Near Infrared and Nuclear Magnetic Resonance Spectrometry in Analysis of Butadiene Polymers A. J. DURBETAKI and C. M. MILES Chemical Research and Development Center, FMC Corp., Princeton, N. J.
b Near infrared and high-resolution nuclear magnetic resonance spectrometry have been used to study the microstructure of polybutadiene polymers prepared b y sodium-, butyllithium-, and free radical-catalyzed polyrnerizations. Good agreement was obtained between the total unsaturation as determined b y NMR and Wijs’ iodine number. Likewise, the ratio of oxirane oxygen to the total saturation as determined b y NMR and chemical methods showed good agreement. Characteristic near infrared spectra between 1.2 and 2.5 microns were obtained. Comparative analysis of data with those from NMR show that a t any given wavelength, each group has a constant unit value of absorption. The absorption for the entire molecule will therefore b e the value of the absorption for a given group, multiplied b y the number of such groups. The molar absorptivity, E , a t a given wavelength, defines the number of groups and the number average molecular weight. It i s characteristic of the type of polymerization used.
0
The ratios of 1,4 to 1,2 and t h a t of trans to cis in a given polymer are dependent on the type of polymerization catalysts and reaction conditions used (1, 15-13). The polymerization of butadiene by alkali metals and their alkyls and free radical-initiated polymerizations have been known for a long time. However, only recently has the microstructure of polybutadienes been elucidated ( 1 ) . The structural elucidation of butadiene polymers, to date, has been studied by infrared techniques in the 3- to 15micron region of the electromagnetic spectrum and by classical chemical and physical methods (1-3, 12-17, 20, 2223). Suclear magnetic resonance (SNR) is of considerable interest and importance for the study of organic compounds (13, 19). During the past 10 to 12 years, investigations of a variety of polymer systems have been published. These studies have dealt with solid polymers and the spectra obtained have been of the so-called broad-band type ( 4 ) . However, when disolved in suitable solvents, polymers give highresolution N l I R spectra in which the resonance lines are only a fraction (10-3 to of the nidth shown in the solid state (4-7’). The fingerprint region (2.5 to 15 microns) of the infrared spectrum can present many difficulties in quantitative analysis except in some favorable cases ( 2 ) . It is possible to obtain spectra which are more simple and
in the polymerization of olefins and diene-: have been made in recent years. I hci most significant development has becn the extent to which the propagation reaction may be directed so as t.0 bring the detailed molecular structure of the product under control. The generd problem of diene polymerizat,ion is of great importance as the physical properties of a polybutadiene depend to a large extent on the distribution of the monomer units. The distribution of CT5TANVING
ADVAXCES
, 7
EXPERIMENTAL
X l I R spectra \$ere obtained using 20% m./v. solution of the polymer in dry spectrograde carbon tetrachloride with the Varian A-60 analytical spectrometer system, operated a t 60 mc. per second for proton resonance a t 14,092 gauss H , field intensity. The position of a given chemical shift was measured with reference to tetramethyl-
-CHz
\
CH=CH
CH=CH
\ 4
CHz-CHz
/CHz-
hans-1,4
/
\ -+
-CH2
\ -CHz
CH=CH
\
/
CH
the monomer in the polymerization of butadiene may take place in three ways to give rise to trans-1,4, cis-1,4, and 1, 2(vinyl) configurations.
predictable in character b y observing the near infrared region, between 1 and 2.5 microns, of the electromagnetic spectrum. I n this region, spectra are almost entirely caused by groups involving a hyd1og.n atom. The bands are widely spaced and a clear nonoverlapped band of known origin can often be selected. Furthermore, because of the relatively constant molar absorptivities, i t is often possible to analyze with reasonable accuracy compounds for which standards are not available, provided their molar absoriitivity is known. The accuracy and precision of a near infrared analy-’ bis are comparable to those obtained in ultraviolet and visible analyses (10, 21). I n this paper is described the use of near infrared in conjunction with highresolution S M R spectrometry for the study of the microstructure of polybutadiene polymers prepared by sodium-, butyllithium-, and free radicalcatalyzed polymerizations. Methods for the determination of the concentration of fmctional groups and the number average molecular weight from spectrometric analyses are giwn.
+
I
CH
/
CHz-CHz
CH
\
/
CH
I
\
C Hz-
CH=CH
/
cis-1,4
1, 2 or 3, 4
CH
VOL. 37, NO. 10, SEPTEMBER 1965
1231
P
+..I
I
f
"I
6
I
,
,
8
,
'
7
,
,
6
,
/
,
,
4 5 2 P PM Figure 1 . NMR spectra
'
'
'
)
..-
-I I.
!
I m
I
5
'
i
0
1, Sodium-catalyzed polybutadiene; 2, partially epoxidized sample of 1
b Figure 2.
NMR spectra 8
3, Butyllithium-catalyzed polybutadiene; 4, partially epoxidized sample of 3; 5, free radical-catalyzed polybutadiene
Table
I. Chemical Shifts of Model Compounds
Reference compound Octene-1 Oct ene-2 Dodecene-1
Type of proton0 -CH=CHZ--CH=CHCI+CH&CH-CH=CH2-
''p.m. from (CH3)4Si 5.10 4 87 5.43 1 63
5.02 4.81 5.73
-CH=CH2 I-Methylcyclohexene, mono-substituted
0.69
Cyclohexene
1.52
1,2-Epoxydodecane
0.58
H
\ c-c / \o/
R
H
H
2.29
/-
- , cis
\H
H
\
C-C
/ \o/
n R
\
c-c
/-
/
2.57
,trans
H 2.74
H -
Underlined protons represent hydrogens whose chemical shifts are given.
1232
ANALYTICAL CHEMISTRY
6
5
4 PPM
3
2
1
0
silane, used as a n internal standard directly from the precalibrated charts with a n accuracy of i l C.P.S. Peak assignments were made on t h e basis of recorded chemical shifts and a comparison of the epoxidized counterparts and model compounds (Table I, Figures 1 and 2). Integration of the peak areas of the spectra was accomplished using a sweep time of 50 seconds. To assure correctness of data, five separate integrations were performed for each sample analyzed and the average value was used for all calculations. Xear infrared absorption spectra were obtained with the Cary Model 1411 recording spectrophotometer. Polymer solutions of 0.257,, 0.5yo, and 1% w./v. in carbon tetrachloride were utilized. All measurements were carried out using 10-em. optical cells. For this work commercial and laboratory preparations of polymers (11) were used as received or after fractionation according to standard methods (18).
\H
/ \J \H
0
7
The average molecular weights were determined in triplicate with the Mechrolab vapor pressure osmometer. The iodine numbers were determined by Wijs' method. Hydrogen bromide in acetic acid was the method used for determination of oxirane oxygen content of the epoxidized polymers (8). RESULTS AND DISCUSSION
NMR Analysis. Using the relationships given below, detailed quantitative group analysis by XhIR is only
Table 11. Ratio of Oxirane Oxygen to Total Unsaturation in Epoxidized Polybutadienes"
Chemical analysis Sample
NMW
(8, 1 4 )
A B
0.78 0.87 0.76 0.88 0.74 0.94 0.52
0.75 0.87 0.76 0.85 0.74 0.90 0.50
C D E
F G
Values represent ratio of number of oxirane oxygen groups to number of double bonds. Calculations carried out using integrated areas of chemical shifts of protons corresponding to internal and terminal oxirane oxygens and internal and terminal double bonds. a
Table 111. Comparisons of Total Unsaturation per Average Molecule of Polybutadiene Determined by NMR and Wijs' Iodine Number Method ( I 3)"
Sample
N3f R
Wijs
I
10 14 20 30 40 48 22 21 10
11 14 18 28 38 50 21 22 10 10 ~~
10 J a Values shown are number of double bonds.
possible for the well resolved spectra of polybutadiene polymers (Figures 1 and 2). h z x 2;ratio of
100 __
ath structural
f f I
i
=
Z
=
hi = e, =
S, =
s,
=
*UR, 7Rimi
=
m, =
number average molecular weight of polymer weight of ith structural group
Group resonance line broadening and low resolution a e r e obtained for the majority of epoxidized polybutadiene samples. This, no doubt, resulted from intermolecular interactions which reduce the mobility of the molecules and thus broaden the peak area. Typical NRfR spectra of epoxidized polybutadienes are given in Figures 1 and 2. Only an
Table IV. Peak Assignments for Polybutadiene and Epoxy Polybutadiene
Type of ProtonoP
?VIeasur ed peak shift, p.p.m. from (CHI)Si 5.52 5.31 4.81 5.02 1.99 1.60
111). The versatility of N M R in structural analysis is demonstrated by the identification of cyclization in some of the samples (Figures 1 and 2, Tables I and IV). This has been postulated in the literature; however, it is difficult to de'ermine by other techniques (1). The use of variable temperatures for measurement of chemical shifts should prove useful for a more detailed analysis of epoxidized polybutadiene. Because of the unavailability of a variable temperature probe a t the time of completion of this work, examination of the polymers at variable temperatures was not possible. N e a r Infrared Assignments. Assignments in the near infrared region are not simple. If one looks a t t h e near infrared spectrum of a n y hydrocarbon, a multiplicity of bands is observed rather t h a n a single maximum occurring for the first and second overtone of each of the fundamental stretching modes. Only a few of these are actual overtones. T h e rest are combination frequencies of two or more modes. The possible number of these combination bands is larqe because they may be made up of the overtone and fundamental frequencies not only of the C-H stretching, but also of all the other vibrational modes. The usual approach has been to make group assignments because of the difficulty and uncertainty of theoretical assignments-that is, assigning a maximum as being an absorption because of the C-H in methyl, methylene, or other type of group. For practical purposes, this is all that is necessary.
Table V.
i=l
-
JI
group to remaining groups in average molecule 1,2,3. . . .n stiuctural group total integrated area of all structural grou1)s integrated area of ith structural group number of protons in i t h structuial group total number of i t h structural groups per average molecule
accurate measurement of the ratio of oxirane oxygen to total residual unsaturation is feasible for the epoxidized polymers. The agreement between the data from the NMR and those of the chemical methods (8, f4) is good for all epoxidized polymer samples (Table 11). Likewise, the total unsaturation of polybutadienes determined by N l I R is consistent with the values obtained by the Wijs' iodine number method (Table
1.54 1.28 0.91 0.69 0.58
R
H
\
/-2.23 , cis
R
H
R
R'
2.77 a Underlined protons represent hydrogens whose chemical shifts are given. b R' and R" can be alternately a methylene group or a hydrogen.
Near infrared band assignments for butadiene polymers are given in Table V. Epoxidized butadiene polymers, in addition to bands observed in polybutadiene, have bands at 1.652 and 2.213 microns characteristic of the terminal oxirane oxygen methylene group, The 1.652-micron band, although weak in intensity, is free from interference because there is no overlap
N e a r Infrared Band Assignments for Butadiene Polymers in Carbon Tetrachloride Solution
Functional group -CH=CH2
Molar absorptivity, e, liter/ mole-cm.a
Max., Remarks microns Combination band 2.119 4.06 1.636 2.50 1st overtone >CH2 Max. for methylene 1.718 3.00 C-H, combination band Symmetric overtone 1.762 1.93 -CHI Asymmetric overtone 1.698 2.43 Sample run as 0.016M solution in 10-em. cells. Average number molecular weight of polymer used for molar absorptivity calculations was 662. 5
VOL. 37, NO. 10, SEPTEMBER 1965
1233
-9
-9
ICGraw Hill, Sew York, 1959. (20) Richardson, W. S., J . Polymer Sci. 13. 229 (1954). (21) ‘Rose,‘F. W’., Jr., J . Res. Natl. Bztreau Std. 20, 129 (1938). (22) Schmaltz, Schmaltz, E. O., Geiseler. Geiseler, G. L.. L., 2. Anal. Chem. 190, 293 (1962): (1962). (23) Silas, R . S., Yates, J., Thornton, V., AXAL.CHEM.31, 529 (1959). RECEIVED for review November 27, 1964. Accepted July 12, 1965. Division of Analytical Chemistry, 145th hleeting, ACS, New York, S . Y., September 1963.
Liquid-Liquid Extraction of Metal Ions from Aqueous Solutions of Organic Acids with High-Molecular-Weight Amines The Triva lent Actin ide-La ntha nide Elements FLETCHER L. MOORE Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn, N e w liquid-liquid extraction systems for the trivalent actinide and lanthanide elements are described. Highmolecular-weight amines are excellent extractants for anionic complexes of these elements from aqueous solutions of most organic acids. Liquid-liquid extraction behavior is described for the acid systems-citric, tartaric, oxalic, (ethylenedinitri1o)tetraacetic (EDTA), ahydroxyisobutyric, and acetic-with various primary, secondary, tertiary, and quaternary amines. The high extractability of the anionic EDTA complexes of trivalent actinide, lanthanide, and other metal ions from both acid or alkaline solution is of considerable practical importance. In the actinide-lanthanide series the order of decreasing extractability is amerieuropium cium, curium, californium samarium promethium cerium yttrium thulium. Several potential applications for the separations chemist are discussed.
>
C
>
> >
> >
interest has developed recently in discovering better separation methods for the trivalent actinide and lanthanide elements; both OXSIDERABLE
inter- and intragroup separations are needed. Liquid-liquid extraction methods hold much promise for solving some of the current problems in the actinide-lanthanide element field. Several workers ( 1 , 4-6) have cited the problems and described new solutions to some of them. A11 the previous systems utilized extractions of metal inorganic complexes, such as nitrate, chloride, or thiocyanate. The trivalent actinide and lanthanide elements form their strongest compleses with the organic ligands, such as citrate, tartrate, osalate, (ethylenedinitril0)tetraacetate (EDT-I), and a-hydroxyisobutyrate. This fact renders them inestractable with the commonly used solvents -alcohols, ketones, chelating agents, organophosphorus compounds. Recently the writer discovered a new area of considerable potential -1iquidliquid estraction of the trivalent actinide and lanthanide elements from aqueous solutions of organic acids with highmolecular-weight amines. This intriguing possibility, previoualy unexplored, of effecting valuable separations based on differences in anionic organic ligand complexes prompted a
preliminary investigation of several systems. I n this paper early results are described with some typical actinidelanthanide and miscellaneous metal ions in aqueous systems containing the organic acids, citric, tartaric, oxalic, EDTA, a-hydrosyisobutyric, and acetic. A primary purpose is to describe the great potential of these new systems, which estend the scope of liquid-liquid estraction considerably. EXPERIMENTAL
Apparatus. S a 1 (Tl) well-type gamma scintillation counter, 1 3 / 4 x 2 inches. Interchangeable aluminum and lead absorbers (1.88 inches high, 0.75inch o d . , and 0.4-inch i d . ) were used for selective counting. Internal methane flow proportional counter. Alpha counting x a s done at 2900 volts, beta counting a t 4300 volts. Reagents. Priniene J l I - T is a mixture of primary amines, principally in the C18-22 range. Primene 81-R is a mixture of primary amines, principally in the C12-14 range. Xmberlite L-4-1 (S-dodecenyltrialkylmethylamine) and Xmberlite LA-2 (S-lauryltrialkylmethylamine)are secondary amines. These secondary amines and the primary amines listed VOL. 37, NO. 10, SEPTEMBER 1965
0
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