Analysis of Polyester by a Combination of Curie-Point HeatingTechniques and Preparative Liquid Chromatography

Naoki Oguri*, Akira Onishi*, Sigeki Uchino*, Keiji Nakahashi* and Xigao Jin***Japan Analytical Industry Co., Ltd., 208, Musashi, Mizuho, Nishitama, Tokyo 190-12, Japan**Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080, China
A Curie-point heating technique has already been introduced to pyrolysis-gas chromatography, which was developed byus. We analyzed thecomponent ofa multi-component polyestercompletely by using acombination ofthe technique andpreparative HPLC. We used Curie-point pyrolysis-GC/ MS, direct injection/ MS, headspace-GC / MS and preparative
HPLC for this study. We could thus determine the composition ofthe uncured polyester for manufacturing man-mademarble consisting of an uncured polyester prepolymer, a crosslinking accelerator, an acrylate copolymer as themodification agent and some additives (surfactant and plasticizer). This analytical method is an available, convenient
way for compositional analysis of complex polymers materials.

Keywords Curie-point pyrolysis, Curie-point direct injection probe, headspace gas chromatography, mass
spectrometry, preparative liquid chromatography, polyester

Pyrolysis gas chromatography-mass spectrometry(PyGC/MS) has recently become popular for polymer
analysis owing to its simplicity and capacity for providing
important compositional and structural information,
especially regarding multi-component materials. Oneof the advantages of this method is that all compositionsof the polymer(s), and additive(s) employed in thematerial can be investigated without any pretreatment.1 2
On the other hand, headspace-GC/MS is a powerfulmeasurement technique for volatile compounds insolids.3 Moreover, it is suggested that that data becompared with the Py-GC results for a distinction ofvolatile components from pyrolyzates on a pyrogram ofa multi-component polymer material. An on-line direct
injection/MS(D1/MS) technique could separate thepyrolyzates and volatile components of a polymer sample
according to the mass on a liner scale with very highsensitivity; it thus enables a rapid analysis with athroughput of up to one sample per minutes. 4.5 For
the most complex material system, fractional separationby preparative liquid chromatography is helpful,and sometime necessary, to obtain pure fractions
and then identify them individually by Py-GC or
pyrolysis-DI/MS in order to determine definite mass
data.6 Due to the high heating speed (less than 0.2 s of
the temperature raise time), accurate temperature
reproducibility ( ± 1°C) and a wide temperature range(160 - 1040°C), the Curie-point heating technique has
successfully been applied to Py-GC/MS, Dl/MS andh e a d s p a c e - G C / M S . 2,3,7,8 I n t h i s w o r k , a l l o f t h emeasurements mentioned above were used tocharacterize a multi-component thermosetting polymer
system composited by the uncured unsaturated polyester
resin, curing agent modification agent and additives.
Experimental

SampleA set of uncured unsaturated polyester resin (BX-923,Synthetic Resin Co. of Beijing, China) comprised twoparts (coded as part A and B), including a prepolymer,
reactive monomer, curing accelerator, modificationmaterial and additives in the sample. This polymer wasmixed with marble powder, and used for manufacturing
man-made marble.
Apparatus
Pyrolysis or headspace sampling was carried out using
a Model JHP-3 Curie-point Pyrolyzer or a Model JHS100 Curie-point Headspace Sampler (Japan AnalyticalIndustry Co., Ltd.), which was combined with an on-line
Model QP-2000A GC/MS system (Shimadzu Co.,Japan). The GC/MS was equipped with a highresolution, fused-silica capillary column (J&W Sci., DB1, 0.25mmi.d.X30m) coated withimmobilizedpoly(dimethyl silicone) of 0.25urn thickness, and aquadrupole mass spectrometer with an El ionization
source(70eV). A JDI800Curie-point DI Probe(JapanAnalytical Industry Co., Ltd.) was inserted in a QP

2000A mass system up to the position where the sample
cell (9 mmX2mm i.d.) at the tip of the probe could beconnected to the ion source.8 The sample was wrappedin Pyrofoil ® with tight contact. The amounts ofsamples to be injected were less than 2ug, 0.1 mg and0.4 mg for DI/ MS, Py-GC/ MS and headspace-GC/ MS,
respectively. The GC column temperature was initiallymaintained at 35°C for 5 min, and then programmed to300°C at 8°C / min. From the carrier gas of helium,
50ml/min was split at a ratio of 50:1. The volatile
fractions of the headspace samples extracted at 220°C
for 10 min were transferred to an adsorbent, (Tenax®) at-40°C, and then desorbed at 255°C for 10 s by
Pyrofoil ® with Curie-point heating. A Model LC-908,
preparative liquid chromatograph (HPLC) was equippedwith the series of columns (GPC) of ModelJaigel-1 H andJaigel-2H and a refractive index detector (JapanAnalytical Industry Co., Ltd.). Chloroform was used asthe solvent (40kg/cm2, 3.8 ml/min). The sample size
injected was 50 mg in 3 ml of the chloroform.

the pyrolyzate peaks in Fig. 1 corresponded to then u m b e r s i n Ta b l e 1 . P e a k s 2 a n d 3 ( w i t h s h o r t e rretention times) indicate unsaturated hydrocarbon andalcohol derived from the hexylene sequences in thepolymer chains. In particular, the α , ω -diens are most
likely formed through the predominant pyrolysis
mechanism involving a cyclic transition state at twoneighboring ester linkages for the polyester (Scheme 19).
The 1, 5, and 7 peaks correspond to benzene, phthalicanhydride, and cyclohexenyl phthalate, respectively,
which were also the main peaks on the pyrogram of thepolyester synthesized by phthalic acid and hexenediol.10
A mostly characteristic pyrolyzate, dihexenyl phthalate
as the monomer (peak 11), was reflected on the repeat
units of poly(dihexenyl phthalate). The relationshipbetween the polymer structure and the pyrolyzates issummarized in Scheme 2. The presence of phenyl
benzoate (peak 8) and polycyclic aromatic pyrolyzates(peak 6, 9 and 10) on the pyrogram ofthe resin would becaused either by the secondary and tertiary thermal
processes ofthe polyester, or by a thermal decomposition
Results and Discussionof other aromatic component mixed with the polyester.
To distinguish the different conclusions, part A of theResin and its additives
sample was separated and collected into two fractions (FA total ion current (TIC) pyrogram obtained from Py- 1 and F-2),as shown in Fig. 2, by preparative HPLC with
GC/MS of the uncured resin (part A) pyrolyzed at high-performance columns; F-l and F-2 were then
500°C, as shown in Fig. 1. The structures assigned to identified by Py-GC individually. The pyrogram of F-l
the mass signals of the pyrolyzates are listed in Table 1; also showed all of the characteristic pyrolyzates of
the identification was carried out mainly on basis of mass
spectral fragmentation patterns. The code numbers ofpoly(dihexenyl phthalate) and reconfirmed the same
results mentioned above. The pyrogram of F-2,performed at a relatively lower temperature of 220°C for
3 s, is shown in Fig. 3. The sufficient decomposition ofF-2 in a weaker thermal environment indicated that it
could be a thermally labile compound. Some of the of 133°C was observed in the differential scanningassigned pyrolyzates of F-1 (see Table 1) corresponded to calorimetry (DSC) profile of F-2,which was identicalbenzoic acid (peak 4) and phenyl benzoate (peak 8) and with the thermal decomposition behavior of BPO.
implied the scission, elimination, and recombination of a Finally, a weaker mass signal(peak 12) with a longer
aromatic peroxide. A rearrangement of the peroxide retention time in Fig. 1 indicated the presence of a highwith subsequent cyclization to polycyclic compuuds aliphatic alcohol in the resin, implying that component as(acenaphthene, methoxydibenzofuran and dihydrona- a kind of additives (a surfactant, perhaps).
phathacene, as peak 6, 9, and 10 on the pyrogram) has
a l s o b e e n c o n s i d e r e d t o a s i g n i f i c a n t e x t e n t . Curing agent and modification agent
Figure 4 shows a TIC pyrogram of part B carried out
Summarizing all of this information, F-2 was identified
as benzoyl peroxide (BPO), a crosslinking accelerator for by Py-GC/MS, pyrolyzed at 500ｰC for 5s, on whicht h e u n s a t u r a t e d p o l y e s t e r. T h e d e c o m p o s i t i o n some acrylate monomer peaks, methyl acrylate (MA,mechanism of BPO is shown in Scheme 3. In addition, peak 1), methyl methacrylate (MMA, peak 2) anda broadly exothermic peak with a maximum temperature isohexyl methacrylate (HMA, peak 3), were identified.

As is well known, acrylate polymers and copolymers
thermally degrade mainly to the correlative monomers in
the absence of oxygen.12-13 Based on that information, asolid sample of part B was reasonably deduced as being a
copolymer of MA, MMA and HMA. Otherwise, peak
4 and 5 on the pyrogram assigned to a high aliphatic
alcohol and dioctyl phthalate (DOP) would reflect thethermal volatilization of some additives, which areconsidered to be a surfactant and a plasticizer in thematerial, respectively.
Pyrolysis-DI/ MS is a simple, rapid analytical pyrolysis
measurement technique without any chromatographic
separtaion process. Since the mass profiles of all
pyrolyzates are labeled on a linear mass scale, it is suitablefor fingerprint idenitification purposes. 78 Figure 5 isthe TIC pyrogram of part B pyrolyzed at 500°C for 3 s byDI/MS. The corresponding mass spectrum indicatedthat the observed species was a co(MA-MMAHMA)polymer identified by the related monomer
fragments with m/z values of 86(MA), 100(MMA), and170(HMA), respectively. Though the conclusion is thesame as that by Py-GC, since the throughput of up to one
sample was within a few minutes, the analysis is more
effective.
An important point remained regarding the previous
discussion, i.e. the monomer peaks of MA, MMA andHMA on both of Py-GC and DI/MS pyrograms of thepart B must have originated from two considerable ways;
thermal pyrolysis of the copolymer to the corresponding
monomers or / and thermal volatilization of the freemonomers dissolved in the copolymer. 14 To confirm
that, headspace GC/MS was carried out at a purging
temperature of 220°C with in 1 min for both part B and amonomer-free co(MA-MMA) polymer for the same
sample size and condition. Since no significant peak
showed on the headspace chromatogram of them o n o m e r- f r e e c o p o l y m e r, t h i s i n d i c a t e d t h a t n odetectable pyrolyzate formed at that temperature for thep u r i f i e d c o ( M A - M M A ) p o l y m e r. A h e a d s p a c e T I C
chromatogram of part B at 225°C is shown in Fig. 6, in
which the monomer peaks of MMA and HMA presented
with the obvious intensities are compared to the standard
copolymer. The results show that there were somereactive monomers (MMA and HMA) dissolved in thecopolymer as the crosslinking agents of the unsaturated
polyester. Therefore, it could be deduced that thecopolymer in part B acted as a modification material andan adsorbent for the reactive monomers.
In conclusion, all of the components in a set of uncured
unsaturated polyester system, including an unsaturated
polyester prepolymer, a crosslinking accelerator, anacrylate copolymer as the modification agent and someadditives (surfactant and plasticizer) were well identified
by a combination of Curie-point Py-GC/MS, Dl/MS,
headspace-GC/MS and preparative HPLC. A
flowchart diagram of the analytical measurements usedin this work is illustrated in Fig. 7. The results showedthat the Curie-point heating technique combined tomulti-chromatographic and mass spectroscopic methods
is an available and convenient way for the compositional
analysis of complex polymer materials.
The authors express their sincere thanks to Ms. H. J. Hsu(Research Center, Eternal Chemical Co., Ltd., Kaohsiung,China) for her useful help and discussions.