Journal of Analytical and Applied Pyrolysis, 12 (1987) 293-300
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
YSIS OF ACRYLIC THEMOSETTINGCOMPOSITIONAL ANALANALYSISACRYLICCOATINGSPYROLYSIS-GAS
CHROMATOGRAPHY
COA
TINGS BY PYROLYSIS-GAS CHROMATOGRAPHY
SHIGEHIKO YAMAGUCHI * JIRO HIMNO and YOSHIHIRO ISODA
Nippon Oil & Fats Co., Lid., Tsukuba Research Laboralory, Tokodai 5-10, Toyosato-machi,
Tsukuba-gun, Ibaraki, 300-26 (Japan)(Received January 7th, 1987; accepted January 30th, 1987)
ABSTRACTA method for compositional analysis of acrylic coatings by pyrolysis-gas chromatography(Py-GC) is described. 2-Hydroxyethyl methacrylate (HEMA)-butyl acrylate (BA)-ethyl
methacrylate (EMA) terpolymers cross-linked with butoxy melamine resin, containing either
TiO2,Fe2O 3 or Carbon black pigment were used as model coating compounds. Pyrolysis wasperformed at 590°C using a Curie-point pyrolyzer.When the ratio of acrylic resin / melamine
resin in the coating sample varied, the HEMA/EMA ratio in the pyrolytic products varied.
This ratio was also affected by the kind and the amount of the pigment. Therefore, tile
HEMA/EMA ratio in the sample could not be determined directly. On the other hand, theBA content could be directly determined from the BA monomer/diner ratio in the pyrolyticproducts. The composition of the acrylic resins in the coating samples could be calculated
from the BA content and the BA/EMA ratio, directly by Py-GC.
Coatings; gas chromatography; polymers; pyrolysis; resins.
INTRODUCTION
Acrylic resins are widely used as coating materials. Most of the coatings
are cross-linked with, for example, melamine resins by thermosetting andcontain various pigments [1]. Such coatings have been characterized using
I R o r N M R a f t e r r e m o v a l o f t h e p i g m e n t s . H o w e v e r, t h e r e i s a n e e d t oestablish a direct and simple method of characterization for very small
samples of material, e.g. sub-milligram quantities.
Pyrolysis-gas chromatography (Py-GC) has been used for the characterization of very small samples of polymers regardless of their form [2-5] andhas been successfully applied to the compositional analysis of acrylic polymer by using the characteristic peak area ratios on the pyrogram [6-8].
In this paper, the 2-hydroxyethyl methacrylate (HEMA)-butyl acrylate(BA)-ethyl methacrylate (EMA) terpolymers cross-linked with a butoxymalamine resin, containing T iO 2 , Fe 2 O 3 or carbon black pigment wereprepared as model compounds for acrylic coating polymers, and theircompositional analysis was studied.
EXPERIM ENTA LSamples
T h e H E M A - B A - E M A terpolymers listed in Table 1 were synthesized as
described in a previous paper [6], These acrylic resins were mixed with abutoxy melamine (Melane 22, Hitachi Chemical Co.) in dif ferent ratios,
coated on a glass plate with or without pigments such as T iO2 (JR-602,Teikoku KaKo Co.), Fe2O3 (Bayferrox Iron Oxide Red 160M, Bayer) or
carbon black (Neospectramark II, Columbian Chemical Co.) and were thenthermoset at 170°C for 30 min. As summarized in Table 2, the preparedcoating samples were classified into three series: A, B and C.
Pyrolysis -gas chromatographic conditions
An induction heating Curie-point pyrolyzer (Japan Analytical Industry,Model JHP-2) was used. A sample by less than 0.1 mg wrapped with a pieceof foil, whose Curie temperature was 590°C, was subjected to pyrolysis
under a flow of nitrogen carrier gas. A glass column (2 m x 3 mm LD.)
packed with 10% Thermon 3000 on Chromosorb W (60-80 mesh) was used
for the gas chromatographic separation. The column temperature was programmed from 50°C to 220°C at a rate of 5 °C /min.

TABLE1
Composition of terpolymer samples
sampleNo.
12
3456789composition(mole%)
HEMA
10.0
10.0
20.0
20.0
20.0
40.0
40.0
40.0
40.0

BA
20.0
45.0
70.0
20.0
40.0
60.0
20.0
30.0
40.0

EMA
70.0
45.0
20.0
60.0
40.0
20.0
40.0
30.0
20.0

TABLE 2
Prepared coatjng samples
SampleAcrylic resin
NoA-1
2A-2
2A-3
2A-4
2A-5
8A-6
8A-7
8A-8
8B-l
2

Acrylic resin/melamine resin
9/1
8/2
7/3
6/4
9/1
8/2
7/3
6/4
7/3

Pigment/resin
TiO2, Fe2O3
1/1
-B-2
B-3
B-4
B-5
B-6
B-7B-8
B-9
B-10
B-11
B-12
C-1
C-2
C-3
C-4
C-5
C-6
C-7
C-8
C-9

7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3
7/3

2/1
1/1
2/1
2/1
2/1
2/1
2/1
2/1
2/1
2/1
2/1
2/1

2
2
2
22
88
8
8
8
8
12
3
4
5
6
7
8
9

1/2
1/1
1/2
1/1
-

Carbon
1/10
1/5
1/10
1/5
-

Identification of the peaks was carried out by a pyrolysis-gas chromaiography-mass spectrometer system (JEOL, JMS-DX 303, electron impact, 70eV).

RESULTS AND DISCUSSION
Effect of cross-linked melamine resin
The pyrograms of H E M A - B A - E M A terpolymer with or without crosslinking with the butoxy melamine resin and that of butoxy melamine resin
are shown in Fig. 1.The main pyrolytic products of the butoxy melamineresin are isobutanol and n-butanol, and those of the cross-linked polymer
consist of the products of HEMA-BA-EMA terpolymer in addition to thecharacteristic ones of the melamine resin.
Fig. 2 shows the HEMA/EMA and BA/EMA peak area ratios on thepyrogram for the A-series samples in Table 2 as a function of the mixed
melamine content. The dashed line in Fig.2 indicates the values for theH E M A - B A - E M A terpolymer without butoxy melamine resin. These data
show that as the melamine resin content increases the HEMA/EMA ratio
decreases but the BA/EMA ratio is almost constant regardless of thecoexisting melamine resin. The variation of the HEMA/EMA ratio in Fig. 2is a consequence of the fact that the - OH functional group of HEMA
monomer reacts with theN-CH2OR functional group of melamine resinby thermosetting.
Effect of pigment
The effect of typical pigments such as TiO2, Fe2O 3 and carbon black isshown for the B-series samples in Table 2.
Table 3 shows the variations of HEMA/EMA and BA /E M A ratios in
the pyrolytic products with the pigment content in the samples. It is notedthat the HEMA/EMA ratio changes depending on the kind and the amountof the pigments. In the case of carbon black pigment, this ratio is almost
constant, but in the case of the T iO 2 and Fe 2 O 3 pigments, this ratio
decreases as the pigment content increases. The rate of decrease in TiO 2 islar ger than that in Fe 2O 3.
The BA/EMA ratio is constant regardless of the kind and the amount ofthe pigments. These data suggest that the ef fect of the pigments is moresignificant for the degradation of the HEMA unit than for that of the BA
and EMA units.
Compositional analysis of acrylic resin
The results from Fig. 2 and Table 4 indicate that the HEMA/EMA ratio
among the pyrolytic products is affected by the ratio of acrylic resin/melamine resin, and the kinds and the amount of the pigments. Therefore, thesample composition could not be directly obtained using the associated peakratios in the pyrolytic products. On the other hand, the BA/EMA ratio in
the sample might be determined directly from the corresponding pyrolyticproducts, because the associated peak ratios are almost constant regardlessof the coexisting reagents. The BA/EMA ratio of the acrylic resin in thecoating is determined by the method reported in a previous paper for theHEMA-acrylate-methacrylate terpolymers [6]. Fig. 3 shows the analyticalresults for the C-series coating samples. The results are in good agreementwith those of the original terpolymer samples.
Then, the determination of BA content in the coating samples wasstudied. In the usual radical reaction, the distribution is controlled by theratio of monomer feed in the reaction system. Furthermore, the acrylic
monomer/dimer ratio in the pyrolytic products changes depending on thedistribution of acrylate monomer units in the acrylate-metacrylate copolymer [8]. Fig. 4 shows the relationship between the BA content in theterpolymer in Table 1 and the observed BA monomer/dimer ratio in thepyrolytic products. As the observed monomer/dimer ratio changes as afunction of the BA content, the composition of a given sample can bedetermined using these relationships directly. Fig. 5 shows the relationships
between the BA content in the coating samples and the observed results
using the BA monomer/dimer ratio. These show good agreement.

Finally by combining the observed data for the BA/EMA ratio and theBA content in the coating samples, the whole composition of the
H E M A - B A - E M A terpolymers can be calculated. As shown in Table 5,
there is good agreement between them. The relative error was within 9.1% by
the method described.
Reproducibility of data was studied for sample No. C-5. In six repeatedmeasurements of the monomer area ratio in the pyrogram, the standard
deviation and the coefficients of variation of BA/EMA were 0.02 and 3.7%,
those of HEMA/EMA were 0.01 and 6.9%, and those of BA monomer/dimer were 1.58 and 9.3%, respectively.