Modified polyisophthalamides bearing furamido pendant groups

Eur. Pofym. 1. Vol. 31, No. 8, pp. 761-767. 1995 Copyright 0 1995 Elscvier Scicncc Ltd Printed in Gwtt Britain. All rights reserved 0014-3057/95 $9.50 + 0.00

Pergamon

MODIFIED POLYISOPHTHALAMIDES BEARING FURAMIDO PENDANT GROUPS CONSTANTINOS Chemical

Technology

D. DIAKOUMAKOS

Laboratory,

Department

and JOHN

of Chemistry, Greece

A. MIKROYANNIDIS*

University

of Patras,

GR-26500

Patras,

(Received 22 April 1994: accepted in final form 27 July 1994) Abstract-A new series of modified polyisophthalamides containing pendant furamido groups was prepared from S-(furamido)isophthalic acid and various aromatic diamines by the phosphorylation method. The chemical, physical and thermal properties of these polyamides were compared to those of the analogous unmodified ones. The modified polyamides exhibited better solubility in certain solvents such as m-cresol, cyclohexanone and trichloroacetic acid than their unmodified counterparts. In addition, the incorporation of the pendant furamido groups in the polyisophthalamide backbone brought about some substantial increase of the thermal stability as measured by TGA and isothermal gravimetric analysis. The crosslinked modified polyamides obtained upon curing at 300°C for 20 hr were stable up to 321-340°C in N? or air and afforded anaerobic char yields of 6147% at 800°C. Water absorption and X-ray measurements were also performed

FT-IR spectra were recorded on a Perkin-Elmer 16PC FT-IR spectrometer with KBr pellets. ‘H-NMR spectra were obtained using a Varian T-60A spectrometer at 60 MHz. Chemical shifts (6 values) are given in parts per million with tetramethylsilane as an internal standard. Differential thermal analyses (DTA) and thermogravimetric analyses (TGA) were performed on a DuPont 990 thermal analyser system. DTA measurements were made using a high temperature (1200°C) cell in N, atmosphere at a flow rate of 60cm’/min. Dynamic TGA measurements were made at a heating rate of ZO”C/min in atmospheres of N, or air at a flow rate of 60 cmj/min. Thermal studies were also carried out in static air with a heating rate of YC/min using

INTRODUCTION

Aromatic polyamides are among the modem heat-resistant polymers [l, 21. Numerous attempts have been made to modify their chemical structure by incorporating bulky substituents as pendant groups, in order to change their properties [3-51. Polyisophthalamides are one of the most interesting families of aromatic polyamides. Several researchers have previously reported the preparation of new series of modified polyisophthalamides with voluminous substituents on the 4 or 5 position of the isophthaloyl moiety [6-141. In previous papers we have reported the synthesis and characterization of polyisophthalamides with N-benzylidene [15] or phthalimide [ 161 pedant groups. They possessed higher thermal stability and enhanced solubility in comparison to the corresponding conventional polyisophthalamides. The present investigation is concerned with the synthesis and characterization of certain new modified polyisophthalamides prepared by the phosphorylation polycondensation method of 5-(furamido)isophthalic acid with various aromatic diamines. It is expected that the introduction of pendant furamido groups would give rise to aromatic polyamides with a favorable balance of properties. Such properties as solubility, thermal transitions, heat-resistance and hydrophilicity were studied and compared with those of the unsubstituted homologous polyisophthalamides.

COOH

HOOC

+

:I

ClocQ

q tiH*

- HCI I HOOC

NH EXPERIMENTAL

Characterization

I

co

‘,O c

methods

Melting temperatures were determined on an electrothermal melting point apparatus IA6304 and are uncorrected.

*To whom all correspondence

should

be addressed.

Scheme 1 761

(1)

162

Constantinos D. Diakoumakos and John A. Mikroyannidis Reagents and sohems

the thermal mechanical analyser (TMA) model 943. attached to a DuPont 2000 thermal analyser. The inherent viscosities of polymers were determined for solutions of 0.5 g/l00 ml in N,N-dimethylformamide (DMF) or in H,SO, 98% at 30°C using an Ubbelohde suspended level viscometer. Elemental analyses were carried out with a Hewlett-Packard model I85 analyser. The wide angle X-ray diffraction patterns were obtained for powder specimens on a X-ray PW-1840 Philips diffractometer. To determine the equilibrium water absorption, polymer samples were previously conditioned at 120°C in an oven for I2 hr. They were subsequently placed in a desiccator where 65% relative humidity (r.h.) was maintained by means of an oversaturated aqeous solution of NaNOz at 20°C and were periodically weighed.

5-Aminoisophthalic acid was recrystallized from a mixture of DMF/water (volume ratio 3: I). 4,4’Diaminodiphenylmethane, 4,4’-diaminodiphenylether and 4.4’-diaminodiphenylsulphone were recrystallized from toluene. acetonitrile and methanol respectively. l,4Phenylenediamine was sublimed under reduced pressure. 2-Furoyl chloride, triphenyl phosphite and pyridine were purified by distillation. N,N-dimethylformamide (DMF) was dried by refluxing and fractionally distilled from CaH,. All reagents and solvents were obtained from Aldrich. Preparation of 5-Cfuramido)isophthalic acid (1) (Scheme I).

A flask was charged with a mixture of 5-aminoisophthalic acid (6.0000 g, 33. I2 tnmol), DMF (30 ml) and triethylamine (12 ml). 2-Furoyl chloride was added dropwise to the strrred solution at 0 C under N,. It was stirred at ambient

HOOC +

HPN_Ar_NH;,

HO

OC

Tpp’~H~;F’Lic’

CO -

HN -Ar-NH

t 233

2d:R=

3a:RzH I

Ar=--@HZ+

3b:RzH

k:R=H

3d:R=H

1

Ar =

Scheme 2

),

Modified polyisophthalamides

bearing furamido pendant groups

temperature for I hr and then it was heated at 60°C for 3 hr in a stream of N,. It was subsequently poured into water and acidified with hydrochloric acid. The whitish solid precipitated was filtered off, washed with water and dried to afford 1 (7.50 g, yield 82%). A purified sample obtained by recrystallization from a mixture of DMF/water (1: 1 v/v) had m.p. > 340°C. Anal. Calc. for: C,,H,NO,: C, 56.72%; H, 3.30%; N, 5.09%. Found: C, 56.08%; H, 3.31%; N, 4.76%. IR (KBr) cm-‘: 3339 (N-H stretching); 3150-2619 (O-H stretching); 1704 (carboxylic c--O); 1659 (amide CkS); 1624, 1028, 856 (furan); 1586 (aromatic); 1419, 1296 (C-O stretching and O-H deformation); 1340 (C-N stretching and N-H bending).

3000

‘H-NMR (DMSO-dJ 6: 10.67 (b. 2H, carboxylic, exchangeable to D,O); 9.36 (b, lH, NHCO); 8.73-7.96 (m, 3H, aromatic); 7.46-6.67 (m. 3H, furan). Preparation of polyamides 2a-Ai and 3a-.M (Scheme 2).

A typical phosphorylation polycondensation for the preparation of polyamide 21 is given: a flask was charged with a mixture of compound 1 (1.5000 g, 5.45 mmol), 4,4’-diaminodiphenylmethane (1.0850 g, 5.45 mmol), DMF (25 ml), triphenyl phosphite (3.3812 g, 10.90 mmol), pyridine (2 ml) and lithium chloride (0.3 g). It was stirred and heated at 100°C under N, for 3 hr. The viscous solution was subsequently poured over crushed ice. The brown solid precipitated was filtered off, washed with water and dried to afford polyamide 2~ (2.34 g, yield 98%).

I

I

I

IO

763

2000 WAVENUMBER

I 1600

I

I

1200 (Cm-‘)

Fig. 1. FT-IR spectra of polyamides 2a (top) and 3a (bottom).

I

800

Constantinos D. Diakoumak :os and John A. Mikroyannidis

764 Curing of polyamides

The isolated polyamides were each placed in an aluminium dish and curing was accomplished by heating in an oven at 300°C for 20 hr in static air. RESULTS AND DISClESION

5-(Furamido)isophthalic acid (1) was synthesized from the condensation of 5-aminoisophthalic acid with 2-furoyl chloride in the presence of triethylamine (Scheme 1). The reaction was carried out in DMF due

0

to the limited solubility of 5-aminoisophthalic acid and heating was applied because of the low nucleophilicity of this reagent. Excess triethylamine was used since 5-aminoisophthalic acid could form salts and the product was isolated by pouring the reaction mixture into water containing hydrochloric acid. Scheme 2 shows the preparation of modified polyisophthalamides as well as the corresponding unmodified ones by reacting various aromatic diamines with compound 1 or isophthalic acid respectively. The polycondensation was carried out

60

Fig. 2. X-ray diffractograms of modified polyisophthalamides Za-2d and unmodified polyisophthalamide 3c

Modified poiyisophthalamides

bearing furamido pendant groups

Table 1. Inherent viscositiesand solubilitv bchaviour

765

of aolvamides’

Solvents

Sample 2a 2b

2c M 3s 3b 3c 3d “Solubility: blnherent

4”h (dl/g)

0.27b 0.2gb 0.26b 0.26b 0.25b 0.24b 0.23b 0.25c

DMF”

++ ++ + + + + ++ ++ ++ _

( + + ) soluble viscosity

NMPF

DMSO’

++ ++ + + + + ++ ++ ++ _

_ _ _ _ -

++ ++ + + + + ++ ++ ++ _

at room temperature;

in N,N-dimethylformamide

mCresol

1,4-Dioxane

( + ) soluble (0.5 a/l00

CH’

+ + + + -

H2S0, 98%

+ + + + _ -

+ in hot temperature;

CCI,COOH

++ ++ ++ ++ ++ ++ ++ +

++ ++ ++ + + + + -

( - ) insoluble.

ml) at 30°C.

‘Inherent viscosity in H,SO, 98% -(0.5 g/l00 ml) at !KI”C. dDMF = N,N-dimethylformamide. ‘NMP = N-methylpyrrolidone. ‘DMSO = dimethylsulphoxide. BCH = cyclohexanone.

by the phosphorylation method [17, 181 utilizing triphenyl phosphite and pyridine as condensing agents. Compound 1 was characterized by elemental analyses as well as by FT-IR and ‘H-NMR spectroscopy (see Experimental section). Figure 1 presents typical FT-IR spectra for the pair of polyisophthalamides 2a and 3a. The modified polyisophthalamide 2a showed absorptions at 1019 and 884 cm-’ assigned to the furan ring whereas the unmodified polyisophthalamide 3a lacked these absorptions. Both compounds displayed characteristic absorptions associated with the amide structure around 3260 (N-H stretching), 1654 (c--O), 1596 (N-H deformation) and 1322 cm- ’ (C-N stretching and N-H bending). The ‘H-NMR spectrum of polyisophthalamide 2d in DMSO-d, solution displayed multiplets at 8.50-8.21 (NHCO and aromatic of isophthalic ring) and 7.766.53 (furan and other aromatic). The X-ray diffractograms of modified polyisophthalamides revealed their amorphous nature (Fig. 2). It is seen that they showed a different pattern than that of unmodified polyisophthalamide 3e and displayed an additional peak near 28 = 30” associated with the pendant furamido groups. The incorporation of the pendant furamido groups along the polyisophthalamide backbone increased their solubility in certain solvents. Table 1 summarizes the solubility behaviour of modified and unmodified polyisophthalamides. The modified polyisophthalamides dissolved upon heating in m-cresol and cyclohexanone whereas the corresponding unmodified ones were insoluble in these solvents. Only 3c dissolved by heating in m-cresol. In addition, the modified polyisophthalamides compared to the corresponding unmodified, displayed a better solubility in trichloroacetic acid. Both categories of polyamides showed comparable solubilities in polar aprotic solvents, H,SO, 98% and acetonitrile. The inherent viscosities of modified polyisophthalamides are also shown in Table 1 which ranged from 0.27 to 0.29dl/g. No considerable differentiations in the ninhvalues of modified and unmodified polyisophthalamides were observed. The isothermal moisture absorption for a typical pair of polyisophthalamides 2d and 3d is shown in Fig. 3. The mole of the absorbed water per amide

‘Or

2d

8 E 4

6

5 ki

4

z

3d

2

l-~--*

-e-•0 0

20

40

80

60 Time

LOO

120

(hr)

Fig. 3. Water absorption (%) vs time for polyamides 2d and 36.

equivalent weight was 0.53 and 0.13 respectively, after a time exposed of 120 hr. The modified polyisophthalamide 26 showed a remarkably higher hydrophilicity. This feature was attributed to the disruption of the chain packing caused by the pendant furamido groups, which is in line with the enhanced solubility in common organic solvents of modified polyisophthalamides. Figure 4 presents the stereoscopic view for two repeat molecule units of 2d indicating the increased degree of disorder. On the other hand, the additional amido groups in the modified polyisophthalamide molecule increased its water absorption ability[8]. The modified polyisophthalamides 2 were thermally crosslinked through their furan olefinic bonds according to the following reaction to afford heat resistant resins.

On the other hand, it is well known [19] that the furan ring can behave both as a diene and dienophile to afford by heat-curing a Diels-Alder polymer. Thus an oligomer or polymer could be

766

Constantinos D. Diakoumakos and John A. Mikroyannidis

OH lc @N 00 Fig. 4. Stereoscopic drawing for two repeat molecule units of the modified polyisophthalamide (ChemDraw 3D Plus S. Cambridge Scientific Computing Inc.).

obtained rings.

by intermolecular

reaction

2d

of the furan n

Dimer

Trimer

n-2

Polymer

Tetramer

The cured polymers are expected, therefore, to possess a complex network structure. Even though the unmodified polyisophthalamides 3 lack furan rings and therefore cannot be crosslinked, they were also cured under same experimental conditions for comparing their thermal properties. 100

80

E

0

I 200

1 400

\

._____ 600

_jJ 800

TEMPERATUREW

Fig. 5. TGA thermograms of cured polyamides 2a’, M’, 3a’ and 3d’ in Nz and air. Conditions: gas flow 6Ocm”/min; heating rate ZO”C/min.

The cured polymers

obtained

from polyamides

2a-2d and 3a-3d by curing at 300°C for 20 hr are referred to by the designations 2a’-2d’ and 3a’-3d’

respectively. Their thermal stability was evaluated by dynamic TGA and isothermal gravimetric analysis ([GA). Figure 5 presents typical TGA curves in N, and air for the pairs of cured polymers 2a’, 3a’ and 2d’, 3d’. The initial decomposition temperature (IDT), the polymer decomposition temperature (PDT). the maximum polymer decomposition temperature (PDT,,,) both in N, and air as well as the anaerobic char yield (I’,) at 800°C for all cured polymers are summarized in Table 2. The IDT and the PDT were determined for a temperature at which 0.5 and 10% weight loss was observed respectively. PDT,,, corresponds to the temperature at which the maximum rate of weight loss occurred. Taking the IDT as criterion of thermal stability, it is seen that the cured polymers 2’, compared to the corresponding reference polymers 3’, were more thermally stable due to their network structure. In addition, the cured modified polyisophthalamides

Modified polyisophthalamides Table

hearing furamido pendant groups

2. Thermal stabilities of cured polyamides N*

PDTb W) 467 463 460 498 460 381 492 530

ID-I-” (“C) 325 320 333 340 317 305 325 326

Sample za’ 2b’ 2c’ M’ 3n’ 3b’ 3c’ 3d’

761

Air

PDT,,, (“C) 498 482 461 507 508 314 501 533

V W) 66 61 60 65 52 63 60 62

IDT (“C) 321 315 329 336 310 303 319 321

PDT (“C) 441 420 441 460 367 374 422 426

PDT,,, (“C) 523 522 516 533 371 381 492 463

“Initial decomposition temperature. bPolymerdecomposition temperature. ‘Maximum polymer decomposition temperature. ‘kZhar

yield

at 800°C.

afforded a somewhat higher anaerobic Y, at 800°C than did the corresponding unmodified ones. More particularly, polymers 2’ were stable up to 321340°C in N, or air vs 303-326°C of 3’ and afforded anaerobic Y, at 800°C of 61-67% vs 5243% of 3’. The cured polymers obtained as dark brown solids

were insoluble in solvents for the untreated samples. In addition, the glass transition (T,s) temperatures for a typical pair of cured polyisophthalamides 2a’ and 3s’ were determined by the thermal mechanical analysis (TMA) method. More particularly, modified polyisophthalamide 2a’ had a TB of 240°C whereas the corresponding value for the reference polyisophthalamide 3a’ was 246°C. The comparable T, values of both resins showed that the incorporation of the pendant furamido groups along the polymer backbone did not reduce significantly the Tg. That means that the great volume and the polar nature of the furamido group, which on the other hand contributes to a higher density of hydrogen bridges is overcome by the effect of assymetry and irregularity introduced by the pendant groups which should decrease the T,. Figure 6 presents the IGA traces in static air at 320°C for the pair of cured polymers 2d’ and 3d’. They exhibited weight losses of 16.60 and 46.67% respectively, after 20 hr isothermal ageing. These

results confirmed the remarkably higher thermal stability of the cured modified polyisophthalamides. REFERENCES I. J. Preston and J. Economy (Eds). High Temperature and Flame-Resistanr Fibers. Interscience, New York (1973). 2. E. Cassidy. Thermally Stable Polymers, Syntheses and Properties. Dekker, New York (1980). 3. P. W. Morgan. Condensation Polymers: By Interfacial and Solution Methods. Interscience, New York (1980). 4. V. Guidotti and N. J. Johnston. Polym. Prep. 15, 570 (1974). 5. A. K. Chauduri, B. Y. Min and E. M. Pearce. J. Poiym. Sci., Polym. Chem. Edn. 18, 2949 (1980). 6. J. De Abajo and E. de Santos. Angew. Makromolek. Chem. 17, 111 (1983). 7. E. Guijarro, J. G. de la Campa and J. de Abajo. J. Polym. Sci., Polym. Chem. Edn. 22, 1531 (1984). 8. J. G. de la Campa, E. Guijarro, F. Serna and J. de Abajo. Eur. Polym. J. 21, 1013 (1985). 9. J. de Abajo, F. Serna, E. Guijarro and J. G. de la Campa. J. Polym. Sci., Polyrn. Chem. Edn. 24, 483 (1986). 10. A. Melendez, J. G. de la Campa and J. de Abajo. Polymer 29, 1142 (1988).

1I. A. E. Lozano, J. de Abajo, J. G. de la Campa and J. Preston. J. Polym. Sci.: Part A: Polym. Chem. 30, 1327 (1992). 12. J. A. Mikroyannidis. J. Polym. Sri.: Part A: Polym. Chem. 30, 2371 (1992).

13. A. E. Lozano, J. de Abajo and J. G. de la Campa. J. Polym. Sri.: Part A: Polym. Chem. 31, 1203 (1993). 14. A. E. Lozano, J. de Abajo, J. G. de la Campa and J. Preston. J. Polym. Sci.: Part A: Polym. Chem. 31, 1383 (1993).

A

50

0

I 4

I

I 8

I

I I2

I

I I6

I

I 20

TIMElhrl

Fig. 6. IGA traces in static air at 320°C of cured polyamides 2d’ (A) and 3d’ (B).

15. A. E. Lozano, J. de Abajo, J. G. de la Campa and J. Preston. Polymer 35, 872 (1994). 16. C. D. Diakoumakos and J. A. Mikroyannidis. Polymer 35, 1986 (1994). 17. N. Yamazaki, F. Higashi and J. Kawabata. J. Polym. Sci. Chern. Edn. 12, 2149 (1974). 18. N. Yamazaki, M. Matsumoto and F. Higashi. J. Polym. Sci. Chem. Edn. 13, 1373 (1975). 19. J. K. Stille. Fortschr. Hoch Polym. Forth 3, 48 (1961).