1

 

Certification of the Relative Molecular Mass and the Intrinsic Viscosity of SRM 

2885, a Polyethylene 

C. M. Guttman, J. R. Maurey, W.R. Blair, and C. R. Schulteisz

Polymers Division

NIST

Gaithersburg, MD 20899

Certain commercial materials and equipment are identified in this paper in order to specify 

adequately the experimental procedure. In no case does such identification imply 

recommendation or endorsement by the National Institute of Standards and Technology, nor does 

it imply necessarily the best available for the purpose.

According to ISO 31-8, the term "Molecular Weight" has been replaced by Relative Molecular 

Mass, symbol Mr. Thus, if this nomenclature and notation were followed in this publication, one 

should write Mr,w instead of the historically conventional Mw for the weight average molecular 

weight with similar changes for Mn, Mz, and Mv. Mw would be called the "Mass Average 

Relative Molecular Mass." The conventional notation, rather than the ISO notation, has been 

used in this publication.

Final report prepared for the sponsors, the NIST Standard Reference Materials Program (SRMP).
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ABSTRACT

The certification of a polyethylene standard reference material, SRM 2885, is described. The Mw

of SRM 2885 by light scattering was determined to be 6.28x10+3 g/mol with a sample standard 

deviation of 0.39x10+3 g/mol. A combined expanded uncertainty for this light scattering Mw 

determination, including systematic and random uncertainties, was estimated to be 0.56x10

+3

g/mol. The intrinsic viscosity of SRM 2885, by solution viscosity, in 

1,2,4-trichlorobenzene was determined to be 22.3 mL/g with a sample standard deviation of

0.17 mL/g. A combined expanded uncertainty for this intrinsic viscosity determination, 

including systematic and random uncertainties, was 0.20 mL/g. The bottle-to-bottle variation of 

the SRM was checked by size exclusion chromatography (SEC) and found to be negligible.
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1.0 Introduction

This report describes the certification of the Mw by light scattering and intrinsic viscosity (often 

called the limiting viscosity number [1]) in 1,2,4-trichlorobenzene (TCB) at 130 °C of a linear 

polyethylene, SRM 2885. The material was obtained from fractionating SRM 1475, as described 

previously [2]. In the early 1970's, some of this fractionated material was used in the preparation 

of SRM 1482, SRM 1483, and SRM 1484. Other fractions from the separation had been stored in 

the Polymers Division in the intervening years. From this material three new narrow mass 

fraction SRMs are being certified. This reports describes the cleanup, the Mw by light scattering 

and the intrinsic viscosity measurements on one of these fractions, a low molecular mass 

polyethylene. Bottle-to-bottle homogeneity on the final packaged material was determined by 

size exclusion chromatography (SEC).

2.0 Preparation, Bottling, and Handling of SRM 2885 

2.1 Preparation of the SRM

The Mw standard, SRM 2885, is a fraction of SRM 1475. The fractionation was described in 

reference [2]. Fractions of SRM 1475 that had nearly the same SEC trace were combined to 

obtain enough material for the SRM 2885. The fractions contained both fine powders and larger 

aggregates and some dirt particles were evident, as well a slight yellowing. It was evident that 

these fractions needed to be cleaned by recrystallization from solution prior to certification. This 

process is described in section 2.1.1. Details of the recrystallization procedure and apparatus are 

given in Appendix I of reference [3].

Subsequent to recrystallization from solution as fine powders the material was sieved together 

through a sieve with 1.65 mm openings (C E Tyler, Mentor Ohio, 10 meshes to the inch) and 

then well mixed dry in a stainless steel tray 30 cm x 50 cm. SEC was performed on samples 

taken from different positions in this tray to confirm the adequacy of mixing. The contents of the 

tray were sent to NIST Standard Reference Materials Program (SRMP) for packaging.

2.2 Packaging and Sampling of SRM 2885

Of the approximately 240 g of purified material approximately 200 g was packaged in about 620 

amber vials containing about 0.3 g each. In the following report, the containers holding SRM 

2885 will be referred to as vials. The remaining polymer was divided into two lots, designated 

division 1 supply and division 2 supply. These large lot samples were used to supply some of the 

material used in the light scattering and intrinsic viscosity measurements. Prior to the use of 

material from these division supply lots, however, we ascertained that these samples were 

identical to the material in the vials (See Section 2.3).
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The entire set of SRM 2885 vials was divided into 12 subsets of 51 or 52 vials. One vial was 

randomly selected from each subset of SRM 2885 for homogeneity testing. The first and last 

bottled vials were also taken. These vials and the two division supply lots were used in the SEC 

homogeneity testing described below. All these materials were used in the light scattering 

determinations and intrinsic viscosity determinations described in later sections.

2.3 Homogeneity Testing

Homogeneity testing was accomplished using SEC. In this study, a Waters 150-C ALC/GPC 

Liquid Chromatograph (Waters Corp., Milford, MA) with a differential refractive index (DRI) 

detector and three Waters styragel columns, HT-6, HT-4, and HT-3, were used. The 

chromatograms were taken at 0.8 mL/min solvent flow rate. The injector and column 

compartments of the Waters 150-C ALC/GPC were controlled at 130 oC for all measurements. 

The solvent, 1,2,4-trichlorobenzene (TCB), was obtained from Aldrich Chemical (1,2,4-

trichlorobenzene, 99+ %, spectrophotometric grade, Aldrich Chemical, Milwaukee, WI) and used 

as received. Santonox (5-tert-Butyl-4-hydroxy-2-methylphenyl sulfide), also obtained from 

Aldrich Chemical, was added to the solvent at about 0.1 g/L as an antioxidant. 

Vials of SRM 2885 were obtained from SRMP as described above. Polymer from the two 

division supply lots was also included in this test. A mass of 4.0 mg to 6.0 mg of the 

polyethylene was weighed into the 4 mL SEC glass vial with a Teflon septum in the cap 

assembly along with 4 mL of solvent yielding a concentration of approximately 1.0 g/L. No 

filtering was done on these samples as the purification done above produced a quite clean 

sample. Hexadecane, at 0.03 mL/L, was added to the solutions of polymer and solvent as a 

marker to indicate the reproducibility of the solvent volume delivered by the SEC pump for all 

measurements. Each SEC glass vial was heated to 150 oC in an oven for about 1.5 h and the 

solution was shaken at frequent intervals to aid the dissolution. The filter assemblies were placed 

in the Waters 150-C ALC/GPC injection compartment held at 130 oC . Chromatograms were 

then run with these solutions.

Solutions were prepared from each vial of SRM 2885 and from each of the division supply lots. 

Two solutions were prepared from each vial selected from those received from SRMP and four 

solutions were prepared from each division supply lot. The order used to run the solutions was 

randomized following the method described in section 1-4 of the handbook by Natrella [4]. Two 

injections were made from each solution. Because of difficulties with the instrument a few 

solutions had to be run twice. All chromatographic data were obtained during a five-day period, 

with 8 solutions measured per day.

After baseline subtraction, the SEC chromatograms were normalized to unit peak height and 

compared initially by overlaying to determine if there were visible differences outside the noise. 

We found both the pump peaks and the peak attributed to SRM 2885 shifted slightly over the 
5

period during which we ran the experiment. This indicated variation in the pump during the run. 

A simple lining up of the pump peak showed that the chromatograms from different solutions of 

SRM 2885 superimpose fairly well on each other. For further data analysis the elution volume 

from each chromatograms for the SRM 2885 were shifted by the amount of the pump peak shift. 

Further statistical analysis of the chromatograms is discussed in section 2.3.1

2.3.1 Statistical Method to Compare Chromatograms 

2.3.1.1 Match Factor

In previous SEC studies on SRM homogeneity, the match factor was used to compare one 

chromatogram to all others [5]. The match factor is a correlation coefficient between one 

chromatogram and another. The match factor is defined by Huber [6] as

Match Factor = 103 {3x*y-(3x*3y)/p}2/[{3x

2

-3x*3x/p}{3y

2

-3y*3y/p}] (1)

The values x and y are the measured signal in the first and second chromatograms, respectively at 

the same time in the chromatograms; p is the number of data points. The sums are taken over all 

data points. 

At the extremes, a match factor of zero indicates no match and 1000 indicates identical 

chromatograms. Generally, values above 990 indicate that the chromatograms are similar. 

Values between 900 and 990 indicate there is some similarity, but the result should be interpreted 

with care. All values below 900 are thought to mean that the chromatograms are different [6,7]. 

The method we describe here has been used previously [8]. We obtained the match factor of the 

entire set of chromatograms, which include two injections for each solution prepared, against the 

average chromatogram. In the following discussions we will compare chromatograms against the 

average chromatogram. 

An ANOVA study, using OMNITAB [9], was made on the match factors obtained from the 

chromatograms. It indicated that the match factors for the chromatograms from the same vial 

were no different than those from different vials on a level of significance with α = 0.05 [10]. 

Moreover, the match factors of chromatograms from the two division supply lots and the vials 

were indistinguishable using the same significance level with α = 0.05. The samples were run in 

groups of 10 on different days. Using the match factor we found that chromatograms showed no 

day to day variation. The same statements can be made for the match factor for the pump peaks. 

 .

From this we conclude that there is no statistically significant difference between the contents of 

vials sampled from the SRMP supply of SRM 2885 and no difference between the SRMP supply 

and the two division supply lots.

3.0 Estimation of Impurity Peaks and Polydispersity Index of SRM 2885
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SEC measurements described in the Section 2.3 were used to estimate the polydispersity index 

(PD). We used the solvents as described in Section 2. Columns for this part of the work were two 

Waters Styragel HT-6E and one Waters Styragel HT-2 (Waters Corp., Milford, MA). The 

instrument used for this work was a Waters Alliance GPCV 2000 (Waters Corp., Milford, MA), 

which is equipped with a differential refractive index detector (DRI) and a viscosity detector. 

Columns were calibrated with SRM 1482, SRM 1483, SRM 1484, SRM 1475, SRM 2885, SRM 

2886, and SRM 2887. From the SEC curves for SRM 2885 we estimated the PD (PD = Mw /Mn) 

to be 1.13. No effects of column broadening were taken into account in this measurement, so we 

expect the value of 1.13 to be an overestimate of the PD. 

In a separate calculation, we tried to take the effects of column broadening into account using the 

Waters Corporation Millennium Software (Waters Corp., Milford, MA) . Using their Axial 

Dispersion Calculation with peak compression, we found a PD of 1.09. 

We should note that while using the viscosity detector of the Waters Alliance system we saw a 

shoulder on the high molecular mass edge of the SRM 2885 signal. We call this peak the minor 

component. From the elution volume assigned to the shoulder, we judged the minor component 

molecular mass to be about 72 x 103 g/mol. There is little or no signal from the DRI detector in 

this range aside from the expected main peak upsweep, which explains why we initially did not 

see this peak using the older Waters 150-C ALC/GPC, which had only a DRI detector. 

From a study of 9 chromatograms of this material, we estimated, using data from the Alliance 

DRI detector, the area attributable to the minor component. The area attributable to the minor 

component on the chromatograms gave an estimate of the mass fraction of 0.36% to a mass 

fraction of 0.61% with an average mass fraction of 0.46%. Thus, we take 0.6 % as the upper 

limit of the maximum fractional mass in the minor component. The Mw measured by light 

scattering will, of course, include the minor fraction.

 Mw-LS = (1-f ) Mw-main + f Mw-minor 

where Mw-LS is the mass averaged molecular mass from light scattering, Mw-main is the mass 

averaged molecular mass of the main SRM 2885 peak, Mw-minor is the mass averaged molecular 

mass of the minor component, taken to be 72 x 103 g/mol, and f is the mass fraction of signal in 

the minor component. We can then estimate the main peak Mw-main as

 Mw-main = (Mw-LS - f Mw-minor)/(1-f)

Using our estimate of Mw-minor and f we calculate the value of 

 Mw-main = 5880 g/mol.

The maximum error in taking the measured light scattering mass average molecular mass, Mw-LS, 

as the estimation of the Mw-main is 400 g/mol, less than our estimated overall uncertainty in the 
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light scattering mass average molecular mass, Mw-LS.

4.0 Intrinsic Viscosity of SRM 2885 

4.1 Measurement of the Intrinsic Viscosity

 

Viscosity measurements were made with a Schott-Gerate Ubbelohde micro-viscometer (SchottGerate GMBH, Hofheim, Germany) with a Schott-Gerate constant temperature bath held at 

130 oC. Flow times were measured by the Schott-Gerate AVS 400. The solvent, 1,2,4-

trichlorobenzene (TCB), was obtained from Aldrich Chemical (1,2,4-trichlorobenzene, 99+ %, 

spectrophotometric grade, Aldrich Chemical, Milwaukee, WI) and used as received. Butylated 

hydroxytolulene (2,6-Di-tert-butyl-4-methylphenol), also obtained from Aldrich Chemical, was 

added to the solvent at about 0.7 g/L as an antioxidant.

Solution concentrations ranging from 0.2 g/L to 2 g/L were prepared from independent weighing 

of polymer and solvent, rather than employing successive dilution techniques. Concentrations 

were calculated from densities and partial specific volumes determined earlier in this laboratory 

[11]. 

The polymer was dissolved by heating the mixture to 135 oC to 140 oC in a hot air oven with 

occasional stirring. Solutions were then transferred to a viscometer by filtering the solution 

though a syringe and syringe filter heated in the same oven. The syringe filter assembly used was 

a Swinny Stainless 25 mm (Millipore Corp., Bedford, MA) while the filter membrane was a PallGelman Sciences ZEFLOUR all Teflon 0.5 μm pore size 25 mm diameter membrane (Pall Corp., 

Port Washington, NY).

For each polymer concentration, flow times were measured for both solvent and solutions. The 

AVS 400 is designed to perform a number of preconditioning runs to insure that the solution or 

solvent comes to temperature equilibrium before the actual measurements were made and 

recorded. The operation of the AVS 400 took about 2 min to 2.5 min for each of the five 

preconditioning runs. Five flow times were measured on each aliquot of the solvent or the 

solution. Flow times measured in this viscometer ranged from 40 s to 60 s.

At the beginning of an overall measurement on a solution, the viscometer was flushed with at 

least three solvent aliquots. Then, at least two aliquots of solvent were introduced for flow time 

measurements. Three aliquots of solution were used to flush the viscometer. Three aliquots of 

solution were then measured. Three aliquots of solvent were used to flush the viscometer. 

Finally, flow time measurements were made on three aliquots of solvent.

4.2 Results of Solution Viscosity

The solution viscosity, η(c), may be expanded as a power series in solution concentration, c, 
8

[12] 

η(c) = η(0) (1+ a1c+a2 c

2

 + ...) (2)

where η(0) is the solvent viscosity.

The viscosity is defined as

(η(c) - η(0))/( η(0) c) = a1 + a2 c (3)

The intrinsic viscosity, [η] = a1, is the zero concentration limit of the viscosity.

 

For a properly designed capillary viscometer, the solution viscosity is almost proportional to the 

product of the solution density, ρ(c), and the measured flow time, t(c). The deviation from 

proportionality is due to a combination of kinetic energy effects and hydrodynamic effects at the 

end of the capillary. The manufacturer of the viscometer gives tables to correct the measured 

times for each viscometer. These corrections, designated by the manufacturer as the Hagenbach 

correction [13], are approximately of the form 1/tm

2

, where tm is the measured time. The 

manufacturer’s corrections were fitted to this form to interpolate their correction data. This 

correction is applied to each average flow time for solvent or solution yielding t(c) where the c 

refers to the concentration of the solution being measured.

From eq. 2 then

K ρ(c)t(c)= K ρ(0)t(0)(1+ a1 c+a2 c

2

.....) (4)

where the solvent viscosity is 

η(0) = K ρ(0)t(0) (5)

and where K is the viscometer constant.

Finally, we do not need to know K since the quantity of interest is the limiting value of 

[η] = (η(c)- η(0))/(η(0) c) = a1 (6)

Thus, we may rewrite eq. 4 as 

ρ(c) t(c) = ρ(0)t(0) (1 + a1 c + a2 c

2

...) (7)

On any given day measurements on only one concentration and related solvents as described 
9

above were practical. As viscometers became dirty, they were taken out of service and similar, 

but not identical, clean ones used in their place. Thus, the ratio, T(c), is expected to be invariant 

at any concentration where T(c) is

T(c) = (ρ(c)t(c)- ρ(0)t(0))/(ρ(0)t(0)) (8)

Following the normal definition of [η] as the zero concentration limit of T(c)/c , we fit T(c)/c 

to the expression

T(c)/c = a1 + a2 c. (9)

The value of a1 so obtained was 22.3 mL/g with a standard deviation of 0.17 mL/g. For our study 

of uncertainty, we consider the value of the standard deviation reported above to be the 

expanded uncertainty in the repeatability of the measurement. This is reported in Table 1 with 

other contributions to the reported uncertainty of this measurement.

Earlier, Wagner and Verdier [12] studied other fractions of the same base material, SRM 1475, 

certified as SRM 1482, SRM 1483 and SRM 1484. They measured and reported intrinsic 

viscosities in TCB on these materials. Fitting their data for the intrinsic viscosities, [η], of SRM 

1482, SRM 1483 and SRM 1484, we obtain

lne { [η]w } = 0.7312 lne{Mw }- 3.247 (11)

where [η]w is their measured intrinsic viscosity.

Using the Mw of our polymer obtained in Section 5, we estimate a extrapolated value of [η]w 

from eq. 11 for SRM 2885 of 23.3 mL/g, in good agreement with our measured value. 

4.3 Estimating Uncertainties in the Intrinsic Viscosity Measurement

 

The likely sources of uncertainty are discussed in the following subsections and the table referred 

to herein. For this analysis, we largely follow the paper of Wagner and Verdier [12]. 

4.3.1 Shear Rate Dependence of Viscosity

Low molecular mass polymers in dilute solution are expected to show little, or no shear rate 

dependence. Wagner and Verdier [2] were unable to detect shear rate dependence, even for SRM 

1484, a linear polyethylene with an Mw of 114,000 g/mol. The capillary in their viscometer had a 

smaller diameter than that in the Schotte-Gerate viscometer we are using. Thus, we expect no 

shear rate dependence of the intrinsic viscosity of SRM 2885, which has a lower mass average 

molecular mass that SRM 1484. We assume the uncertainty introduced in the intrinsic viscosity 
10

by disregarding this contribution is zero.

4.3.2 Solution Concentration and Density

According to Wagner and Verdier [12], their reported value of ρ(0) has an estimated relative 

expanded uncertainty of 0.2 % . We used their values ρ(0) in our calculations. The solvent 

density uncertainty leads to 0.05 mL/g expanded uncertainty in intrinsic viscosity. Wagner and 

Verdier [12] estimated a relative uncertainty 0.03 % in intrinsic viscosity due to the disregard of 

the buoyancy correction. Since we corrected for buoyancy, we take this uncertainty to be less 

than 0.01 %, or negligible. 

All solutions but one were prepared so that at least 100 mg SRM 2885 was used. For the 

remaining solution 100 mg of SRM 2885 was used. We estimated that the balance used for this 

measurement had an expanded uncertainty of less than 0.1 mg. For those solutions where at least 

100 mg was used, we estimate a 0.1 mg expanded uncertainty due to weighing would lead to an 

expanded uncertainty of 0.003 mL/g, which is negligible.

Solvent masses were measured with an expanded uncertainty of 0.01 g. A minimum of 30 g of 

solvent was used. This uncertainty had negligible effect on the results and so was taken to be 

zero.

4.3.3 Specific Volume of the Polymer

The intrinsic viscosity, [η], is the limit of

[η] = L {(ρ(c)t(c)- ρ(0)t(0))/(ρ(0)t(0)c)} (12)

where L { } is taken to mean the limit at zero concentration. Following Wagner and Verdier 

[12] using the fact that the limit of the product is the product of the limit, they find

[η] = ρ(0)-1(1+2K'/tm(0)+3)/(1-K'/tm(0)+3) * L {(tm(c)-tm(0))/(tm(0)w)}+ρ(0)-1-vavg

 (13)

where w is the mass fraction of solute in the solution and K' is the kinetic energy term derived 

from corrections given by the viscometer manufacturer [13]. 

This formula corrects a typographical error in their formula 11. The formula shows that the 

intrinsic viscosity as made up of two terms if we disregard the kinetic energy (KE) corrections of 

the viscometer. Assuming these KE corrections are zero we get then
11

[η] = ρ(0)-1 L {(tm(c)-tm(0))/(tm(0)w)} + ρ(0)-1-vavg (14)

The last two terms are the difference between the specific volume of the solvent, ρ(0)-1 , and the 

specific volume of the polymer in solution, vavg. This difference is small, about a few tenths of 

an mL/g, compared to an overall intrinsic viscosity of about 22.4 mL/g for this polymer. Since 

vavg was determined on other fractions of this polymer previously [11,12], we estimate that our 

value of vavg has an uncertainty of no more than 0.04 mL/g. Thus, we take 0.04 mL/g to be the 

expanded uncertainty in intrinsic viscosity from this contribution.

4.3.4 Timer Uncertainties

Individual flow times were recorded to 0.01 s. We take this to be the expanded uncertainty of the 

timer measurements. Since the intrinsic viscosity is the ratio of the time differences over a time, 

only the uncertainty in the time in the denominator is important. Since total flow times were 

between 40 s and 60 s, a 0.01 s timer uncertainty would cause an expanded uncertainty of no 

more than 0.01 mL/g. 

4.3.5 Kinetic Energy or Hagenbach Corrections

As noted above, kinetic energy, or Hagenbach, corrections were estimated from tables given by 

the viscometer manufacturer [13] and obey a G/t(c)2 law. The value of G estimated from the 

manufacturer’s table is 412 s3 for our viscometer. We take our value of G to have a relative 

expanded uncertainty of 20 %, twice that assumed by Wagner and Verdier [12] for their value of 

G. This leads to an expanded uncertainty of 0.07 mL/g in the intrinsic viscosity of SRM 2885.

If we do not consider kinetic energy corrections to the measured data, we compute the apparent 

intrinsic viscosity different from the measured intrinsic viscosity of 0.33 mL/g. If we take 20 % 

of this difference as a measure of the uncertainty, this result is consistent with the expanded 

uncertainty estimated above.

4.3.6 Uncertainties Arising from Temperature Uncertainties

Wagner and Verdier [12] estimate the relative temperature dependence of the intrinsic viscosity 

of polyethylene to be no more than 0.2 % / oC for polyethylene in theta solvents. The temperature 

dependence is expected to be less in TCB, which is a good solvent for polyethylene. Following 

Wagner and Verdier, we take 1 %/ oC as the outside limit of the temperature dependence of 

intrinsic viscosity. We believe the Schott-Gerate constant temperature bath controls the 

temperature much better than 0.3 oC, including effects of temperature gradients. This conclusion 

arises partly because we have a reproducibility of better than 0.10 s out of about 41 s for the 
12

solvent flow times taken over a period of weeks. Further, we found a 1 oC change in temperature 

altered the measured flow time of the solvent by 0.32 s. Thus, we take 0.07 mL/g as the 

expanded uncertainty from the temperature.

4.3.7 Estimated Combined Expanded Uncertainty

In Table 1, the estimated expanded uncertainties from all sources are listed. Following NIST 

guidelines [15] we obtain the combined expanded uncertainties as the root sum of squares of 

these quantities. 

5.0 Determination of Mw of SRM 2885 by Light Scattering 

5.1 Solvent Preparation for Light Scattering and for Specific Refractive Index Increment

The light scattering solvent, 1-chloronaphthalene, was purchased from Aldrich Chemical 

(Aldrich Chemical, Milwaukee, WI ). According to the supplier, this 1-chloronaphthalene was 

90 % pure with 2-chloronaphthalene as the only detectable impurity. A two-step purification 

method described in Appendix II of reference [3], involved crystallizing out the 2-

chloronaphthalene followed by vacuum distillation of the 1-chloronaphthalene.

The antioxidant Santonox, 3-tert-Butyl-4-hydroxy-2-methylphenyl sulfide (Aldrich Chemical, 

Milwaukee, WI), was added to the purified 1-chloronaphthalene in order to protect the 

polyethylene from oxidative degradation during the high temperature light scattering experiments 

and differential refractive index determinations. The antioxidant was dissolved in the 1-

chloronaphthalene at a concentration of 0.1 g/L at 130°C.

The 1-chloronaphthalene was sparged with dry nitrogen gas for a few hours immediately before 

adding solvent to polymer samples in preparing solutions to conduct experiments. The nitrogen 

sparging was used to minimize residual oxygen content in the solvent. 

Solvent recovered from light scattering experiments was recycled. After the solutions had been 

allowed to cool and the polymer had separated out, the recovered material was drained through a 

filter. The collected solvent was redistilled by the process described in Appendix II of reference 

[3]. Since the 2-chloronaphthalene impurity had already been removed exhaustively from such

recovered solvent earlier, the preparatory refluxing process to remove the isomer was omitted.

5.2 Determination of Specific Refractive Index Increment

5.2.1 Instrumentation 

The specific refractive index increment (dn/dc) for SRM 2885 was determined using a 
13

Chromatix KMX-16 (Thermo-Separation Products, Sunnyvale, CA) differential refractometer. 

The refractometer light source was a helium-neon (He-Ne) laser operating at a wavelength of 

632.8 nm. For room temperature calibration, the measurement cell was controlled at 25 °C. The 

measurement cell was heated to 130 °C for the solution and solvent measurements.

5.2.2 Calibration of Instrument at Room Temperature

The differential refractometer was calibrated with aqueous NaCl solutions at 25 °C. Kruis [16] 

reported refractive increments versus concentration for several aqueous electrolyte solutions at 

several wavelengths of light. Refractive increments for the same solutions at the He-Ne laser 

wavelength, 632.8 nm, have been determined from interpolation of the data in the Kruis’ tables 

[16,17]. A cubic equation for these refractive increments as a function of NaCl concentration in 

aqueous solution at 25 °C is given in the instrument manual, and was used to compute the 

refractive increments of the aqueous NaCl solutions prepared as standards for calibrating the 

differential refractometer.

Analytical reagent NaCl (Baker and Adamson, Allied Chemical and Dye Corp, New York, NY) 

was dried in a hot air oven for approximately 18 h at a temperature of 140 °C in preparation to be 

used as a calibrant. Distilled water was degassed by boiling and left to cool to ambient 

temperature overnight in storage bottles tightly capped with zero headspace. The storage bottles 

had been leached out with several changes of boiling distilled water before being used to contain 

the degassed distilled water. Both salt and water components of each solution were measured 

gravimetrically, and atmospheric buoyancy corrections were applied to compute the 

concentrations as g NaCl/100 g H2O.

Following instructions in the instrument instruction manual [17] calibration measurements for 

the differential refractometer were conducted on four NaCl solutions ranging in concentration 

from 0.5 g NaCl/100 g H2O to 2.0 g NaCl/100 g H2O in intervals of 0.5 g NaCl/100 g H2O. The 

calculated refractive increments of the solutions were fitted to their average image displacements 

to generate a linear calibration equation of refractive increment versus image displacement, 

dn/dc. The instrument calibration was found to be insignificantly changed from calibrations 

made years earlier indicating that we were simply verifying an earlier calibration. In fact, the plot 

of the calibration verification points, when overlaid on an earlier instrument calibration plot, 

produced a graph in which the two data sets were indistinguishable.

5.2.3 Solution Preparation and Handling

Polymer solutions were prepared using 1-chloronaphthalene solvents with a mass fraction of 

0.01% Santonox (Aldrich, Milwaukee, WI) antioxidant. The 1-chloronaphthalene (Aldrich, 

Milwaukee, WI) was purified by distillation before use as described in Appendix II of reference 

[3]. Solution concentrations in ranges described in section 5.2.4 were made directly by weighing, 

without employing successive dilution techniques. Concentrations were calculated from densities 
14

and partial specific volumes determined earlier in this laboratory [11]. A general-purpose 

laboratory convection oven set at a temperature of approximately 145 °C was used to dissolve the 

polymer solutions. Glass bottles with ground glass necks and caps were used as dissolution 

vessels for the polymer samples. Experiments conducted earlier (private communication, R.C. 

Christensen) demonstrated that solvent loss at 130 °C through the ground glass joint was 

negligible.

Transfer of the polymer solutions from the glass dissolution vessels into the refractometer 

measurement cell was accomplished with a specially constructed glass funnel/valve assembly 

heated to approximately 145 °C. A 6.8 cm diameter Pyrex glass powder funnel was modified by 

having the barrel of a 5 mL glass luer lock syringe attached to the funnel stem. An on-off valve 

(Popper & Sons, Inc., New Hyde Park, NY) was attached to the luer fitting and a shortened 20-

gage needle attached to the valve. The funnel was placed in a heating mantle (Glas-Col, Terre 

Haute, IN) and a flexible electric heating tape (Barnstead/Thermolyne, Dubuque, IA) was 

wrapped around the stem, valve and needle that protruded below the heating mantle. The funnel 

assembly was supported by a three-jaw clamp attached to the funnel stem and an adjustable 

height rack and pinion post (Edmund Industrial Optics, Barrington, NJ). The rack and pinion 

post was lowered to position the needle in the sample cell for filling the cell with polymer 

solution and raised above the cell to provide access to the cell by suction tubing, which was used 

to empty the cell. Heating mantle and heat tape temperature were measured with a digital 

thermocouple thermometer (John Fluke Mfg. Co., Palatine, IL) and adjusted by Variac 

autotransformers (General Radio Co., Cambridge, MA). Dissolved polymer solutions were 

removed from the oven and poured from the dissolution bottle into the heated funnel. Using the 

on-off valve on the funnel stem, the refractometer measurement cell was filled with hot polymer 

solution. Following the instrument instruction manual [18], the cell was filled and emptied five 

times before measurements were made on the solution. 

5.2.4 Measurement of (dn/dc) at 130 °C 

Refractive index increments between solvent and solutions of polyethylene in 1-

chloronaphthalene were determined on solutions that had been prepared on the morning of the 

day the measurements were made. Five solutions with concentrations between 3.5 g/L to

7.2 g/L of SRM 2885 were prepared by the procedure describe in Section 5.2.2. For each solution 

two repeated image displacement measurements were conducted on these solutions of SRM 2885 

following methods as outlined in KMX 16 manual. Solvent-versus-solvent measurements were 

made before and after each solution-versus-solvent measurement. The incremental image 

displacement by each solution was obtained by subtracting the mean of the bracketing solvent 

average image displacements from the average image displacement by the solution. The 

refractive index increment of each solution was computed by application of the calibration 

equation to the incremental image displacement of the solution. The specific refractive index 

increments were obtained by dividing the refractive index by the concentration of the solution. 

The average value of the specific refractive index increment of the solutions was found to be, 

dn/dc = -0.1867 mL/g, for SRM 2885 in 1-chloronaphthalene at 130 °C with a standard deviation 
15

of 0.0014 mL/g. The issues of uncertainty and fit of this measurement will be discussed in 

section 5.10.3.

Previous reports of the differential refractive index at 632.8 nm for other comparable 

polyethylenes in 1-chloronaphthalene gave values ranging from -0.178 mL/g to -0.183 mL/g at 

135 oC [19-21]. Our value is slightly outside the range of these reported values. The molecular 

mass of the polymer is about 6000. This is in the range we expect end groups to contribute to 

dn/dc [19]. Earlier measurements on dn/dc at a wavelength of light of 546 nm on PE solutions in 

TCB and 1-chloronaphthalene showed the dn/dc getting more negative as the molecular mass 

decreases, consistent with our results [20, 21, 25]. 

5.3 Refractive Indices of Solvent and Calibrant 

The primary standard for this measurement is benzene; other standards are derived from it. The 

refractive index of the benzene primary standard at 23 oC and 632.8 nm is taken to be 

1.4941[12].

G. B. Arrowsmith, G. H. Jeffrey, and A. I. Vogel [24] tabulated the refractive index at the 

Sodium D line nD=1.63315 at 20 oC and a density at 20 oC of 1.1932 g/mL for 1-

chloronaphthalene. Christensen [11] reports the density of 1-chloronaphthalene as 1.098 g/cm3at 

130 oC and Wagner [25] reports the density of 1-chloronaphthalene as 1.098 g/cm3at 135 oC. The 

Lorentz-Lorenz molar refraction relation is used to estimate the refractive index for 1-

chloronaphthalene at 130 oC from the densities at 20 oC and130 oC and the refractive index at 20 

oC. Since the refractive index of 1-chloronaphthalene at 130 oC, nD=1.5772, is only used in the 

reflection correction to the Mw the limited accuracy of this value is acceptable.

Dow Corning 705 silicone oil is used as the vat fluid. The Lorentz-Lorenz molar refraction 

relation was applied to the refractive index at 632.8 nm at 25 oC, and the density at various 

temperatures (Dow technical consultant Gary McIntyre) to estimate the refractive index of the 

Dow Corning 705 silicone oil at 130 oC as nD = 1.516. Since the refractive index of Dow Corning 

705 silicone oil 130 oC is only used in the reflection correction to the Mw the limited accuracy of 

this value is acceptable.

 

5.4 Design of Light Scattering Instrument

Dr. Charles Han of the NIST Polymers Division designed and constructed the light scattering 

apparatus. We review here some of the details of the instrument. A Universal circular dividing 

table (Universal Vise & Tool Co.), with a center bore design, is used as the goniometer. This 

goniometer is mounted on a rigid optical table (Newport Research Corporation). A beam of 

vertically polarized incident light (wavelength = 632.8 nm) is provided by a 10 mW He-Ne laser 

(Melles-Griot) also mounted.

The goniometric axis is defined by the center of the goniometer and aligned with a tapered center 
16

bore in the goniometer. The vat housing, which contains the sample cell, is mounted on an 

aligning rod with a precision-machined taper to engage the complementary taper of the center 

bore of the goniometer. The receptacle hole for the sample cell is machined at the cylindrical 

axis in the top flange plate of the vat housing. By this arrangement the center axis of the 

cylindrical cell and the vat housing are held coincident with the goniometric axis. The intensity 

of light scattered at varied angles from the sample cell is measured by a photomultiplier in the 

receiving optics mounted on a rigid beam attached to the goniometer. 

The vat is thermostatted by a copper cylinder, which is built onto the underside of the vat housing 

cover plate, and extends down into the vat fluid. The vat temperature is controlled and indicated 

by a PID temperature controlling system, a copper constant current supplier, a four wire RTD and 

a voltage comparitor. The controlling system receives a voltage imbalance signal from a fourwired platinum resistance temperature probe in the thermostatting cylinder and the voltage 

comparitor, and sends energy to cartridge heaters in the thermostatting cylinder. When working 

at high temperatures, significant thermal gradients can develop inside the vat between the 

thermostatting cylinder and the peripheral region of the vat. Such thermal gradients were 

repressed by applying a flexible heating mantle to the external cylindrical surface of the vat 

housing, and controlling the mantle temperature at a few degrees Celsius below the experimental 

temperature. The mantle was specially constructed for this apparatus, and the control provided by 

HPS Division, MKS Instrument, Inc. (MKS Instrument, Inc, 5330 Sterling Drive, Boulder, CO 

80301).

Light scattering cells were fabricated from precision ground and polished glass tubing to uniform 

wall thickness (Wilmad Glass Co.), with both inside and outside cylindrical surfaces polished. 

The tubing is of 33 mm outside diameter and has a refractive index nD = 1.50.

5.5 Instrument Calibration Protocol at 130oC

1,2,4-trichlorobenzene (TCB) (Aldrich Chemical high purity, Milwaukee, WI) was employed as 

the working light scattering calibration standard at 130 oC. The calibration of TCB as the 

working standard is traced to the Rayleigh ratio (RV) of benzene at ambient temperature (23 oC) 

in vertically polarized incident light of 632.8 nm wavelength, determined by Kaye & McDaniel 

[26]. 

First, a Durasil optical glass rod was calibrated by comparing its scattering intensity at a 90o

angle with that of a benzene cell at the same angle, with the glass rod and benzene cell both at

21 oC. Then the vat temperature was increased to 130 oC in which environment three TCB cells 

were calibrated by comparison of their scattering intensities with that of the glass rod. The 

effective RV of the glass rod is assumed to be invariant with temperature in this range. However, 

relating the scattering intensity measurements at the two temperatures requires conservation of 

the optical alignment with change in temperature. The only significant disturbance in the optical 

alignment results from the change in refractive index of the vat fluid with change in temperature. 

This problem was solved by conducting the measurements at 21oC with the vat filled with anisole 
17

which has nD = 1.5160 at 20 oC, and conducting the measurements at 130 oC with the vat filled 

with Dow Corning 705 silicone oil which has nD = 1.516 at that temperature. 

The scattering intensities at 90o angle (I90) of the benzene standard cell and the glass rod standard 

were measured alternately at 21oC. A total of 40 such pairs of measurements were conducted 

over an interval of two days. The resulting population of experimentally determined scattering 

intensity ratios yielded an average [I90(GLASS)/I90(BENZENE)] with a relative standard 

uncertainty of 1.16 %.

A series of TCB standard cells was prepared by filtering high purity TCB into each cell through a 

double layer of Millipore cellulose acetate-nitrate membrane with 0.2 ìm pore size. Filtration of 

TCB into the cells was conducted at ambient temperature. It was found that a TCB sample could 

be maintained at the experimental temperature (130 oC) and slightly higher for at least two days 

without detectable change. A new TCB standard cell was prepared for use with each set of 

solutions during the characterization of this polymer by light scattering. The I90 of the glass rod 

standard was compared with the I90 of each of three TCB cells at 130 oC. The I90 values of the 

glass rod and the TCB cell were measured alternately. A total of 14 pairs of such I90

measurements were conducted with the glass rod and each of the TCB cells, resulting in three 

average values for the ratio [I90(TCB)/I90(GLASS)] in very close agreement. The three 

determinations resulted in a single average value for the ratio with a relative standard uncertainty 

of 0.2 %.

As small error was introduced because we measured the ratio of scattering from benzene to the 

glass cell, S, at 21 oC, not at 23 oC where the Rv was measured by Kaye and McDaniel [26]. Ehl, 

Loucheux, Reiss, and Beniot [27] have measured this temperature variation. Our measurements 

of S give us S21, the S at 21 OC. We need S23, the ratio measured with benzene and the glass rod 

at 23 OC. From Ehl, Loucheux , Reiss and Beniot [27] we estimate

S23 = 0.9946 S21

As noted earlier, Kaye and McDaniel [26] determined the value RV =12.63x10-6 for benzene 

under these optical conditions, with a standard uncertainty of 0.21x10-6. The product of ratios, 

[I90(GLASS)/I90(BENZENE)] and [I90(TCB)/I90(GLASS)] gave a value of S21. This was applied 

to the RV for benzene by Kaye and McDaniel to estimated working value of RV=35.6 x10-6 for 

the TCB at 130oC in vertically polarized incident light of 632.8 nm wavelength. The standard 

uncertainty for this value of S21 is computed as the root sum of squares of the standard 

uncertainties of the two ratios.

The molecular mass (Mw) of the polyethylene standard SRM 1483 was determined to test this 

method of calibration using TCB as the working standard in light scattering experiments. The 

resulting Mw from these experiments conducted with TCB as the calibrating standard were 

statistically indistinguishable from the certificate value of the Mw for SRM 1483 [2]. 

 
18

5.6 Solution Preparation

SRM 2885 samples from the SRMP vials were weighed on an OHAUS GA200D analytical 

electrobalance (Ohaus Corp., Florham Park, NJ), with 0.0001 g resolution, and transferred to 

sample bottles. All polymer samples weighed 30 mg or greater in order to repress relative 

uncertainty in the sample mass. The 1-chloronaphthalene was sparged for 2 h with dry N2 gas. 

The sparged solvent was then measured into bottles containing the polymer samples, plus two 

empty bottles to contain solvent samples. The solvent mass was determined by mass difference 

on a Mettler PE 3600 electrobalance (Mettler Toledo, Columbus, OH). Atmospheric buoyancy 

corrections and densities of solvent and polymer were applied to calculate absolute solution 

concentrations at the experimental temperature. Both balances were checked during the 

certification period often by a NIST calibrated 50 mg mass for the Ohaus balance and a NIST 

calibrated 50 g mass for the Mettler. The balances read with accuracy to the last reading value.

Solution concentrations in range described in Section 5.9 were made directly by weighing, 

without employing successive dilution techniques. Concentrations were calculated from densities 

and partial specific volumes determined earlier in this laboratory [11]. The bottles were capped 

with ground glass tops and placed in an oven at about 150 oC. They were heated and agitated 

occasionally for about 2 h before commencing filtration.

The syringe filter assembly used was a 25 mm diameter stainless steel Swinny type (Millipore 

Corp., Bedford, MA). The Swinny filter was attached to a glass syringe modified by adding a 

spherical joint at the top end, to provide connection to a dry nitrogen source used to apply an 

inert low-pressure gas to propel solution through the filter at a realistic rate. Each Swinny was 

assembled with a double layer of Pall-Gelman Sciences ZEFLUOR all-Teflon filtering 

membrane with 0.5 ìm pore size (Pall Corp., Port Washington, NY). These filtering assemblies 

were heated to 150 oC in the oven along with the solvent and solution bottles.

After the polymer samples had dissolved to form clear homogeneous solutions, the solvent and 

solution samples were filtered into their respective light scattering cells.

The hot filtration was conducted in a thermostatted apparatus that maintained both cell and 

filtering assembly in the range 140oC to 150oC. The filtering assembly was heated in a vertical 

glass cylinder wrapped with a nichrome coil heating element. The cell was mounted in an 

aluminum block heater below.

After the solution sample was poured into the filtering assembly, and the low nitrogen gas 

pressure was applied, the first (5 to10) cm3 filtrate was collected in a waste vial and discarded. 

The next approximately 20 cm3 filtrate was directed into the light scattering cell. The N2 gas 

pressure was adjusted to obtain a filtration flux of about 1 drop per few seconds to a few drops 

per second.

Subsequent light scattering measurements generally indicated a high success rate in obtaining 

solution and solvent samples free from dust contamination. At the conclusion of an experiment, 
19

the cell components and filtering assembly components were cleaned with refluxing hot xylene 

vapors. This cleaning process appeared successful in removing dust and polymer exhaustively. 

5.7 Measurement Protocol 

The temperature was controlled at 130.0 oC ± 0.2 oC in all light scattering measurements on 

polyethylene in 1-chloronaphthalene. In all experiments, the intensity measuring system was 

calibrated with the scattering intensity at 90o angle (I(90)) by a TCB standard cell described 

above; the scattering intensity from the solvent and each solution was measured at seven angles 

in the range from 60o to 120o. Scattering intensity measurements versus angle (I(è)) were 

conducted with the solvent cell immediately following the calibration against TCB, and twice 

more after I(è) measurements had been conducted on all the solution cells.

All cells containing the TCB secondary standard and samples of solvent or solution were stored 

in an oven at (140 to150) oC. Each cell was transferred from the oven to the vat in preparation 

for scattering intensity measurements, and allowed to remain undisturbed in the vat for at least

10 min to thermally equilibrate at the experimental temperature before initiating the 

measurements.

At the conclusion of each experiment, the TCB secondary standard cell was withdrawn from the 

oven and stored at ambient temperature. In two cases replicate light scattering experiments were 

conducted with a set of solution and solvent samples on the day following the initial experiment, 

after the polyethylene had been in hot solution environment for longer than 24 h. The TCB 

secondary standard cell was returned to the oven a few hours before initiating the replicate 

experiment in order to heat it up to the range of experimental temperature. These replicate 

experiments gave results, which appeared to indicate thermal stability of this polymer in its high 

temperature solution state over an interval of at least 24 h. 

5.8 Analysis of Light Scattering Data 

Light scattering data from polymer solutions of concentration c and scattering angle Θ may be 

analyzed by fitting the scattering signal I(Θ,c) to [28]

I(Θ,c)=I(Θ,0)+c IG/ {(sin Θ)∑Cijc

i

sin2j(Θ/2)}. (15)

 ij

 

In eq. (5), IG is the scattering signal from the TCB working standard at Θ = 90°.

We must first decide how many terms on the right-hand side of eq. (15) need to be included to 

provide an adequate fit to the experimental data. The dependence of c/Ic, where Ic = sinΘ[I(Θ,c)-

I(Θ,0)]/IG, upon c and upon sin2(Θ/2) reflects solute-solvent interactions and solute size, 

respectively. Accordingly, preliminary scattering data for SRM 2885 were first analyzed as c/Ic
20

versus sin2(Θ/2) and c and c2 , to see whether as series retaining only C00, C01, C10 and C20

would provide an adequate fit. The analysis revealed that this approximation was adequate at 

concentrations below 1.5 g/L for SRM 2885 (see Section 5.10.13 for a more complete 

discussion). 

Thus, we used for the final analysis

I(Θ,c) = I(Θ,0) + c IG/{sin Θ (C00 + C01 sin2(Θ/2) +C10c + C20c

2 )} (16)

The coefficients in eq. (16) are related to the Mw, molecular mean-square radius of gyration, RG

2

, 

 the second viral coefficients, A2, and the third virial coefficients, A3, by [28,29]:

Mw = (K'C00)

-1

(17)

RG

2

 = 3[λ0/(4πn)]2C01/C00 (18)

A2 = K'C10 /2 (19)

A3 = K'C20 /3 (20)

K' = 4π

2

nB

2

(dn/dc)2/(λ0

4NARvB

 S23) (21)

where:

λ0 is the wavelength in vacuum of the scattered light, 632.8 nm in this work, n and nB are the 

indices of refraction of the solvent at 130 oC and benzene at 23 oC taken as 1.5772 and 1.4941, 

respectively calculated as described in Section 5.3, dn/dc is the specific refractive index 

increment of the solution, measured as described in 5.2, NA is Avogadro's number, taken as 6.022 

x 1023 /mol, Rv

B

 is the Rayleigh ratio for the total scattering of vertically polarized light from 

benzene at 23 oC, used as the calibration standard. S23 is the ratio of the scattering of the benzene 

at 23 oC to the TCB working standard at 130 oC. The method of obtaining S23 is described in 

section 5.5. 

Preliminary fitting was done in the Zimm form, that is, plots of c/Ic versus sin2(Θ/2) and c, or if 

we wish to include third virial terms as c/Ic versus sin2(Θ/2) and c and c2 . We then fit to the 

nonlinear form in eq 16 using the parameters from the Zimm fit to estimate the starting 

parameters to the non-linear fit. This allows us to include the correct weighting of the data and 

also the zero concentration terms. We found only small changes in all fitting parameters between 

the fit to the Zimm form and the fit to the form of eq.16 even when we included c2 terms in the 

form of eq. 16.

5.9 Results for SRM 2885 
21

Five sets of light scattering solutions were analyzed for SRM 2885 using 1-chloronaphthalene as 

solvent. Each set consisted of eight or ten independently prepared solutions with concentrations 

from (0.4 to 2.5) g/L. One set had a solution concentration of 0.2 g/L. The polymer for each 

solution within each set was taken from the SRM sample vials or the division supply lots. 

Intensities were measured at five to nine scattering angles in the range from 60o to 120o. The 

intensities of scattered light in each set were fitted by least squares as explained above, and the 

results were used to calculate Mw, A2, A3 and Rg using eqns (17)-(21). The values of Mw, A2, A3

and Rg obtained from the six sample sets were then averaged. Light scattering gave an Mw of 

about 6.28 x10+3 g/mol with a sample standard deviation of 0.39 x10+3 g/mol, a value of A2 of 

0.00204 mol mL/g2 with a sample standard deviation of 0.00047 mol mL /g2, a value of A3 of 

0.0045 mol mL/g2 with a sample standard deviation of 0.017 a value of Rg of 16.9 nm with a 

sample standard deviation of 2.0 nm. For one set the value of C10 was negative giving a negative 

value to Rg

2

. We shall discuss this in the next paragraph.

The value of A2 is in close agreement with that estimated by Han, Wagner and Verdier [28] in 

the previous certification of SRM 1482, SRM 1483 and SRM 1484. They estimate A2 = 0.00159 

mol mL/g2 for SRM 1482 which has an Mw = 13.6x10+3 g/mol and A2 = 0.00109 mol mL/g2 for 

SRM 1484 with Mw =32.1 x10+3 g/mol. Our value of 0.00204 mol mL/g2 is consistent with the 

trend these values display as a function of molecular mass considering our estimated uncertainty 

in A2. They estimate Rg = 13.2 nm for SRM 1482 and Rg = 8.2 nm for SRM 1483, clearly the 

wrong order for the molecular masses of these molecules. For SRM 1482, they consider the 

possibilities of large systematic uncertainties in Rg. We have the same problems with the Rg we 

estimate. This is due to an alignment problem we find with our I sin(È). This is clear from the 

fact that for one of our set we obtain an apparent negative value of Rg

2

 Considering all these 

problems, our value of 16.9 nm is in reasonable agreement with their values.

The standard deviation of the mean for the average Mw of SRM 2885 is 0.20 x10+3 g/mol. In 

compliance with the NIST policy [15] on reporting uncertainties in measurement, the component 

uncertainty due to variance among the five Mw determinations is computed as the standard 

deviation of the mean. Table 2 reports twice this value as the expanded uncertainty.

5.10 Estimation of Uncertainties Due to Systematic Effects in the Light Scattering

We list the likeliest sources of systematic uncertainty in the determination of Mw by light 

scattering measurements described in the preceding sections, and attempt to estimate upper limits 

for their magnitudes. For this purpose, we employ a scheme similar to that used in ref. [28] for 

the estimation of systematic uncertainties in SRM's 1482, 1483 and 1484 and ref [29] on the 

recertification of SRM 706a. These uncertainties are listed in Table 2 for SRM 2885.

5.10.1. Indices of Refraction 

Following Ref. [28], we estimate that 0.1% is a proper upper limit for systematic relative 
22

standard uncertainties in Mw arising from uncertainties in the literature values of benzene index 

of refraction, the calibrating liquid. 

5.10.2 Calibration of the Differential Refractometer 

5.10.2.1 Literature Values of dn/dc for Aqueous NaCl 

Calibration of the differential refractometer required interpolation of the data of Ref. [16,17,18] 

to the 632.8 nm wavelength used in the light-scattering measurements. We estimate the relative 

standard uncertainty in the interpolated values of Än as 0.6 %, due primarily to uncertainties in 

the interpolation process. The calibration factor determined for our differential refractometer had 

a relative standard deviation (rsd) of 0.097 %. Applying a coverage factor of 2 to this rsd yields a 

Type A expanded uncertainty of 0.19 % for this measurand [15]. Combining this uncertainty 

with an allowance for possible linear uncertainties in the refractometer, we estimate that a proper 

upper limit for relative uncertainty in dn/dc is 1%. Considered as a 95 percent confidence 

interval estimate, this quoted uncertainty provides a expanded uncertainty in dn/dc of 1 % which 

would contribute a 2 % or 0.13 x10+3 g/mol expanded uncertainty in Mw determination.

5.10.3 Measured Value of dn/dc of SRM 2885 

The differential refractive index dn/dc of SRM 2885 in 1-chloronaphalene at a temperature of 

130 oC was determined as described in Section 5.2.4. The mean value obtained for dn/dc was

-0.1867 mL/g , with a standard deviation of 0.0013 mL/g. The uncertainty in the mean is then 

0.0007 mL/g. We take the expanded uncertainty of this measurement as 0.0014 mL/g or a 

relative uncertainty of 0.8 %.

There appears to be no concentration drift in the data. When we refit the data dropping the 

highest concentration and found a dn/dc of -0.1869, a number well within our expected expanded 

uncertainty. 

As the dn/dc appears as the second power in the Mw calculation, the uncertainty in the calculated 

Mw that results from the uncertainty in the dn/dc is estimated as twice the estimated relative 

expanded uncertainty in the dn/dc, or 1.6 % . This gives an expanded uncertainty in the Mw of 

0.1 x 10+3 g/mole. 

Contributions to the uncertainty of the value of the density of the solvent to dn/dc are discussed 

in section 5.10.8.

5.10.4 Wavelength of Radiation

For the He-Ne laser employed in this work, uncertainties in the wavelength of the radiation are 
23

completely negligible compared with uncertainties from other sources.

5.10.5 Calibration Constant for Light Scattering

The protocol for the calibration is described earlier. For each step, we estimate an uncertainty.

5.10.5.1 Rayleigh Ratio of Benzene at room temperature

For benzene at 632.8 nm, Ref. [24] gives: RV,V+H = 12.63x10-6 cm-1. We abbreviate RV,V+H by 

R. The authors of Ref. [24] apparently believed that their R-values have a relative standard 

uncertainty of < 2 % (all from systematic uncertainty). They quote a relative standard deviation 

for their R-value for benzene of 0.21/12.63, or 1.7 %. This yields a relative expanded uncertainty 

of 3.9 %, or 0.25 x10+3 g/mol. 

5.10.5.2 Estimating Ratio of Benzene Scattering to Glass Rod Scattering at Room Temperature

We have run 20 repeats of the measurements of the ratio of the scattering of the benzene 

calibrant to the scattering of the glass rod as described in Section 5.5. We take the uncertainty in 

the repeatability of this experiment as the overall uncertainty of the measurement. The relative 

standard deviation of this measurement is given as 1.2 %. The relative standard deviation of the 

mean is 0.27 %. We take 0.6 %, or 0.04x10+3 g/mol, as the expanded uncertainty from the ratio 

of the benzene scattering to the glass rod scattering.

A small correction is introduced arising from the fact we calibrated our rod against benzene at

21 oC rather than benzene at 23 oC. We estimated that correction was 0.9946 from literature 

value on the temperature variation of the scattering from benzene [27]. We estimate from that 

work as a generous estimate of the relative expanded uncertainty from this calculation to be

0.2 %, or less than 0.01x10+3 g/mol. 

From both above corrections we take an expanded uncertainty from all these contributions to be 

0.05 x10+3 g/mol.

5.10.5.3 Temperature Dependence of Scattering of Glass Rod from 21 oC to 130 oC

Han, Wagner and Verdier [28] discussed this issue in Section 4.1.3 of their paper on Mw

determinations of SRM 1482, SRM 1483, and SRM 1484. Since the uncertainty is in the 

calibration it appears as a percentage of the final result. In that paper, they concluded the 

maximum relative expanded uncertainty of assuming the scattering of the rod is unchanged from 

23 oC to130 oC is 0.4% of the Mw. Here, we accept their estimate as the expanded uncertainty. 

This leads to an expanded uncertainty of Mw for this polymer of 0.03x10+3 g/mol.
24

5.10.5.4 Estimating ratio of Glass Rod Scattering to TCB Scattering at 130 oC

We have 42 repeat measurements of the ratio of the scattering of the glass rod to the scattering 

from the TCB working standard, described in Section 5.5. We take the uncertainty in the 

repeatability of this experiment as the overall uncertainty in this measurement. Fourteen 

measurements of the ratio of the glass rod scattering to that of TCB, the working standard, were 

made for each of three different scattering cells containing TCB. The relative standard deviation 

of the mean is 0.2 %. We take 2 times this uncertainty as the expanded uncertainty from the 

ratio of the benzene scattering to the glass rod scattering. This yields 0.4 % as the relative 

expanded uncertainty, or 0.03 x10+3 g/mol.

5.10.6. Uncertainties in the Polarization of Light

There are two uncertainties associated with the laser light. First, the "vertically polarized" laser 

beam actually contains "horizontally polarized" components for two reasons: the polarizer inside 

the laser head lets through a small fraction ε of the "wrong" polarization and the principal axis of 

polarization of the light from the laser may not be exactly perpendicular to the optic plane 

defined by the incident and scattered beams. Both uncertainties will cause light, assumed to be 

vertically polarized, to contain a small admixture of horizontally polarized light. The effect upon 

scattering signals from SRM 2885 will be slight, but the effect upon the benzene calibration 

signals is to change the effective Rayleigh ratio that should have been used toward the RH,V+H

value. The resulting uncertainty in Mw is ε/(1-ε) for the first effect and tan2α, where α is the 

angular mis-setting, for the second. We take ε = 1/500 and α = 5

o

. Then the relative expanded 

uncertainty from ε is less than 0.2 % with at least a 95 % level of confidence considering the 

liberal boundaries assigned to the constituent uncertainties. The uncertainty from α is less than 

0.8 % with at least a 95 % level of confidence considering the liberal boundaries assigned to the 

constituent uncertainties. Following NIST guidelines we take the root-sum-of-squares from 

these contributions to yield the standard uncertainty of 0.85 % and the relative expanded 

uncertainty from this contribution of 1.7 %, or 0.11 x10+3 g/mol.

5.10.7 Ratio of Working Standard Scattering to Sample Scattering

Since photon-counting techniques were employed, there should be no systematic uncertainties 

from this source. Random uncertainties are reflected in the overall random uncertainty of the 

Mw.

5.10.8 Solvent Density

For the density of 1-chloronaphalene at 130 °C, we used the value 1.098 g/mL as given in 

references [11,25]. Following Han, Wagner and Verdier [28], we estimate that this value has a 

relative expanded uncertainty of < 0.1 %. The resulting relative expanded uncertainty on Mw is 
25

just 0.2 %, or 0.01x10+3 g/mol.

5.10.9. Solute and Solvent Masses

For the measurements actually used in the final determination of Mw for SRM 2885, solvent 

masses were chosen so that the solute masses were always about 0.05 g. Using the uncertainty 

limit of 0.05 mg we usually assign to the balance used to weigh the PE samples, we have relative 

expanded uncertainties of 0.1 % in the solute masses. The balance used for solute measurements 

was regularly checked with a 50 mg mass standard calibrated by the NIST Mass Division and 

was found to vary by less than 0.01 mg from the standard. The uncertainty in Mw is then the 

relative uncertainty in solute masses, or about 0.1 % with at least a 95 % level of confidence. 

This 95 % confidence interval estimate provides a relative expanded uncertainty of 0.2 %, or 

0.01x10+3 g/mol. 

Solvent masses of at least 30 g were used in solution preparation. The solvent balance was 

checked against a 100 g mass standard and found to be off by less than 0.01 g. The solvent 

masses were measured to 0.01 g. Thus, there are negligible uncertainties in solvent masses.

5.10.10 Reflection Correction 

The refractive index of 1-chloronaphalene at 130 °C is given as nD = 1.5772 by an estimate 

described in Section 5.3. The refractive index of the sample cell is given by the vendor as n D = 

1.500. Although the wavelength of the reported refractive index of 1-chloronaphthalene and of 

the cell are different from that uses in our experiments, these values should be adequate to 

estimate what will turn out to be an extremely small uncertainty. Han, Wagner and Verdier [28] 

assumed that the refractive index difference between the sample cell and 1-chloronaphalene was 

about 0.1, an extreme overestimation for our case. With that assumption, they found for a 

scattering system like ours, a reflection correction of 0.1 yields a reflectance factor f = 2 x 10-3. 

Comparison calculations of Mw for SRM 1484 with and without this correction show the 

resulting relative standard uncertainty to be less than 0.01%. The equivalent calculation for SRM 

2885 would yield a standard uncertainty of less than 0.01%. We take the uncertainty to the 

molecular mass from this contribution to be zero.

5.10.11 Instrumental Misalignment 

The effects of instrument misalignment are difficult to estimate. For the geometry of the current 

high temperature light scattering instrument, it is expected that any deviation from constancy of

I sin(Θ) is indicative of instrument misalignment. We look at this effect in two different ways.

First, I sin(Θ) values calculated from solvent scattering indicated alignment problems. Whereas 

these values divided by the intensity at 90° should be independent of Θ they showed a fractional 
26

variation of 0.6 % to 1.0 % . If we assume that the data scales with this uncertainty, we would 

estimate a relative expanded uncertainty of 0.6 % to 1.0 % in Mw.

Second, from our experience with the alignment, we would also estimate the maximum 

misalignment to be 0.2°. We have examined two sets of data by purposefully recomputing the 

Mw putting in a misalignment of 0.2°. They consistently both show for a systematic angle 

variation of +0.2° the Mw varies by about a fraction of 1.0 % and for an angle of -0.2° the Mw

varies by -1.0 %. 

Since both estimates of uncertainty yield a maximum expanded uncertainty of about 1 % from 

misalignment, we estimate a total relative expanded uncertainty arising from instrument 

misalignment of 1.0 %, or 0.06 x10+3 g/mol for SRM 2885.

5.10.12.Anisotropy of Solute 

Following Han, Wagner, and Verdier [28], we find that equations for Mw and K' in Section 5.8 

are derived on the assumption that the light scattering from the polyethylene is not depolarized. 

When the solute is optically anisotropy, Mw should be replaced with Mw(1+ε) where the 

correction term is given by:

ε = (1/45)(1/Mw) (<γ

2

>/Mw)[4πnsNa/(dn/dc)2

 where < γ

2

 > is given approximately by 267 x10-50 cm6 per CH2 group [31, 32]. Thus < γ

2 >/M 

is 1.91 x 10-49 mL2 /g. We estimate ε for SRM 2885 as less than 0.0003. We take this to be a 

relative expanded uncertainly of 0.03 % on Mw. We consider this correction and uncertainty on 

this measurement negligible.

 5.10.13 Cutoff of Virial Expansion for SRM 2885

 

We refit the data on all 5 sample sets with and without including a third virial term. The average 

computed Mw changed from 6.28 x 10+3 with the third virial to 6.28 x 10+3 with the second virial 

term in the series only. As a result we found a change in the Mw using a fit including only the 

second virial coefficient and that with a third virial of +1.5%, +1.5 %, + 4.5%, +4.0 % and -

4.5%. We take the average of the above percentages to be the standard uncertainty, 1.5%, and 

twice that to be the expanded uncertainty. Thus, we take the expanded uncertainty from the virial 

fit to be 0.19 x10+3 g/mol.

5.10.14 Scattering Changing during the Measurement: Degradation and other Sources 

By their nature light scattering experiments are of short duration. A number of solutions can be 

prepared and examined by light scattering in a single day. To avoid instability problems solutions 
27

used in the certification of Mw were prepared and measured on the same day. To test stability we 

conducted a second set of measurements on the same solutions a few days later. Of the two runs 

of SRM 2885 where stability was investigated, Mw was seen to increase by 2.2 %, or 0.14 x10+3

g/mol, and 4.4 %, or 0.28x10+3 g/mol, when the solutions were stored at 130 °C as long as 2 d 

after preparation. Studies of time effects on another polyethylene fraction being certified, SRM 

2887, revealed both increases and decreases in the measured molecular mass as a function of 

time. We estimate that the light scattering data used in certification of SRM 2885 were acquired 

within12 h after the solutions were first heated. We take the contribution to the uncertainty due to 

changes during the first 12 h of heating to be at most 2 %, or 0.13 x10+3 g/mol. We take this to be 

our expanded uncertainty from this part of the measurement. 

5.10.15 Summary

The combined expanded uncertainties, Uc, of SRM 2885 are computed as root-sum-of-squares of 

the component expanded uncertainties, ui', following the formal NIST policy for evaluating and 

expressing uncertainty in measurements [15]. In Table 2, we find that the combined expanded 

uncertainty, Uc, of SRM 2885 is 0.56 x10+3 g/mol. 

6.0 Conclusions

The Mw of SRM 2885 by light scattering was determined to be 6.28 x10+3 g/mol with a sample 

standard deviation of 0.39 x10+3 g/mol. A combined expanded uncertainty for this light 

scattering Mw determination including all type A and type B uncertainties was 0.56x10+3 g/mol 

The intrinsic viscosity of SRM 2885 by solution viscosity in 1,2,4-trichlorobenzene was 

determined to be 22.3 mL/g with a sample standard deviation of 0.17 mL/g. The standard 

deviation on the mean value was 0.17 mL/g. A combined expanded uncertainty for this intrinsic 

viscosity determination including all type A and type B uncertainties was 0.20 mL/g. The bottleto-bottle variation of the SRM was check by size exclusion chromatography and found to be 

negligible. 

Acknowledgements

The authors would like to thank Charles Han for the use of his high temperature light scattering 

instrument and his help and discussions concerning this project. Sachin Bhatt assisted with the 

intrinsic viscosity measurements.
28

Table 1

Contributions to Expanded Uncertainty in Measured Intrinsic Viscosity of SRM 2885

 

Source of Uncertainty Uncertainty (mL/g)

Shear rate dependence 0.0

Solvent density, ρ(0) 0.05

Polymer specific volume, Vave 0.04

Buoyancy corrections 0.0

Solute masses 0.0

Solvent masses 0.0

Timer 0.01

Flow time correction factor 0.07

Measurement temperature 0.07

Sample uncertainty in fit of data 0.17

Combined Expanded Uncertainties 0.20

 

.

.

.

.

 . 

 . 
29

Table 2

Contributions to Combined Expanded Uncertainty

 Of the Mw of SRM 2885

Source of Uncertainty Contribution

(10+3 g/mol)

Expanded Uncertainty from standard deviation of the mean 0.39

Solvent index of refraction 0.01

Calibration of differential refractometer 0.13

Differential refractive index 0.09

Wavelength of light <0.01

Rayleigh ratio of scattering standard, benzene 0.25

Ratio Scattering Benzene to glass rod 0.05

Temperature Dependence Glass Rod 0.03

Ratio Scattering glass rod to TCB scattering standard 0.03

Polarization of light 0.11

Ratio of standard scattering to sample scattering <0.01

Solvent density 0.01

Solute and solvent masses 0.01

Light reflection 0.0

Instrumental misalignment 0.06

Anisotropy of polymer in solution <0.01

Truncation of virial expansion 0.19

Scattering change during the scattering measurement 0.13

Combined expanded uncertainty *, Uc 0.56

* by root-sum-of-squares [15]
30

References

[1] "Standard Practice for Dilute Solution Viscosity of Polymers" D2857-93, Annual Book of 

ASTM Standards, Vol 08.02 1995, ASTM, Philadelphia, PA

[2] Peter H. Verdier and Herman L. Wagner, "The Characterization of Linear Polyethylene 

SRM's 1482, 1483, and 1484. I. Introduction" NBS Special Publication 260-61, P.H. Verdier 

and H.L. Wagner ed. December 1978 or National Bureau of Standards, Journal of Research, Vol. 

83, No. 2, March - April, 1978, pg. 169-171.

[3] Charles M. Guttman, John R. Maurey, and William R. Blair “Certification of the Relative 

Molecular Mass and the Intrinsic Viscosity of SRM 2886, a Polyethylene of Narrow Molecular 

Mass Distribution”, NISTIR 6454, 2001.

[4] M. G. Natrella, "Experimental Statistics", National Bureau of Standards Handbook 91, U.S. 

Department of Commerce, 1963

[5] Charles M. Guttman and John R. Maurey, "Recertification of Standard Reference Material 

1475a, A Linear Polyethylene Resin", NISTIR 5199, 1993 

[6] L. Huber, "Application of the Diode-Array Detector in HPLC", Hewlett Packard, France, 

08/89, pg. 89-100

.

[7] Barry J. Bauer, Brian Dickens and William Blair, "Chromatographic Examination of Intaglio 

Inks, Resins and Varnishes", NISTIR 4949, 1991 

[8] Charles M. Guttman, William R. Blair, John R. Maurey, "Recertification of SRM 1482a, a 

Polyethylene", NISTIR 6054, 1997 

[9] "PC-OMNITAB: An Interactive System for Statistical and Numerical Data Analysis, 

available from National Technical Information Service, Technology Administration, U.S. 

Department of Commerce, Springfield, VA 22161

[10] See for example Howard W. Alexander "Elements of Mathematical Statistics", John Wiley 

& Sons, 1961, pg. 165-170 or K. A. Brownlee "Statistical Theory and Methodology in Science 

and Engineering," John Wiley & Sons, Inc., 1960, pg. 56.

 [11] Richard G. Christensen, "The Characterization of Linear Polyethylene SRM 1475 V. 

Solution Viscosity Measurements" NBS Special Publication 260-42, H.L. Wagner and P.H. 

Verdier, Editors. September 1972 or National Bureau of Standards, Journal of Research, Vol. 

76A, No. 2, March - April 1972, pg. 147-148.

[12] Herman L. Wagner and Peter H. Verdier, "The Characterization of Linear Polyethylene 

SRM's 1482, 1483, and 1484. IV. Limiting viscosity number Numbers by Capillary Viscometry" 

NBS Special Publication 260-61, P.H. Verdier and H.L. Wagner ed. December 1978 or National 

Bureau of Standards, Journal of Research, Vol. 83, No. 2, March - April, 1978, pg. 195-201.
31

[13] "Operating Instructions for the Viscosity Measuring System AVS 400", Schott Gerate, 

Yonkers NY and Hofheim, Germany 

[14] See for example F.W. Billmeyer, Jr, "Textbook of Polymer Science, 2nd edition", Wiley 

Interscience, NY (1971) pg 84.

[15] B. N. Taylor and C. E. Kuyatt, "Guidelines for Evaluating and Expressing the Uncertainty of 

NIST Measurement Results." NIST Technical Note 1297, January 1993.

[16] A. Kruis, Z. Physik. Chem. B 34, 13-50 (1936).

[17] R. J. Anderson, Appl. Opt. 8, 1508-1509 (l969

[18] LDC Analytical, "Instruction Manual for KMX-16 Laser Differential Refractometer" 

Section 5.3, "Calculation of Calibration Constant," Riviera Beach, FL, USA.

[19] H. L.Wagner and C.A.J.Hoeve, J. Poly. Science, Part A-2, 9, 1763-76 (1971). Although this 

is at a different wavelength we do not expect the overall variation to be wavelength dependent.

[20] J. Horska, J. Stejskal, and P. Kratochvil, "Refractive Increments of Polyolefins", J. Appl. 

Polym. Sci.,Vol 28, p3873(1983) 

[21] J. Horska, J. Stejskal, and P. Kratochvil, "Refractive Increments of Polyolefins", J. Appl. 

Polym. Sci.,Vol 24, p1845(1979) 

[22] J. A. Riddick and W. B. Bunger, "Organic Solvents, Phys. Properties and Methods of 

Purification," Wiley-Interscience, New York, 1970, Table 58, pg 145 or Table 30, pg 107. Also 

see B. L. Johnson and J. Smith, "Refractive Indices and Densities of Some Common Polymer 

Solvents," Ch. 2 in "Light Scattering from Polymer Solutions," Ed M. B. Huglin, Academic 

Press, London and NY (1972).

[23] "Instruction Manual for Laser Light Scattering Goniometers", Brookhaven Instrument 

Company, Ronkonkoma, New York, May 1984, catalog number BI-IM version 1.4

[24] G. B. Arrowsmith, G. H. Jeffrey, and A. I. Vogel, J. Chem. Soc., pg 2072 (1965)

[25] H. L. Wagner, "The Characterization of Linear Polyethylene SRM 1475. VI. Differential 

Refractive Index of Polyethylene Solutions" NBS Special Publication 260-42, H.L. Wagner and 

P.H. Verdier, Editors. September 1972 or National Bureau of Standards, Journal of Research, 

Vol. 76A, No. 2, March - April, 1972, pg. 151-155

[26] W. Kaye and J. B. McDaniel, Appl. Opt., 13, l934-1937 (l974).

[27] J. Ehl, C. Loucheux, C. Reiss, and H. Benoit, Makromol. Chem., 75, 35 (1964).

[28] Charles C. Han, Herman L. Wagner, and Peter H. Verdier, "The Characterization of Linear 

Polyethylene SRM's 1482, 1483, and 1484 III Weight-Average Molecular Weights by Light 
32

Scattering." NBS Special Publication 260-61, P.H. Verdier and H.L. Wagner ed. December 1978 

or National Bureau of Standards, Journal of Research, Vol. 83, No. 2, March - April, 1978, pg. 

185-193.

[29] Charles M. Guttman, William R. Blair, John R. Maurey, "Recertification of SRM 706a, a 

Polystyrene", NISTIR 6091, 199.

[30] H. Yamakawa, "Modern Theory of Polymer Solutions," Harper & Row, N.Y., (1971).

[31] "Instruction Manual for Laser Light Scattering Goniometers", Brookhaven Instrument 

Company, Ronkonkoma, New York, May 1984, catalog number BI-IM version 1.4

[32] H. Utiyama, "Calibration and Correction Factors," Ch. 4 in "Light Scattering from Polymer 

Solutions," Ed M. B. Huglin. pp 61-88, Academic Press, N.Y., (1972).
33

National Institute of Standards & Technology

Certificate of Analysis

Standard Reference Material® 2885

Polyethylene

(Mw, 6 280 g/mol)

This Standard Reference Material (SRM) is intended primarily for use in calibration and performance evaluation of

instruments used to determine the molar mass* and molar mass distribution by size exclusion chromatography. A unit of 

SRM 2885 consists of approximately 0.3 g of polyethylene powder. The certified values and uncertainties for massaverage molar mass and intrinsic viscosity are presented in Table 1.

Table 1. Certified Properties

Property Certified Value

Mass-Average Molar Mass* (Mw ) 6.28 x 103 g/mol ± 0.56 x 103 g/mol

Intrinsic Viscosity [η] in 

1,2,4-trichlorobenzene at 130 °C 22.3 mL/g ± 0.20 mL/g

* Previously expressed as molecular weight [1].

Certified Values and Uncertainties: The certified value for Mw was measured using static light scattering with

1-chloronaphthalene as the solvent at 130 °C [2]. The certified value for the intrinsic viscosity was determined in 1,2,4-

trichlorobenzene at 130 °C.

The certified measurement uncertainty is expressed as a combined expanded uncertainty with a coverage factor, k = 2, 

calculated in accordance with NIST procedure [3]. Type A and Type B contributions to the expanded uncertainty of the

measured mass-average molar mass include the uncertainties in the Rayleigh ratio of the scattering standard, optical 

alignment, and calibration of the differential refractometer.

Expiration of Certification: The certification of SRM 2885 is valid until 01 January 2008, within the measurement 

uncertainties specified, provided that the SRM is handled in accordance with the storage instructions given in this

certificate. This certification is nullified if the SRM is modified or contaminated.

Maintenance of SRM Certification: NIST will monitor this SRM over the period of its certification. If substantive 

technical changes occur that affect the certification before expiration of this certificate, NIST will notify the purchaser. 

Return of the attached registration card will facilitate notification.

The technical coordination leading to certification of this SRM was provided by B.M. Fanconi of the NIST Polymers 

Division. Technical measurements and data interpretation were provided by C.M. Guttman, W.R. Blair, J.R. Maurey, 

and C.R. Schultheisz of the NIST Polymers Division.

The support aspects involved in the preparation, certification, and issuance of this SRM were coordinated through the 

NIST Standard Reference Materials Program by J.W.L. Thomas.

Eric J. Amis, Chief

Polymers Division

Gaithersburg, MD 20899 Nancy M. Trahey, Chief

Certificate Issue Date: 06 April 2001 Standard Reference Materials Program

Storage: The SRM should be stored in the original bottle with the lid tightly closed and under normal laboratory
34

conditions.

Homogeneity and Characterization: The homogeneity of SRM 2885 was tested by size exclusion chromatography 

analysis of solutions in 1,2,4-trichlorobenzene at 130 °C. The characterization of this polymer is described in Reference

3. SRM 2885 is the result of a clean-up, blending, and rebottling of the fractionation of SRM 1475. It was produced in 

the same fractionation as SRM 1482, SRM 1483, and SRM 1484 [4].

REFERENCES

[1] Taylor, B.N., “Guide for the Use of the International System of Units (SI),” NIST Special Publication 811, 1995 

Ed., (April 1995).

[2] Guide to the Expression of Uncertainty in Measurement, ISBN 92-67-10188-9, lst Ed. ISO, Geneva, Switzerland, 

(1993): see also Taylor, B.N. and Kuyatt, C.E., “Guidelines for Evaluating and Expressing the Uncertainty of

NIST Measurement Results,” NIST Technical Note 1297, U.S. Government Printing Office, Washington DC,

(1994); available at http://physics.nist.gov/Pubs/.

[3] Guttman, C.M., Maurey, J.R., and Blair, W.R., “Certification of the Relative Molecular Mass and the Limiting 

Viscosity of SRM 2885, a Polyethylene of Narrow Molecular Mass Distribution,” NISTIR 6454.

[4] Verdier, P.H. and Wagner, H.L., “The Characterization of Linear Polyethylene SRM’s 1482, 1483, and 1484, I.

Introduction,” NBS Special Publication 260-61, (December 1978); or National Bureau of Standards, Journal of 

Research, 83, No. 2, pp. 169-171, (1978).

Users of this SRM should ensure that the certificate in their possession is current. This can be accomplished by

contacting the SRM Program at: telephone (301) 975-6776; fax (301) 926-4751; e-mail srminfo@nist.gov; or via the 

Internet http://www.nist.gov/srm.