Acetylene-terminated amide oligomers

Makromol. Chem. 194,953 -962 (1993) 953

Acetylene-terminated amide oligomers

Francisca Martinez, Javier de Abajo*

Instituto de Ciencia y Tecnologia de Polimeros, CSIC, Juan de la Cierva, 3, 28006 Madrid, Spain

Regis Mercier

CEMOTA, BP 3, 63390 Vernaison, France

(Received: January 27, 1992; revised April 29, 1992)

SUMMARY Six new acetylene-terminated (AT) oligomers were synthesized by reaction of 3-ethynylbenzoyl

chloride and 4-ethynylbenzoyl chloride with three aromatic diamines containing four aromatic rings. The functionalization led quantitatively to AT oligomeric diamides of well defined composition, as confirmed by IR, 'H NMR and 13C NMR spectroscopy. The materials exhibited comparatively high melting points, over 200 O C ; thus, heating promoted curing before melting or simultaneously with melting, with the only exception of one sample that could be isolated in the amorphous state. Heating at 325 "C led to insoluble cured materials, with excellent thermal resistance and glass transition temperatures Tg around 300 "C.

Introduction

Acetylene-terminated oligomers (ATs), and the subsequent cross-linked polymers, have been the subject of considerable study over the past two decades. Although a great number of these materials have been evaluated, acetylene-terminated amides (ATAs) have been scarcely considered. On the contrary, AT oligoimides ' s 2 ) , AT aryl-ether~~), and other AT aromatic o l i g o m e r ~ ~ - ~ ) have been intensively studied and evaluated as organic thermally stable matrices for high-performance composites and structural adhesives ').

Therefore, it is of interest to investigate the potential of ATAs, since aromatic polyamides are among a series of linear polymers that provide a favourable balance between processability and performance. Today, new aromatic diamines are available which contain the appropriate structural elements to provide polymer materials with a comparatively high thermal stability, and without the intractability of the conventional thermally stable aromatic polymers prepared from structurally rigid aromatic diamines Q.

This paper is concerned with the synthesis, characterization and curing of acetylene- terminated diamides on the basis of aromatic diamines containing diphenyl ether and diphenylsulfone moieties. By using different diamines and different reagents bearing terminal acetylene groups, structure-property relationships may be derived. It is particularly interesting, for instance, to combine various diamines and reagents, in order to change the meta-to-para ratio of phenylene rings in the ATAs. In this sense, the work has been oriented towards elucidation of the most convenient formulation relative to the properties of the final material.

0 1993, Hiithig & Wepf Verlag, Basel CCC 0025-1 16X/93/$05.00

954 F. Martinez, J. de Abajo, R. Mercier

Experimental part

Materials

Raw materials were commercial reagents or technical grade chemicals, and were used without purification. Solvents were purified by conventional means and finally distilled prior to use.

The diamines were supplied by Mallinckrodt Inc., St. Louis, MO, USA. They were recrystallized from ethanol, and their purity was tested by means of high-performance liquid chromatography (HPLC), giving the following melting points: 2,2-Bis-[4-(4-aminophenoxy)phenyl]propane*): 128 "C. Bis[4-(4-aminophenoxy)phenyl] sulfone**): 199 "C. Bis[4-(3-aminophenoxy)phenyl]sul- fane***): 135 "C.

3-Ethynylbenzoyl chloride (3-EBC) and 4-ethynylbenzoyl chloride (4-EBC) were prepared by the methods described in the previous paperg). 3-EBC: b.p. 53-55 "C (0,l mmHg), 4-EBC, recrystallized from hexane: m. p. 79- 80 "C (Lit. "I: m. p. 74-77 "C).

Synthesis of acetylene-terminated diamides

All of the functionalized oligomers were prepared by the same general procedure, from a diamine and 2,l mol of the acetylene-bearing reagent. As an example, the synthesis of the ATA SMM (see Tab. 1) is described:

5,OO g (0,0304 mol) of 3-ethynylbenzoyl chloride, dissolved in 12 mL of dry tetrahydrofuran (THF) w a s added to a stirred solution of 6,25 g (0,0145 mol) of bis[4-(3-aminophenoxy)phenyl] sulfone and 2,92 g (0,0289 mol) of triethylamine in 20 mL of dry THE The acyl chloride was added very slowly from a dropping funnel in order to avoid heating of the mixture. Once the 3-EBC addition was complete, the reaction was continued under nitrogen for 1 h with stirring. By that time the reaction was complete, as confirmed by thin-layer chromatography (TIE). The mixture was filtered to eliminate the solid triethylamine hydrochloride, and the solution was vacuum- concentrated to dryness. The diamide was purified by column chromatography using a 80/20 (v/v) ethyl acetate/hexane mixture to obtain 9,95 g (quantitative) of pure oligomer SMM.

C,H,,N,O,S (688,78) Calc. C 73,23 H 4,11 N 4,07 S 4,65 Found C 72,54 H 4,43 N 4,14 S 4,31

Measumrnents

Elemental analyses were carried out by the Analysis Service of the CNQO (Madrid). IR spectra were recorded on a Perkin-Elmer 457 spectrometer on KBr pellets. NMR spectra were recorded on a XG300 Varian spectrometer in dimethyl sulfoxide (DMSO), at room temperature, with tetramethylsilane (TMS) as reference.

Melting points were determined visually in a Buchi apparatus, and occasionally by differential scanning calorimetry (DSC).

HPLC experiments were performed with a Scharlau reverse phase column (Nucleosil 120 A , 5 pm, Cis) of 10 cm length in a 250 binary LC Perkin-Elmer pump with an LC-95 UV/Vis Perkin- Elmer spectrophotometer detector at 254 nm.

DSC curves were run in a Perkin-Elmer DSC-4 device linked with a 3600 Data Station, using aluminium pans. The experiments were performed under N, at 10 K/min heating rate.

Thermogravimetry (TC) measurements were conducted with a Perkin-Elmer TGS-2 thermobalance, by the dynamic method, under N, at 10 K/min heating rate.

*)**)***) IUPAC names: *) 4,4'-Isopropylidenebis(l,4-phenyleneoxy)dianiline, **) and ***) 44'- (or 3,3')-sulfonylbis( 1,4-p heny1eneoxy)dianiline.

Acetylene-terminated amide oligomers 955

Thermomechanical analyses (TMA) were performed with a Perkin-Elmer TMS-2 device. Penetration and expansion modes were used, and the measurements were carried out under N, at 10 K/min. Samples were prepared by melting the reactive oligomers in small moulds and applying to them an appropriate cure schedule.

Wide-angle X-ray scattering (WAXS) measurements were carried out with a Philips Geiger counter X-ray diffractometer with an Anton Ponar 300 temperature camera. The diffractograms were recorded in the 20 range between 3 and 32" at a rate of 2 K/min using Ni-filtered CUK, radiation.

Results and discussion

For the preparation of acetylene-terminated amide oligomers (ATAs), three commercial diamines containing four benzene rings were chosen. The effectiveness of this type of diamine for the preparation of aromatic polymers and oligomers has been well established ' ' 9 '2). The presence of comparatively flexible C-0-C and C-SO,-C linkages provides a degree of molecular mobility that brings about a better solubility and processability than for other polymers, i. e., polyamides from short fully aromatic diamines such as rn-phenylenediamine or p-phenylenediamine, or even two-ring diamines like bis(4-aminophenyl) ether or bis(4-aminophenyl) sulfone 1 3 ) .

The diamines were acetylene end-capped by reacting with the appropriate acetylene- bearing reagents, as depicted in Eq. (1).

THF/TEA H2N-Ar-NH, + 2 HC=C - HC=C-Ar'-CO-HN-Ar-NH-OC-Ar'-C=CH

CH3

The reaction was carried out at room temperature in solution of dry tetrahydrofuran (THF) and using triethylamine (TEA) as an acid acceptor. All the oligomers were attained in high yields, as can be seen from Tab. 1.

ATAs were purified by preparative column chromatography, since they could not be recrystallised from low-boiling solvents. The solvents for these oligomers boil above 100 "C, and at those temperatures cross-linking was favoured. Column chromatography proved to be an effective purification method in all cases. After having been isolated from the chromatographed ethyl acetate/hexane solution, they showed a


Tab. 1.

HC= C-Ar'-CO-HN-Ar-0 ~-X-@O-Ar-NH-OC-Ar'-C=CH

Synthesis of acetylene-terminated diamides:

Code X Ar Art Yield Elemental analyses in Vo

Vo C '70 H Vo N Vo S

SPP SO, -@ -@ 95 Calc. 13,26 4,Ol 4,Ol 4,65 Found 11,89 4,55 4,40 4,30

SPM SO, -@ 99 Calc. 73,26 4,Ol 4,Ol 4,65 Found 12,35 4,69 4,30 4,60

SMP SO, a -f=& 91 Calc. 13,26 4,Ol 4,Ol 4,65 Found 72,12 4,63 4,28 4,25

SMM SO, a a 100 Calc. 13,26 4,Ol 4,Ol 4,65 Found 72,54 4,43 4,14 4,31

PP C(CH,), -@ --@ 95 Calc. 81,08 5,lO 4,20 - Found 79,86 5,41 4,56 -

PM C(CH,), -@ a 94 Calc. 81,08 5,lO 4,20 - Found 79,88 5,49 4,45 -

unique peak in HPLC, with less than 1 Yo impurities. Consequently, these oligomers must be considered to have a well-defined composition.

They were also characterized by elemental analyses and spectroscopic methods. IR frequencies for the most significant absorption bands, and NMR chemical shifts of the acetylenic hydrogens and carbons, are listed in %bs. 2 and 3, respectively. By IR spectroscopy the strong absorptions due to the carbonyl stretching vibration (amide band I) at 1650 cm-', N-H bending vibration (amide band 11) at 1 530 cm-' and C-0-C stretching of aromatic ethers in the region 1225 - 1260 cm-' were clearly discernible. The N-H stretching vibration of amide was detected at 3340 cm-', along with the bands ascribed to the C-H stretching of the ethynyl group at 3290 cm-'. The bands attributed to the sulfone stretching vibration (asymmetric and symmetric), for the oligomers with this functional group, were present at 1320 and 1150 cm-', respectively, and the stretching vibration of CH,, for the last two oligomers, at 2960 cm -'. The C s C stretching, which should appear near 2 100 cm -', was invisible for all the compounds. As an example, the IR spectrum of oligomer SMP is reproduced in Fig. 1.


Tab. 2. IR wavenumbers (in cm-l) for absorption bands of acetylene-terminated diamides (ATAs)

1320 1255 1530 1150 1230

1320 1255 1525 1150 1230

1320 1265 1535 1150 1235

1320 1260 1530 1150 1235

SPP 3 340 3 295 1650

SPM 3 420 3 300 1650

SMP 3 370 3 280 1670

SMM 3 390 3 280 1660

PP 3 420 3 290 1650 1525

PM 3 420 3 290 1650 1530

1250 2960 1225

1255 2970 1225

Tab. 3. dimethyl sulfoxide)

NMR chemical shifts (in ppm from TMS) of acetylene-terminated diamides (solvent:

Oligomer 'H '3c code

NH =CH -c= =C-H c=o

SPP 10,44 4,42 83,21 82,86 164,69 SPM 10,44 4,34 81,72 82,83 164,53 SMP 10,45 4,43 83,27 82,81 164,89 SMM 10,45 4,33 81,74 82,74 164,70 PP 10,36 4.42 83,05 82,86 164,49 PM 10,36 4,33 8 1,63 82,83 164,31

s 100 .C 80

60 2 LO

20

6 0

I

+ LOO0 3000 2000 1600 1200 800 LOO Wavenurnber in crn-'

Fig. 1. IR spectrum (KBr) of oligomer SMP


NMR gave reliable and complete information on the chemical structure of the ATAs. Accumulation of 64 transients was enough to achieve 'H NMR spectra with a reasonable signal-to-noise ratio. As an example, the 'H NMR spectrum of PM is shown in Fig. 2, together with the assignments for the signals. The amide protons gave a signal at 10,5 ppm. The complicated pattern between 6 and 8 ppm could be correctly resolved, since the overlapping of the aromatic protons did not greatly disturb the assignment of all the peaks. On the other hand, the integral of this region correctly fitted with the number of aromatic protons relative to the area of the two acetylene protons that appeared at about 4,3 ppm. It is worth noting that special conditions had to be set to obtain correct 'H NMR spectra in most cases. For instance, long acquisition times (10 s) between pulses must be applied, in order to receive correct signals for all the protons. In particular, the protons at positions 1 and 2 (see Fig. 2), with no neighbouring hydrogen, did not relax fast enough and did not give correct peak areas unless long acquisition times were used.

7

10 9 8 6 in ppm

7 6 5

- 5-

3 v

2 1

Fig. 2. 'H NMR spectrum of oligomer PM (solvent: dimethyl sulfoxide)

In Fig. 3 the l3C NMR spectrum of oligomer SMP is reproduced. In this case, the assignments of the signals could be made without difficulty, and the same is true for the other members of the series. Furthermore, the absence of other non-assignable peaks, here and in the 'H NMR spectra, should be taken as a proof of the high degree of purity achieved in the synthesis of the oligomers.

A first investigation of the thermal properties by means of differential scanning calorimetry (DSC) showed that the ATAs had comparatively high melting points, in the proximity of the cross-linking temperature ('kb. 4). For that reason, overlapping of the endothermal and the exothermal peaks ascribed to the two individual processes took place in every case (see Fig. 4). The only exception to this was the oligomer SMM, which did not show any melting endotherm (Fig. 5) . The reason for this anomalous behaviour is that SMM was unexpectedly synthesized in an essentially amorphous state.


I60 150 1LO 130 120 110 100 90 80 6 in ppm

Fig. 3. l3C NMR spectrum of oligomer SMP (solvent: dimethyl sulfoxide)

Tab. 4. Thermal properties of acetylene-terminated diamides a)

Oligomer q)/ oc Tm/ "C T,/ "C Tf ' / "C Td/ "C code

435 SPP - - 252 - SPM - 217 235 - 430

455 SMP - 234 237 - SMM 81 - 222 310 435

470 - - 247 - PP PM - 20 1 229 300 435

a) T f ) : Glass transition temperature (DSC, 10 K/min); T,: oligomer melting point (endothermal onset, by DSC, 10 K h i n ) ; T,: exothermal peak temperature (DSC, 10 K/min); 3'): glass transition temperature of the cured material (TMA, 20 K/min); Td: onset temperature of the thermal decomposition (TG, 10 K/min).

Fig. 4. DSC trace of oligomer PM

PM

90 150 210 270 330 Temperature in "C


SMM

Fig. 5. DSC trace of oligomer SMM

90 150 210 270 330 Temperature in O C

This was confirmed by means of wide-angle X-ray scattering. The diffractogram of this oligomer (Fig. 6) was the only one that did not give a pattern with sharp reflexions due to crystalline order, and, in contrast, it gave a halo typical of amorphous materials. Furthermore, SMM was the only oligomer that showed a clear Tg inflection at 81 "C by DSC (see Fig. 5). It is not a matter of chance that SMM is the oligomer that contains the highest degree of m-substitution, and, as a result of its higher asymmetry in comparison to p-oriented ATAs, it has a greater difficulty in obtaining the necessary population of trans conformers to achieve crystalline order. On the other hand, it was the most suitable ATA to clearly detect the curing exotherm by DSC.

Fig. 6. WAXS diffractogram of oligomer SMM ' I 28 0, 30" 200 l G o 20

In spite of the virtually non-existent processing windows for most of the ATAs, all of them were subjected to the same thermal treatment, in order to obtain cross-linked materials. The samples were heated at a maximum temperature of 350"C, and the effect of the thermal treatment on the properties was investigated.

Homogeneous, isotropic materials could be obtained only from SMM and SMP. However, all the ATAs cured by virtue of the thermal treatment, as verified by IR spectroscopy and solubility measurements. Although the C-H stretching bands of acetylene, at ca. 3 100 cm-', were not well resolved in the IR spectra of the uncured materials, in each case a clear reduction of the absorbance (width and intensity of the bands) in this region took place after curing. The N-H stretching band kept its relative

Acetylene-terminated amide oligomers 96 1

G

u E

a 3

c c ';n

3 50

intensity in every case, but the relative absorbance corresponding to the acetylene C-H stretching was diminished. All the ATAs became insoluble in organic solvents after curing, and no residual exotherm appeared in the DSC curve.

The cross-linking of short oligomers, like the ATAs considered here, always leads to amorphous materials. The investigation of the transition temperature is, therefore, interesting from both a practical view point and in order to better characterise these systems. Cured ATAs showed neither measurable inflections nor slope changes in DSC attributable to a glass transition, but some information could be drawn from thermomechanical analyses (TMA). For those ATAs that build tough materials after curing, it was possible to fabricate small discs (approx. 1 mm thick) and test them by TMA. The onsets observable in the TMA curves (see Fig. 7) around 300°C were ascribed to the Tg's of the materials. Penetration and expansion modes gave essentially the same transition temperatures. It is remarkable that these Tg values are clearly higher than those of linear aromatic polyamides synthesized from isophthaloyl chlorides and the same diamines 14).

I 100.-

I

1 0 ._ c z c a, C a, a I 1 0 200 300

Temperature in "C

Fig. 7. TMA curve of cross-linked oligomer PM

The thermal resistance of the current ATAs was investigated by means of thermogravimetry (TG). The TG curves show a common behaviour, in that thermal decomposition (onset of the curve: weight residue vs. temperature) began in the temperature range 400-420 "C. As demonstrated by Fig. 8, rapid degradation does not occur until 450 "C.

100 200 300 LOO 500 600 Temperature in "C

Fig. 8. TG curves of cross-linked SMM (1) and cross-linked PM (2)


The authors are grateful to the CICYT (Mat 88-0579-C02-01) for the financial support.

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Acetylene-terminated amide oligomers