Instrumentation
Polymer Analysis Using Pyrolysis-GC-FTIR-MS and GC-AED
Rimiko Oguchi, Ayako Shimizu, Satoru Yamashita, and Kenji Yamaguchi
Analytical Instruments Sales Department. Yokogawa EIectric Corporation, 2-11-19 Nakacho. Musashho-shi. Tokyo

Philip Wylie
Hewlett-Packard Co.. Po. Box 900, Rt. 41 and Starr Rd., Avondale, PA 19311. USA

1 Introduction
Key Words:
system consists of a pyrolysls GC equipped
During the last decade. analytical instru- Capillary gas chromatography
with an atomic emission detector (AED)
ments employed in polymer analysis have Pyrolysis
developed greatly. Fourier transform nu- Mass spectrometry
The AED is an element-selective GC
clear magnetic resonance spectroscopy
Fourier transform infrared detector detector which can be used to determine(FTNMR) and Fourier transform infrared Atomic emission detector
the elemental composition corresponding
spectroscopy (FTIR) are often used toPolymer analysis
to each GC peak Column eluate enters aobtain structural information needed for
microwave-induced helium Plasma where
the Identification of monomers, and theSummary
the very high temperatures cause thedetermination of copolymer cornposition
molecules to become atomized In thisand differences in isomeric structure [1-6]. Volatile pyrolysates of a methyl methprocess. the molecules constituent atoms
Acrylate-butadiene-styrene copolymer
are raised to electronically excited states
Pyrolysis GC has recently become popular (MBS) have been analyzed using a capil- or are ionized by the plasma as they returnfor polymer analysis because of its simplic- lary gas Chromatograph equipped with a to lower electronic energy levels photons
ity and its capacity for providing important and a gas Chromatograph-atomic emisare emitted at wavelengths that are charstructural information. A typical system Among the volatile compounds observed acteristic of the particular element. A phoconsists of a low dead-volume pyrolyzer. a were monomers used for synthesis of the todiode-array-based optical emission
high resolution capillary GC and a detec- polymer. Numerous oligomers of higher
spectrometer is used to measure the wavetor. Polymers are degraded in the pyrolyzer boiling point were also found; identifilength and intensity of the emitted light.
and the volatile pyrolysates are swept into cation of these could be used to give
This data may be used to identify thethe high resolution GC for separation and structural information about the parent elements present and determine their reladetection. The advantage of this system is polymer.
tive amounts It is possible. in principle, tothat both monomer and polymer composi- Combining information from these tech- detect any element in the periodic table,tion can be investigated qualitatively.
niques was found to be extremely useful except helium. present in molecules which
for the analysis of polymer pyrolysis useful can be eluted from a GC So far methods
The value of pyrolysis GC data is very
for the analysis of polymer pyrolysis pro- have been developed for 23 different elemuch dependent upon the GC detector
ducts. In characterizing each compound ments and four isotopes (13C. 14C. 15N. andemployed The most popular detector has
it was found paeticularly helpful to juxta- D) [7-13].
been the mass spectrometer because it can pose feature-specific chromatograms
In this study au three spectral detectors
provide structural information about the (e.g., single ion monitoring from the(IR, MS, and AED) were used to characterpyrolysis fragments. More recently. a com- mass-selective detector and the selectedize compounds eluting following pyrolysis
pact FTIR spectrometer has been comof an MBS copolymer.
wavelength chromatography frome thebined with a mass spectral detector toMBS copolymer is one of the most popular
infrared detector.)
construct a tandem GC-FTIR-MS system.
plastics because of its good transparency
This system can provide both mass specand high strength. It can be molded intotral and complementary infrared data frommany different components and is often
a single GC injection. Another powerfuladded to other polymers as a modifier Itcan be produced with a wide variety ofpolymer compositions, depending upon
the amounts of butadiene, styrene, andmethyl methacrylate used, and also
because various graft ratios are possible.
Tsuge and Otani [1] have reported theanalysis of one MBS copolymer using pyrolysis capillary GC. The chromatogram
obtained from our study was similar totheirs, except that the pattern of compounds of low volatility was different.
Differences in monomer sequence andpolymer additives may be responsible forthis discrepaney.

2 Experimental
MBS copolymer pellets were obtained froma molding factory. The sample. consisted ofa straight chain MBS copolymer with nografts, a type of MBS copolymer widelyused in industry. Pyrolysis was performed
with a JHP-3 Curie Point Pyrolyzer (JaphnAnalytical Industry Corp.. Tokyo, Japan).
Approximately 1 mg of MBS polymer was
cut from the pellet and wrapped in metal
foil. The sample was pyrolyzed for 5 s at590°C: volatiles were swept into the GC
inlet by a flow of helium through a length of0.53 mm i.d. fused silica tubing which washeld at 200°C.
The tandem GC-IR-MS system used in thisstudy consisted of a Hewlett-Packard
5890A Gas Chromatograph, an HP5965A
Infrared Detector (IRD) equipped with a

100µ L internal volume Pyrex light-pipeand an HP5970B Mass Selective Detector(MSD). The IRD and MSD were connected
in series by means of a 1 m length of 0.1 mm
i.d. fused silica capillary tubing extending
from the light-pipe to- the MSD. The MBScopolymer was also analyzed using asystem consisting of the pyrolysis unit
coupled to an HP5890A gas chr6matograph equipped with an HP5921A atomic
emission detector. Although AED canmonitor up to 23 different elements andfour isotopes (13C, 14C, 15N and D),
5 channels (carbon, hydrogen, oxygen,nitrogen, and sulfur) were used for thisstudy. MBS pyrolysis products could bemonitored using the carbon, hydrogen,and oxygen channels while heteroatomcontaining additives to the polymer could
be observed with the nitrogen and sulfurchannels.
A 30 m x 0.32 mm i.d. x 0.53µm film HP-5
(5 % diphenylpolydimethyl siloxane) fusedsilica capillary column was used in bothGC systems under the same conditions. Allconditions and parameters used for thisstudy are listed in Table l.
3 Results and Discussion
3.1 Chromatographic-Analysis
Figure 1 shows the total ion chromatogram (TIC) and total response chromatogram (TRC) obtained from the GC-IR—MS
system following pyrolysis of MBS-

Table1Analytical conditions used in the investigation.

GCChromatograph oven temperature
Injection method
Injection temperature
Column head pressure
GC-MSTransfer line temperature of MSD
GC-IR
Light-pipe temperature
Make-up gas
Scan speed
Transfer line temperature (of IRD)
GC -AED
Transfer line temperature (of AED)
Make-up gas
Reagent gases

40°C (1 min) –4°/min–250°C
Split, split ratio 1: 50
250°C
103 kPa
250°C
280°C
Inlet: helium 0.5 ml/min
Outlet: helium 0.1 ml/min
3 scans/s
280 ‘C
280°C
30 ml/minoxygen, hydrogen for carbon, sulfur, and nitrogen
oxygen for carbon and hydrogenhydrogen 10% methane in nitrogen for oxygen

Figure 2 shows the 5 elemental profiles
obtained from the GC-AED system.
The TIC and the carbon and hydrogen
profiles from the AED showed more than
50 peaks. Fewer peaks were observed in
the TRC and in the oxygen- end sulfurspecific chromatograms : no peaks wereobserved in the nitrogen-specific chromatogram, suggesting that the polymer had
no nitrogen-containing additives such asacrylonitrile. The six peaks observed in thesulfur-specific chromatogram a[e, in fact,indicative of sulfur- containing compounds
and do not result from imperfect selectivityof the AED: many of the large peaks in thecarbon chromatogram (such as 19. 24, and42) do not have corresponding peaks in thesulfur chromatogram. Neither the TIC nor
the TRC gave sufficient information to
enable determination of the structures ofthe compounds generating the sulfur-specific peaks.
Several of the peaks observed in the TIC(e.g. , 11 , 31 , and 44) were from compounds
generating only a small response in theTRC. Several others (e.g., 12, 13, 14, and36) were not observed at all in the TRC.
Interestingly, the compounds which were
not detected by the IRD probably contained no oxygen since they gave no peaksin the AED oxygen-specific chromatogram.
MBS pyfolysis can generate two types ofvolatile compound. One group contains
oxygen and is derived from methyl methacrylate while the other. .containing only

hydrocarbons. is derived from butadienearid styrene. Compounds generating little
IR response are hydrocarbons While those
producing a greater response are mostly
esters. Peaks from compounds containing
ester functions could be identified by
selected wavelength chromatography(SWC) in the 1700-1780 cm-1 and 11001280 crn-1 regions. Using this procedurethe major peaks in the IRD trace. except forPeak 15. were all shown to be produced byesters. SWC showed the presence of acarbonyl group but no ester bond in thecompound generating peak 15 while themass spectrum was indicative of a phenylgroup (m/z77). From the infrared and massspectra. peak 15 was identified as that ofacetophenone: this was consistent with its

elemental content determined by GCAED.
Before the individual compounds wereactually identified, they could be grouped
into distinct classes based on the results
obtained using the AED. selected ion
monitoring (SIN) arid SWC. The TIC. TRC.
and AED elemental profiles were then used
to identify individual peaks,

the tentative identifications. For this compound the top three choices horn the MS
library search were an aromatic ester andtwo aromatic hydrocarbons (Table 2).
Only the first, methyl 2-methenyl-3-phenylpropionate. has a match quality large
enough for serious consideration and evenits value of 83 left some doubt about thecompound’s identity.

The IRD library search gave six choiceswith match qualities between 862 and 889
since the IR spectral library is considerablyMore than halt the compounds were idensmaller than the MS library, the chances oftified by combining information from GCIR-MS and GC-AED analyses The identifi- its containing the correct compound werecation of the compound generating peak 19 lower. Such library search results are.
carl be used to illustrate how data from the however, still very useful because thecompounds selected usually have functhree detectors were combined to provide
3.2 Identification

tional groups similar to those present inthe unknown. For peak 19. none of thechoices matched the MS results. but all of
the top choices were esters In addition,
the first two choices were esters of itaconic
acid. a compound having a terminal
methylene group. The remaining choices
were au aromatic. Only the first MS librarychoice, methy1 2-methenyl-3-pherlylpropionate. was consistent with the functional groups indicated by the IR library
search.

calibration standard as long as it contains
all the elements of interest and can be
resolved chromatographically.
The three spectral detectors provide complementary evidence for compound identification. Far more confidence may beplaced in structural determinations Whendata from all three detectors are consistent.
3.3 Monomers. Diners and Trimers

Using procedures already described[14-16]. C : H : O ratio of the unknown was
found to be 11 : 11.57 : 2.21 suggesting
empirical formulas of C11H1202, C11H1102.
or C22H2304. The last two had odd molecular weights and could thus be ignored. The
first possibility. C11H1202, is the correct
molecular formula for methy1 2-methenyl3-phenylpropionate.

From their retention times and molecularweights. the pyrolysates could be easily
categorized into three groups. The firstincluded compounds generating peaks 2 to
15: these had molecular weights between
54 and 132 and were identified by MS andIR as monomers and monomer derivatives
produced by pyrolysis. Peak 2 was butadiene and 3. 4 arid 5 were identified as
being from methyl propionate. methyl
isobutyrate, and methyl methacrylatemonomer respectively. Esters 3 and 4 areprobably pyrolysis products from methyl
methacrylate units in the polymer Compound 9. the major pyrolysis product. wasfound to be styrene and 6. 10. 11. 12, 13, 14.
and 1 5 were from minor pyrolysis products
related to styrene.

Methyl 2lmethy1-4-phenyl-4-pentenoate(peak 22) was used as the calibration
standard for determining the elemental
ratios since it could be identified reliably
by all three detectors. While it is helpful toinclude an internal standard for this purpose. the use of such a standard wasproscribed by the nature of the pyrolysis
experiment. Any known compound in thesample may. however. be used as theDiners span the region from peaks 16 to36. The early peaks were assigned as
methyl methacrylate diners (MM). followed by methyl methacrylate-styrene
diners (MS), and then, at the end of therange. styrene diners (SS).
The trimers elute in the last region of thechromatogram. From the infrared andmass spectra and the element-specificchromatogram for carbon, hydrogen. andThe AED showed that the compound contained carbon. hydrogen. and oxygen
which eliminated the hydrocarbons
chosen by the MS library search. No sulfur
or nitrogen were found.
Several authors have discussed using theAED to determine approximate empiricalformulas [4-16].

oxygen it was possible to determine themonomeric constituents of the trimers; amore detailed structural analysis was,however. beyond the scope of this studyWhile the total peak area attributed to thediners was less than that for monomers ortrimers. nearly half the peaks were found in
this range. This complexity arises because
styrene can dimerize in at least-five different ways to Produce the structures shownin Table 3. These styrene-based dimers,
compounds 25. 29. 31, 32. and 34. could be
detected easily because they had no carbonyl absorbances or peaks in the oxygenspecific chromatogram. The variety ofdiners present suggests that the MSS
polymer had a complex composition. The
compounds identified in the MBS pyrolysates are listed in Table 3.