- Email: [email protected]
Pendant adamantyl poly(ether imide)s: synthesis and a preliminary study of properties
European Polymer Journal 35 (1999) 2097±2106
Pendant adamantyl poly(ether imide)s: synthesis and a preliminary study of properties G.C. Eastmond a,*, M. Gibas b, J. Paprotny a a Donnan Laboratories, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK Department of Physical Chemistry and Technology of Polymers, Silesian Technical University, Gliwice, Poland
b
Received 12 February 1999; accepted 3 March 1999
Abstract Adamantyl-substituted dihydroxybenzenes were prepared by reacting 1-bromoadamantane with dihydroxybenzenes. The major products were 4-(adamantyl-1)-1,2-dihydroxybenzene, 4-(adamantyl-1)-1,3dihydroxybenzene and 2-(adamantyl-1)-1,4-dihydroxybenzene. The ®rst was not isomerically pure and the third was contaminated with a small proportion of di(adamantyl-1)-1,4-dihydroxybenzene. These adamantyl-substituted diols were converted to bis(ether anhydride)s. Poly(ether imide)s were prepared by reacting the adamantyl-substituted bis(ether anhydride)s with aromatic diamines. Solubilities and thermal transition temperatures of the poly(ether imide)s were compared with data for poly(ether imide)s with other alkyl-substituents and with main-chain adamantyl units. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Synthesis; Adamantyl-substituted; Thermal properties; Poly(ether imide)s
1. Introduction For several decades, chemists have been fascinated by the structure and properties of adamantane (tricyclo[3.3.1.1]decane) which has an arrangement of carbon atoms similar to that in a diamond lattice. The molecule is highly symmetrical and has good thermal and chemical stability; 1-ethynyl-adamantane does not polymerize and can be recovered in good yield after vacuum pyrolysis at 8008C [1,2]. Considerable research was undertaken into adamantane and its derivatives after an inexpensive source of adamantane was found [3,4] and particularly after it was discovered that 1-
* Corresponding author. Fax: +44-151-794-3534.
aminoadamantane is a potent inhibitor of several viruses [5]. Polymer chemists interested in `high-performance' polymers have incorporated adamantane into almost every type of polymer in order to achieve high glasstransition temperatures and to enhance thermal and hydrolytic stabilities. Since the 1960s, hundreds of papers and patents on the topic have appeared and Khardin and Radchenko have presented a good review of the literature [6]. There has recently been a resurgence of interest in polymers based on adamantane, such as polyimides [7], poly(ether ketone)s [8], polyphenylenes [9] and poly(benzoxazole)s [10]. We previously synthesized a bis(ether anhydride) based on adamantane which allowed the synthesis of poly(ether imide)s (I):
0014-3057/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 9 ) 0 0 0 9 2 - 0
2098
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
with adamantane units in the polymer backbone [11]. Here, we report poly(ether imide)s with pendant adamantyl units in the bisanhydride residue. The bis(ether anhydride)s were prepared from the products of nitrodisplacement reactions between 4-nitrophthalodinitrile and aromatic diols with adamantyl substituents. For this purpose it was necessary to synthesize appropriate adamantyl-substituted diols and these were prepared from various dihydroxybenzenes. The alkylation of phenols by 1-bromoadamantane (II), known for some time, [12,13] leads to 4-(adamantyl-1)-substituted phenols. It is believed that with phenol itself the product is entirely 4-(adamantyl-1)phenol; Hardy et al. [14] quoted a yield of 88% and Jensen et al. a yield of 92% 4-(adamantyl-1)phenol [15], although Ong established that protracted reaction could lead to proportions of di- and tri-substituted products [13]. It was also reported that reaction of 1chloroadamantane with phenol led to a mixture of ortho and para isomers; 2-(adamantyl-1)phenol formed initially was converted to the thermodynamically stable 4-(adamantyl-1)phenol in the presence of phenol and hydrogen chloride [16]. Similar reactions between (II) (or 1-hydroxyadamantane) and simple aromatic diols (III) are less well known and present potential complications [17±22]. Shvedov et al. described the synthesis of 4-(adamantyl-1)resorcinol (i.e. 4-(adamantyl-1)-1,3dihydroxybenzene) (IVb) by reacting excess resorcinol (IIIb) with (II) in boiling benzene, Scheme 1, and obtained a single product in 79% yield [17,18]. We repeated the reaction in Scheme 1 with (IIIb) and also applied it to catechol (IIIa) and hydroquinone (IIIc) to obtain a series of adamantyl-1 diols. From these substituted diols we have prepared a corresponding series of adamantyl-1-substituted bis(ether anhydride)s and from these a series of poly(ether imide)s. We have previously reported the synthesis and properties of poly(ether imide)s derived from bis(ether anhydride)s based on unsubstituted dihydroxybenzenes [23]. We have also investigated the properties of poly(ether imide)s with bulky, main-chain units, including
the adamantyl unit [11]. In the former case, the thermal properties of the poly (ether imide)s were greatly in¯uenced by the structure and ¯exibility of the diamine moiety while in the latter case the bulky groups dominated properties such as glass-transition temperatures. Here, we provide a comparison of the thermal properties of poly(ether imide)s of several structures including those with adamantyl units in dierent situations and with a selection of diamines.
2. Experimental 2.1. Materials All reagents were commercially available compounds and were used as received except that para-phenylene diamine and meta-phenylene diamine were sublimed before use; bis(4-aminophenyl)ether was an ultra-pure sample from BP plc. 2.2. Procedures 2.2.1. Polymer characterization Molecular weights of poly(ether imide)s were determined by gel permeation chromatography (gpc), using Polymer Laboratories PL-gel 5 mm columns, DMF with 0.1M LiCl as eluant, a pumping rate of 1 ml minÿ1 and a refractive index detector (Knauer). The system was calibrated with polystyrene standards (Polymer Laboratories). Glass-transition temperatures were determined with the aid of a Perkin-Elmer DSC2. Solubilities of the polymers were determined in a series of solvents by allowing samples of polymer to stand in solvents for periods of 2 weeks. NMR spectra were determined using a Varian UNITY/INOVA 300 MHz spectrometer. 2.2.2. Alkylation of aromatic diols with 1-bromo-adamantane: general procedure A solution of diol (III) (0.10 mol) and 1-bromoada-
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
2099
Scheme 1.
mantane (II) (0.05 mol) (molar ratio of (III) : (II) was a minimum of 2 : 1 and preferably greater) in benzene (25 cm3), to which water (two or three drops) had been added was re¯uxed for 4 h. During this period, a slow stream of nitrogen was used to aid removal of the hydrogen bromide evolved; for syntheses on a larger scale, it is preferable to use a hydrogen bromide trap. The solvent was then removed by rotary evaporation. The crude product was washed thoroughly with warm water and dried. Yields were between 30% and 80%, depending on the diol used. Puri®cation required two or three recrystallizations from toluene or toluene/
cyclohexane. Finally, the adamantyl diols were sublimed once or twice under vacuum at 0.5 torr. Details of yields and crystallization solvents for speci®c adamantane-substituted diols are given in Table 1.
2.2.3. Synthesis of (adamantyl-1)dihydroxybenzene diacetates (Adamantyl-1)dihydroxybenzenes were acetylated by heating with acetic anhydride for 2 h; crystalline products were recovered.
Table 1 Synthesis and characterization data for (adamantyl-1)-substituted dihydroxybenzenes. R 1-adamantyl
a
Yields are after recrystallizations from solvents the number of times speci®ed and sublimation. Ref. [24]. c Ref. [17,18]. d Ref. [29]. e Ref. [30]. f Ref. [21,22]. b
2100
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
Scheme 2.
2.2.4. Synthesis of 1-adamantyl-substituted bis(ether dinitrile)s and bis(ether anhydride)s (Adamantyl-1)dihydroxybenzenes (0.1 mol) (IV) were reacted with 4-nitrophthalodinitrile (V) (0.2 mol) in DMSO, in the presence of potassium carbonate (Scheme 2) to form bis(ether dinitrile)s (VI). The bis(ether dinitrile)s were then hydrolyzed to bis(ether diacid)s (VII) by heating with potassium hydroxide in methanol. The bis(ether diacid)s were then dehydrated to bis(ether anhydride)s (VIII) by re¯uxing with acetic anhydride in the presence of acetic acid. Details of these several standard procedures have been reported elsewhere [25±27]. 2.2.5. Synthesis of poly(ether imide)s with pendant adamantyl groups Bis(ether anhydride)s were reacted with aromatic diamines in NMP solution to form intermediate poly(amic acid)s which were then imidized chemically with acetic anhydride/pyridine (1 : 1). Poly(ether imide)s were isolated by precipitation into methanol and were dried, as described in detail elsewhere [25±27].
3. Results and discussion 3.1. Synthesis of 1-adamantyl diols Each dihydroxybenzene (IIIa±c) was reacted individually with 1-bromoadamantane as described above, Scheme 1. The characteristics of the aromatic diol products with pendant 1-adamantyl units so formed, are presented in Table 1. Reaction with catechol (IIIa) could lead to two sin-
gly-substituted diols, viz., 3- and 4-substituted catechols. We found that the reaction product from 1bromoadamantane and catechol was indeed a mixture of 3-(adamantyl-1)-1,2-dihydroxybenzene and 4-(adamantyl-1)-1,2-dihydroxybenzene. The product, when recrystallized twice from toluene and sublimed (180± 1908C, 0.5 torr), had a precise mass, determined by mass spectrometry, of 244.14662, compared with a calculated value of 244.14633 (an error of 1.2 ppm or 0.29 mDa). Nevertheless, despite repeated crystallization and sublimation, gas chromatography of the product showed two peaks in a ratio of 12 : 1; each component had the same mass when analysed by mass spectrometry. 1 H NMR data of the aromatic protons (400 MHz) were also inconsistent with those expected for a single tri-substituted aromatic ring, but were consistent with a mixture of 4- and 3-(adamantyl-1)-1,2dihydroxybenzenes. Comparison of integrated peak intensities indicated a molar ratio of 76 : 24; 3-(adamantyl-1) catechol was the minor product. The melting point quoted in Table 1 is for the mixture of isomers obtained after recrystallization and sublimation; the relatively low value of the melting point (compared with products from other diols) is consistent with a mixture of isomers. The observation that a mixture of isomers was produced is consistent with the work of Sokolenko et al., who prepared (adamantyl-1)-1,2dihydroxybenzene by reacting (IIIa) with 1-hydroxyadamantane and obtained a mixture of 4- and 3-isomers in the proportions 3.8 : 1 [19,20]; these workers quoted a melting point of 204±2068C for 3-(adamantyl-1)-1,2dihydroxybenzene, but did not quote a melting point for 4-(adamantyl-1)-1,2-dihydroxybenzene. The original synthesis of 4-(adamantyl-1)-1,2-dihydroxybenzene
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
was apparently achieved by a similar process to that used here, with a yield of 75%, but no mention was made of a mixture of products; the melting point quoted was identical to that obtained by us [24]. When the mixture of isomers was acetylated, the initial product gave two peaks by gas chromatography, but, during subsequent work up (recrystallization from ethanol) a 60% yield of crystalline product was separated; this product gave a single peak by gas chromatography. This major product was identi®ed as 4(adamantyl-1)-1,2-dihydroxybenzene diactetate by 1 H and 13 C NMR; data are presented in Table 2 and the melting point is given in Table 1. We did not attempt to obtain the pure 3-isomer which concentrated in the mother-liquor during crystallization. These results con®rmed that the major isomer in the mixture of (adamantyl-1)-1,2-dihydroxybenzenes was 4-(adamantyl-1)1,2-dihydroxybenzene. Reaction of (II) with (IIIb), to obtain (adamantyl-1)1,3-dihydroxybenzene, gave a product (Table 1) which, after crystallization and sublimation, showed a single peak by gas chromatography. This result is consistent with the observations of Shvedov et al. who also obtained a single product in 79% yield with similar
melting point, identi®ed as 4-(adamantyl-1)-1,3-dihydroxybenzene, from the same reaction [17,18]; Mathias and coworkers reported products with slightly higher melting points (Table 1) from the same reaction [28,29]. The identity of our product was further con®rmed by 1 H NMR on the diol and by 1 H and 13 C NMR on the diacetate, Table 2. One possible alternative isomer 5-(adamantyl-1)-1,3-dihydroxybenzene has been prepared by a dierent route and had a melting point of 284±2858C [30]; the other possible isomer, 2(adamantyl-1)-1,3-dihydroxybenzene, is apparently unknown. Only a single mono-adamantyl-substituted hydroquinone isomer is possible, i.e., 2-(adamantyl-1)-1,4dihydroxybenzene. Reaction of (II) with (IIIc) produced a product which, after several puri®cation, gave good analytical data but a rather broad melting point, Table 1. The 1 H NMR spectrum was not clean and, as with the other adamantyl-substituted diols, the product was acetylated to aid analysis. 1 H and 13 C NMR spectra of the product were not clean but were consistent with 2-(adamantyl-1)-1,4-dihydroxybenzene diacetate as the main product admixed with a little bis(adamantyl-1)-1,4-dihydroxybenzene diacetate; the proportions
Table 2 NMR data for (adamantyl-1)dihydroxybenzene diacetates, observed and (calculated) chemical shifts and coupling constants Structure
1 H NMR Chemical shift (ppm) H(2) H(3) H(5) H(6)
Coupling constant (Hz) J2±6 J3±5 J5±6
± 7.13 (7.28) 7.22 (7.49) 7.10 (6.94) 2.24, 2.25
6.81 (6.75) ± 7.31 (7.24) 6.94 (6.96) 2.26, 2.33
± 2.31 8.55
2.44 ± 8.79
13
C NMR Chemical shift (ppm) C(1) C(2) C(3) C(4) C(5) C(6) C(CO)
2101
139.6 (142.0) 141.7 (144.7) 120.0 (120.0) 150.2 (149.6) 123.0 (124.1) 122.6 (123.0) 168.3, 168.4
149.4 (149.7) 117.4 (115.3) 148.6 (149.4) 138.5 (141.9) 127.6 (127.7) 118.6 (119.4) 169.0, 169.1
2102
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
Table 3 Characterization data for (adamantyl-1)-substituted bis(ether dinitrile)s and bis(ether anhydride)s
Structure
VIa
Elemental Calc.:
analysis Found:
Yield % and crystallization solvent
Melting Point/ 8C
C 77.40 H 4.87 N 11.28
C 77.31 H 4.85 N 11.34 C 77.50 H 4.85 N 11.27 C 77.70 H 4.89 N 11.22
76 (82) MeCN
248.5±249.4
VI VIc
84 (94) EtOH
135±137
67 (85) MeCN
240±242
Structure
Elemental Calc.:
analysis Found:
Yield %
Melting Point/ 8C
VIIIa
C 71.63
C 71.69
89
188±189
H 4.50 VIIb
H 4.49 do
92
194±195
VIIIc
do
C 71.39 H 4.54 C 71.47 H 4.48
91
255±257
and substitution patterns could not be accurately estimated but the good elemental analysis data indicated that the content of the disubstituted product must have been small. Previously, Korsakova et al. undertook a similar reaction between (II) and (IIIc) and demonstrated that their product was a mixture of 2(adamantyl-1)-1,4-dihydroxybenzene and 2,5-bis(adamantyl-1)-1,4-dihydroxybenzene [21,22]. Thus, a series of adamantyl substituted phenylene diols have been prepared, which could be used in the synthesis of polymers albeit they were not all isomerically pure.
3.2. Synthesis of bis(ether anhydride)s and poly(ether imide)s from 1-adamantyl-substituted aromatic diols To prepare bis(ether anhydride)s based on (adamantyl-1)dihydroxybenzenes, species (IV) were reacted with (V) in DMSO in the presence of potassium carbonate in order to prepare bis(ether dinitrile)s (VI), which were then hydrolysed with methanolic potassium hydroxide to bis(ether diacid)s (VII) and dehydrated with acetic anhydride/acetic acid to bis(ether anhydride)s (VIII) according to Scheme 2 and as described elsewhere [25±27]. Bis(ether anhydride)s were
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
2103
recrystallized from acetic anhydride. Characterization data for the products are presented in Table 3. Poly(ether imide)s (IX):
above 01108C. Where the poly(ether imide) product is soluble in the solvent used, a one-step, high-temperature polymerization can be performed. To perform such reactions, diamines were dissolved in NMP and
were synthesized from the bis(ether anhydride)s (VIII) by a standard two-step reaction, ®rst forming the poly(amic acid) at room temperature in an aprotic solvent (NMP) (12±15 wt% solids), followed by chemical imidization with pyridine/acetic anhydride mixture to give poly(ether imide)s (IX). Three simple aromatic diamines were used in polymer syntheses; para-phenylene diamine (PPD), metaphenylene diamine (MPD) and bis(4-aminophenyl)ether (ODA). Molecular weights (peak values from gel permeation chromatograms, calibrated with polystyrene standards) are recorded in Table 4. In Table 4, sets of columns refer to polymers derived from dierent dihydroxybenzenes and are identi®ed by the locations of OH groups on the initial diol and resulting catenation in the polymer. The positions of adamantyl or other substituent groups on the diol moieties are given in each case. Polymers based on adamantyl-catechol bis(ether anhydride) (VIIIa) and adamantyl-resorcinol bis(ether anhydride) (VIIIb) were soluble both as poly(amic acid) and as poly(ether imide). Problems were encountered when synthesizing poly(amic acid)s from adamantyl-hydroquinone bis(ether anhydride) (VIIIc) with all three diamines. These poly(amic acid) solutions, synthesized in NMP, gelled within hours with less reactive diamines (MPD, ODA) and within 15 min with PPD. Gelation occurred even when reactant concentrations were reduced to 5 wt% solids. A similar phenomenon (apparently unique to polyimides and particularly in poly(ether imide)s containing adamantane units) was described by Novikov [31] when poly(amic acid)s were prepared from 1,3-bis-(3 ',4'dicarboxyphenyl)adamantane dianhydride and aromatic or adamantane-containing diamines. They overcame the problem by dissolving potassium chloride or lithium chloride in the aprotic polymerization solvent. We found the poly(amic acid) gels (without added salt) to be thermally reversible; systems became liquid
the anhydride was added together with some xylene. The mixture was heated to 1608C with stirring and water was removed as the xylene azeotrope. The temperature was gradually raised to 2008C. Polymers prepared with MPD and ODA, when precipitated and dried, were soluble in chloroform and were reprecipitated into methanol. Polymers prepared with PPD were soluble only in hot NMP. 3.3. Polymer properties It is well known that the introduction of bulky pendant substituents often enhances polymer processability (especially solubility and processability from solution) and also increases glass-transition temperatures. For example, introducing a methyl or tert-butyl substituent into a bis(ether anhydride) tends to raise the glass-transition temperatures of poly(ether imide)s. In this case, we examine the eects of introducing very bulky adamantyl groups pendant to the main chain. In order to assess the eects of this structural modi®cation, we compare the properties of these polymers with those of their unsubstituted analogues, with similar poly(ether imide)s with alkyl substituents and with similar poly(ether imide)s having main-chain, adamantyl units. The solubilities and glass-transition temperatures of these several polymers are summarised in Table 4. Solubilities were tested in a series of solvents for which the solubility power for poly(ether imide)s generally increases in the order CHCl3
PPD MPD ODA
PPD MPD ODA
PPD PPD MPD ODA ODA
MPD ODA
MPD ODA
None
Tert-butyl
Di-tert-butyl
Methyl
Adamantyl in chain (I)
3 3 4
3,5 3,5 3,5 3,5
4 4 4
4 4 4
Group position
Imidized thermally. trg = thermally reversible gel.
PPD MPD ODA
Adamantyl
a
Amine
Anhydride substituent
Catenation
119 K 106 K
79 K
103 K 30 K 58 K 123 K 17 K
± 51 K 58 K
± 112 K 287 K
24 K 26 K 44 K
MW/kg molÿ1
1,2
255 253
222 216 213
275 256 250 244 228
± 226 219
>420 220 208
257 249 252
Tg/8C
s s
s s s s s
± s s
insoluble s s
NMP s s
Solvent
93 K 136 K
29 K 118 K
4,6 4,6
5 5
±
± ± ±
20 K 13 K 26 K
MW/kg molÿ1
4,6
4 4 4
Group position
Table 4 Synthesis and characterization of adamantyl-substituted and related poly(ether imide)s
217 210
248 254
269
± ± ±
>420 225 209
291 260 260
Tg/8C
1,3
s s
s s
s, insoluble in DMAC
insoluble NMP NMP,trg DMAC,trg
s s s
Solvent
2
2,5 2,5
2,5
2 2 2
2 2 2
Group position
±
153 K 205 K
±
± 107 K 61 K
± ± ±
±a 20 Ka 45 Ka
MW/kg molÿ1
218
272 265
300
>420 254 236
>420 0 245 238
304 289 285
Tg/8C
1,4
s?
s s, insoluble in NMP
H2SO4
insoluble s s
insoluble NMP NMP
hot NMP s s
Solvent
2104 G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
alkyl substituents. When comparing properties, it should be noted that the molecular weights of the adamantyl-substituted poly(ether imide)s, as measured by gel permeation chromatography, are low compared with those of other polymer series [32]. Although molecular weights of aromatic poly(ether imide)s are normally higher than true molecular weights by a factor of about three [32], it cannot be assumed the same factor applies to poly(ether imide)s with very bulky adamantyl substituents. Gelation encountered during polymer synthesis does not necessarily imply high-molecular-weight poly(amic acid), but probably re¯ects reduced solubility of poly(amic acid) with large aliphatic groups in the polymerization solvent. A similar eect could modify the hydrodynamic volumes of the adamantyl-substituted polymers in the gpc solvent of DMF/LiCl(0.1 M). The absence of any molecular weight data for individual polymers in Table 4 implies lack of solubility in DMF/LiCl. We have previously observed, in general, that only poly(ether imide)s with molecular weights in excess of 60 kg molÿ1, as measured by gel permeation chromatography in our system, are capable of forming good, non-brittle, solvent-cast ®lms. Despite the apparent low molecular weights of the adamantyl-substituted poly(ether imide)s good free-standing polymer ®lms were obtained when the polymers were cast from solution in chloroform. Consistent with established trends, a high degree of para-catenation leads to decreased solubility and higher Tgs and this pattern holds within the family of adamantyl-substituted poly(ether imide)s. Thus, the poly(ether imide) from (VIIIc) and PPD is the least soluble polymer and has the highest Tg. Also, for the polymers prepared from (VIIIa) that with PPD is the least soluble and has the highest Tg, especially when it is noted that the polymer is in the regime where Tg might be expected to be molecular weight dependent; in a few cases Tgs for related polymers with two tertbutyl substituents are quoted for two dierent molecular weights to highlight this eect. Thus, Tgs for highmolecular-weight polymers might be up to 208C higher than those quoted. A second general trend is that 1,2-catenation tends to give higher solubility than 1,3-catenation, but with relatively little dierence in Tg. This trend is not strictly observed with the adamantyl-substituted poly(ether imide)s but solubilities might be molecular weight dependent. Thirdly, poly(ether imide)s based on ODA generally have the lowest Tg (of the three diamines used) but in this case polymers based on ODA have higher Tgs but also have highest molecular weights. Thus, within the family of adamantyl-substituted poly(ether imide)s, the results are probably consistent with established trends given that the polymer molecu-
2105
lar weights are probably low and Tgs possibly molecular-weight dependent. The incorporation of alkyl substituents is known to in¯uence properties, increasing both solubility and Tg. The exception to this rule is poly(ether imide)s with PPD as diamine for which we were unable to observe Tgs below 4208C, the limit of our DSC observations. To provide comparisons, we have included in Table 4 previously determined data for comparable poly(ether imide)s with no substituents, with one methyl substituent, with one tert-butyl substituent (which has its carbon atoms in a similar disposition to part of the adamantane structure) and with two tert-butyl substituents. From these data it is clear that, in general and within the limits of comparability of molecular weight, there is a tendency for Tg to increase with the bulk of the substituent groups and with the number of tertbutyl groups. Nevertheless, there is a marked increase in Tg for the adamantyl-substituted poly(ether imide)s which, for similar molecular weights, have the highest Tgs and high-molecular-weight adamantyl-substituted poly(ether imide)s could have even higher Tgs. It is appropriate to compare Tgs of poly(ether imide)s with adamantyl groups pendant and in-chain (I). As noted previously, Tgs of poly(ether imide)s with bulky in-chain moieties are largely determined by the nature of the bulky group rather than the structure of the diamine and both polymers (I), derived from MPD or ODA, have Tgs of 253±2558C (Table 4) [11]. Given that these polymers probably had higher absolute molecular weights than the adamantyl-substituted poly(ether imide)s, the Tgs of the latter polymers, for comparable molecular weights, are at least as high, if not higher than, those with main-chain adamantyl units. In comparison with the lack of variation in Tg with diamine structure for poly(ether imide)s with bulky main-chain units in the anhydride moities, apart from polymers prepared from PPD, there is little variation in Tg with diamine structure but there is a marked increase in Tg in going from 1,2 to 1,3 to 1,4-catenation of the adamantyl-phenylene unit. Given the bulky nature of the pendant units but high Tgs, it would be of interest to investigate interchain packing in and gas permeability through these materials and to compare the results with those from chains with smaller substituents. 4. Conclusions Dihydroxybenzenes were reacted individually with 1bromoadamantane. It was demonstrated that in each case, a single (adamantyl-1)dihydroxybenzene was the main product. However, consistent with the observations of previous workers, it was con®rmed that in the reaction with catechol the main product was 4-
2106
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
(adamantyl-1)-1,2-dihydroxybenzene but some 3-(adamantyl-1)-1,2-dihydroxybenzene was also formed and was not readily removed. 3-(Adamantyl-1)-1,4-dihydroxybenzene was contaminated with a little di(adamantyl-1)-1,4-dihydroxybenzene. The 4-(adamantyl-1)1,3-dihydroxybenzene was a pure product. The (adamantyl-1)-substituted dihydroxybenzenes, as prepared, were converted to bis(ether anhydride)s by reaction with 4-nitrophthalodinitrile, subsequent hydrolysis to bis(ether diacid) and dehydration to bis(ether anhydride). The bis(ether anhydride)s were converted to poly(ether imide)s by reaction with selected amines and the solution and thermal properties of the polymers were compared within the group of polymers and with related poly(ether imide)s with alkyl substituents. Molecular weights of the polymers, as measured by gel permeation chromatography, were apparently low but good, non-brittle ®lms were obtained by solvent casting; quantities of polymers prepared were insucient to determine mechanical properties. Glass-transition temperatures of the polymers were shown to be high, from 250 to 3008C depending on the substitution pattern and the diamine. The main factor in¯uencing Tg was the substitution pattern of the dihydroxybenzene and Tg increased as the substitution pattern was changed from ortho to meta to para. Glasstransition temperatures of adamantyl-substituted polymers were found to be higher than those of similar poly(ether imide)s with methyl or one or two tert-butyl substituents and higher than poly(ether imide)s with main-chain adamantane units and prepared from similar diamines. The adamantyl-substituted poly(ether imide)s were found to be more soluble than related poly(ether imide)s in a variety of solvents; many were soluble in chloroform as well as aprotic solvents. However, poly(amic acid) intermediates synthesized from 1,4bis(3',4 '-dicarboxyphenoxy)-2-(adamantyl-1)benzene dianhydride gelled and thermal imidization in solution was preferred to chemical imidization. Acknowledgements The authors wish to thank EPSRC and DRA for ®nancial support. References [1] Brown RFC, Eastwood FW, Jackman GP. Aust J Chem 1977;30:1757. [2] Archibald TG, Malik AA, Baum K, Unroe MR. Macromolecules 1991;24:5261.
[3] Schleyer P. J Am Chem Soc 1957;79:3292. [4] Schleyer P, Donaldson MM, Nicholas RD, Cupas C. Org Syntheses 1962;42:8. [5] Davies WL, Grunert RR, Ha RF, McGahen JW, Neumayer EM, Paulshock M, Watts JC, Wood TR, Hermann EC, Homann CE. Science 1964;144:862. [6] Khardin AP, Radchenko SS. Russ Chem Rev 1982;51:272. [7] Chern Y-T, Chung W-H. J Polym Sci, Part A, Polym Chem 1996;34:117. [8] Mathias LJ, Lewis CL. Polym Prep Am Chem Soc Polym Div Inc 1995;36(2):140. [9] Tullos GL, Mathias LJ. Polym Prep Am Chem Soc Polym Div Inc 1995;36(2):316. [10] Grub TL, Mathias LJ. Polym Prep Am Chem Soc Polym Div Inc 1996;37(1):551. [11] Eastmond GC, Paprotny J. J Mater Chem 1997;7:589. [12] Reinhardt HF. J Org Chem 1962;27:3258. [13] Ong SH. Chem Commun 1970:1180. [14] Hardy ADV, MacNicol DD, Wilson DR. J Chem Soc Perkin Trans II 1979:1011. [15] Jensen JJ, Grimsley M, Mathias IJ. J Polym Sci A Polym Chem 1996;34:397. [16] Aigami K, Inamoto Y, Takaishi N, Hattori K. J Medicinal Chem 1975;18:713. [17] Shvedov VI, Safonova OA, Korsakova IYa, Bogdanova NS, Nikolaeva IS, Peters VV, Pershin GN. Khim-Farm Zh 1980;14:54. [18] Shvedov VI, Safonova OA, Korsakova IYa, Bogdanova NS, Nikolaeva IS, Peters VV, Pershin GN. Pharm Chem Ind 1980;14:127. [19] Sokolenko VA, Kuznetsova LN, Orlovskaya NF. Russ Chem Bull 1996;45:485. [20] Sokolenko VA, Kuznetsova LN, Orlovskaya NF. Izv Akad Nauk Ser Khim 1996:505. [21] Korsakova IYa, Safonova OA, Ageeva OI, Shvedov VL, Nikolaeva IS, Pushkina TV, Pershin GN, Golovanova EA. Pharm Chem J 1982;16:127. [22] Korsakova IYa, Safonova OA, Ageeva OI, Shvedov VL, Nikolaeva IS, Pushkina TV, Pershin GN, Golovanova EA. Khim-Farm Zh 1982;16:189. [23] Eastmond GC, Paprotny J. Reactive and Func Polym 1996;30:27. [24] Miryan NI, Yurchenko AG, Kirienko EI. Ukr Khim Zh 1990;56:183. [25] Eastmond GC, Page PCB, Paprotny J, Richards RE, Schaunak R. Polymer 1994;35:4215. [26] Eastmond GC, Paprotny J. Polymer 1994;35:5148. [27] Eastmond GC, Paprotny J. Macromolecules 1995;28:2140. [28] Mathias LJ, Lewis CM, Wiegel KN. Macromolecules 1997;30:5970. [29] Grub TL, Mathias LJ. J Polym Sci A Polym Chem 1997;35:1743. [30] Dominianni SJ, Ryan CW. Ger. Pat. DE2726393, 1977; C.A. 1978;88:152225. [31] Novikov SS, Khardin AP, Novakov IA, Radchenko SS. Vysokomol Soedin 1976;A18:1146. [32] Eastmond GC, Paprotny J, Webster I. Polymer 1993;34:2865.
Pendant adamantyl poly(ether imide)s: synthesis and a preliminary study of properties G.C. Eastmond a,*, M. Gibas b, J. Paprotny a a Donnan Laboratories, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK Department of Physical Chemistry and Technology of Polymers, Silesian Technical University, Gliwice, Poland
b
Received 12 February 1999; accepted 3 March 1999
Abstract Adamantyl-substituted dihydroxybenzenes were prepared by reacting 1-bromoadamantane with dihydroxybenzenes. The major products were 4-(adamantyl-1)-1,2-dihydroxybenzene, 4-(adamantyl-1)-1,3dihydroxybenzene and 2-(adamantyl-1)-1,4-dihydroxybenzene. The ®rst was not isomerically pure and the third was contaminated with a small proportion of di(adamantyl-1)-1,4-dihydroxybenzene. These adamantyl-substituted diols were converted to bis(ether anhydride)s. Poly(ether imide)s were prepared by reacting the adamantyl-substituted bis(ether anhydride)s with aromatic diamines. Solubilities and thermal transition temperatures of the poly(ether imide)s were compared with data for poly(ether imide)s with other alkyl-substituents and with main-chain adamantyl units. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Synthesis; Adamantyl-substituted; Thermal properties; Poly(ether imide)s
1. Introduction For several decades, chemists have been fascinated by the structure and properties of adamantane (tricyclo[3.3.1.1]decane) which has an arrangement of carbon atoms similar to that in a diamond lattice. The molecule is highly symmetrical and has good thermal and chemical stability; 1-ethynyl-adamantane does not polymerize and can be recovered in good yield after vacuum pyrolysis at 8008C [1,2]. Considerable research was undertaken into adamantane and its derivatives after an inexpensive source of adamantane was found [3,4] and particularly after it was discovered that 1-
* Corresponding author. Fax: +44-151-794-3534.
aminoadamantane is a potent inhibitor of several viruses [5]. Polymer chemists interested in `high-performance' polymers have incorporated adamantane into almost every type of polymer in order to achieve high glasstransition temperatures and to enhance thermal and hydrolytic stabilities. Since the 1960s, hundreds of papers and patents on the topic have appeared and Khardin and Radchenko have presented a good review of the literature [6]. There has recently been a resurgence of interest in polymers based on adamantane, such as polyimides [7], poly(ether ketone)s [8], polyphenylenes [9] and poly(benzoxazole)s [10]. We previously synthesized a bis(ether anhydride) based on adamantane which allowed the synthesis of poly(ether imide)s (I):
0014-3057/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 9 ) 0 0 0 9 2 - 0
2098
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
with adamantane units in the polymer backbone [11]. Here, we report poly(ether imide)s with pendant adamantyl units in the bisanhydride residue. The bis(ether anhydride)s were prepared from the products of nitrodisplacement reactions between 4-nitrophthalodinitrile and aromatic diols with adamantyl substituents. For this purpose it was necessary to synthesize appropriate adamantyl-substituted diols and these were prepared from various dihydroxybenzenes. The alkylation of phenols by 1-bromoadamantane (II), known for some time, [12,13] leads to 4-(adamantyl-1)-substituted phenols. It is believed that with phenol itself the product is entirely 4-(adamantyl-1)phenol; Hardy et al. [14] quoted a yield of 88% and Jensen et al. a yield of 92% 4-(adamantyl-1)phenol [15], although Ong established that protracted reaction could lead to proportions of di- and tri-substituted products [13]. It was also reported that reaction of 1chloroadamantane with phenol led to a mixture of ortho and para isomers; 2-(adamantyl-1)phenol formed initially was converted to the thermodynamically stable 4-(adamantyl-1)phenol in the presence of phenol and hydrogen chloride [16]. Similar reactions between (II) (or 1-hydroxyadamantane) and simple aromatic diols (III) are less well known and present potential complications [17±22]. Shvedov et al. described the synthesis of 4-(adamantyl-1)resorcinol (i.e. 4-(adamantyl-1)-1,3dihydroxybenzene) (IVb) by reacting excess resorcinol (IIIb) with (II) in boiling benzene, Scheme 1, and obtained a single product in 79% yield [17,18]. We repeated the reaction in Scheme 1 with (IIIb) and also applied it to catechol (IIIa) and hydroquinone (IIIc) to obtain a series of adamantyl-1 diols. From these substituted diols we have prepared a corresponding series of adamantyl-1-substituted bis(ether anhydride)s and from these a series of poly(ether imide)s. We have previously reported the synthesis and properties of poly(ether imide)s derived from bis(ether anhydride)s based on unsubstituted dihydroxybenzenes [23]. We have also investigated the properties of poly(ether imide)s with bulky, main-chain units, including
the adamantyl unit [11]. In the former case, the thermal properties of the poly (ether imide)s were greatly in¯uenced by the structure and ¯exibility of the diamine moiety while in the latter case the bulky groups dominated properties such as glass-transition temperatures. Here, we provide a comparison of the thermal properties of poly(ether imide)s of several structures including those with adamantyl units in dierent situations and with a selection of diamines.
2. Experimental 2.1. Materials All reagents were commercially available compounds and were used as received except that para-phenylene diamine and meta-phenylene diamine were sublimed before use; bis(4-aminophenyl)ether was an ultra-pure sample from BP plc. 2.2. Procedures 2.2.1. Polymer characterization Molecular weights of poly(ether imide)s were determined by gel permeation chromatography (gpc), using Polymer Laboratories PL-gel 5 mm columns, DMF with 0.1M LiCl as eluant, a pumping rate of 1 ml minÿ1 and a refractive index detector (Knauer). The system was calibrated with polystyrene standards (Polymer Laboratories). Glass-transition temperatures were determined with the aid of a Perkin-Elmer DSC2. Solubilities of the polymers were determined in a series of solvents by allowing samples of polymer to stand in solvents for periods of 2 weeks. NMR spectra were determined using a Varian UNITY/INOVA 300 MHz spectrometer. 2.2.2. Alkylation of aromatic diols with 1-bromo-adamantane: general procedure A solution of diol (III) (0.10 mol) and 1-bromoada-
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
2099
Scheme 1.
mantane (II) (0.05 mol) (molar ratio of (III) : (II) was a minimum of 2 : 1 and preferably greater) in benzene (25 cm3), to which water (two or three drops) had been added was re¯uxed for 4 h. During this period, a slow stream of nitrogen was used to aid removal of the hydrogen bromide evolved; for syntheses on a larger scale, it is preferable to use a hydrogen bromide trap. The solvent was then removed by rotary evaporation. The crude product was washed thoroughly with warm water and dried. Yields were between 30% and 80%, depending on the diol used. Puri®cation required two or three recrystallizations from toluene or toluene/
cyclohexane. Finally, the adamantyl diols were sublimed once or twice under vacuum at 0.5 torr. Details of yields and crystallization solvents for speci®c adamantane-substituted diols are given in Table 1.
2.2.3. Synthesis of (adamantyl-1)dihydroxybenzene diacetates (Adamantyl-1)dihydroxybenzenes were acetylated by heating with acetic anhydride for 2 h; crystalline products were recovered.
Table 1 Synthesis and characterization data for (adamantyl-1)-substituted dihydroxybenzenes. R 1-adamantyl
a
Yields are after recrystallizations from solvents the number of times speci®ed and sublimation. Ref. [24]. c Ref. [17,18]. d Ref. [29]. e Ref. [30]. f Ref. [21,22]. b
2100
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
Scheme 2.
2.2.4. Synthesis of 1-adamantyl-substituted bis(ether dinitrile)s and bis(ether anhydride)s (Adamantyl-1)dihydroxybenzenes (0.1 mol) (IV) were reacted with 4-nitrophthalodinitrile (V) (0.2 mol) in DMSO, in the presence of potassium carbonate (Scheme 2) to form bis(ether dinitrile)s (VI). The bis(ether dinitrile)s were then hydrolyzed to bis(ether diacid)s (VII) by heating with potassium hydroxide in methanol. The bis(ether diacid)s were then dehydrated to bis(ether anhydride)s (VIII) by re¯uxing with acetic anhydride in the presence of acetic acid. Details of these several standard procedures have been reported elsewhere [25±27]. 2.2.5. Synthesis of poly(ether imide)s with pendant adamantyl groups Bis(ether anhydride)s were reacted with aromatic diamines in NMP solution to form intermediate poly(amic acid)s which were then imidized chemically with acetic anhydride/pyridine (1 : 1). Poly(ether imide)s were isolated by precipitation into methanol and were dried, as described in detail elsewhere [25±27].
3. Results and discussion 3.1. Synthesis of 1-adamantyl diols Each dihydroxybenzene (IIIa±c) was reacted individually with 1-bromoadamantane as described above, Scheme 1. The characteristics of the aromatic diol products with pendant 1-adamantyl units so formed, are presented in Table 1. Reaction with catechol (IIIa) could lead to two sin-
gly-substituted diols, viz., 3- and 4-substituted catechols. We found that the reaction product from 1bromoadamantane and catechol was indeed a mixture of 3-(adamantyl-1)-1,2-dihydroxybenzene and 4-(adamantyl-1)-1,2-dihydroxybenzene. The product, when recrystallized twice from toluene and sublimed (180± 1908C, 0.5 torr), had a precise mass, determined by mass spectrometry, of 244.14662, compared with a calculated value of 244.14633 (an error of 1.2 ppm or 0.29 mDa). Nevertheless, despite repeated crystallization and sublimation, gas chromatography of the product showed two peaks in a ratio of 12 : 1; each component had the same mass when analysed by mass spectrometry. 1 H NMR data of the aromatic protons (400 MHz) were also inconsistent with those expected for a single tri-substituted aromatic ring, but were consistent with a mixture of 4- and 3-(adamantyl-1)-1,2dihydroxybenzenes. Comparison of integrated peak intensities indicated a molar ratio of 76 : 24; 3-(adamantyl-1) catechol was the minor product. The melting point quoted in Table 1 is for the mixture of isomers obtained after recrystallization and sublimation; the relatively low value of the melting point (compared with products from other diols) is consistent with a mixture of isomers. The observation that a mixture of isomers was produced is consistent with the work of Sokolenko et al., who prepared (adamantyl-1)-1,2dihydroxybenzene by reacting (IIIa) with 1-hydroxyadamantane and obtained a mixture of 4- and 3-isomers in the proportions 3.8 : 1 [19,20]; these workers quoted a melting point of 204±2068C for 3-(adamantyl-1)-1,2dihydroxybenzene, but did not quote a melting point for 4-(adamantyl-1)-1,2-dihydroxybenzene. The original synthesis of 4-(adamantyl-1)-1,2-dihydroxybenzene
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
was apparently achieved by a similar process to that used here, with a yield of 75%, but no mention was made of a mixture of products; the melting point quoted was identical to that obtained by us [24]. When the mixture of isomers was acetylated, the initial product gave two peaks by gas chromatography, but, during subsequent work up (recrystallization from ethanol) a 60% yield of crystalline product was separated; this product gave a single peak by gas chromatography. This major product was identi®ed as 4(adamantyl-1)-1,2-dihydroxybenzene diactetate by 1 H and 13 C NMR; data are presented in Table 2 and the melting point is given in Table 1. We did not attempt to obtain the pure 3-isomer which concentrated in the mother-liquor during crystallization. These results con®rmed that the major isomer in the mixture of (adamantyl-1)-1,2-dihydroxybenzenes was 4-(adamantyl-1)1,2-dihydroxybenzene. Reaction of (II) with (IIIb), to obtain (adamantyl-1)1,3-dihydroxybenzene, gave a product (Table 1) which, after crystallization and sublimation, showed a single peak by gas chromatography. This result is consistent with the observations of Shvedov et al. who also obtained a single product in 79% yield with similar
melting point, identi®ed as 4-(adamantyl-1)-1,3-dihydroxybenzene, from the same reaction [17,18]; Mathias and coworkers reported products with slightly higher melting points (Table 1) from the same reaction [28,29]. The identity of our product was further con®rmed by 1 H NMR on the diol and by 1 H and 13 C NMR on the diacetate, Table 2. One possible alternative isomer 5-(adamantyl-1)-1,3-dihydroxybenzene has been prepared by a dierent route and had a melting point of 284±2858C [30]; the other possible isomer, 2(adamantyl-1)-1,3-dihydroxybenzene, is apparently unknown. Only a single mono-adamantyl-substituted hydroquinone isomer is possible, i.e., 2-(adamantyl-1)-1,4dihydroxybenzene. Reaction of (II) with (IIIc) produced a product which, after several puri®cation, gave good analytical data but a rather broad melting point, Table 1. The 1 H NMR spectrum was not clean and, as with the other adamantyl-substituted diols, the product was acetylated to aid analysis. 1 H and 13 C NMR spectra of the product were not clean but were consistent with 2-(adamantyl-1)-1,4-dihydroxybenzene diacetate as the main product admixed with a little bis(adamantyl-1)-1,4-dihydroxybenzene diacetate; the proportions
Table 2 NMR data for (adamantyl-1)dihydroxybenzene diacetates, observed and (calculated) chemical shifts and coupling constants Structure
1 H NMR Chemical shift (ppm) H(2) H(3) H(5) H(6)
Coupling constant (Hz) J2±6 J3±5 J5±6
± 7.13 (7.28) 7.22 (7.49) 7.10 (6.94) 2.24, 2.25
6.81 (6.75) ± 7.31 (7.24) 6.94 (6.96) 2.26, 2.33
± 2.31 8.55
2.44 ± 8.79
13
C NMR Chemical shift (ppm) C(1) C(2) C(3) C(4) C(5) C(6) C(CO)
2101
139.6 (142.0) 141.7 (144.7) 120.0 (120.0) 150.2 (149.6) 123.0 (124.1) 122.6 (123.0) 168.3, 168.4
149.4 (149.7) 117.4 (115.3) 148.6 (149.4) 138.5 (141.9) 127.6 (127.7) 118.6 (119.4) 169.0, 169.1
2102
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
Table 3 Characterization data for (adamantyl-1)-substituted bis(ether dinitrile)s and bis(ether anhydride)s
Structure
VIa
Elemental Calc.:
analysis Found:
Yield % and crystallization solvent
Melting Point/ 8C
C 77.40 H 4.87 N 11.28
C 77.31 H 4.85 N 11.34 C 77.50 H 4.85 N 11.27 C 77.70 H 4.89 N 11.22
76 (82) MeCN
248.5±249.4
VI VIc
84 (94) EtOH
135±137
67 (85) MeCN
240±242
Structure
Elemental Calc.:
analysis Found:
Yield %
Melting Point/ 8C
VIIIa
C 71.63
C 71.69
89
188±189
H 4.50 VIIb
H 4.49 do
92
194±195
VIIIc
do
C 71.39 H 4.54 C 71.47 H 4.48
91
255±257
and substitution patterns could not be accurately estimated but the good elemental analysis data indicated that the content of the disubstituted product must have been small. Previously, Korsakova et al. undertook a similar reaction between (II) and (IIIc) and demonstrated that their product was a mixture of 2(adamantyl-1)-1,4-dihydroxybenzene and 2,5-bis(adamantyl-1)-1,4-dihydroxybenzene [21,22]. Thus, a series of adamantyl substituted phenylene diols have been prepared, which could be used in the synthesis of polymers albeit they were not all isomerically pure.
3.2. Synthesis of bis(ether anhydride)s and poly(ether imide)s from 1-adamantyl-substituted aromatic diols To prepare bis(ether anhydride)s based on (adamantyl-1)dihydroxybenzenes, species (IV) were reacted with (V) in DMSO in the presence of potassium carbonate in order to prepare bis(ether dinitrile)s (VI), which were then hydrolysed with methanolic potassium hydroxide to bis(ether diacid)s (VII) and dehydrated with acetic anhydride/acetic acid to bis(ether anhydride)s (VIII) according to Scheme 2 and as described elsewhere [25±27]. Bis(ether anhydride)s were
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
2103
recrystallized from acetic anhydride. Characterization data for the products are presented in Table 3. Poly(ether imide)s (IX):
above 01108C. Where the poly(ether imide) product is soluble in the solvent used, a one-step, high-temperature polymerization can be performed. To perform such reactions, diamines were dissolved in NMP and
were synthesized from the bis(ether anhydride)s (VIII) by a standard two-step reaction, ®rst forming the poly(amic acid) at room temperature in an aprotic solvent (NMP) (12±15 wt% solids), followed by chemical imidization with pyridine/acetic anhydride mixture to give poly(ether imide)s (IX). Three simple aromatic diamines were used in polymer syntheses; para-phenylene diamine (PPD), metaphenylene diamine (MPD) and bis(4-aminophenyl)ether (ODA). Molecular weights (peak values from gel permeation chromatograms, calibrated with polystyrene standards) are recorded in Table 4. In Table 4, sets of columns refer to polymers derived from dierent dihydroxybenzenes and are identi®ed by the locations of OH groups on the initial diol and resulting catenation in the polymer. The positions of adamantyl or other substituent groups on the diol moieties are given in each case. Polymers based on adamantyl-catechol bis(ether anhydride) (VIIIa) and adamantyl-resorcinol bis(ether anhydride) (VIIIb) were soluble both as poly(amic acid) and as poly(ether imide). Problems were encountered when synthesizing poly(amic acid)s from adamantyl-hydroquinone bis(ether anhydride) (VIIIc) with all three diamines. These poly(amic acid) solutions, synthesized in NMP, gelled within hours with less reactive diamines (MPD, ODA) and within 15 min with PPD. Gelation occurred even when reactant concentrations were reduced to 5 wt% solids. A similar phenomenon (apparently unique to polyimides and particularly in poly(ether imide)s containing adamantane units) was described by Novikov [31] when poly(amic acid)s were prepared from 1,3-bis-(3 ',4'dicarboxyphenyl)adamantane dianhydride and aromatic or adamantane-containing diamines. They overcame the problem by dissolving potassium chloride or lithium chloride in the aprotic polymerization solvent. We found the poly(amic acid) gels (without added salt) to be thermally reversible; systems became liquid
the anhydride was added together with some xylene. The mixture was heated to 1608C with stirring and water was removed as the xylene azeotrope. The temperature was gradually raised to 2008C. Polymers prepared with MPD and ODA, when precipitated and dried, were soluble in chloroform and were reprecipitated into methanol. Polymers prepared with PPD were soluble only in hot NMP. 3.3. Polymer properties It is well known that the introduction of bulky pendant substituents often enhances polymer processability (especially solubility and processability from solution) and also increases glass-transition temperatures. For example, introducing a methyl or tert-butyl substituent into a bis(ether anhydride) tends to raise the glass-transition temperatures of poly(ether imide)s. In this case, we examine the eects of introducing very bulky adamantyl groups pendant to the main chain. In order to assess the eects of this structural modi®cation, we compare the properties of these polymers with those of their unsubstituted analogues, with similar poly(ether imide)s with alkyl substituents and with similar poly(ether imide)s having main-chain, adamantyl units. The solubilities and glass-transition temperatures of these several polymers are summarised in Table 4. Solubilities were tested in a series of solvents for which the solubility power for poly(ether imide)s generally increases in the order CHCl3
PPD MPD ODA
PPD MPD ODA
PPD PPD MPD ODA ODA
MPD ODA
MPD ODA
None
Tert-butyl
Di-tert-butyl
Methyl
Adamantyl in chain (I)
3 3 4
3,5 3,5 3,5 3,5
4 4 4
4 4 4
Group position
Imidized thermally. trg = thermally reversible gel.
PPD MPD ODA
Adamantyl
a
Amine
Anhydride substituent
Catenation
119 K 106 K
79 K
103 K 30 K 58 K 123 K 17 K
± 51 K 58 K
± 112 K 287 K
24 K 26 K 44 K
MW/kg molÿ1
1,2
255 253
222 216 213
275 256 250 244 228
± 226 219
>420 220 208
257 249 252
Tg/8C
s s
s s s s s
± s s
insoluble s s
NMP s s
Solvent
93 K 136 K
29 K 118 K
4,6 4,6
5 5
±
± ± ±
20 K 13 K 26 K
MW/kg molÿ1
4,6
4 4 4
Group position
Table 4 Synthesis and characterization of adamantyl-substituted and related poly(ether imide)s
217 210
248 254
269
± ± ±
>420 225 209
291 260 260
Tg/8C
1,3
s s
s s
s, insoluble in DMAC
insoluble NMP NMP,trg DMAC,trg
s s s
Solvent
2
2,5 2,5
2,5
2 2 2
2 2 2
Group position
±
153 K 205 K
±
± 107 K 61 K
± ± ±
±a 20 Ka 45 Ka
MW/kg molÿ1
218
272 265
300
>420 254 236
>420 0 245 238
304 289 285
Tg/8C
1,4
s?
s s, insoluble in NMP
H2SO4
insoluble s s
insoluble NMP NMP
hot NMP s s
Solvent
2104 G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
alkyl substituents. When comparing properties, it should be noted that the molecular weights of the adamantyl-substituted poly(ether imide)s, as measured by gel permeation chromatography, are low compared with those of other polymer series [32]. Although molecular weights of aromatic poly(ether imide)s are normally higher than true molecular weights by a factor of about three [32], it cannot be assumed the same factor applies to poly(ether imide)s with very bulky adamantyl substituents. Gelation encountered during polymer synthesis does not necessarily imply high-molecular-weight poly(amic acid), but probably re¯ects reduced solubility of poly(amic acid) with large aliphatic groups in the polymerization solvent. A similar eect could modify the hydrodynamic volumes of the adamantyl-substituted polymers in the gpc solvent of DMF/LiCl(0.1 M). The absence of any molecular weight data for individual polymers in Table 4 implies lack of solubility in DMF/LiCl. We have previously observed, in general, that only poly(ether imide)s with molecular weights in excess of 60 kg molÿ1, as measured by gel permeation chromatography in our system, are capable of forming good, non-brittle, solvent-cast ®lms. Despite the apparent low molecular weights of the adamantyl-substituted poly(ether imide)s good free-standing polymer ®lms were obtained when the polymers were cast from solution in chloroform. Consistent with established trends, a high degree of para-catenation leads to decreased solubility and higher Tgs and this pattern holds within the family of adamantyl-substituted poly(ether imide)s. Thus, the poly(ether imide) from (VIIIc) and PPD is the least soluble polymer and has the highest Tg. Also, for the polymers prepared from (VIIIa) that with PPD is the least soluble and has the highest Tg, especially when it is noted that the polymer is in the regime where Tg might be expected to be molecular weight dependent; in a few cases Tgs for related polymers with two tertbutyl substituents are quoted for two dierent molecular weights to highlight this eect. Thus, Tgs for highmolecular-weight polymers might be up to 208C higher than those quoted. A second general trend is that 1,2-catenation tends to give higher solubility than 1,3-catenation, but with relatively little dierence in Tg. This trend is not strictly observed with the adamantyl-substituted poly(ether imide)s but solubilities might be molecular weight dependent. Thirdly, poly(ether imide)s based on ODA generally have the lowest Tg (of the three diamines used) but in this case polymers based on ODA have higher Tgs but also have highest molecular weights. Thus, within the family of adamantyl-substituted poly(ether imide)s, the results are probably consistent with established trends given that the polymer molecu-
2105
lar weights are probably low and Tgs possibly molecular-weight dependent. The incorporation of alkyl substituents is known to in¯uence properties, increasing both solubility and Tg. The exception to this rule is poly(ether imide)s with PPD as diamine for which we were unable to observe Tgs below 4208C, the limit of our DSC observations. To provide comparisons, we have included in Table 4 previously determined data for comparable poly(ether imide)s with no substituents, with one methyl substituent, with one tert-butyl substituent (which has its carbon atoms in a similar disposition to part of the adamantane structure) and with two tert-butyl substituents. From these data it is clear that, in general and within the limits of comparability of molecular weight, there is a tendency for Tg to increase with the bulk of the substituent groups and with the number of tertbutyl groups. Nevertheless, there is a marked increase in Tg for the adamantyl-substituted poly(ether imide)s which, for similar molecular weights, have the highest Tgs and high-molecular-weight adamantyl-substituted poly(ether imide)s could have even higher Tgs. It is appropriate to compare Tgs of poly(ether imide)s with adamantyl groups pendant and in-chain (I). As noted previously, Tgs of poly(ether imide)s with bulky in-chain moieties are largely determined by the nature of the bulky group rather than the structure of the diamine and both polymers (I), derived from MPD or ODA, have Tgs of 253±2558C (Table 4) [11]. Given that these polymers probably had higher absolute molecular weights than the adamantyl-substituted poly(ether imide)s, the Tgs of the latter polymers, for comparable molecular weights, are at least as high, if not higher than, those with main-chain adamantyl units. In comparison with the lack of variation in Tg with diamine structure for poly(ether imide)s with bulky main-chain units in the anhydride moities, apart from polymers prepared from PPD, there is little variation in Tg with diamine structure but there is a marked increase in Tg in going from 1,2 to 1,3 to 1,4-catenation of the adamantyl-phenylene unit. Given the bulky nature of the pendant units but high Tgs, it would be of interest to investigate interchain packing in and gas permeability through these materials and to compare the results with those from chains with smaller substituents. 4. Conclusions Dihydroxybenzenes were reacted individually with 1bromoadamantane. It was demonstrated that in each case, a single (adamantyl-1)dihydroxybenzene was the main product. However, consistent with the observations of previous workers, it was con®rmed that in the reaction with catechol the main product was 4-
2106
G.C. Eastmond et al. / European Polymer Journal 35 (1999) 2097±2106
(adamantyl-1)-1,2-dihydroxybenzene but some 3-(adamantyl-1)-1,2-dihydroxybenzene was also formed and was not readily removed. 3-(Adamantyl-1)-1,4-dihydroxybenzene was contaminated with a little di(adamantyl-1)-1,4-dihydroxybenzene. The 4-(adamantyl-1)1,3-dihydroxybenzene was a pure product. The (adamantyl-1)-substituted dihydroxybenzenes, as prepared, were converted to bis(ether anhydride)s by reaction with 4-nitrophthalodinitrile, subsequent hydrolysis to bis(ether diacid) and dehydration to bis(ether anhydride). The bis(ether anhydride)s were converted to poly(ether imide)s by reaction with selected amines and the solution and thermal properties of the polymers were compared within the group of polymers and with related poly(ether imide)s with alkyl substituents. Molecular weights of the polymers, as measured by gel permeation chromatography, were apparently low but good, non-brittle ®lms were obtained by solvent casting; quantities of polymers prepared were insucient to determine mechanical properties. Glass-transition temperatures of the polymers were shown to be high, from 250 to 3008C depending on the substitution pattern and the diamine. The main factor in¯uencing Tg was the substitution pattern of the dihydroxybenzene and Tg increased as the substitution pattern was changed from ortho to meta to para. Glasstransition temperatures of adamantyl-substituted polymers were found to be higher than those of similar poly(ether imide)s with methyl or one or two tert-butyl substituents and higher than poly(ether imide)s with main-chain adamantane units and prepared from similar diamines. The adamantyl-substituted poly(ether imide)s were found to be more soluble than related poly(ether imide)s in a variety of solvents; many were soluble in chloroform as well as aprotic solvents. However, poly(amic acid) intermediates synthesized from 1,4bis(3',4 '-dicarboxyphenoxy)-2-(adamantyl-1)benzene dianhydride gelled and thermal imidization in solution was preferred to chemical imidization. Acknowledgements The authors wish to thank EPSRC and DRA for ®nancial support. References [1] Brown RFC, Eastwood FW, Jackman GP. Aust J Chem 1977;30:1757. [2] Archibald TG, Malik AA, Baum K, Unroe MR. Macromolecules 1991;24:5261.
[3] Schleyer P. J Am Chem Soc 1957;79:3292. [4] Schleyer P, Donaldson MM, Nicholas RD, Cupas C. Org Syntheses 1962;42:8. [5] Davies WL, Grunert RR, Ha RF, McGahen JW, Neumayer EM, Paulshock M, Watts JC, Wood TR, Hermann EC, Homann CE. Science 1964;144:862. [6] Khardin AP, Radchenko SS. Russ Chem Rev 1982;51:272. [7] Chern Y-T, Chung W-H. J Polym Sci, Part A, Polym Chem 1996;34:117. [8] Mathias LJ, Lewis CL. Polym Prep Am Chem Soc Polym Div Inc 1995;36(2):140. [9] Tullos GL, Mathias LJ. Polym Prep Am Chem Soc Polym Div Inc 1995;36(2):316. [10] Grub TL, Mathias LJ. Polym Prep Am Chem Soc Polym Div Inc 1996;37(1):551. [11] Eastmond GC, Paprotny J. J Mater Chem 1997;7:589. [12] Reinhardt HF. J Org Chem 1962;27:3258. [13] Ong SH. Chem Commun 1970:1180. [14] Hardy ADV, MacNicol DD, Wilson DR. J Chem Soc Perkin Trans II 1979:1011. [15] Jensen JJ, Grimsley M, Mathias IJ. J Polym Sci A Polym Chem 1996;34:397. [16] Aigami K, Inamoto Y, Takaishi N, Hattori K. J Medicinal Chem 1975;18:713. [17] Shvedov VI, Safonova OA, Korsakova IYa, Bogdanova NS, Nikolaeva IS, Peters VV, Pershin GN. Khim-Farm Zh 1980;14:54. [18] Shvedov VI, Safonova OA, Korsakova IYa, Bogdanova NS, Nikolaeva IS, Peters VV, Pershin GN. Pharm Chem Ind 1980;14:127. [19] Sokolenko VA, Kuznetsova LN, Orlovskaya NF. Russ Chem Bull 1996;45:485. [20] Sokolenko VA, Kuznetsova LN, Orlovskaya NF. Izv Akad Nauk Ser Khim 1996:505. [21] Korsakova IYa, Safonova OA, Ageeva OI, Shvedov VL, Nikolaeva IS, Pushkina TV, Pershin GN, Golovanova EA. Pharm Chem J 1982;16:127. [22] Korsakova IYa, Safonova OA, Ageeva OI, Shvedov VL, Nikolaeva IS, Pushkina TV, Pershin GN, Golovanova EA. Khim-Farm Zh 1982;16:189. [23] Eastmond GC, Paprotny J. Reactive and Func Polym 1996;30:27. [24] Miryan NI, Yurchenko AG, Kirienko EI. Ukr Khim Zh 1990;56:183. [25] Eastmond GC, Page PCB, Paprotny J, Richards RE, Schaunak R. Polymer 1994;35:4215. [26] Eastmond GC, Paprotny J. Polymer 1994;35:5148. [27] Eastmond GC, Paprotny J. Macromolecules 1995;28:2140. [28] Mathias LJ, Lewis CM, Wiegel KN. Macromolecules 1997;30:5970. [29] Grub TL, Mathias LJ. J Polym Sci A Polym Chem 1997;35:1743. [30] Dominianni SJ, Ryan CW. Ger. Pat. DE2726393, 1977; C.A. 1978;88:152225. [31] Novikov SS, Khardin AP, Novakov IA, Radchenko SS. Vysokomol Soedin 1976;A18:1146. [32] Eastmond GC, Paprotny J, Webster I. Polymer 1993;34:2865.