Journal of Analytical and Applied Pyrolysis, 1 (1979) 77-84
Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
PYROLYSIS-GAS CHROMATOGRAPHY OF METHYLMETHACRYLATE-STYRENE AND METHYLMETHACRYLATE-α-METHYLSTYRENE COPOLYMERSTATSUHISA SHIMONO, MINORU TANAKA and TOSHIYUKI SHONO ⋆Department of Applied Chemistry. Faculty of Engineering, Osaka University, Yamadakami, Suite, Osaka 565 (Japan)(Received January 22nd, 1979)
SUMMARY
The pyrolysis-gas Chromatographic behaviour of methyl methacrylate copolymers
with styrene or α-methylstyrene was investigated with a Curie-point pyrolyzer. Monomer
yield from each copolymer was very high as a result of the high probability of unzipping.
Though only small quantities of diners and/or trimers are formed on the pyrolysis of twocopolymers, they reflect the sequence distribution of copolymers. Under some assumption, the run number of each copolymer is calculated using the amounts of dimer and/ortrimer formed.
INTRODUCTION
Many polymers with unique primary structures have been produced andsome show specific properties resulting from their primary structures. It istherefore important to investigate the latter. Pyrolysis-gas Chromatography(PyGC) is one of the most effective methods for this purpose. It has provided much useful information about polymers, including concentration ofchain branches and crosslinks [1-3], mechanisms of thermal degradation[4-6], and structures of multipolymers [7].
In our previous work, the relationships between the pyrolyzates and theprimary structures of five butadiene copolymers were reported [8]. In thiswork, we describe the PyGC investigation of methyl methacrylate-styreneand methyl methacrylate -αmethylstyrene copolymers.
EXPERIMENTAL
Alternating copolymers of methyl methacrylate (MMA) with styrene (St)[9] and α-methylstyrene (MSt) [10] were synthesized by complexed copolymerization with ethylaluminium sesquichloride. Homopolymers and low-

conversion random copolymers were prepared by radical polymerization
with azobisisobutyronitrile as initiator.
Table 1 shows the copolymer compositions calculated using elementalanalysis.
A Curie-point pyrolyzer (Japan Analytical Industry JHP-2) was coupleddirectly to a gas chromatograph (Shimadzu GC-6AM) equipped with a dual
flame ionization detector. Samples of 40-80 μg were pyrolyzed, and a stainless-steel column (2 m X 3 mm I.D.) packed with 10% SE-30 on 60-80 mesh
Chromosorb W was used. In the case of MMA-St copolymers, the column
temperature was maintained at 120℃ for the first five minutes and controlled up to 250℃ at a program rate of 10℃ min-1. With MMA-MSt
copolymers, the temperature was controlled between 140℃ and_ 220℃ at aprogram rate of 5℃ min-1. The nitrogen flow-rate was 50 ml min-1, thehydrogen and air pressures were 0.5 kg cm-2 and 1.0 kg cm-2, respectively.
The peak areas were measured by an integrator (Shimadzu ChromatopacE1A). Identification of the peaks was carried out by comparison with retention data of known substances and/or by a pyrolysis-gas chromatographmass spectrometer system (Shimadzu PYR-10A and GC-MS-7000) .
RESULTS AND DISCUSSION

Methyl methacry late-styrene copolymers
Fig. 1shows the pyrograms of poly(methyl methacrylate), polystyreneand MMA-St copolymers at the pyrolysis temperature of 560℃. Similar tothe monomer yields of two homopolymers, the yields of copolymers arehigh. It is therefore possible to determine the copolymer composition easily
from the amounts of two monomers produced on pyrolysis [11] . The peaksof the two monomers were separated completely at the isothermal column
temperature of 60℃ (not shown in the figure). Including the alternating
copolymer, the yield of St was plotted against the St content of the copoly-mer, where the yield is taken as the St mole fraction in MMA and St of thepyrolyzates, i.e. St/(St + MMA), and a very good linear relationship was obtained. From least squares regression analysis, the regression line of the St
content of copolymer (y) on the St yield (x) was y = 0.99lx + 0.60, and theerror variance ( Vyx) was 1.64.
Information on the sequence distribution of copolymers can be obtained
from investigation of the specific products which correspond to the dimerand trimer. On the pyrograms of copolymers, two peaks, D1 and D2, are observed in the dimer region. D2 also appears on the pyrogram of polystyrene
and is identified to be the St dimer (2,4-diphenyl-1-butene). On the otherhand, D1 is concluded to be the St-MMA hybrid dimer from the mass spectrum (M+ = 204). In this hybrid dimer, the position of the double bond isnot clear.
If the probability of dimer formation from the dyad which corresponds toeach dimer is constant through its entire range of copolymer composition,
peak areas of dimers, A(dimer), can be given as follows.

In these equations, ND is the total number of dyads in the copolymer samples; P(dyad) is the dyad concentration; k1 and k2 are constants containing
the dimer formation probability of each dyad and the molar sensitivity to aflame ionization detector. The accurate value of ND is not clear because it isdifficult to measure the small sample size exactly. So, ND is eliminated from

This equation means that the ratios of peak areas are proportional to theratios of dyad concentrations. The ratios of peak areas are estimated fromthe pyrograms, and those of dyad concentrations are calculated using thecopolymerization theory [12]. Therefore, the value of kl/k2 can be determined. Fig. 2 shows the values of the fraction of St-MMA peak area in thetotal peak area of dimers, A(St-MMA)/[A(St-MMA) + A(St-St)], together
with the theoretical values calculated as kl/k2 = 0.52. Using the run number,
R, and St mole% of copolymer, X, eqn. 3 can be rewritten as follows:

If kl/k2 is known, the run number can be calculated from the values of Xand A(dimer) obtained on pyrolysis. The calculated run number of eachcopolymer, RD, is shown in Table 2.
There are four peaks in the trimer region on the pyrograms of copolymers. Being identified from the mass spectra, Tl and T2 are the St-St-MMA
hybrid trimers (M+ = 308), T3 is the St-MMA-St hybrid trimer, and T4 theSt trimer (2,4,6-triphenyl-1-hexene). The difference between alternating andrandom copolymers is obviously seen in the trimer region on the pyrograms:
the alternating copolymer hardly gives trimers other than T3.
Applying an assumption similar to that made for dimers to the trimer formation. each Peak area of trimer can be described as fouows:In these equations, NT is the total number of the triad in copolymer samples;P(triad) is the triad concentration., Kl, K2, and K3 are the constants containing the trimer formation probability of each triad and the molar sensitivityof each trimer to the detector. From eqns. 5-7 the following two equations
are obtained :The values of Kl/K3 and K2/K3 are determined by a method similar to thatapplied to diners. Fig. 3 shows the observed values for the fraction of

St-MMA-St peak area in the total peak area of trimers and the theoreticalcurve calculated as Kl/K3 = 2.7 and K2/K3 = 0.80. The fraction of St-MMA-St
peakarea,FA(St-MMA-St) = A(St-MMA-St)/[A(St-St-St)+

A(St-MMA-St) + A(St-St-MMA)] , can be written as follows:

where R is the run number, X and Yare St mole% and MMA mole% ofcopolymer, respectively. Similarly to the case for diners, the run number
can be calculated from the values of X, Y, and FA(St-MMA-St) if Kl/K3and K2/K3 are known. The run number of each copolymer thus obtained,
RT, is also shown in Table 2.
It is shown on the pyrogram that the alternating copolymer gives a small
amount of the St dimer. The St trimer, however, is not observed on thepyrogram of this alternating copolymer. This leads to the following interpretation. The alternating structure of the copolymer synthesized with
Et1.5AlCl1.5 is not perfect: this copolymer has few St-St dyads besides thealternating units. Being calculated from the amount of dimers, the run number of the alternating copolymer is as small as that of the random copolymer.
This is supposed to result from the predominant formation of St diner from
St-St dyads having MMA units on both sides. There are some deviations ofthe observed values (the filled circles) from the calculated line in Fig. 2, andthe order of the run numbers for random copolymers is apparently abnormal,
considering the composition of copolymers. On the other hand, the observed values of FA(St-MMA-St) are in good agreement with the theoretical values; the run number calculated from the amounts of trimer shows areasonable value for each copolymer.

Methyl methacrylate-α-methylstyrene copolymers
Fig. 4 shows the pyrograms of poly(α-methylstyrene) and MMA-MSt
copolymers at the pyrolysis temperature of 434℃. These copolymers havehigher monomer yields than MMA-St copolymers. On the pyrograms nopeaks with retention times longer than that of D5 were Observed under theGC condition at the column temperature of 260℃. The MSt yield, MSt mole
fraction in two monomers, indicates the copolymer composition. The regression line of the MSt content of copolymer (y) on the MSt yield (x) was y =0.946x + 4.17 and Vyx was 5.63.
The difference between the alternating and random copolymers isobvious, as shown in Fig. 4. Dl is a compound having one phenyl group; inthe case of copolymers, D2 is a mixture of the compound found in the pyrogram of poly(α-methylstyrene) and other unknown products from copolymers. Dl and D2 can not be identified from the mass spectrometric data. D3
is the MMA-MSt hybrid dimer (M+ = 232), D4 the MSt dimer (M+ = 222,2,4-diphenyl-1-pentene), and D5 the MSt dimer (M+ = 236, not 4-methy12,4dipheny1-1-pentene). Using the same treatment for the MMA-St copolymers, the ratio of peak areas can be mitten asFig. 5 shows the observed fraction of D3 Peak area in the total peak area of
three dimers (D3, D4 and D5) and the theoretical curve calculated withkl/k2 = 0.30. By the method applied to MMA-St copolymers, the run number can be calculated from eqn. 4 and these values are shown in Table 3. It isreasonable that the alternating copolymer has a highly alternating structure,
as shown by the high value of the run number in Table 3.
As described above, the monomer yield indicates the copolymer composi-tion satisfactorily in the case of these two copolymers. Although theamounts of dimer and/or trimer in the pyrolyzates are small, these dimers
and/or trimers reflect the sequence distribution of copolymers. Hence, thediscrimination of alternating from random copolymers can be achieved fromthe investigation on these pyrolyzatcs.
ACKNOWLEDGEMENT
The authors thank Mr. a. Maeda for his assistance and helpful discussions
during this study. We also thank Mr. S. Takahashi (Shimadzu SeisakushoLtd.) for gas chromatography-mass spectrometry experimentation.
The present work was partially supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education.