A New Curie-point Direct Injection Probe for Mass Spectrometry
2. Application to Synthetic Polymer Analysis
Naoki OGURI*a), Akira ONISflla), Sigeki UcHINOa),
Keiji HASHIMOTOb), and Xigao JINC)(Received November 11, 199l)

A Curie-point direct injection probe to be coupled to a mass spectrometer was developed.
Its flash heating, wide range temperatures (160 〜 l.040°C), reproducible temperature ( ± 1°C)
and direct connection to the ion source of a mass spectrometer were effectively applied to thepolymer analysis. Pyrolysis-mass spectrometry by use of this device enabled the discrimination between a copolymer and the corresponding blended polymer of {poly(styrene) andpoly(fluorostyrene)}, because of the decreased secondary reactions among the pyrolyzates,when compared with pyrolysis gas chromatography (Py-GC). As compared with Py-GC, the
new technique can elute larger pyrolyzates, only within a few minutes, which provide
compositional and structural information of the polymer samples. The rapid analysis of anadditive in a polymer is also reported in this paper.

1 Introduction
The concept of combining a pyrolysis
inlet system with a mass spectrometer(MS) has been utilized to provide fingerprint analysis and to study thermal degradation of materials 1). pyrolysis-MS(Py-MS) has found application in a wide
range of analytical fields, including thestudy of synthetic polymers, biochemistry, geochemistry and environmental
studies 2). However, its development has
been severely hindered by the lack ofpractical instrumentation, which has restricted the number of laboratories toaccess to this technique3).
An ordinary furnace-pyrolysis probe is
not suitable for some Py-MS analyses because of its low maximum temperature(about 300°C) and long temperature risetime (TRT). In addition, pyrolysis of thermally resistant polymers is very difficult
in some instruments because of their lowmaximum temperature caused by an insulator between the heat source and thesample, or the remote sample cell locationfrom the heat source. Curie-point pyrolysis provides a precise and reproducible
method, with a maximum heating temperature of 1,040°C and a TRT of less than
0.2sec 4). Although Curie-point Py-MSsystems have been described 3).5), the detection limit of m/I values is quite low(200•`300) in those systems, which may
be mainly caused by condensation ofpyrolyzates on the surface between thesample cell and the ionization source ofthe MS, due to the long distance between
them. A Curie-point direct injection
probe (JDI-800) was developed in ourlaboratory for use with an MS 6 ) • ` 8 ) . At thetop of this probe. a small silver tube
which served as a thermal conductor andallows the sample cell to be closer to theentrance of the ion source was inserted.
This prevented condensation of higher
boiling point pyrolyzates, which enabled
to analyze synthetic polymers. Some applications of the Py-MS system equippedwith the JDI-800 to the analysis of synthetic polymers is described in this paper.
2. Experimental
2.1 Materials
A styrene-2-nuorostyrene copolymer[P(S-FS)] and poly(2-fluorostyrene) (PFS)
were synthesized by radical polymerization in solution. The content of 2-flourostyrene (FS) units in the polymer was49.7%, as determined by elemental analysis. Polystyrene (PS) with Mn=l3,000
was a standard sample purchased fromPressure Chemical Co., USA.
A series of styrene-divinylbenzenepyrenonyl propyonic isopropylether copolymers were polymerized in an aqueous
suspension, and purified with water, glacial acetic acid, acetone and chloroform toremove the residual monomers. The
pyrene contents in the copolymers wereanalyzed by fluorescence spectrometry
using an internal standard.
A poly(phenylene sulfide) (PPS) used as
the standard polymer was obtained from
Polyscience, Inc., USA.
A commercial grained polypropylene(PP) containing trace amounts of anantioxidant, di-i-butyl-4-hydroxytoluene(BHT), and a polyphenylene oxide (PPO),
were supplied by Mitsui Petrochemical
Industries Ltd. and General Electric Co..

USA, respectively.
2.2 Curie-point direct injection probe
The Curie-point direct injection probe
assembly JDI-800, was described in detailelsewhere 7).8). It consisted of an injection
probe and a radio frequency power (RF)supply.
At the top of the probe, there is a small
silver tube which serves as a thermal
conductor and allows the sample to becloser to the entrance of the ion source.
This prevents condensation of higher
boiling point fractions, and hold thepyrofoil® tightly to ion source while theinjection probe is inserted into the MS. A
cross section of the silver tube is shown in
the previous papers). A slit in the silver
tube can effectively prevent the sample
cell from breaking and releasing the tube.
The Curie-point heating area of the injection probe was made of ceramics andmetals. Organic material was not used inorder to prevent noise. By unscrewing
the two screws at the terminals, the ceramic bobbin with the RF coil could be
separated from the shaft, and contaminants could then be removed by washingit with an appropriate solvent or baking
at 300°C.
A quartz sample cell (9 mmx2 mm i.d.)
was held inside the RF induction coil by aceramic bobbin. A small Viton® 0-ringseal (without grease) was placed far fromthe Curie-point heating area, at thebottom of the sample cell inside the probe,
to maintain the cell’s position.
The power supply delivered 48 W at 10MHz, and pyrolysis time was controlledfrom 0.1 to 10sec. Twenty kinds ofpyrofoils® with Curie points from 160°C
to 1,040°C and temperature accuracy ofset into the quartz sample cell with thesilver tube, and then the ceu was inserted
into the RF coil.
2.3 Mass spectrometry
The mass spectra were measured with aShimadzu QP 2000A quadrupole MS
which wasoperated with EI at 70 eV. The
temperature of the ion source was 250°C
and the scan rate was 0.5 see/scan.

3. Results and Discussion
3.I Thermal degradation of styrene
polymers
lt is well known that in the absence ofoxygen, PS thermally degrades mainly tomonomer, with some diners and trimers.

2.4 Sample inlet
The amount of the sample injected was The formation of the dimers and trimer
less than 2 ì g, to prevent contamination has been said mostly to occur by intraof the ion source. For soluble samples, I molecular transfers from the secondary
pl of sample solution (about 0.1 wt%) was macroradicals, followed by a-scission. Onthe contrary, Dean9) and Ohtani et al.10)
placed on the center of a piece of
pyrofoil® (1.8 X 8 mm, 50 ì m thick) with a recently suggested that the dimers andmicro-syringe, and was dried at 80°C in a trimers may be formed to some extent bymonomer recombination in the pyrolysis.
vacuum oven. Then the sampled
Figure 1 shows high resolution pyropyrofoil® was put into the standard cell.
lysis-gas chromatograms of P(S-FS) andFor insoluble, or solid samples, thesamples were wrapped in the Pyrofoil®. in mixture (1:1, in solution) of PS and PFS
pyrolyzed at 500°C with a CDS 190 Pyrotight contact with each other, and theprobe coupled to an HP 5890 capillary gas
pyrofoil® was then folded at the center
chromatograph. The hybrid dimers (S-Fand bent into “V” shape as described inelsewhere7). The sampled Pyrofoil® was and F-S) can still be seen on the pyrogramof the polymer mixture, which suggests

that the diner formation could have been mer blend.
caused by recombination in the pyrolyzer
or in the transfer pipe, or both after degradation. Therefore, by this data it is im- 3.2 Polymer characterization
possible to distinguish the blend from the The larger fragments and oligomers in
copolymer. Mass pyrograms of the same the pyrolysis products usually provide
samples pyrolyzed at 500°C for 5 sec with more detailed information regarding themicrostructure (stereoregularity, confora JDI-800 are shown in Fig. 2. In thismation, sequence distribution. etc.). The
case,pyrolyzates with higher molecular weight
no hybrid dimers were observed on thepyrogram of the PS-PFS blend. This in- sometimes cannot be eluted by Py-GC
dicates that the pyrolysis direct injection because of condensation in the transfer
probe almost completely suppressed the pipe or the sparation column, or both11).
secondary reaction. Thus. the copolymer However, by use of the pyrolysis direct
can easily be distinguished from the poly- injection probe inserted and connecteddirectly to ion source of the MS, the condensation of the higher boiling point
pyrolyzates is limited and they can bedetected more easily than by Py-GC.
Figure 3 is a mass pyrogram of PPO.
measured by the Py-MS system with theJDI-800, in which peaks up to tetramers
are clearly observed. Therefore, thismethod gives more information for themicrostructural analysis and for the investigation of thermal degradation ofpolymers.
Figure 4 is a mass spectrum of PPS,
measured with the same system, in which

up to the tetramer of phenylene sulBde isobserved. When this analysis is done by
Py-GC about 50 min is needed 12) due to thecolumn elution required to repeat theassociated temperature programing forthe column oven. With Py-MS, only threeminutes elapsed from the time that thepps was put on the Pyrofoil® until themass spectrum was recorded. The identified pyrolyzates were benzene, phenylmercaptan, 1.4-dimercaptobenzene, diphenylene sulfide, mercaptodiphenylthioether, trimer and tetramer.
Figure 5 shows the mass pyrogram of a

styrene-pyrene containing copolymer inwhich the pyrene content was 3% by mo1.
The mass pyrogram of the copolymer,
measured at 358°C had some characteristic peaks related to pyrene groups and theidentification of trace comonomers in thiscopolymer was greatly simplified by thistechnique.
Figure 6 shows another application to
the analysis of a polymer additive performed without any sample preseparation. PP was heated at 220°C for 3 sec,
which was lower than the polymer pyrolysis temperature. On this mass spectrum, the molecular peak of the added
antioxidant, BHT is clearly observed atm/z 220 in addition to its fragments atm/z 206, 205 and l49.
4. Conclusions
Curie-point Py-MS is a rapid and simple
technique for the analysis of synthetic
polymers. The data presented here indicate that this method can yield compositional and structural information. A
copolymer is distinguished from the associated polymer blend by the Py-MSsystem which eliminates most of the secondary reactions.