentration of solute eluting from thechromatographic column(s). Consequently, the detector mustbe sufficiently sensitive and respond linearly to the soluteconcentration. Additionally, the detector must not appreciablydistort the concentration gradient in the emerging stream. Thisrequire
25、ment imposes severe limitations on the volume ofsolution available for detection. For example, use of detectorswith cell volumes greater than 15 L generally will not beacceptable for this practice. A differential refractometer hasmoderate sensitivity and general utility. The differential refrac-tome
26、ter provides a signal proportional to the difference inrefractive index (RI) between the solvent and the columneluate. The detector should respond to a change of no morethan 107to 108RI unit and have a cell volume#10 L. Othertypes of detectors may be used.NOTE 3The principal disadvantage of the diff
27、erential refractometer isthat precise control of temperature, pressure, and flow rate is required tomaintain a stable signal for an appropriate level of sensitivity. Forexample, most organic liquids have a temperature coefficient of 104RIunits per K. Consequently, the temperature within the RI detec
28、tor cellmust be controlled to within 104C.6.6 Tubing and FittingsAll tubing between the sampleinjector and the detector should be no greater than 0.25 mm(0.010 in.) in internal diameter and of sufficient thickness foruse at pressures up to 42 MPa. Connecting tubing should bekept as short as possible
29、, and all fittings and connectors mustbe designed to prevent backmixing and to have low deadvolumes.6.7 Data Handling SystemsMeans must be provided fordetermining chromatographic peak heights or integrated areasegments at prescribed intervals under the chromatogram andfor handling and reporting the
30、data. This can best be accom-plished by means of a computer or a real-time data acquisitionsystem with either off-line or on-line data processing.NOTE 4Data acquisition and handling systems for SEC have not beenstandardized. However, a number of manufacturers provide chromatogra-phy data systems tha
31、t include SEC software. Also, some users havedeveloped their own specialized software.6.8 Recorder/Plotter (OptionalEither a recording poten-tiometer or a printing device connected to a data handlingsystem may be used to plot the chromatographic data. Penresponse and signal-to-noise ratio should be
32、chosen so that theconcentration signal is not appreciably perturbed.6.9 Other Components (Optional)Special solvent linefilters, pressure monitors, pulse dampers, flowmeters, thermo-stated ovens, syphon counters, plotters, raw data storagesystems, software, and so forth, are often incorporated with t
33、heessential components previously listed.6.10 The interrelationships of the components are shownschematically in Fig. 1. Use of a degasser located in the solventreservoir or between the reservoir and pumping system isrecommended to remove air from the solvent.6.11 Analytical Balance, sensitive to 60
34、.0001 g.7. Reagents and Materials7.1 Low-MW StandardsLow-MW compounds, such astoluene, xylene, or o-dichlorobenzene, that are used for deter-mining plate count, or as internal standards, must be of highpurity.7.2 Polystyrene StandardsUnimodal, narrow, MW stan-dards that bracket the desired range of
35、the resins beingcharacterized. Selection of a minimum of three standards perdecade in molecular weight spanning the effective molecularweight range of the column set is recommended.7.3 Solvent-Tetrahydrofuran (THF)Stabilized, high pu-rity. Depending on the detector used, ultraviolet (UV) gradeTHF ma
36、y be required, however, caution should be used due tothe risk of peroxides in unstabilized THF.8. Preparation of Apparatus8.1 AssemblyThe SEC system shall be assembled asshown in Fig. 1 and readied for operation. For commercial SECsystems, follow the manufacturers guidelines and recommen-dations for
37、 assembly and operation.D65790628.2 TemperatureAn operating temperature is not specifiedin this practice. However, precise control of the temperature ofthe components (injection loop, column(s), detector, and con-necting tubing) is critical for controlling the reproducibility ofthe SEC molecular wei
38、ghts and will significantly reducebaseline drift. In addition, the temperature of the previouslymentioned internal components during an analysis must bewithin 3C of their temperature at calibration.8.3 Flow RateFollow the column and instrument manu-facturers recommendations when selecting a flow rat
39、e andstarting the solvent pumping system. A flow rate of 1 6 0.1mL/min is suggested, with the pumping system adjusted todeliver a relatively constant and pulseless flow of eluent fromthe detector outlet. Flow rate may be measured by determiningeither the volume or weight of solvent eluted over a suf
40、ficientlylong period of time and under suitable conditions to guaranteea precision of at least 60.3 %. Alternatively, an internalstandard or control may be used to monitor flow rate. Flowrates must be determined during calibration and before or aftereach analysis.8.4 DetectorDetector settings should
41、 provide optimumsensitivity for solute detection without causing undue baselinenoise or overloading of the output signal.8.5 Data Handling SystemUsers are advised to follow therecommendations of their computer or data system manufac-turer for setting data acquisition and integration parameters.9. Pr
42、eparation of Solutions9.1 Polystyrene StandardsThe typical concentrationrange for polystyrene standards is from 0.2 to 1 mg/mL.Prepare solutions by weighing an aliquot of the standard into asuitable clean, dry, solvent-resistant stoppered flask or screw-capped vial, then add an appropriate amount of
43、 solvent fromthe mobile phase reservoir. Dissolve the standard at roomtemperature. Do not stir or filter the solutions. Mixtures of twoor more narrow MWD polymer standards may generally beprepared in the same flask. The standards selected for eachsolution should differ in Mw values by a factor of 10
44、 or greater.However, it is recommended that any higher MW polymerstandards (MW 800 000 g/mol) be prepared as single, moredilute solutions to reduce problems relating to polymer size insolution and concentration during calibration.NOTE 5Low-molecular weight standards may be resolved into dis-tinct ol
45、igomeric components on high-resolution column sets. In such case,see the information supplied by the manufacturer for assigning theapproximate molecular weight to each oligomer peak.9.2 Reference StandardThe same procedure as describedin 9.1 can be used to prepare dilute solutions (0.1 % w/v) oflow-
46、MW materials such as toluene, xylene, oro-dichlorobenzene for determining the column plate count orfor use as an internal standard.NOTE 6Alternatively, the dissolved oxygen peak may be used as thereference standard.9.3 Resin SamplesThe typical concentration range forresin solutions is from 0.2 to 1
47、mg/mL. Solutions are preparedas described in 9.1, dissolving with a minimum of agitation.Magnetic stirring devices or laboratory shakers may be used toaid dissolution, however, excessive shear, temperature orultrasonic devices may cause the polymer to degrade, andtherefore must not be used with this
48、 practice. It is a goodpractice to analyze the resin solutions within 24 h of theirpreparation.9.4 FiltrationIt is recommended that all resin solutions befiltered through membrane filters to remove any materialslikely to obstruct the columns and other system components.Membrane filters with pore siz
49、es in the range from 0.2 to 0.5m are recommended. (The membrane pore size must notexceed 5 m.) The filters must be inert to the solvent and notbecome clogged during filtration.NOTE 7Filtration often reveals the presence of gel in solutions eventhough the solutions appear clear to the eye, as is the case with manymicrogels. During filtration, gel particles are likely to plug the pores of thefilter, noticeable by an excessive pressure needed for filtration. If such anFIG. 1 Schematic of a SEC SystemD6579063obstruction occurs, the soluble porti
