Synthesis and characterization of aromatic amine functional semicrystalline aryl ether ketone macromers

Synthesis and Characterization of Aromatic Amine Functional Semicrystalline Aryl Ether Ketone Macromers

Y. BOURGEOIS,’* J. DEVAUX,’ R. LECRAS,’ Y. CHARMER,’ and J. 1. HEDRICK’

’Unit6 de Physique et de Chimie des Hauts Polymgres, Universitb Catholique de Louvain, Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium, *IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California 951 20-6099

SYNOPSIS

From earlier experiments it was observed that the reactions of aryl fluoride functional aryl ether ketone oligomers (PEK) with rn-aminophenol lead to poor levels of amine incorpo- ration because of side-reactions. In this article, a method is presented to protect the rn- aminophenol by converting it into a triarylimine group. This protected rn-aminophenol was used together with 4-fluoro,4’-hydroxybenzophenone in a typical poly(ary1 ether) synthesis. PEKs of different molecular weights were synthesized with number average molecular weights M,) of 2600,4500, and 5400 g/mol. The deprotection of the triarylimine chain end was carried out by an acid treatment to afford a monofunctional aromatic amine end group, amenable towards copolymerization. 0 1995 John Wiley & Sons, Inc. Keywords: poly(ether ketone) amine functionalization monofunctional macromer

INTRODUCTION

During the last two decades numerous high-temperature thermoplastic polymers have been devel- oped including poly (a ry la te )~ , poly (ether imide)~ , poly ( s u l f o n e ) ~ and poly (ether ketone)^. The poly (ether ketone) ( PEK, 1 ) and poly (ether ether ketone) (PEEK, 2 ) have achieved significant commercial importance, due to their attractive combination of properties which include excellent mechanical properties, good thermal stability, and solvent resistance.’ These properties result, in part, from their semicrystalline morphology which imparts, in particular, the solvent resistance. Consequently, PEEK and related structures have received little attention as reactive oligomers (i.e., maleimide, ethynyl, or amine functionalities ) or as components in block copolymer syntheses.

The synthesis of both PEEK and PEK is generally carried out through a nucleophilic aromatic substitution polymerization, where the electron-de- ficient ketone moiety activates an otherwise un-

* To whom all correspondence should be addressed. Journal of Polymer Science: Part A Polymer Chemistry, Vol. 33,779-785 (1995) 0 1995 John Wiley & Sons, Inc. CCC 0887-624X/95/050779-07

reactive aryl fluoride towards displacement.’ Such semicrystalline polymers generally require the use of high boiling solvents and polymerization tem- peratures in excess of 300°C to maintain the req- uisite solubility for obtaining a high polymer. The use of an excess of 4,4’-difluorobenzophenone, as de- termined by the Carother’s equation, provides a good control of the molecular weight and of the nature of the chain ends.2

Although this synthetic approach was a successful route to aryl fluoride terminated PEKs, this strategy is not suitable for the preparation of aromatic amine functional oligomers by the use of n-aminophenol as endcapper, due to some side-reactions in these conditions. The synthesis of amine-ended PEEK oligomers has already been reported and was carried out via poly(ary1 ether ketimine) o l ig~mers .~ Due to the amorphous character of the poly(ary1 ether ketimine) oligomers, the solubility in common organic solvents allows the synthesis and the functionalization with m-aminophenol under mild conditions. The ketimine can be readily hydrolyzed to the ketone yielding the semicrystalline PEEK. This approach has been applied to both the preparation of PEEK functional oligomers and block copolymers.

Likewise, we sought to use this approach to

779

780 BOURGEOIS ET AL.

PEEK (2)

Figure 1. (2).

Molecular structures of PEK ( 1 ) , and PEEK

protect the m-aminophenol to the thermally stable triarylimine monosubstituted endcapper in the PEKs synthesis in diphenylsulfone at elevated temperature, which is the objective of preparing monoamine functional macromers upon hydrolysis of the ketimine.

EXPERIMENTAL

Materials

The 4-fluoro,4'-hydroxybenzophenone, 4,4'-difluorobenzophenone and diphenylsulfone (DPS) were kindly supplied by ICI. The 4-fluoro,4'-hydroxybenzophenone was washed on charcoal and recrystallized twice from ethanol. The 4,4'-difluorobenzophenone and DPS were used as received. The m- aminophenol (Aldrich) was recrystallized twice from water, whereas benzophenone (Janssen) was used as received. Sodium carbonate (Merck) was finely sieved and dried a t 120°C during 2 h before use. Hydrochloric acid (37%) UCB) was used as received.

Monomer Synthesis

Synthesis of Hydroxytriphenylirnine, 3

In a three-necked flask, fitted with a Dean-Stark trap with condenser and a thermoregulated electrical heating mantle, m-aminophenol (21.8 g, 0.2 mol), benzophenone (36.4 g, 0.2 mol), and p-toluenesul- fonic acid (0.2 g, 1.05 X lop3 mol) were charged and dissolved in 400 mL toluene. The solution was heated a t 95°C under magnetic stirring and water was removed as a toluene azeotrope over a 24 h pe- riod. The toluene was then evaporated and the crude product was recovered as small crystals. These crystals were washed twice with cool absolute EtOH. The purified product (43.68 g, 80%) was finally dried at room temperature under vacuum. The product exhibits a melting endotherm at 171.8"C.

Polymerizations

Synthesis of a PEK Macromer, 4

A typical synthesis designed to prepare a monoamine functional oligomer of PEK (z : 5400) is described here. In a three-necked round-bottomed flask, 4-fluoro-4'-hydroxybenzophenone (100 g, 0.463 rnol), hydroxytriphenylimine (8.69 g, 3.04 X mol) and finely ground and dried sodium carbonate (83.65 g, 0.789 mol), were reacted under dry nitrogen in 900 g of diphenylsulfone at 300°C for 3 h. Thereafter, 4,4'-difluorobenzophenone (65.9 g, 0.302 mol) was added and the solution was stirred for an additional hour. The solution was then poured in an aluminum pan and allowed to cool. The crude product was then milled and leached three times with refluxing MeOH, twice with refluxing water and once with refluxing MeOH.

Deprotection of 4

The oligomer (10 g) was slurried in - 50 mL of MeOH/HCl (50/50) solution during 2 h at room temperature. The resulting oligomer, 5, was then slurried twice in refluxing water and once in refluxing MeOH.

Characterization

The 13C-NMR spectra were taken on a spectrometer Briicker AM 500 a t the frequency of 125.76 MHz. The spectral width was 25,000 Hz. The pulse width was 10 ps (pulse a t 90" : 15 ps). The relaxation time was 15 s in 1NVERSE.GATE and 5 s in GATE.DECOUPLING. Approximately 150-200 mg of the sample were dissolved in 4 mL of triflic acid and stirred over 4 h. The lock signal was obtained by introducing a capillary tube containing a deuter- ated solvent, centered in the sample one. The hydroxytriphenylimine analyses were performed in DMSO-d6 in the same conditions as described above on a Briicker WM 250 spectrometer.

"F-NMR spectra were obtained with a Brucker WM 250 spectrometer working a t 235.34 MHz for 19F. The experimental conditions were as follows: FT size, 16K; spectral width, 20,000 Hz; pulse width, 13 ps (90"). The measured relaxation time for the polymer was 0.3 s. For quantitative work, a delay of 5.6 s was imposed between successive pulses. The samples were dissolved in H,SO, (99-loo%, UCB). The difluorodiphenylsulfone (99%, Aldrich) was used as internal standard. The dryness of this stan-

ARYL ETHER KETONE MACROMERS 781

dard was verified periodically. The solutions (ca. 5% w/w) were prepared at room temperature.

The DSC analyses were carried out on a Perkin- Elmer differential scanning calorimeter (DSC 7) calibrated with indium and zinc, and operating under nitrogen. From 7 to 15 mg of the sample was weighed and analyzed in open aluminum DSC pan. The heating and cooling ramps were carried out at 20"C/min.

Thermogravimetric experiments were performed on a Perkin-Elmer TGA2 thermomicrobalance under nitrogen. The samples were heated from 30°C up to 400°C by 10"C/min.

The SEC chromatography was constituted of a HPLC 590 Waters pump, 3 PL gel columns from Polymer Lab. (500,100, and 50 A), a variable wave- length UV detector (Waters 484) set at 254 nm. The data were processed on a Trivector Trilab 200 com- puter. The solvent was unstabilized THF (Lab Scan) at 25°C. The flow rate was 0.6 mL/min and the sample concentration 0.1 g/L.

RESULTS AND DISCUSSION

Two synthetic approaches were surveyed as means to monoamine functional PEK oligomers. The polymerizations were carried out in diphenylsulfone containing sodium carbonate at elevated temperature. The first approach involved the endcapping of preformed mono (aryl fluoride) terminated PEK oligomers with m-aminophenol. However, it should be pointed out that ether interchange and subse- quent molecular weight control were of concern, and it was realized that this approach, although conve- nient, showed little chance of success. The second approach involved the protection of the amine group of m-aminophenol with benzophenone to the more thermally stable ketimine, followed by the use of this monofunctional monomer as an endcapping agent in the PEK synthesis.

Thus, the first approach to amine functional PEK

DPS, 300°C + Na,CO,

Figure 2. nophenol with a preformed fluorine ended PEK.

Synthesis of PEK-NH2 by reacting m-ami-

Retention time (secondes)

Figure 3. nealing for 1 h at 280°C.

Chromatogram of rn-aminophenol after an-

oligomers was the derivatization of preformed aryl fluoride endcapped PEK with m-aminophenol at 300°C using the standard procedure (Fig. 2 ) . NMR characterization showed, as expected, only minimal conversion of the fluorine chain end to the amine end groups. However, several important observations were noticed. First, the boiling temperature of m-aminophenol is 284°C which is below the polymerization temperature (300°C). Therefore, it is possible that some m-aminophenol can evaporate from the solution prior to the phenate formation. Secondly, the onset for thermal degradation of m- aminophenol is approximately 220°C. Low molecular weight SEC chromatography (Fig. 3 ) of m-

N H Z 0

m+-j - + D'6q-J - -

Toluene,

azetrope distillation, I 24H

N= 8 C

TF'I-OH (3)

Figure 4. Synthesis of TPI-OH ( 3 ) .


1 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 ~ 1 1 1 1 1 1 1 1 1 ~ 1 1 1 1 ~ 175 I70 16.5 160 IS5 Is0 I45 140 I3S 1.70 I25 120 1 I S 110 I05

PPM

Figure 5. 13C-NMR spectrum of TPI-OH.

aminophenol which was heated for 1 h in an evac- uated glass tube at 280°C showed many different degradation products. Finally, the m-aminophenol was also observed to condense with the aromatic ketone groups of PEK (or on the ketone group of a benzophenone moiety) at the polymerization tem- p e r a t ~ r e . ~ This led to imine linkages and to an hydroxyl pendant group which can provide either ether interchange reactions or chain branching.

From the above observations, it was evident that the amine group of the m-aminophenol should be chemically protected to preclude or minimize side- reaction with ketone groups, degradation, or vola-

Table I. Chemical Shift Assignment for TPI-OH

Atom No. Chemical Shifts

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15

157.37 107.26 152.25 111.03 128.96 109.97 166.81 138.93 128.61 128.17 130.64 135.87 128.61 127.85 128.35

tilization of the endcapper. Since triphenylimine (TPI ) is known to be stable at high t empera t~ re ,~ the formation of a phenylimine should be an easy and efficient method to protect the amine group. Such a protection scheme should prevent the reaction with the monomer, polymer, or solvent. More- over, the imine bond is also stable in the presence of basic reagent^.^-^ Thus, the amine group of m- aminophenol was converted into an imine group by reaction of the m-aminophenol with benzophenone, following the reaction scheme presented in Figure 4. The product obtained is the hydroxytriphenylimine (TPI-OH) . The TPI-OH was characterized by 13C-NMR. The spectrum is reported in Figure 5 and Table I presents the assignment of the chemical shifts for the different C atoms.

It is well known that triarylimines are very stable at high temperature due to their fully conjugated

rn-AP --- E h loo I '-\ -TPI-OH

v1 80

40 ̂ I , , . , , , , ) \ , . , 20

0 1

0 1 0 0 200 300 400

Temperature ("C)

Figure 6. Thermogravimetric analysis of m-aminophenol and TPI-OH.


Q + n w + ! ! e F

DPS, 300"C, 3h

I +NazC03

c 0

PEK macromer (4)

Figure 7. Synthesis of PEK macromer ( 4 )

molecular structure. This prevents any thermal degradation. A further advantage of the use of TPI- OH instead of rn-aminophenol for the nucleophilic substitution of PEK F-end groups lies in their difference in volatility due to the higher molecular

Table 11. Synthesized PEK-NHp

Number-Average Molecular Weights of the

PEK 1 PEK 2 PEK 3

5400 2600 4500

weight of the former (273 g/mol) than the phenol ( 109 g/mol) . This difference in volatility was confirmed by thermogravimetric analysis ( Fig. 6 ).

In a preliminary experiment, it was observed that the endcapping of aryl fluoride PEK oligomers with hydroxytriphenylimine in DPS in the presence of alkaline carbonate led to the formation of hydroxyl endgroups presumably due to transetherification.8 Thus, again, the use of preformed fluorine ended PEK oligomer with the hydroxytriphenylimine endcapper was not a viable route to amine-func- tionalized oligomers. However the side-reactions, thermal degradation, and volatility of rn-aminophenol were no more concerned.

An alternative route to PEK macromers involved condensing the 4-fluoro,4'-hydroxybenzophenone with hydroxytriphenylimine in diphenylsulfone containing base (Fig. 7 ) . In this approach, the hydroxytriphenylimine was used to control both the molecular weight and end functionality of the polymer. Upon completion of the polymerization ( - 3 h ) ,4,4'-difluorobenzophenone was added to endcap

3


Table 111. 4'-hydroxybenzophenone in CF3S03H

Chemical Shifts of PEK and 4-Fluoro,

4-Fluoro, F-PEK-NH2 4'- hydroxybenzophenone

Atom Chemical Atom Chemical No. Shifts No. Shifts

1 2 3 4 5 6 7 8 9

10

165.42 120.48 139.1 125.4 201.56

172.3 and 170.2 6' 170.7 and 168.6 117.9 and 117.7 7' 117.4 and 117.2

8' 137.0 and 136.9 9' 125.7

202.65 lo' 198.91

the phenolic chain ends. The absence of any fluorine endgroup before addition of the endcapping agent was confirmed by "F- and 13C-NMR analyses.

Owing to the higher reactivity of 4,4'-difluorobenzophenone with nucleophiles, true asymmetri- cally terminated molecules are expected. PEKs of different molecular weights were synthesized and the number average molecular weights (K) ) deter- mined by "F-NMR,' are shown in Table 11.

The imine endcapped PEK oligomer was subse- quently treated with a methanol/HCl mixture to hydrolyze the imine to the aromatic amine end group. Although methanol is a nonsolvent of PEK, it diffuses sufficiently into the PEK powder to allow derivatization of the end groups.''?" The hydrolysis of the T P I chain ends was readily achieved under these conditions.

The 13C-NMR spectra of the PEKs were similar and comparable to the spectra presented in Figure 8. Assignment of the C atoms in the main chain has been previously reported in the literature.12 Assign- ment of the C atoms close to the fluorine chain ends was performed by comparison with the chemical

Figure 9. of F-PEK-NH2 ( 5 ) and of its model compound.

Molecular structures of the fluorine chain end

Figure 10. the model compound of its chain ends.

Molecular structures of PEK-NH2 ( 5 ) and

shifts of 4-fluoro,4'-hydroxybenzophenone (Table I11 and Fig. 9).

For characterizing the amine chain end by 13C- NMR, the spectrum of PEK-NH2 was compared to a model compound of the amine chain end. The molecular structure of this model compound is presented in Figure 10.

The complete assignment of the C atoms of the amine chain ends of the model compound was dif- ficult to perform by a classical method.I3 Indeed, the resolution of the undecoupled spectrum was not fine enough to observe the J3c-H couplings in triflic acid. Some uncertainties remained concerning C22, C24 )

C26 carbon atoms. An attempt, made to calculate the chemical shifts contributions to the amine group on an aromatic ring in triflic acid by using aniline, proved to be unsuccessful in this solvent, due to the same lack of resolution. Therefore, to assign the carbon atoms of aniline in the triflic acid, the displacement of the chemical shifts of the different C atoms of the aniline was followed from a classical solvent (DMSO, in which the chemical shifts contributions of the amine group are well known) by adding step-by-step some triflic acid until obtaining the spectrum in the pure acid. Then the contributions of the amine group were calculated by sub- tracting from the observed chemical shifts in the pure acid the value of the chemical shifts of a carbon atom of the phenyl ring ( 128.5 ppm) . The measured chemical shifts and the calculated contributions of the amine group on an aromatic ring in these con-

Table IV. Aniline in Triflic Acid

Chemical Shifts and Contributions for

Atom No. Chemical Shift Contribution

129.60 123.85 130.68 130.38

-1.27 -6.62

1.09 1.25


Table V. PEK-NH2 3 End Groups from Model Compound Observed and Calculated Values

Assignment of 13C Shifts in Triflic Acid for

Model Model Compound Compound (Observed (Calculated

PEK-NH2 3 Values) Values)

Atom Chemical Atom Chemical Atom Chemical No. Shift No. Shift No. Shift

11 12 13 14 15 16 17 18 19 20 21

200.3 123.4 138.0 118.3 169.25 154.2 115.6 129 120.1 132.3 122.9

11’ 12‘ 13’ 14’ 15’ 16’ 1 7’ 18’ 19’ 2 0 2 1’

199.37 123.54 138.70 118.12 167.99 154.43 115.33 128.87 120.09 132.11 122.64

11’ 12’ 13’ 14’ 15’ 1 6 17’ 18’ 19 2 0 2 1‘

197.2 122.4 138.4 120.0 169.7 153.9 111.1 128.6 119.4 131.0 118.9

ditions are presented in Table IV in which ipso, or- tho, meta, and para positions to the amine group are respectively numerated atom nos. 1, 2, 3, and 4.

Adding these chemical shift contributions to the chemical shifts of the external phenyl unit of thep- diphenoxybenzophenone leads to the calculated values of the chemical shifts for the amine chain end model compound. Table V presents these calculated values, the observed ones for the model compound and the observed ones the PEK-NH23. The small differences in some chemical shifts between the model compound and the chain ends of the polymers can be understood as the model compounds are symmetrical molecules while the chain ends are not. This procedure allowed to assign all the carbon atoms of the amine chain end model compound. There is a good agreement between the calculated values and the observed ones. The agreement between the observed values for the model compound and those of PEK-NH23 is quite good.

CON CLUS 10 N

The synthesis and the characterization of aromatic amine functional PEK macromers of different molecular weights was reported. From detailed NMR analyses, the polymer chains appeared effectively terminated on one side by an amine group and by a fluorine atom on the other side in near quantitative yields. In a view of the synthesis of block copolymers, such a functionalization opens a wide range of pos- sibilities.

REFERENCES AND NOTES

1. R. N. Johnson, A. G. Farnham, R. A. Clendinning, W. F. Hale, and C. N. Merriam, J. Polym. Sci. A-I, 5 , 2375 (1967).

2. T. E. Attwood, D. A. Barr, G. G. Faesey, V. Ju. Leslie, A. B. Newton, and J. B. Rose, Polymer, 354 (1977).

3. J. L. Hedrick, W. Volksen, and D. K. Mohanty, Po- lyimides and Other High-Temperature Polymers, El- sevier, Amsterdam, 1991, p. 83.

4. D. K. Mohanty, S. D. Wu, and J. E. McGrath, Polym. Prepr., 29 ( 1 ) , 352 ( 1988).

5. D. K. Mohanty, R. C. Lowry, G. D. Lyle, and J. E. McGrath, Int. SAMPE Symp., 32 ,408 (1987).

6. D. K. Mohanty, J. S. Senger, C. D. Smith, and J. E. McGrath, Int. SAMPE Symp., 33,970 (1988).

7. S. Patai, The Chemistry of the Carbon-Nitrogen Double Bond, Interscience, New York, 1970, p. 64.

8. I. Fukawa, T. Tanabe, and H. Hachiya, Polym. J., 24 ( 2 ) , 173 (1992).

9. J. Devaux, D. Daoust, R. Legras, J. M. Dereppe, and E. Nield, Polymer, 30, 161 (1989).

10. D. Daoust, J. Devaux, R. Legras, J. Mercier, and E. Nield, GB Appl. 8,401,411.

11. D. Leblanc, Ph.D. thesis, Universitb Catholique de Louvain, Belgium, 1988.

12. I. Fukawa, T. Tanabe, and T. Dozono, Macromolecules, 24, 3838 ( 1991 ) .

13. E. Pretsch, Th. Clerc, J. Seibl, and W. Simon, Tables of Spectral Data for Structure Determination of Organic Compounds, Springer-Verlag, New York, 1989.

Received February 9, 1994 Accepted September 17, 1994

Documents

Synthesis and characterization of aromatic amine functional semicrystalline aryl ether ketone macromers