Journal of Analytical and Applied Pyrolysis, 1 (1980) 189-196
Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
PYROLYSIS-GAS CHROMATOGRAPHY OF
POLY(3-METHYL-1-ALKENES)
TATSUHISA SHIMONO, MINORU TANAKA and TOSHIYUKI SHONO
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Yamadakami, Suita, Osaha 565 (Japan)(Received July 9th, 1979)
SUMMARY
The pyrolysis-gas Chromatographic behaviour of poly(3-methy1-1-butenes) andpoly(3-methyl-1-pentenes) with different monomer units was investigated. Both polymers have two different units in their polymer chains, that is, 1, 2- and 1,3-structures.
The amounts of the pyrolysis products vary because of the different degradation mechanism of each unit. With poly(3-methy1-1-butenes) the amounts of the two units can beevaluated from the amounts of some of the pyrolysis products.
INTRODUCTION
With cationic catalysts, 3-methy1-1-alkenes polymerize with rearrangementof the propagating carbonium ion from secondary to tertiary [1,2]. This
rearrangement proceeds at low polymerization temperatures. Cationicallypolymerized polymers, therefore, have two units, viz. 1,2- and 1,3-structures.

For poly(3-methyl-1-butenes), the amounts of the two units were evaluatedfrom the near-infrared spectral data [3]. For poly(3-methy1-1-pentenes),
the ratios of the two units were estimated from a comparison of the opticalactivities between the optically active monomers and their polymers [4].
Pyrolysis-gas Chromatography (Py-GC) is a useful method for the analysis of polymer microstructures, and is especially powerful with insoluble
polymers. In previous work, the sequence distributions of some copolymers
were investigated by Py-GC [5,6]. In this work, the relationships between
the amounts of the two units and the pyrolysis products of cationical1y polymerized poly(3-methyl-1-butenes) and poly(3-methyl-1-pentenes) werestudied.

EXPERIMENTAL
Each monomer was obtained by dehydration of the corresponding alcohol over activated alumina at 350℃ and was redistilled over sodium metal
before use.
The polymerization conditions are given in Table 1.
The 13C NMR spectra were obtained by using a 15-MHz high-resolution
Fourier transform NMR spectrometer system (JEOL, JNM-FX60) andCDCl3 or C6D6 as solvent.
A Curie-point pyrolyzer (Japan Analytical Industry, JHP-2) was coupleddirectly to a gas chromatograph (Shimadzu GC-6AM) equipped with dual
flame-ionization detectors. Samples of 40-80 μg were pyrolyzed and a stainless-steel column (3 m X 3 mm I.D.) packed with 10％. Apiezon L on 60-80
mesh Celite 545 was used. The column temperature was maintained at 60℃
for the first 5 min and increased to 180℃ at a programming rate of 5℃
min-1. The nitrogen flow-rate was 40 ml min-1 and the hydrogen and airpressures were 0.5 kg cm-2 and 1.0 kg cm-2, respectively.
The peak areas were measured by an integrator (Shimadzu ChromatopacEIA). Identification of the peaks was carried out by comparison with theretention data of known compounds and/or by use of a pyrolysis-gas chromatograph-mass spectrometer system (Shimadzu PYR-10A and GC-MS7000).
RESULTS AND DISCUSSION
Poly(3-methyl-1 -butenes)
Fig. 1 shows the 13C NMR spectra of some poly(3-methy1-1-butenes). By
comparison of observed and calculated chemical shifts [7,8], it is concluded

that Polymer I is composed of 1,3-units only and that Polymer VII IS composed of 1,2-units only. In the 13C spectrum of Polymer I are observed and thesesignals are attributed to the presence of some 1,2-units among many 1,3units. The 13C NMR spectra of Polymers II-VI show similar patterns to thatof Polymer III. The ratio of the two units could not be obtained by 13C
NMR spectrometry owing to the poor solubilities of some of the polymers.

The evaluation of the ratio of the two units by Py-GC is discussed below.
The pyrograms of Polymers I and VII are shown in Fig. 2. Large differences between the two polymers are observed. In the region of the pyro1ysis products with lower boiling points, Polymer I gives more C4 and C5hydrocarbons, and Polymer VII gives more C3 than other hydrocarbons.
Moreover, a relatively large peak is observed in the dimer region on the pyrogram of Polymer I, while a large peak is observed in the trimer region on thepyrogram of Polymer VII. These differences can be explained by the degradation mechanisms of 1,2- and 1,3-structures. In the degradation of Polymer I, composed of 1,3-units only, scissions at the main chains to produce
tertiary radicals are most probable:

Hence, isobutylene (C4), 3-methy1-1-butene monomer (C5) and other C4
and C5 compounds are easily produced. The dimer (3,3,6-trimethyl-1heptene) may be produced by β-scission after the intramolecu1ar radicaltransfer via the six-membered ring [9] :On the other hand, with Polymer VII, composed of 1,2-units only, scissions at the side-chains are as probable as those at the main chains. Therefore, a large amount of C3 hydrocarbons are produced by scissions at theside-chains, as observed on the pyrogram. Scissions at the main chains produce monomer (C5), dimers and trimers (mainly 7-methy1-2,4-diisopropyll-octene) by scissions after "back-biting":

By considering the degradation mechanism of the two units stated above,
the amounts of the two units were evaluated. Table 2 shows the relative
peak-area ratios of the major pyrolysis products of Polymers I and VII.
Polymers II-VI have small amounts of 1,2-units as judged by the 13C NMR
spectra. Because these polymers have few 1,2-continuous units, dimer ortrimer formation from such units can be neglected in the following discussion. In Table 2, therefore, the ratios of dimer and trimer produced fromPolymer VII have been omitted.
In the pyrolysis of Polymers II-VI, it is assumed that the peak areas ofthe major pyrolysis products can be described as follows: the sum of thepeak areas comes from both 1,2- and 1,3-units:

where A is the peak area,N(1,3) and N(1,2) are the amounts of 1,3- and 1,2units in the sample, respectively, and h is a constant containing the formation constant of each pyrolysis product and the sensitivity to the flameionization detector as well as h'. In the peak area of dimer, the contributionof the 1,2-unit has been omitted for the reason given above.
Other pyrolysis products are hardly produced and can be neglected. The
ratio of the relative peak-area ratio for each pyrolysis product to the sum of
the peak-area ratios in Polymer I can be considered to show the portion of
the peak area of the corresponding pyrolysis product from the 1,3-unit in
Polymers II-VI, i.e., each value of h in the above equations. Similarly, values

of k' are obtained from the ratio of the relative peak-area ratio for each pyrolysis product in Polymer VII. Values of h and k' are given in Table 3. The
most remarkable difference in the degradation of the two units is observedin the formation of C3 and C4 hydrocarbons, as shown in Fig. 2. The
amounts of the two units were evaluated by the use of these compounds.
The ratio of the peak areas of C3 and C4 hydrocarbons can be describedas follows:

By the use of the value of Q =A(C3)/A(C4) Obtained from the pyrogramand the values of k2, k’2, k3 and k’3, the proportion of the 1,2-unit,x, can becalculated. The values of Q and x thus obtained are given in Table 4. Thechange in the value of x with variations in the polymerization temperatureand solvent used is similar to the values obtained by Kennedy e+ a1. [3] byusing near-infrared spectrometry.

Poly(3-methyl-1 -pentenes)
Fig. 3 shows the 13C NMR spectra of two poly(3-methy1-1-pentenes). In
spite of the low polymerization temperature of –78℃, Polymer I showssome signals resulting from the presence of a small amount of 1,2-units, as
judged from the calculated chemical shifts. The patterns of the 13c NMR
spectra of Polymers II-IV are similar to that of Polymer I. Polymer V is
composed of 1,2-units only. Because of the lack of a polymer composedcompletely of 1,3-units, the amounts of two units could not be evaluated. On
pyrolysis, however, a degradation mechanism similar to that of poly(3-methyl-1-buterTeS) Was observed, i.e., the difference in the mechanism of formation of products for 1,2- and 1,3-units is clear.
Fig. 4 shows the pyrograms of Polymer I, Polymer V and poly(4-methyl1-pentene) polymerized with a Ziegler-Natta type of catalyst. Polymer I, the1,3-unit-rich polymer, produces more C5 and C6 compounds and Polymer V
more C4 compounds than other hydrocarbons. poly(4-methy1-1-pentene),composed of 1,2-units only, produces more C3 and C4 hydrocarbons. Moreover, the pyrogram of Polymer I has a relatively large peak in the dimer
region, whereas those of Polymer V and poly(4-methyll-pentene) have large
peaks in the trimer region.
Table 5 lists the relative peak-area ratios of hydrocarbons with lower boiling points for poly(3-methy1-1-pentenes) and poly(4-methyl-1-pentene).

As discussed above, the difference in the degradation mechanism of each
unit is clear. Hence, evaluation of the amounts of the two units in the polymers is possible, if the polymer composed of 1,3-units only is obtained forpoly(3-methy1-1-pentene).