J. MATER. CHEM., 1991, 1(6), 977-988 Synthesis and Characterization of Isomeric Biphenyl-containing Poly(ary1 ether-bisketone)s. Part 1.-Polymers derived from 4,4'-(p-FluorobenzoyI)biphenyl and Bisphenols Atul Bhatnagar, Rajarathnam S. Mani, Barry R. Weeks and Dillip K. Mohanty* Department of Chemistry and Center for Applications in Polymer Science, Central Michigan University, Mt. Pleasant, MI, 48859, USA A series of amorphous and semicrystalline poly(ary1 ether-bisketone)s have been synthesized from bisphenols and 4,4'-bis(p-fluorobenzoyl)biphenyl via nucleophilic aromatic substitution reactions. Model compound studies were carried out with a variety of substituted phenols, 4,4'-bis( p-fluorobenzoyl)biphenyl and 4,4'-bis( p-chloroben- zoy1)biphenyl. The bishalide monomers were synthesized by the reaction of biphenyl-4,4'-dicarboxylic acid with thionyl chloride followed by Friedel-Crafts acylation with the appropriate aryl halide.Potassium carbonate mediated reaction of these monomers in dimethylacetamide or diphenyl sulphone gave high-molecular-weight polymers in excellent yield. Polymers with semicrystalline morphologies were synthesized from soluble high- molecular-weight amorphous precursors with removable bulky substituents. Unlike the corresponding mono-ketone analogues, the amorphous poly(ary1 ether-bisketone)s exhibited poor solubility in a wide variety of solvents, indicative of improved solvent resistance. The glass-transition and melting temperatures of the polymers are among the highest known for poly(ary1 ether-ketone)s.In addition, the polymers exhibit excellent thermal stability and afford tough films by compression moulding. Keywords: Nucleophilic aromatic substitution ; Amorphous material; Glass-transition temperature Poly(ary1 ether-ketone)s belong to a class of materials known as engineering thermoplastics. 1*2 During the past decade ICI has commercialized an aromatic poly(ary1 ether-ket~ne),~~' PEEK (l),which has contributed to the enhanced scientific interest in this class of materials. Poly(ary1 ether-ketone)s exhibit many desirable characteristics including exceptional thermo-oxidative and dimensional stability, resistance against radioactive irradiation and excellent mechanical properties. The introduction of crystallinity into a poly(ary1 ether-ketone) backbone results in improving the solvent resistance and modulus.PEEK exhibits a high degree of crystallinity and a melting point (T,) of 335 "C. On the other hand, PEEK suffers from poor creep behaviour above its relatively low glass- transition temperature (T,) of 145 oC.6 Therefore, attempts have been made to either increase the glass-transition tempera- tures of semicrystalline poly(ary1 ether-ketone)s in general or to introduce cross-link sites into the PEEK The amorphous poly(ary1 ether-ketone)s, characterized by back- bones containing sp3 or sp3d2 hybridized atoms (e.g. 2 and 3, respectively) in addition to the ether and carbonyl linkages, are useful for a variety of applications, such as fabrication of foils, films or membranes.Such materials exhibit lower glass- transition temperatures than the analogous amorphous poly(ary1 ether-sulphone)s, 4 and 5.lO-l' In order to achieve higher glass-transition temperatures and/or higher melting points, two carbonyl groups (in contrast to PEEK which contains one such group) have been introduced into the polymer repeat unit structures (e.g. 6a and 6b).12-14 Polymer 6a was synthesized by the reaction of isopropylidenebiphenyl- diol (bisphenol-A) with either 7a or 7b via nucleophilic aro- matic substitution reactions. Electrophilic aromatic substitution reactions have been used also for the synthesis of poly(ary1 ether-ketone)s. For example polymer 8a, prepared via this procedure, exhibits high Tg (170 "C) and T, (381 "C)." Furthermore, according to a recent patent claim, polymer 8b containing two keto substituents and one biphenyl linkage in the polymer repeat unit could also be synthesized by following the same procedure.I6 A wide variety of aromatic polymers containing a biphenyl linkage in the basic repeat unit of the polymer have been synthesized.For example, conventional biphenyl functional poly(ary1 ether-sulphone), synthesized by the reaction of biphenol with 4,4'-dichlorodiphenyI sulphone, exhibits excel- lent thermo-oxidative stability and high toughness2 These desirable properties have been attributed to the presence of the biphenyl linkage. l7 Furthermore, we have recently reported the synthesis and characterization of a series of poly(ary1 ether-bissu1phone)s containing a biphenyl moiety in the repeat unit structures.These polymers exhibit some of the highest known Tgs for poly(ary1 ethers)." In order to achieve some of these improved characteristics with poly(ary1 ether-ketone)s, we have synthesized a number of monomers, 9, suitable for the synthesis of poly(ary1 ether-bisketone)s. These monomers, which contain a biphenyl linkage and two keto groups were prepared from isomeric biphenyldicarbox- ylic acids. In this paper, which is the first of a series, we report the synthesis of bisketo functional monomers (derived from biphenyl-4,4'-dicarboxylic acid), related model compound studies and polymers based upon isopropylidenebiphenyldiol (bisphenol-A), hydroquinone, tert-butyl hydroquinone, biphe- nyl-4,4-diol and 4,4'-dihydroxydiphenyl sulphone (bisphenol- S).The polymers have been characterized by spectroscopic, thermal and thermomechanical means. Experimental Materials Dimethylacetamide (DMAc) (Aldrich) was dried over calcium hydride and then distilled at reduced pressure. Chlorobenzene (Fisher) and aniline (Aldrich) were purified following the same procedure. Diphenyl sulphone (DPS) (Aldrich) was recrys- tallized from acetone. 4,4'-Isopropylidenebiphenyldiol (bisphenol-A), kindly sup- plied by Dow Chemical, was purified by recrystallization from toluene and dried at reduced pressure at 80°C for 24 h. Hydroquinone, biphenol and 4,4'-dihydroxydiphenyl sul-phone (bisphenol-S) (Aldrich) were recrystallized from acetone.J. MATER. CHEM., 1991, VOL. I 1 0I:: II I2 x=c, Y=C; 3 x=s02 Y=C ; 4 x=c, Y=S02 I I 6 7 8a 8b X=CI, F 9 tert-Butylhydroquinone (Aldrich) was crystallized from hex- ane-ether. Molecular sieves (3 A) (Fisher), were dried over- night in an oven at 100 "C. Thionyl chloride was stirred over triphenyl phosphite and distilled at normal pressure prior to use. Anhydrous potassium carbonate (Fisher) was dried over- night in an oven at 100 "C. The required diacid, biphenyl- 4,4'-dicarboxylic acid was purchased from Spectrum. All other reagents were used as received. Biphenyl-4,4'-dicarbonyl DichEoride (10) A 1000 cm3, three-Decked, round-bottomed flask fitted with a condenser, a nitrogen inlet and a mechanical stirrer was charged with 60.5 g (0.25 mol) of biphenyl-4,4'-dicarboxylic acid, 600 cm3 of thionyl chloride (5.0 mol, excess) and 10 cm3 of dimethylformamide (DMF).A nitrogen blanket was main- tained during the course of the reaction. The reaction mixture was heated under reflux for a period of 4h. Upon the formation of the acid chloride, excess thionyl chloride was removed by distillation. The crude product was then crys- tallized (dichloromethane) to afford 10 as a white crystalline solid: m.p. 184-186 "C; v/cm-' 1788, 1723, 1598, 1206, 885, 845; mass spectrum (rule) (relative intensity) 278 (1 5), 243 (loo), 152 (39), 76 (10). 4,4-Bis(p-chlorobenzoyl)biphenyl(11) A 1000 cm', three-necked, round-bottomed flask fitted with a condenser, a nitrogen inlet and a mechanical stirrer was charged with 54.45g (0.25mol) of 10 and 500cm3 of dry chlorobenzene.The reaction vessel was cooled in an ice bath and anhydrous aluminium chloride (52.8 g, 0.40 mol) was added in small increments to the reaction mixture. After the initial exotherm, the ice bath was removed and the mixture was refluxed for 10 h. The deep-orange reaction mixture was then poured into strongly acidified cold water with vigorous stirring. The precipitated solid was collected by filtration at reduced pressure and washed with copious quantities of water J. MATER. CHEM., 1991, VOL. 1 followed by saturated aqueous sodium hydrogencarbonate solution. The crude product was crystallized five times (boiling 1,2-dichlorobenzene) and extracted with dichloromethane to remove residual 1,2-dichlorobenzene to afford 11 as white needles (63% yield): m.p.308.9 "C (DSC); v/cm-' 1645, 1604, 1587, 1290, 856; mass spectrum (m/e) (relative intensity) 432 (66), 43 1 (33), 430 (92), 3 19 (loo), 141 (22), 139 (65), 11 1 (28). (Found: C, 72.52; H, 3.58; C1, 16.40. Calc. for C26H1602C12: C, 72.56; H, 3.72; C1, 16.28%.) 4,4-Bis(p-jluorobenzoyl)biphenyl (12) Compound 12 was prepared by the procedure described for 11 by using 60.0 g (0.216 mol) of 10, 55 g (0.58 mol) of fluorobenzene and 58.1 g (0.44 mol) of anhydrous aluminium chloride. The reaction mixture was refluxed for 18 h. The product was isolated in high yield and purified by recrystalliz- ation (chloroform) to afford white flakes (67% yield): m.p.274.5 "C (DSC); v/cm-' 1641, 1601, 850; mass spectrum (m/e) (relative intensity) 398 (loo), 303 (77), 123 (68), 95 (26); 'H NMR (CDCI,) 6 7.45(m), 7.9(m); I9F NMR (CDC1,) 6 106.1; 13C NMR (CDCI,) 6 115.56 (d, JC-F=21 Hz), 127.3, 130.6, 132.63 (d, JCpF=9 Hz), 133.73 (d, JC-F=4 Hz), 136.9, 143.8, 165.42 (d, JCpF=251 Hz), 194.7. (Found: C, 77.98; H, 3.97; F, 9.53. Calc. for C26H1602F2: C, 78.38; H, 4.02; F, 9.65Yo.) Model Compound Synthesis (13a-d) Model compounds 13a-d were synthesized according to the following general procedure." (Analytical data for the com- pounds are summarized in Table 1.) A three-necked, 100 cm', round-bottomed flask fitted with a nitrogen inlet, a ther-mometer, and a Dean-Stark trap fitted with a condenser was charged with 0.005 mol of 11 or 12,0.01 mol of the desired phenol (Table l), 7.0 g (excess) of anhydrous potassium car- bonate, 35 cm3 of DMAc and 20 cm3 of toluene.The reaction mixture was heated at solvent reflux at 145 "C and water, the byproduct of the reaction, was removed by azeotropic distil- lation. The reaction mixture was heated to 160 "C for 8-22 h and then cooled to room temperature. It was filtered and the filtrate was distilled under reduced pressure to remove all solvents. If possible, the residue was dissolved in appropriate solvent and the solution was washed repeatedly with water, dried over anhydrous magnesium sulphate and the solvent was removed by rotary evaporation at reduced pressure.The crude product was purified by crystallization. General Procedure for Polymer Synthesis A typical synthesis of poly(ary1 ether-bisketone) was conduc- ted in a 500 cm', four-necked, round-bottomed flask equipped with a nitrogen inlet, a thermometer, an overhead stirrer, and a Dean-Stark trap. A detailed synthetic procedure used to prepare 14a is provided. The flask was charged with 5.7g (0.025 mol) of bisphenol-A and 10.7501 g (0.025 mol) of 12 and carefully washed in with 125 cm3 of DMAc. Anhydrous potassium carbonate, 10 g (excess) was added followed by 45 cm3 of toluene. The reaction mixture was then heated until toluene began to reflux at 140°C. Water (byproduct of the reaction) was continuously removed via the Dean-Stark trap.The reflux temperature was maintained for 4-6 h until the accumulation of water was no longer evident in the Dean- Stark trap. The reaction mixture became a light yellow at the initial stage of the reaction, owing to the formation of the phenoxide, and slowly deepened to brown with time. The reaction temperature was gradually raised to 165 "C by remov- ing toluene from the Dean-Stark trap. The reaction mixture was heated at that temperature for a period of 18 h. An additional amount (20cm3) of DMAc was added to reduce the high viscosity of the reaction mixture and the heating at 165 "C was continued for an additional 6 h. In reactions involving less reactive phenoxides or phenoxide of lower solubility, 45 g of DPS was added in place of DMAc.These reactions were carried out at 230 "C for a period of 3-4 h. The viscous reaction mixture was allowed to cool to room temperature, diluted with 100cm3 of DMAc and filtered to remove inorganic salts. The filtrate was acidified with several drops of glacial acetic acid to neutralize the phenoxide end groups and the polymer was precipitated with a 10-fold volume of methanol. The polymer was then dried at reduced pressure at 50 "C for 8-10 h. It was redissolved in the appro- priate solvent, the solution was filtered, acidified with glacial acetic acid, and the polymer coagulated in methanol. The fibrous solid was dried as before. For the attempted one-step synthesis of semicrystalline, hydroquinone functional poly(ary1 ether-bisketone), DPS, instead of DMAc, was used as the reaction medium.The reaction was carried out at elevated temperature (see Results and Discussion) and the polymer was coagulated by pouring the reaction mixture while still hot (160 "C) into a 10-fold volume of acetone. The coagulated polymer was then extracted with acetone, water and acetone, in that order, using a Sohxlet apparatus. The polymer was then dried as before. trans De-tert-butylation of tert-Butylhydroquinone Functional Poly(aryl ether-bisketone) (14c) A 100cm3, round-bottomed flask equipped with a magnetic stirrer and a glass stopper was charged with 0.874g (0.0015 mol) of 14c, 12 cm3 of trifluoromethanesulphonic acid and 30 cm3 of toluene.Note that the latter two reagents were taken in excess. The reaction mixture was stirred vigorously for a period of 18 h. The resulting product, polymer 14e, was isolated by pouring the reaction mixture into a large excess of acetone. The coagulated polymer was isolated by filtration at reduced pressure and thoroughly washed with copious quantity of water to remove residual acid. It was then washed with methanol and was dried under reduced pressure at 50 "C for a period of 8 h. Heterogeneous Hydrolysis of Biphenyl Functional Poly(ary1 ether-bisketimine) (14d) Polymer 14d (1.388 g, 0.002 mol) and a stoichiometric amount of hydrochloric acid (0.004 mol, 37 cm3 of 0.108 mol dmP3 aqueous solution) were added to a glass container inside a Parr High Pressure Reactor. The reactor was assembled and the temperature of the reaction vessel was increased to 300 "C.The hydrolysis was carried out with vigorous stirring. At the end of the hydrolysis period (1.5 and 24 h), the vessel was cooled and the polymeric product was collected by filtration. The polymer was extracted with hot water, washed with methanol and dried under reduced pressure at 50 "C for 8 h. 4,4'-Bis(p-fluoro-a-phenyliminobenzyl)biphenyl(15) A 100 cm3 round-bottomed flask fitted with a condenser was charged with 0.398 g (0.001 mol) of 12, 0.023 g (0.0025 mol) of freshly distilled aniline, 30cm3 of dry chlorobenzene and 20 g of 3 A molecular sieves. The reaction mixture was heated under solvent reflux for 24 h.It was then cooled and filtered and the sieves were washed with dry dichloromethane. The solvent was removed from the filtrate by evaporation at reduced pressure. The crude product was isolated in high yield and was purified by recrystallization (dichloromethane) to afford 15 (yield 52%) as a yellow crystalline solid: m.p. 245- 247 "C; v/cm- ' 1630, 1592, 1494; mass spectrum (m/e) (relative intensity) 549 (40), 548 (loo), 547 (29), 473 (32), 381 (23), 198 (43), 77 (52); 'H NMR (CDCl,) 6 6.7(m), 6.95(m), 7.15(m), 7.45-8.0(m); 19F NMR (CDCl,) 6 110.2, 112.0; 13C NMR (CDCI,) 6 115.17 (d, J=21.6 Hz), 115.23 (d, J=21.6 Hz), W Table 1 Analytical data for model compounds 13a-d elemental analysis compound phenol bishalide yield (YO) m.p.1 "C vlcm -6, m/e (rel.intensity) calc. found 13a 4-tert-but ylphenol 11 or 12 ca. 96 233-235 1647, 1593 31.53,34.51, 658(29), C, 83.95 C, 83.97 1496, 1307 117.19,119.83, 644(37), H, 6.43 H, 6.46 1290 127.01,127.05, 643(IOO), 130.65,131.88, 4 17(24), 132.51,137.73, 3 14(56), 14330,147.84, 253(42) 153.28,162.28, 194.98 13b 4-phen ylphenol 11 or 12 ca. 98 338-340 1643, 1597 699(22), C, 85.96 C, 86.08 1487, 1301 698(50), H, 4.87 H, 5.00 1289 453(20), 349(19), 273(loo), 152(21)1% phenol 12 ca. 98 268-270 1645, 1599 546(42), C, 83.52 C, 83.40 1494, 1307 453(1 I), H, 4.76 H, 4.96 1288. 1263 377(2l), 197(loo), 140(15) 13d 4-h ydroxybenzophenone 12 ca. 96 >360 1645, 1592 755(22), C, 82.74 C, 82.56 1501, 1311 677(1I), H, 4.57 H, 4.62 1265 576(loo), 499(3I), 301(87) J.MATER. CHEM., 1991, VOL. 1 98 1 (1) soc12 (2) DMF reflux. 4 h 10 11; X=CI 12; X=F Scheme 1 120.38, 120.9, 123.3, 123.36, 126.48, 126.64, 126.83, 126.98, ation with chlorobenzene and fluorobenzene, respectively 128.62, 129.79, 129.85, 130.09, 130.16, 131.34, 131.39, 131.48, 131.59, 131.90, 131.94, 135.20, 135.78, 135.81, 135.86, 138.77, 138.92, 140.13, 140.35, 142.35, 142.53, 150.96, 162.44 (d, J= 249 Hz), 164.3 (d, J=251 Hz), 166.52, 166.67. (Found: C, 83.10; H, 4.38; F, 6.94; N, 5.13. Calc. for C38H26N2F2: C, 83.21; H, 4.74; F, 6.93; N, 5.1OYo.) Characterization 'H and 13C NMR spectra were recorded using a General Electric QE-300 instrument. 19F NMR was recorded using an IBM NR 80 instrument and fluorotrichloromethane as an internal standard.IR spectra were obtained with a Nicolet DxB FT-IR spectrophotometer. Glass-transition tempera-tures, taken as the midpoint of the change in slope of the baseline, were measured either with a DuPont DSC 2100 or a Perkin-Elmer DSC-7 at a heating rate of 10 "C min-'. Thermogravimetric analysis (TG) of the polymer samples was conducted with a heating rate of 10 "C min-' in nitrogen. Intrinsic viscosity measurements for the amorphous polymers were determined by using a Cannon-Ubbelohde dilution viscometer and solutions in either N-methylpyrrolidone (NMP) or trichloromethane (CHC13) (25 "C). Dynamic mech- anical behaviour was assessed with a Polymer Laboratories dynamic mechanical thermal analyser (DMTA), bending with a heating rate of 4 "C min-' (1 Hz).Results and Discussion Monomer Synthesis The carbonyl group is known to activate a fluorine atom in para orientation, towards nucleophilic aromatic substitution reactions. For example, 4,4'-difluorobenzophenone is used for the synthesis of PEEK and other poly(ary1 ether-ket~ne)s.~*~ On the other hand, under similar reaction conditions, 4,4'- dichlorobenzophenone is thought to be an unsuitable mono- mer for poly(ary1 ether) ~ynthesis.~ This has been attributed to the low reactivity of a chlorine substituent owing to its larger size and lower electronegativity compared to a fluorine atom. It has been shown that the bischlorides 7a or 7b with two keto substituents, are suitable for polymer synthesis with bisphenol-A and other bisphenols.2.'2 However, this list of bisphenols did not include more acidic compounds such as hydroquinone or 4,4'-dihydroxybenzophenone. Therefore, both bischloro- (1 1) and bisfluoro- (12)substituted compounds were synthesized for the present investigation in order to study the feasibility of using 11 as a suitable, yet less expensive monomer for polymer preparations.The bishalides 11 and 12 were prepared starting from biphenyl-4,4-dicarboxylic acid, followed by acid chloride formation and Friedel-Crafts acyl-(Scheme 1). Compound 11 was insoluble in all common low- boiling solvents. It could only be purified by recrystallization from boiling 1,2-dichlorobenzene. In order to obtain monomer grade material, the crude product was recrystallized at least five times.The purity of 11, which was of critical importance, was ascertained by DSC after each recrystallization. The DSC thermogram of 11 after the fifth crystallization is shown in Fig. 1. On the other hand, purification of 12 was relatively simpler. It could be recrystallized from a large volume of trichloromethane to afford monomer grade material. The DSC thermogram of high purity 12 is also shown in Fig. 1. The insolubility of 11, and the highly cumbersome nature of its purification, allowed for the synthesis of the compound in small quantity for model compound studies only. The large- scale preparation of 11 required for polymer synthesis was not undertaken.Model Compound Studies Model compound studies were carried out by treating phenol or substituted phenols with 11 or 12 in DMAc in the presence of excess potassium carbonate (Scheme 2). An analysis of the data in Table 1 indicates that the reaction of p-tert-butylphe- no1 or 4-phenylphenol with either 11 or 12 results in the desired product in essentially quantitative yield. During the reaction with 4-phenylphenol, the resulting product precipi- tates from the reaction mixture. These observations suggest the following. First, it is possible to use the bischloride, 11, or the bisfluoride, 12, to synthesize high-molecular-weight amorphous polymer with bisphenol-A. Secondly, the polymer resulting from 4,4'-dihydroxybiphenyl and either of the bishal- ides would be semicrystalline in nature and a high-boiling I 1 I I 1 I I 1 I 150 200 250 300 350 T/"C Fig.1 DSC thermograms of (a)4,4-bis(p-chlorobenzoyl)biphenyl,and (b)4,4'-bis(p-fluorobenzoy1)biphenylmonomers J. MATER. CHEM., 1991, VOL. 1 DMAc. K2CO3 toluene, 165 "C,8 -10h -H20.-KX 13 ad X Z I 13a IH 13c Scheme 2 solvent such as DPS would be required for the synthesis of the polymer. The reaction of phenol with 12 was also quanti- tative and the resulting product precipitated from the reaction mixture at 165 "C. However, the replacement of the chloro groups of 11 by phenoxide derived from phenol was not satisfactory. Only a 50% yield of the desired compound could be realized. This difference in reactivity of the phenoxide anion as compared with the anions derived from p-tert- butylphenol and 4-phenylphenol towards chlorine displace- ment, may be attributed to the relative nucleophilicities of the anions under consideration.l9 The required set of data needed to support this contention is not available. However, it is possible to correlate the order of basicity of the phenoxide anions with their relative nucleophilicity. That this can be done, is due to the relatively small size of the oxygen anionic centre and also due to the fact that the attacking atom is the same (oxygen) in all three cases under consideration.20 A comparison of the relative acidity con-stants for phenol, 4-phenylphenol and p-tert-butylphenol reveals the following order: 4-phenylphenol -p-tert-butylphenol <phenol.21 It therefore follows that the order of the conjugate base strength and nucleophilicity is Ph-0-<4-Ph-Ph-O--p-(CH3)3C-Ph-O-.Thus, it is not surprising that the anion derived from phenol cannot replace the less reactive chlorine atoms of 11, whereas the more reactive nucleophiles can. This conclusion was further supported by carrying out the reaction of 4-hydroxybenzo- phenone (a stronger acid than phenol)21 with 11 and 12. The reaction was quantitative with the more reactive bisfluoride (12) only (Table 1). In addition to elemental analysis, the structures of the model compounds were verified by mass spectrometry. 13C NMR analysis lent further support for the structure determi- nation of 13a.The observed I3C absorbances (Table 1) are in close agreement with the calculated values.22 The model compound reaction corresponding to the polymer derived from 4,4'-dihydroxydiphenyl sulphone and 12 was not carried out because the required phenol, 4-hydroxyphenyl sulphone, was not readily available. Synthesis and DSC Analysis of Amorphous Poly(ary1 ether- bis ke tone)s Polymerization of the bishalide, 12, with either bisphenol-A or bisphenol-S could be readily carried out in presence of excess potassium carbonate in a DMAc-toluene (2 :1) solvent mixture (Scheme 3). In both reactions, a polymerization tem- perature of 165 "C was sufficient to synthesize high-molecular- weight poly(ary1 ether-bisketone)s.However, for the polymer- ization reaction of bisphenol-S with 12, it took significantly longer time (18 h) to attain a sufficient rise in viscosity compared to the 8 h necessary for the reaction of bisphenol- A with the same bishalide. Since the sulphone moiety is strongly electron withdrawing, the resulting bisphenoxide from bisphenol-S can be regarded as a weak nucleophile in contrast to the bisphenoxide from bisphenol-A. Similar obser- vations have been made for the reactions of the phenoxide from bisphenol-S and a variety of activated halides2.l7 The solubility behaviour of polymers derived from bisphenol-A, 14a, and from bisphenol-S, 14b, was remarkably different from that of the monoketone counterparts, 2 and 3, respectively.For example, poly(ary1 ether-bisketone), 14a, is insoluble in tetrahydrofuran and chlorinated hydrocarbons except for trichloromethane. It is only soluble in dipolar aprotic solvents such as DMAc (Table 2). On the other hand, the corresponding monoketone analogue, poly(ary1 ether-ketone) 2, is soluble in all aforementioned solvents at room temperature. Similarly, the bisphenol-S functional poly(ary1 ether-bisketone), 14b, is insoluble in all common solvents except for N-methylpyrroli- done (NMP) and hot DMAc. Once again, this solubility behaviour is in sharp contrast to that of the monoketone analogue 3 which is soluble in the solvents listed in Table 2 at room temperature. The reason for the difference in solubility behaviour may be attributed to the presence of the biphenyl and two ketone moieties in the repeat unit structures of polymers 14a and 14b.The intrinsic viscosity value for 14a in trichloromethane at 25 "C (q=60 cm3 g- I) and for 14b in NMP at 25 "C (q=60 cm3 g-') (Table 3), suggest a high to moderate molecular weight for these polymers. The molecular structure of the polymers was confirmed by both 13C NMR and FTIR. The 13C NMR spectrum of polymer 14a is shown in Fig. 2. The observed peak positions were in agreement with calculated chemical shifts.22 Further- more, owing to the high molecular weight of the polymers, additional absorbances due to the terminal units were not observed. The FTIR spectra (KBR) afthe polymers established the presence of the ether and keto linkages (absorbances at 1250 and 1655 cm- ', respectively) in the repeat-unit structures.The glass-transition temperatures of amorphous poly(ary1 J. MATER. CHEM., 1991, VOL. I HO-Ar-OH + K2C03, DMAC or DPS toluene, 10-12 h, A -H20, -KFI Y 14C 14d Scheme 3 Table 2 Solubility" behaviour of poly(ary1 ether-bisketone) 14a-f and poly(ary1 ether-bisketimine) 14d solvents polymers methylene chloride trichloromethane tetrahydrofuran dimet h y lacetamide N-methylpyrolidone 14a S 14b S* 14c S 14d S 14e 1 14f i 10% mjv. s =soluble at r.t.; s* =soluble when heated; i =insoluble. Table 3 Intrinsic viscosity data and glass-transition temperatures of amorphous poly(ary1 ether-bisketone) and poly(ary1 ether-bisketimine) 14d po1ymer 14a 14b 14C 14d intrinsic viscosity values glass-transition temperatures (/ "C) (DSC) in chloroform at 25 "C/cm3 g-heating rate 10 "C/min 60 60" 154 99 Solvent =NMP.ether-bisketone)s 14a and 14b were determined by DSC. As expected, polymer 14b exhibited a higher Tg (219 "C) in the second heating than 14a (q=186 "C),which contains a rela- tively less polar isopropylidene linkage (Table 3). This is due to the presence of a sulphone moiety in the polymer repeat unit. The DSC scan from the first heating was not conclusive. Furthermore, these <s observed for 14a and 14b are signifi- cantly higher than the reported values for the analogous poly(ary1 ether-ketone)s, containing only one keto group in the repeat unit structures.2 For example, bisphenol-A func- tional polymer 2 exhibits a Tgat 150 "C, which is ca.36 "C lower than the Tg of 14a and the q of 14b, bisphenol-S functional poly(ary1 ether-bisketone), is ca. 20 "Chigher than that of 3, which contains only one keto group in the repeat unit structure. Finally, these high qvalues for poly(ary1 ether- 186 219 206 21 1 bisketone)s can be attributed to the presence of the biphenyl linkage and the two keto functionalities in the repeat unit structures of the polymers. Synthesis and DSC Analysis of Semicrystalline Poly(ary1 ether- bisketone)s From the solubility behaviour of 13c, and from the reported insolubility of PEEK, 1,3,23in all common solvents at room temperature, except for strong protic acids, the poly(ary1 ether-bisketone) 14e, derived from hydroquinone and suitable bishalide, 12, was expected to be semicrystalline in nature with a high melting point.Therefore, a direct, one-step syn- thesis of 14e from hydroquinone and 12 was attempted in DPS, in the presence of excess potassium carbonate. The 1'"'"''1'''~1"''I 200 150 100 50 0 6 (PPm) Fig. 2 13C NMR spectrum of poly(ary1 ether-bisketone) in CDC1, based on 14a reaction was conducted at 250 "C for 5 h and at 320 "C for an additional 3 h, following a reported procedure for PEEK synthe~is.~During the synthesis, a noticeable rise in solution viscosity was not observed even after holding the reaction mixture at 320 "C.In addition, the reaction mixture was heterogeneous in nature during the entire course of the attempted synthesis. An increase in the reaction temperature to 330°C did not change the heterogeneous nature of the reaction mixture significantly. This is in sharp contrast to what is observed during PEEK synthesis by the same pro- cedure. In the latter case, an initial heterogeneous reaction mixture becomes fairly homogeneous at 320°C as the tem- perature approaches the melting point of PEEK (335 "C). These observations suggested that the resulting oligomers probably have higher melting temperatures than PEEK and continue to remain insoluble even at 320 "C. Furthermore, the precipitated oligomeric material was highly powdery in nature, indicative of the low molecular weight.As expected, it was insoluble in all common solvents except for strong protic acids such as concentrated sulphuric acid and methane- sulphonic acid. The low molecular weight of the polymer was verified by intrinsic viscosity measurements in concentrated sulphuric acid at 25 "C (q=28 cm3 g-'). Sulphonation of the polymer backbone during such measurements resulting in higher than actual qinh value has been The DSC thermogram of the oligomer showed a melting endotherm at 425 "C (80 J g-') in the first heating. The sample was quench cooled and reheated; a Tg at 281 "C, a crystallization exotherm at 351 "C (-3.6 J g-') and a melting endotherm at 404 "C (41.5J g-') were observed.These observations suggest that the direct one-step synthesis of 14e would not be possible unless a solvent with a higher boiling point than DPS is utilized with a boiling point approaching close to 400 "C. This led us to consider a modified methodology for the synthesis of high-molecular-weight poly(ary1 ether-bisketone) 14d. The procedure made use of the previously reported strategy of introducing a bulky substituent to synthesize an amorphous high-molecular-weight precursor followed by sub- sequent removal of the substituent to afford the desired high- molecular-weight semicrystalline polymer. For example, the synthesis of amorphous, tert-butylhydroquinone functional poly(ary1 ether-ketone) of high molecular weight by the reaction of tert-butylhydroquinone and 4,4'-difluorobenzo- phenone has been rep~rted.'~'~~ This was followed by the partial or complete removal of the bulky tert-butyl groups by J.MATER. CHEM., 1991, VOL. 1 treatment with anhydrous aluminium chloride25 or trifluor- omethanesulphonic acid,26 respectively, to yield semicrystal- line PEEK of high molecular weight. This strategy worked remarkably well in this case also. Polymerization of tsrt-butylhydroquinone and the bishalide 12 was conducted in DMAc-toluene (2: 1) in the presence of excess anhydrous potassium carbonate. Very-high-molecular-weight polymer 14c could be synthesized by carrying out the polymerization reaction at 160 "C for a period of 8 h (Scheme 3). The polymer exhibited unlimited solubility in dichloromethane, tetrahydro- furan, trichloromethane and DMAc at room temperature (Table 2).The high-molecular-weight nature of the polymer was assessed by intrinsic viscosity measurements in trichloro- methane at 25 "C (q= 154 cm3 g- I) (Table 3). Fingernail creas- able films of 14c could be obtained upon solvent casting or compression moulding. The poly(ary1 ether-bisketone) 14c exhibited a well defined glass-transition temperature of 206 "C. This value is ca. 30°C higher than that observed for corre-sponding amorphous poly(ary1 ether-ketone), prepared from tert-butylhydroquinone and 4,4'-difl~orobenzophenone.~~~~~ Once again, the higher value can be attributed to the presence of a rigid biphenyl linkage and two keto groups in the repeat unit of poly(ary1 ether-bisketone) 14c.The linear nature and the structure of the repeat unit of 14c was verified by solution (CDC1,) 13C NMR analysis. As in the case of 14a, the calculated and the observed positions of the absorbances were in close agreement.22 The quarternary and the primary carbon atoms of the tert-butyl group exhibited two absorbances at 35.03 and at 30.05 ppm, respectively. Finally, a singlet at 1.38 ppm due to the tert-butyl group in the 'H NMR (CDC1,) spectrum and a peak at 1651 cm-' due to the keto group and at 1233 cm-I due to the ether linkage in the IR spectrum (film), confirmed the structure of 14c. trans De-tert-butylation 14c was carriea out in trifluorome- thanesulphonic acid in the presence of toluene according to a previously reported procedure.26 Trifluoromethanesul- phonic acid acts as the Friedel-Crafts catalyst for the removal of the tert-butyl group as a carbocation, which is subsequently trapped by the aromatic coreagent, toluene.In addition, trifluoromethanesulphonic acid also acts as the solvent for the resulting semicrystalline polymer. The reaction was remarkably effective in completely removing the tert-butyl substituent from polymer 14c (Scheme 4). The toluene layer was analysed by 'H NMR spectroscopy to detect and measure the isomeric ratio of resulting m-and p-tert-butyltoluene. This was done by measuring the intensities of the singlets at 1.25 and at 1.26 ppm due to the tert-butyl groups of meta and para isomers, respectively.The ratio of the isomeric byproduct was determined to be 80:20. Evidence for the complete removal of the tert-butyl group from 14c, came from the 'H NMR of the resulting semicrystalline polymer, 14e, in trifluo- romethanesulphonic acid. Deuterium oxide was used as the internal lock. No residual alkyl groups could be detected in the spectrum. As expected, the resulting semicrystalline polymer was insoluble in all common solvents. It was only soluble in strong protic solvents. The high molecular weight of 14e was deter- mined by intrinsic viscosity measurements in concentrated sulphuric acid at 25 "C (q = 190 cm3 g- '). This is significantly higher than that (q=28 cm3 g-') obtained for the oligomer prepared from the attempted one-step synthesis of 14e.The DSC thermogram of 14e contains a q at 184 "C, a crystallization exotherm (-6.4 J g-') at 206 "C (T,) and a melting point endotherm (27.2 J g-') at 390.5 "C (T,).The q and T, values are ca. 40 and 60 "C, respectively, higher than those reported for PEEK., Upon quench cooling and reheating, polymer 14e exhibits a well defined q at 192 "C, a T, at 285 "C (-8.8 J g-') and a T, at 372 "C (5.2 J g-'). J. MATER. CHEM., 1991, VOL. 1 14c trifluromethanesulphonicacid toluene, 25 "C,18 hI 14e + 0.H. meta :para = 20:80t Scheme 4 From our observations related to hydroquinone functional poly(ary1 ether-bisketone)s 14e, and from the solubility behav- iour of model compound 13b, it was expected that the polymer 14f derived from biphenol and the bisketo functional bishal- ides 11 or 12 would be semicrystalline in nature and would exhibit a higher melting point than 14e.This expectation was consistent with the fact that the melting point of conventional biphenol functional poly(ary1 ether-ketone) derived from biphenol and 4,4'-difluorobenzophenone is ca. 80 "C higher than that of the corresponding hydroquinone functional poly- mer.3,27 Therefore, the direct one-step synthesis of 14f essen-tially would be an impossible task. We have recently reported both homogeneous and controlled heterogeneous hydrolysis of poly(ary1 ether-ketimine)s as alternative routes for the synthesis of high-molecular-weight, semicrystalline poly(ary1 ether-ketone)~.~',~~The latter procedure, which involves the synthesis of amorphous poly(ary1 ether-ketimine) prepolymer followed by hydrolysis in water with a stoichiometric amount of hydrochloric acid to generate poly(ary1 ether-ketone) of semicrystalline morphology, was utilized in the present instance. The required bisketimine functional difluoride mono- mer 15 was synthesized by the reaction of 12 with aniline in the presence of molecular sieves in satisfactory yield (Scheme 5).29 Data from elemental analysis was consistent with the desired structure of the monomer.In addition, the 13C NMR (CDC13) of the monomer revealed two peaks at 166.52 and 166.67 ppm due to the imine groups. This is due to the fact that the two N-substituted rings (ring B) can remain in cis and trans configuration with respect to the fluorine substituted rings (ring A).This can give rise to three possible combinations, namely, cis-cis, trans-trans and cis-trans isomers, resulting in two absorbances due to the imine carbon atom in the 13C NMR of 15. The presence of two absorbances due to the fluorine atoms in the I9F NMR of 15 corroborated the findings from the 13C NMR analysis. Poly- merization of biphenol with 15 was carried out in the presence of potassium carbonate (excess) in DMAc-toluene (2 : 1) using a standard procedure (Scheme 3).30 Owing to the low solu- bility of the bisphenoxide derived from biphenol, an increase in solution viscosity was not observed even after prolonged heating at 165 "C.High-molecular-weight polymer 14d could be synthesized, however, by adding diphenyl sulphone to the reaction mixture and conducting the reaction at 230 "C for a period of 3 h (Scheme 3). The polymer was precipitated from the resulting viscous solution by pouring the mixture into acetone while hot. The polymer was collected by filtration, and extracted with acetone, water and acetone, in that order. It was dried at a reduced pressure at 50 "C for 8 h. The coagulated polymer was fibrous and light-yellow. Intrinsic viscosity measurements (99 cm3g-' in CHC13 at 25 "C) indi- cated the high molecular weight of the polymer. Polymer 14d exhibited solubility behaviour typical of amorphous poly(ary1 2.2 eq 12 chlorobenzene 3A sieves A, 10 hI N0N-15 Scheme 5 ether)s.It was soluble in dipolar aprotic solvents such as dimethyl sulphoxide (DMSO) and DMAc, and in chlorinated hydrocarbons at room temperature (Table 2). Upon solution casting or compression moulding, fingernail creasable films could be obtained. The fact that the imine linkages were not hydrolysed to keto groups under basic reaction conditions2' during the polymer synthesis was verified by solution 13C NMR (CDCl,) of the polymer. Absence of peaks due to aromatic keto carbonyl around 190 ppm and the presence of two absorbances at 167.42 and 167.55 ppm due to the imine linkages confirmed this. The presence of the imine group in the polymer backbone was further confirmed by the IR analysis (film) of the polymer.The IR spectrum of 14d (Fig. 3) exhibits a peak as a weak shoulder at 1620 cm- due to the imine linkages. DSC analysis of the polymer revealed a well defined T, at 211 "C. A melting-point endotherm was not 1620 -1592-u c=c L 1 I I 1784 1675 1565 1455 wavenumber/cm-' Fig. 3 IR spectrum (film) of poly(ary1 ether-bisketimine) 14d J. MATER. CHEM., 1991, VOL. 1 observed. These observations further confirmed the amorph- ous nature of 14d. Hydrolysis of the ketimine group was accomplished by heating a slurry of the polymer in water in a Parr reactor containing a stoichiometric amount of hydro- chloric acid (Scheme 6). This procedure was remarkably effec- tive despite its heterogeneous nature. Aniline hydrochloride, the water-soluble byproduct of the reaction, could be removed easily by simple filtration.Any last traces of the residual salt could be removed by extracting the hydrolysed polymer with water in a Soxhlet apparatus for 24 h. Cleavage of the ketimine group was conveniently estimated by elemental analysis for nitrogen. From earlier findings temperature has been identified as the most critical factor for efficient hydrolysis of the ketimine functional polymers.27 Hydrolysis was very slow at or below the Tp of the polymer. For complete hydrolysis in a reasonable amount of time, it was necessary to raise the hydrolysis temperature at least 70 "C above the Tp of the polymer. Accordingly, polymer 14d was subjected to hetero- geneous hydrolysis at 300 "C [90 "C above the Tp (211 "C) of 14dl for 1.5 and 24 h.The resulting polymers were insoluble in all common solvents at room temperature and upon warming (Table 2). The thermal behaviours of the polymers were identical also. In addition, elemental analysis revealed the absence of nitrogen in both instances. This established the fact that the quantitative hydrolysis could be achieved in 1.5 h. The DSC thermogram of the polymer derived from 1.5 h hydrolysis (14f)reveals a Tgat 219 "C in the first heating. This is essentially identical to the value for the precursor ketimine functional polymer. The sample also exhibited a small melting endotherm at 353 "C (1.9 J g-') in addition to a larger endotherm at 469 "C (40.7 J g-') in the first heat.Similar multiple melting transitions have also been reported for PEEK.31 After it was quench cooled and reheated, the same sample exhibited a well defined T at 219 "C, a crystalliz- ation exotherm at 375 "C (-12.9 J g-P) and a melting endo- therm at 459 "C (14.8 J g-I). The thermal behaviour of 14f demonstrates that it is possible to synthesize high-melting- point semicrystalline poly(ary1 ether-bisketone). On the other hand, the observed melting point is very close to the tempera- ture required for the onset of decomposition (Table 4). This may limit the practical utility of 14f. Nevertheless, it will be possible to introduce a suitable comonomer, such as 4,4- dichlorodiphenyl sulphone so as to lower the melting point 14d 300 "C, HCI.H20. 1.5 h 14f Scheme 6 J. MATER. CHEM., 1991, VOL. 1 while retaining a reasonable degree of crystallinity in the 0.08 r polymer. DMTA and Thermogravimetric Analysis of Poly(ary1 ether-bisketone)s and Poly(ary1 ether-bisketimine) 14d The dynamic mechanical thermal analysis of these polymers (14a-d) corroborated the data obtained from DSC measure-ments. The dynamic mechanical behaviour for the polymers is shown in Fig.4. These data clearly show the high Tg and good dimensional stability exhibited by these materials and also indicate a glassy morphology for this polymeric system (14a-d). In addition, a major low-temperature secondary relaxation (p transition) in the vicinity of -100 "C can also be seen in all cases.Fig. 5 illustrates one such typical transition for 14a. Such transitions have been investigated by dynamic me~hanical~~-~~ The observation ofand NMR techniq~es.~' h ____22_2_ a- I1 > !.u- 8.2- I\ I1 rn --00 II11 -120 -70 -20 30 80 130 180 230 TI"C t I n 341 0.121 i I/ -120 -70 -20 30 80 130 180 230 T/"C Fig. 4 (a)Storage modulus (bending) versus temperature. (6) tan 6 versus temperature for various amorphous poly(ary1ether-bisketone)s and poly(ary1 ether-bisketimine) 14d 0.05 DQ -5 0.04 c 0.03 --0.02 -0.01 -1 50 -1 00 -50 T/"C Fig. 5 tan 6 versus temperature for 14a a p relaxation is believed to be associated with polymers that ran pvhihit diirtile defnrmatinn 32 In spite of the high Tg of these materials, the amorphous poly(ary1 ether-bisketone)s and the poly(ary1ether-bisketim-inpi\ *A1 r* r >I 1_1* * iun rgn 1np TnPrmnTnrmPn nv rnmnrpccinn mniiininu in.LAW,, "Y) "Ic~1--II-vIv'-II"u -J """jf'-"""" lllVllllllb ---contrast to other conventional high-performance rigid-rod polymers.Samples were moulded at ca. 70 "C above the glass-transition temperature. That this can be done is reflective of the excellent thermal stability of these materials. The semicrys-talline poly(ary1 ether-bisketone)s, 14e and 14f, were not compression moulded because of the practical high-tempera-ture limitation of the press. The thermal stability of the polymers 14a-f was further affirmed by thermogravimetric analysis in both the isothermal and the variable-temperature modes.The variable-temperature thermograms of the poly-mers are shown in Fig. 6. From examination of the figure it is apparent that the poly(ary1 ether-bisketone)s demonstrate 110 80 60 50 50 250 450 650 E T/"C Fig. 6 TG thermograms (weight loss uersus temperature) for various poly(ary1 ether-bisketone)s and poly(ary1 ether-bisketimine) 14d Table 4 Thermogravimetric analysis (nitrogen) of poly(ary1 ether-bisketone) and poly(ary1 ether-bisketimine) 14 polymer wt. loss on isothermal ageing at 400 "C (wt.% h-') polymer onset of decomposition temperature/ "C %residue at 750 "C 14a 0.86 512 64.63 14b 1.80 510 56.60 14C 0.96 506 53.21 14d 0.52 49 1 68.74 14e 0.76 516 51.68 14f 0.26 514 64.09 J.MATER. CHEM., 1991, VOL. 1 very good thermal stability with polymer decomposition temperature in excess of 500 "C, except for the poly(ary1 ether- bisketimine) 14d, which exhibits an onset of decomposition temperature at 491 "C (Table4). This is presumably because of the presence of the imine (-C=N-) groups. Among the poly(ary1 ether-bisketone)s, polymer 14c with the tert-butyl substituent is of slightly lower stability than the other poly- mers. From an examination of the data in Table 4, it is clear that the polymers 14a-f decompose with a significant amount (> 50%) of char yield at 750 "C. This would suggest a high level of flame-retardant characteristic^.^^ Isothermal TG (400 "C, 1 h, under a nitrogen atmosphere) was also used to assess the thermal stability of the polymers (Table4).The data consistent with the variable TG scans, demonstrate that the poly(ary1 ether-bisketone)s and the poly(ary1 ether- bisketimine), 14d, are materials of exceptional thermal stab- ility. In all cases, >I% weight loss was observed, except for the bisphenol-S functional poly(ary1 ether-bisketone) 14b. The polymer exhibits a 1.8% weight loss, possibly due to its highly polar nature, resulting in higher moisture uptake under ambi- ent conditions. Conclusions A series of high-molecular-weight poly(ary1 ether-bisketone)s have been synthesized by the reaction of 4,4'-bis(p-fluoroben- zoy1)biphenyl with suitable bisphenols.Model compound studies indicated that both 4,4'-bis( p-fluorobenzoy1)biphenyl and 4,4'-bis(p-chlorobenzoyl)biphenyl were suitable mono-mers for polymer synthesis with bisphenol-A and 4,4'-dihydroxybiphenyl. For more acidic phenols such as hydro- quinone and 4,4'-dihydroxybenzophenone, 4,4'-bis(p-fluoro- benzoy1)biphenyl as the monomer would be required for the synthesis of high-molecular-weight polymers. The amorphous poly(ary1 ether-bisketone)s exhibited high glass-transition temperatures; some of the highest Ts known for the poly(ary1 ether-ketone) family of macromolecules. In addition, these materials showed improved solvent resistance over that observed for the monoketone analogues. The semicrystalline poly(ary1 ether-bisketone)s were synthesized from amorphous high-molecular-weight polymeric precursors by post-removal of bulky substituents from the polymer backbone.Semicrystal- line hydroquinone functional polymer was synthesized by the removal of the bulky tert-butyl substituent, whereas the biphenol functional polymer was synthesized by the hetero- geneous hydrolysis of amorphous poly(ary1 ether-bisketimine) precursor. Both polymers showed very high melting points; significantly higher than the commercially important PEEK. 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