Makromol. Chem. 185,1449 - 1454 (1984) 1449

Investigation of polyesters of adipic acid and sebacinic acid with hydroquinone by pyrolysis-mass spectrometry

Carlos Aguilera

Facultad de Ciencias, Departamento de Quimica, Universidad de Concepci611, Casilla 3-C, Consepcih, Chile

Ingo Liiderwald*

Fachhochschule Fresenius Wiesbaden, Dambachtal20, D-6200 Wiesbaden, Federal Republic of Germany

(Date of receipt: November 17, 1983)

SUMMARY: The structure and thermal degradation behaviour of polyesters of adipic acid and sebacinic

acid with hydroquinone were investigated by direct pyrolysis in the ion source of a mass spectrometer. Poly(oxyadipoy1oxy-1 ,Cphenylene) (1) and poly(oxysebacoy1oxy-1 ,Cphenylene) (2) undergo a cleavage of the ester bond as a very selective thermal degradation reaction (Eq. (iii)). In order to differentiate the thermal and electron impact induced degradation reactions of these polyesters the fragmentation pathways of corresponding low molecular weight esters were followed.

Introduction

In recent works the direct degradation of polyesters of terephthalic acid with aliphatic and aromatic diols in a mass spectrometer has been The application of this technique implies a thermal induced and an electron impact induced degradation step. First the macromolecular samples are heated until the increase of the total ion current (TIC) indicates the initiation of thermal degradation and formation of low molecular weight and volatile ester derivatives. In the high vacuum of the ion source these pyrolysis products are immediatly removed from the hot region and subsequently ionized by electron impact and further fragmented by characteristic mechanisms. The resulting pyrolysis-mass spectra mostly allow to elucidate the structure of the polymer as well as the (selective) thermal degradation reactions.

Whereas polyesters with aliphatic diol components mainly undergo a thermal cis elimination ' 9 2, the degradation of poly(oxyterephthaloy1oxy-1 ,Cphenylene) yields products with thermally formed phenyl ester and benzoic acid endgroups. First results about the therm'al degradation of polyesters of aliphatic dicarboxylic acids with hydroquinone show the favoured formation of ketene and hydroquinone end- groups5). Besides of this and in accordance to literature6-Q cyclic esters have been found in the pyrolysis-mass spectra which may derive from a thermal degradation as well as from ring-chain equilibria.

In order to prove the thermal degradation behaviour of polyesters of aliphatic di- carboxylic acids with hydroquinone under the described conditions and to differen-

0025-1 16X/84/$03.00

1450 C. Aguilera, I. Liiderwald

tiate clearly between thermal induced and electron impact induced degradation mech- anisms, poly(oxyadipoy1oxy-1 ,Cphenylene) (l), poly(oxysebacoy1oxy-1 ,Cphenylene) (2), and the diphenyl esters of adipic acidg) (3) and sebacinic acid'" (4) were investigated in a mass spectrometer.

Results and discussion

In accordance to earlier investigations on aromatic and aliphatic polyesters the polymers 1 and 2 were supposed to degrade into low molecular weight esters of the corresponding structure. To prove the mechanisms of the electron impact induced fragmentation reactions of the expected esters the mass spectra of model compounds 3 and 4 were studied.

1 2

O-CO-(CH,).,-CO-O

3 4

In order to confirm the proposed fragmentation pathways the transitions of metastable ions were followed to calculate the masses of mother and daughter ions").

The favoured fragmentation of the molecular ion of 3 is the cleavage of the C-0 bond into the carboxonium ion m/z 205. The signal of a metastable ion (m* 60) indicates that m/z 205 is further fragmented into m/z 11 1 by elimination of phenol 0%. (9).

Ph-= @

In correspondence to this the sebacinic acid diphenyl ester (4) yields the intensive fragment m/z 261 and subsequently m/z 167 by elimination of phenol. Diagnostic fragments for the dicarboxylic acid components of both diphenyl esters are the ketene-carboxonium ions m/z 111 (Eq. (i)) and m/z 167 (Scheme 1). The fragment m/z 11 1 is further fragmented by subsequent elimination of carbon monoxide and ethylene (Eq. (ii)).

Investigation of polyesters of adipic acid and sebacinic acid. . . 1451

O=C=CH-CH,-CH,-CH,-C I 010 - O=C=CH-CH,-CH,-CH,O - co

m/z 111 m/z 83 (ii)

P O=C=CH=CH~ -CH2=CH2

m/z 55

A complete fragmentation scheme of the electron impact induced degradation reactions of 4 is given in Scheme 1 and have been confirmed by the signals of metas- table ions.

mr 192 I m

m* 107 -PhOH < B

m/z 167 O=C=CH+CH&C4l

m'116 -CO 1. m* 208 -CO 'i

O=C=CH(CH,),CHT mlz 139

m* 88,s -C,H4 1 m * 4 9 -CO, I O=C=CH(CH,),CH? m/z I I I

m* 62 I -ClH4 + O=C=CH(CHz)lCH? mlz 83

IO=-CH=CH, mlz 55

oQ mIz71

Scheme 1. Electron impact induced fragmentation pathways of sebacinic acid diphenyl ester (4) (m* = metastable ion signals)

1452 C. Aguilera, I. Luderwald

s? - 80.

60.

40.

20.

C .-

The most favoured fragmentation pathway of 4 is the cleavage of the ester bond which can be proved by a metastable ion transition (m* 192). The resulting carboxo- nium ion m/z 261 (base peak) is partially further fragmented by mainly three secon- dary fragmentation reactions. The elimination of phenol yields the ketene-car- boxonium ion m/z 167 which can be proved by a signal of the metastable ion m* 107. Less intensive are the elimination of carbon monoxide from m/z 261 into m/? 233 and the elimination of CO and Ph-OH into m/z 139 (Scheme 1).

The further fragmentation of the ion m/z 167 by loss of CO (m/z 139) and stepwise elimination of ethylene via m/z 11 1, 83 to m/z 55 corresponds to the fragmentation of the ester 3 described in Eq. (ii).

The pyrolysis-mass spectrum of the poly(oxyadipoy1oxy-I ,4-phenylene) (1) is shown in Fig. 1.

l ic1 f O ~ O - C C C H 2 ~ C + n 3OO0C 70eV

55

4 41 2 21

165 A0

50 70 90 110 130 150 170 210 230 310 330 440 rn/z

Fig. 1 . Pyrolysis-mass spectrum of poly(oxyadipoy1oxy-1 ,Cphenylene) (1) at 300 "C and 70 eV

At 300°C the polyester 1 is selectively thermally degradaded by cleavage of the ester bond and yields pyrolysis products with ketene and phenol endgroups (Eq. (iii)).

A . . .-Ph-0 /HPCE-(CH2)rCO-. . . ---.--) . . .-Ph-OH O=C=CH-(CH,),CO-. . . (iii)

'C' II 0

After ionization of the pyrolysis products in the gas phase comparably stable cations with two thermally formed phenol endgroups are found at m/z 330.

Investigation of polyesters of adipic acid and sebacinic acid. . . 1453

HO-Ph-O-CO+CH2~COO-Ph-OH@~ m/z 330

In accordance to the fragmentation behaviour of the model compounds 3 and 4 the most favoured electron impact induced degradation mechanism is the formation of a carboxonium ion with either a thermally formed ketene endgroup (m/z 11 1 , O=C=CH-CH2-CH2-CH2-C E 010) or a phenol endgroup (m/z 221 and 441).

0 HO-Ph-O+CO+CH~~COO-Ph-O+,COtCH2-14C 0 I

m/z 221 (n = 0) 441 (n = 1)

The pyrolysis-mass spectrum of the poly(oxysebacoyloxy-I,6phenylene) (2) indica- tes a similar behaviour in both the thermally and the electron impact induced degra- dation steps (Fig. 2).

The favoured pyrolysis mechanism at 350 "C is the cleavage of the ester bond and formation of phenol and ketene endgroups (Eq. (v)). Subsequently fragmented products are the carboxonium ions m/z 277 and 553 with a thermally formed phenol endgroup (Eq. (iv)) and m/z 167 and 443 with a thermally formed ketene endgroup (Eq. (vi)). In accordance to the fragmentation of the model compound 4 m/z 167 is further degradaded by elimination of CO and CH2=CH2 via 139, 11 1, 83 to m/z 55.

HO-Ph-O+CO+CH2+CO-O-Ph-Oj-,CO+CH2+C = 0 l0

m/z 277 (n = 0) 553 (n = 1) (iv)

HO-Ph-O-CO+CH2ACO O-Ph-O-CO+CH~+CO 0-. . + O=C=CH-. . . f I -. t ?

I A H\ I

'C' I , . .-0-Ph-0 / { CH+CH~-)?CO-O-Ph-O-CO+CH~~CO-O-Ph-O-. . . (v)

II 0 I A

. . .-0-Ph-OH + O=C=CH+CH,+CO 0-. . .

( 4

O=C=CH+CH2-)i+CO-O-Ph-O-CO+CH2-)&C = 0l0

m/z 167 (n = 0) 443 (n = 1)

Ions with two hydroxyl endgroups are found at m/z 110 and 386.

HO-Ph-O+CO+CH,j&O-O-Ph-Oj-,H@

m/z 110 (n = 0) 386 (n = 1)

1454 C. Aguilera, I. Liiderwald

100 s 1

50 70

110

0 0 f O ~ O - ! C C H ~ ) & , 35OoC 70 eV

,,, . 1.4.;i , _ _ , 3 i ' , - -4J -J ( A S

90 110 160 270 290 300 400 440 550 570 m/z

Fig. 2. Pyrolysis-mass spectrum of poly(oxysebacoyloxy-1 ,Cphenylene) (2) at 350 "C and 70 eV

The fragment m/z 552 corresponds to the mass of a dimer of the polyester 2; it is supposed to have, in analogy to the cyclic dimers found in aliphatic and aromatic polyester^^-^), a cyclic structure.

+O-Ph-O-CO+CH2j&O+ m/z 552

Experimental part

The pyrolysis-mass spectra and mass spectra were obtained with a Varian CH 7 a spectro- meter operating under the following conditions: 70 eV electron energy (= 1,1215 * J), 3 kV accelerating voltage, 240 "C ion source temperature, 1,6 kV electron multiplier voltage, and resolution 1 OOO. The polymers and model compounds were introduced by direct insertion, and the pyrolysis and sample temperatures are given in the figures.

Acquisition of spectra was carried out by means of a Varian SS 100 computer. High boiling perfluorokerosine (Merck) was used for calibration.

A galvanometric recorder was used to follow metastable ion transitions. The preparation of the polyesters 1 and 2 and of the model compounds 3 and 4 has been

reported elsewhere').

l) I. Liiderwald, H. Urrutia, Makromol. Chem. 177, 2817 (1976) 2, I. Liiderwald, H. Urrutia, Makromol. Chem. 177, 2093 (1976) 3, E. Jacobi, I. Liiderwald, R. C. Schulz, Makromol. Chem. 179, 429 (1978) 4, C. Anguilera, I. Liiderwald, Makromol. Chem. 179, 2817 (1978)

6, J. A. Semlyen, Adv. Polym. Sci. 21, 41 (1976) 7, E. W. Spanagel, W. H. Carothers, J. Am. Chem. SOC. 57, 929 (1935)

F. R. Jones, L. E. Scales, J. A. Semlyen, Polymer 15, 738 (1974) 9, J. W. Hill, J. Am. Chem. SOC. 52, 4110 (1930)

lo) T. Unishi, M. Masegana, J. Polym. Sci., Part A, 9, 3195 (1965) 1 1 ) J. A. Hipple, E. U. Condon, Phys. Rev. 68, 54 (1945)

C. Aguilera, Diplomarbeit, Mainz 1979