Conferences 6th and 7th (31,32).
ACKNOWLEDGMENT The authors thank H. Kruse for writing the computer programs.
LITERATURE CITED (1) K. Nwrish and J. T. Hutton, Geochlm. Cosmhlm. Acta, 33, 431 (1969). (2) E. Jagoutz and C. Palme, work to be published, Max-Planck-Institut fur Chemie, Mainz, 1976. (3) E. Jagoutz, thesis, Mainz, 1976. (4) J. W. Criss and L. S. Birks, Anal. Chem., 40, 1080 (1968). (5) J. Sherman, Spectrochlm. Acta, 7, 283 (1955). (6) T. Shiraiwa and N. Fujino, Jpn. J. Appl. Phys., 5, 886 (1966). (7) T. C. Loomis and H. D. Keith, X-Ray Spectrom., 5, 104 (1976). (8) W. H. McMaster et ai., UCRL - 50174 (1969). (9) J. A. Victoreen, J. Appl. Phys., 20, 1141 (1949). (IO) C. Broyles et ai., Phys. Rev., 89, 715 (1953). (11) F. D. Davidson et ai., J. Appl. Phys., 33, 3528 (1962). (12) R. W. Fink et al., Rev. Mod. Phys., 38, 513 (1966). (13) P. Suortti, J. Appl. Phys., 42, 5821 (1971). (14) W. Bambynek et ai., Rev. Mod. Phys., 44, 716 (1972). (15) H. U. Freund, X-Ray Spectrom., 4, 90 (1975). (16) F. J. Fianagan, Geochim. Cosmochim. Acta, 37, 1189 (1973). (17) E. M. Levin et 81. “Phase Diagrams for Ceramists”, American Ceramic Society, Columbus, 1964.
(18) P. W. McMilian, “Glass Ceramlcs”, Academic Press, London and New York, 1964. (19) H. Scholze, “Gias”, Friedr. Vieweg & Sohn, Bsaunschweig, 1965. (20) H. Rawson, “Inorganic Glass-Forming Systems”, Academic Press, London and New York, 1967. (21) L. Shartsis et ai., J. Am. Ceram. Soc., 41, 507 (1958). (22) W. Skatuila et al., Slllkattechnik, 9, 51 (1958). (23) B. S. R. Sastry and F. A. Hummel, J. Am. Ceram. SOC.,43, 23 (1960). (24) T. J. Rockett and W. R. Forster, J. Am. Ceram. Soc., 49, 30 (1966). (25) S. D. Rasberry and K. F. J. Helnrich, Anal. Chem., 46, 81 (1974). (26) W. K. de Jongh, X-Ray Spectrom., 2, 151 (1973). (27) A. R. Duncan et ai., Proc. 5th Lunar Sci. Conf., Geochlm. Cosmochlm. Acta, Suppl. 5, 2, 1147 (1974), Pergamon Press, Elmsford, N.Y. (28) J. M. Rhodes et ai., ref. 27, p 1097. (29) H. J. Rose et ai., ref. 27, p 1119. (30) Lunar Sample Preliminary Examination Team, Science, 182, 659 (1973), (31) H. Wanke et ai., Proc. 6th Lunar Sci. Conf., Geochim. C o s m h i m . Acfa, Suppl. 6, 2, 1313 (1975), Pergamon Press, Elmsford, N.Y. (32) H. Wanke et al., Proc. 7th Lunar Sci. Conf., Geochlm. Cosmochlm. Acta, Suppl. 7, 3, 3479 (1976), Pergamon Press, Elmsford, N.Y.
RECEIVED for review November 9,1976. Accepted January 18,1977. The paper was presented at the 25th Annual Denver X-Ray Conference, August 4-6,1976, University of Denver, Denver, Colorado. The financial support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged.
Determination of Composition and Molecular Weight of Polyester Urethanes by High Resolution Proton Magnetic Resonance Spectrometry F. W. Yeager” and J. W. Becker Elastomer Chemicals Department, E. I. du Pont de Nemours a n d Company, ExperimentalStation, Wiimlngton, Delaware 19898
The compositional analysts of a polyester urethane and number average molecular weight of the polyester moiety can be determined directly by 220 MHz ‘H NMR. Accuracy of both measurements was wlthln the preclslon llmlts (217) of the method. Precision of the ’H NMR composltlonal analysis for a polybutylene adlpate-TDI or -MDI polymer was f2.5 Yo relative for 1,4-butanedIol, f4.3 % relatlve for adlplc acld, and f19% relative for TDI or f13% relative for MDI. The precision for the number average molecular weight determination was f 1 8 % relatlve for a polyester of about 1000 Mn and f15% relative for one of 2000 Mn.
linear polyurethanes has been reported (8). Here, the end groups are reacted with dimethylamine and the number average molecular weight of the polyester urethane determined from the ratio of NMR absorptions of the chain segments in the polymer backbone to those of the dimethylurea end groups. In this paper, we describe the application of ‘HNMR (220 MWz) for the compositional analysis of polyester urethanes and for the determination of the number average molecular weight of the polyester moiety. Both precision and accuracy of the ‘H NMR technique are reported.
EXPERIMENTAL Proton nuclear magnetic resonance spectroscopy (‘HNMR) is used extensively in our laboratories for both the qualitative and quantitative analysis of polyesters, polyester urethanes, and polyether urethane polymers. Early workers in the field of ‘H NMR established the general utility of this technique for the analysis of polyester polymers (1-5). Proton NMR methods for the identification and compositional analysis of polyester and polyurethane polymers are described in a review by Kasler (6). Brame, e t al., describe the application of ‘HNMR for the analysis of both polyether and polyester urethane polymers (7). This paper gives a table of chemical shift correlations and describes the quantitative analysis of these polymers. Quantitative data from the ‘HNMR analysis of a polyester urethane polymer are compared with data obtained by wet chemical analysis of the same polymer. The application of ‘H NMR for the determination of the number average molecular weight of isocyanate terminated 722
ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
Polybutylene Adipate-MDI Based Polyester Urethane Polymer. The polybutylene adipate-MDI polymer used for the accuracy determination was prepared from a commercial grade polybutylene adipate having a number average molecular weight of 883 g/mol as determined by hydroxyl number analysis and a commercial grade methylene-bis(4-phenylisocyanate)(MDI). Solid MDI (54.4g, 217.6 mmol) was added to a stirred, nitrogen-blanketed reaction flask containing (250g, 283.1 mmol) polybutyleneadipate at 55 “C. The mixture was heated to initiate the reaction. After the reaction exothermed, the product was cast into pans coated with Teflon non-stick finishes. The polybutylene adipate-MDI based polymer used for the precision determination was a commercial polymer and was not modified in any way for this study. Polybutylene Adipate-TDI Based Polyester Urethane Polymer. The polybutylene adipate-TDI based polymer was obtained from a commercial source and used in this work without further modification. Sample Preparation for ‘H NMR Analysis. The polymer samples were prepared for ‘HNMR analysis by dissolving 0.1 g of the polyester urethane polymer in 1 mL of AsC& solvent containing 1% of either tetramethyisilane (TMS) or hexa-
-
TABLE I
CHEMICAL SHIFT DATA FOR POLYBUTYLENE ADIPATE POLYESTER URETHANES C H A I N EXTENDED WITH TDI OR M D I Chemical S h i f t s ppm f r o m HMDSO*
Structure
-
P
P
13
13
Area D e s i g n a t i o n
'-4 1.62
-0CCH2CH2CH2CH2CO-
2.29
-0CCH2CH2CH25CO-
-
3.73
..
3.87 2.13 ( 2 . 1 1 , 2 . 1 8 ) -OCHN
-3C H
-CHN
0 -COCH~CH~CH~CH~O~-
R
-
-
4.06
X1
n
4.15 X
6
"Hexamethyldisiloxane
methyldisiloxane (HMDS). All samples were analyzed using a Varian HR-220 MHz 'H NMR spectrometer. The samples were analyzed in 5-mm 0.d. NMR tubes at various temperatures ranging from ambient to 100 O C . Integration was carried out at a sweep width of 1000 Hz and sweep time of 50 s. Two or three integrations were taken per spectrum and the integration values averaged for calculation. Chemical shifts were referenced to hexamethyldisiloxane and are reported in ppm (6 = 0.00 ppm) for the internal reference. Positive values indicate resonances at lower field strengths.
DISCUSSION The polyester urethane polymers studied in this work were polybutylene adipates chain extended with methylenebis(4-phenylisocyanate) (MDI) or 2,4/2,6-tolylene diisocyanate (TDI). In both cases, the stoichiometry was such that the polymers were hydroxyl terminated. The polybutylene adipate-MDI polymer was synthesized and known to contain polybutylene adipate having a Mn of 883 g/mol and composition of 51.8 mol % 1,4-butanediol, 40.9 mol % adipic acid, and 7.7 mol % MDI. Other polyester urethanes used in this study for a determination of precision of 'H NMR compositional analysis were obtained commercially. A typical 220-MHz NMR spectrum (1000-Hz sweep width) is shown in Figures 1and 2. Chemical shift assignments for the 'H NMR spectra of the polymers are listed in Table I. These assignments are based on chemical shift correlations reported by Brame et al. (7). Two end group structures are possible for the polyester in a hydroxyl terminated polyester urethane, i.e., -CH20H and -NHCOOCH2-. Both of these methylene groups can be observed by 'H NMR and account for the total number of end groups in the polymer. In both cases, the intensity of the 'H
4
3
8
2
o
I
Figure 1. 220-MHz 'H CW-NMR spectrum of the high field region (1000-Hz sweep width) of a polybutylene adipate chain extended with
MDI
___
9
6
6
7
5
8
Flgure 2. 220-MHz 'H CW-NMR spectrum of the low field region (1000-Hz sweep width) of a polybutylene adipate chain extended with
MDI
NMR bands due to these structures is weak compared to those from either the diol or diacid. The polyester urethane polymer based on 1,4-butanediol (BDO), adipic acid, and either TDI or MDI is represented by the general formula, B(AB),II(BA),2BI(BA),,B ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
(1) 723
Table 11. Precision and Accuracy of Compositional Analysis L Accuracy“ Precisionb (Av. + 2 u ) Known Found Commercial polyester urethanes Monomers 51.8 50.4 49.0 c 2.4 50.0 i: 0.84 1,4-Butanediol 40.9 42.2 45.0 i: 2.3 44.2 i: 1.53 Adipic acid 2,4-/2,6-Tolylene diisocyanate ... ... ... 5.9 ? 1.1 Methylene-bis(4-phenylisocyanate) 7.8 7.3 6.0 c 0.76 Average of ten analyses +95%confidence a Polymer composition defined in the first part of the Experimental section. limits for a single determination using commercial polymers of unknown composition. .
where B represents BDO (mol wt 88 g/mol); A, an adipic acid unit (mol wt 112 g/mol); and I, the diisocyanate component in the polyester urethane. The average number of BDO units in the polyester is therefore given by (I?. + 1)and the average number of adipic acid units by I?.. From the 220-MHz spectrum, (I?. 1) can be determined directly from the integrated intensities (Xi, as defined in Table I) according to the following equation:
+
x, + x, t x, x, +
-
BDO=(ii+ 1)=
x3
and the M, of the polyester was calculated from the relationship, -
M,
= (H
+ 1)88 + H(112)
(3)
The monomer composition of the polyester urethane, in mole percent, was calculated directly from the integrated 220-MHz NMR spectrum according to the following equations: mol % BDO =
2(X, - X , ) 2x, + x,
mol % Adipic Acid = mol % MDI =
2x,
2x5
2x,
2x6
+ x,
+ x,
.loo
.loo
Calculation of the monomer composition of a TDI chain extended polybutylene adipate polymer would require a different set of equations since there are three aromatic protons per mole of TDI vs. eight for MDI. The aromatic proton resonances of the polymer used in our work were very weak and so ill-defined that separation of the aromatic and NH bands was not clear. Therefore, the methyl resonances of 2,4-/2,6-tolylene diisocyanate were used to calculate the compositional analysis of the polybutylene adipate-TDI polymer. The accuracy and precision of the ‘H NMR compositional analysis are shown in Table 11. Here, the composition is reported in mole percent and agrees very well with the known polymer composition. Precision of the data is reported for a single determination at the 95% confidence level. Ten determinations were made over a period of several months to calculate precision. As expected, the relative error of the measurement is higher for the diisocyanate than for either the diol or diacid components. This is probably due to the much smaller integrated area of the diisocyanate than for either the diol or diacid. The precision and accuracy of the M, ‘H NMR analysis are shown in Table 111. Accuracy of the method is within the precision limits and is reported for a single determination at the 95% confidence level.
724
ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
.
I
Table 111. Accuracy and Precision of M, ‘HNMR Analysis M, of the Polvester Moietv d m o l Accuracy Precisiona Polymer Known Found Av. c 20 Polybutylene 883 790 790 i: 144 adipate-MDI ... ... 1960 i: 287b Polybut ylene adipate-TDI a Average of ten determinations c95% confidence limits Commercial polyester of unfor a single determination. known composition and polyester M,. The ‘H NMR measurement of the M, of the polyester moiety in these polyester urethanes was not as precise as expected. Part of the problem is that the measurement involves incompletely resolved ‘H NMR analytical bands which differ markedly in relative intensity, see Figure 1. As the M,, of the polyester moiety increases, these effects become more pronounced and even less precise data would be expected from the ‘H NMR analysis. For a 2000 M,, polyester the intensity ratio of the analytical ‘H NMR bands for the M, determination is ~ 1 0 1 At . 5OOO M,, the intensity ratio would be -251. From the preceding, application of this technique would appear to be practical only for polyester urethanes having a M, of less than 5000 for the polyester moiety. However, it should be possible to carry out this analysis for higher molecular weight polyesters using an internal standard and either time averaging or ‘HFT-NMR. In conclusion, the accuracy and precision of the ‘HNMR analyses are such that quantitative data can be obtained from a single analysis. The technique is far superior to gas chromatographyand infrared analysis which require extensive calibration and, in the former case, sample hydrolysis. If even better precision is required, the average of four or six independent analyses for M, should provide improved quantitative data without an unreasonable investment in analysis time or expense.
LITERATURE CITED (1) D. F. Percival and M. P. Stevens, Anal. Chem., 38, 1574 (1964). (2) Y. Mukoyama, K. Fiyieda, and J. Utsumi, Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, 1971. (3) T. S. Khramova, Y. G. Urman, 0. A. Mochalova, F. M. Medvedeva, and I. Y. Sionim, Vysokomol. Soedin, Ser. A , 10 (4), 894 (1968). (4) L. C. Afremow, J . falnt Technol., 40, 503 (1968). (5) M. L. Yeagie, J . faint Technol., 42, 472 (1970). (6) F. Kasler, “QuantkattveAnalysis by NMR Spectroscopy”, Academic Press, New York. N.Y. 1973. (7) E. G. Brarne, Jr., R. C. Ferguson, and G. J. Thomas, Anal. Chem., 39, 517 (1967). (8) Y. Chokki, M. Nakabayashi, and M. Suml, Macromol. Chern., 153, 189 (1972).
RECEIVED for review December 9, 1976. Accepted February 3, 1977.
