dentifkation of Acrylate and ethacrylate Polymers by Gas Chromatography E. A. RADELL and H. C. STRUTZ Industrial Labarato~,Eastman Kodak Ca., Rochester,
.Each acrylate and methacylate polymer, singly and in mixtures, will produce a unique chromatogram when pyrolyzed. By heating a sample in a closed system in an inert gas and feeding the pyrolyzate directly into a gas chromatograph, it is possible to identify the original monomers. A sample size of approximately 5 mg. or l e u is used and the time required for a single analysis is 15 to 45 minutes. By repeating the analysis on two columns with different retention characteristics, qualitative identification of the fraction may be made. Cursory examination of other polymers indicates that this procedure may be applicable to a wide range of polymers and copolymers.
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sample loops on the gas sampling valve (6). A Wood's Alloy bath was used to heat the pyrolysis loop. This type of bath aUnwed rapid and controlled heating which resulted in a simple mixture of pyrolysis products. The temperature of the bath was measured with a Chromel-Alumel thermocouple connected to a pyrometer.
AS chromatography, 'coupled with
a controlled temperature pyrolysis technique, provides a rapid method for the identification of acrylate and methacrylate polymers. Small samples of these polymers are pyrolyzed and the pyrolyzate is fed directly into a gas chromatograph by the use of a gas sampling valve. The work of Zemany (8) and Harms (3) showed that a substance will decompose in a specific wnv. " , if the conditions of uvrolvsis are held constant. In the methods used by Davidsou, Slaney, and Wragg (I) and Haslam and Jeffs (5),the pyrolysis is a separate oneration. Haslam. Hamilton. and Jbffs (4) convert the alkoxy1 g r & n of the monomers to the corresponding iodides and separate them chromatographically. Chromatographing the complete pyrolyzate allows ior the separation and identification of higher boiling monomers and the same esters of acrylic and methacrylic acid.
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I
Figure 1.
EXPERIMENTM
The expected pyrolysis producta of the polymers were introduced into several columns under various conditions, and the most e5cient column was di-n-decyl phthalate. However, columns packed with firebrick coated with diglycol stearate and Dow Corning No. 550 silicone were also found to he satisfactory. The best conditions for the phthalate column were a temperature of 100" C.;a flow of 50 ml. per minute, and a pressure of 20 p.s.i. (Figure 2). The use of a 4meter column allowed better separations but increased the time required for a run. The most satisfactory conditions for pyrolysis were a temperature of 500" C. for 30 seconds in a helium atmosphere. These conditions are similar to those found most applicable by De Angelis. Ippoliti, and Spina (2). Below this temperature the polymers did not appear to hresk down sukliciently; above 550" C. the chromatogram of the pyrolyzate was not reproducible. Under the experimental conditions, the, acrylate polymers appeared to degrade to a mixture of the monomer-various shortchain alcohols and a mixture of various fragments (Figure 3). This laboratory confirmed the original work of Straua and Madorsky (7)-i.e., poly(methy1 methacrylate) degrades primarily to the mnnomer (Figure 4). Under the conditions of the experiment, the ethyi and rbhutyl methacrylate polymers a h degraded primarily to their monomers.
Pyrolysis loop
APPARATUS
A Model 151 Perkin-Elmer Vapor Fractometer equipped with a gas a m pling valve and a %meter column of dindecyl phthalate was used for this work. A IO-mv. recorder was used; however, if a more sensitive recorder were used, smaller samples could be identilied. Helium was used as the carrier gas with a flow of approximately 50 ml. per minute. Figure 1 shows the pyrolysis loop which wan substituted for the gas 18%
ANALYTICAL CHEMISTRY
Figure 2. Gas chromatogram of alcohols and acrylate and methacrylate monomers 8. Methand C. Ethyl alcohd D. Isonropil alcohd E.
F. G.
R
Methyl acrylate Ethyl acrylate Methyl meth~cryldlo Isopropyl ocrybte
1. 1.
".Butyl akohd
Ethyl methacrylate n-Pmpyl acrylde L Lopmpyl methocrylato M. RBUiyl melhh.uylote N. h o b q l nethocrylete 0. ".B"PyI methocrylots I(.
a
A
8
G
10
5
~-
-T
15
0
TIME IN MINUTES
6
5
10
8. C.
E.
Air Methanol Ethyl alcohol
G.
TIME
5
0
IN MINUTES
0
TIME IN MINUTES
Figure 3. Gas chromatogram of pyrolyzate of poly(methY1 acrylate) A.
10
Methyl acrylate Methyl melhacrylate
E
A
Figure 4. Ga.c chromatogram of pyrolyzat5 of poly(methy1 rnettracrylate)
A
Alr
G.
Figure 5. Gas chromatogram of pyrolyzate of ~ o l ~ ( e ahc~~ l a t e ) A. 6.
Methyl methacrylate
Air Ethyl alcohol
F. 1.
Ethyl acrylate Ethyl methacrylate
Figure 7. Gas chromatogram of pyrolyzate of unknown polymer
C
A.
8. C.
E. F. G. a.
Air Methanol Ethyl alcohd Methyl acrylate Ethyl acrylate Methyl methacrylate Ethyl methacrylate
I / /
.
-t 15
IO io
TIME
5
0
IN MINUTES
Figure 6. Gas Chromatogram of pyrolyzate of unknown polymer A.
Air
E.
6. C.
Methanal Ethyl alcohol
G.
Methyl acrylate Methyl methacrylate
While all of the eluted pyrolysis products were not identified, each polymer investigated jielded a unique chromatogram. PROCEDURE
The pyrolysis apparatus was taken apart at the reducing union and a Smg. sample of the polymer was placed in the bottom of the loop. The pyrolysis apparatus was reassembled and connected t o the gas sampler valve in place of the constant volume tube. Plugs were placed in the regular sample inlet and in the vent openings of the gas sampler valve. Helium was used to flush the air from the apparatus and the system was closed. The loop of the apparatus was heated at 500" C. for 30 seconds by immersing it in a Wood's Alloy bath. Products resulting from the pyrolysis were swept into t,he gas chromatographic column with helium.
The identification and composition of the polymer were determined by comparison of the chromatogram of the sample with chromatograms of known monomers and pyrolysates of known polymers. RESULTS AND CONCLUSIONS
Figures 3 and 5 are the chromatograms of the pyrolyzates of poly(methy1 acrylate) and poly(ethy1 acrylate). Comparison of the chromatogram from an unknown acrylate polymer (Figure 6) with the above identified the unknown as being essentially poly(methy1 acrylate). Figure 7 is the chromatogram of the pyrolysate of an unknown polymeric material suspected to be an acrylate and methacrylate copolymer. Comparison of the retention times of the major peak-, with the retention times of the major peaks of various monomem indicated the presence of three monomers. The additional peaks present were accounted for by comparison with the chromatograms of individual polymers. The unknown was identified as being composed of methyl and ethyl methacrylate and methyl acrylate. The method can also be used for the
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semiquantitative determination of acrylate and methacrylate monomers in mechanical mixtures of polymers. This technique may be proved useful in solving problems connected with the production of polymeric materials and for the monitoring of production material. The applicability of this method to the analysis of other types of polymers is being investigated. LITERATURE CITED
(1) Davidson, W. H. T., Slaney, S., Wragg, 0. L., Chem. &- Ind. (London) 1954, 1356. {2) De Angelis, G., Ippoliti, l'., Spina, N., Ricerea sci. 28, 1444-50 (1958); Anal. Abstr. 6,991 (1959). (3) Harms, 1). L., A N A L . CHEM. 2 5 , 1140-55 (1953). (4) Haslarn, J., Hamilton, .I. R., Jcffs, A . R., Analyst 8 3 , 6 6 7 1 (1958). (5) Haslarn, J., Jeffs, .4. R., J . d p p l . Chem. ( L a d o n )7 , 2 4 3 2 (1957). (6) Perkin-Elmer Product Bulletin, No. A-7. (7) Straus, S., Madorsky, S. L., J . Research Nail. Bur. Standards 50, 165-76 (1953). (8) Zernany, P. D., ANAL. CHEW 24, 1709-13 (1952).
RECEIVEDfor review May 6, Accepted August 24, 1959. YOL. 31, NO. 11. NOVEMBER 1959
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