Synthesis of bulky bis(ether anhydride)s and poly(ether imide)s with bulky mainchain units

Article abstract of DOI:10.1039/a607709i

A series of bis(ether anhydride)s has been synthesized from very bulky bisphenols. Poly(ether imide)s have been synthesized from these bis(ether anhydride)s and two diamines in order to provide a series of poly(ether imide)s with bulky main-chain units. T

Full text of DOI:10.1039/a607709i

Synthesis of bulky bis(ether anhydride)s and poly(ether imide)s with bulky main-
chain units†
Geoffrey C. Eastmond* and Jerzy Paprotny
Donnan L aboratories, Department of Chemistry, University of L iverpool, PO Box 147, L iverpool, UK L 69 3BX
A series of bis(ether anhydride)s has been synthesized from very bulky bisphenols. Poly(ether imide)s have been synthesized from
these bis(ether anhydride)s and two diamines in order to provide a series of poly(ether imide)s with bulky main-chain units. The
polymers have been characterized in terms of molecular weight, solubility, glass-transition temperature and thermal stability in
order to identify a series of high-performance polymers which are processable and potentially useful for applications which require
soluble poly(ether imide)s for fabrication into, for example, gas separation membranes.
Polyimides are now well established as high-performance
polymers with a number of applications including microchip
encapsulation, films and membranes.1 Their lack of solubility
requires that they are normally applied as poly(amic acid)
intermediates which are subsequently imidized. There have
been many attempts to produce more soluble and processable
alternatives. A successful development was the commercial
poly(ether imide) Ultem;2 the incorporation of main-chain
ether linkages imparts solubility and melt processability.
Subsequently, several groups have atttempted to produce other
members of this family (1) in order to further enhance pro-
cessability and tailor properties for specific applications; in 1,
Ar is an aromatic unit derived from an aromatic diol and
species 1 are usually derived from a bis(ether anhydride),
formed by a reaction sequence involving nitro displacement
between the diol and a suitable nitrophthalic acid derivative
(often a nitrophthalodinitrile), and a diamine. Approaches
which have been used to enhance solubility include incorporat-
ing substituent groups on Ar and/or Ar∞ groups and changing
the susbstitution patterns of aromatic residues.3–6
inherently rigid, bulky main-chain units into poly(ether imide)s.
To this end we have identified a number of available bulky
diols 2a–e and have investigated their abilities to undergo
nitro displacement reactions with 4-nitrophthalodinitrile and
thus be converted into bis(ether anhydride)s 5a–e (Scheme 1).
We have also undertaken a preliminary assessment of the
abilities of the anhydrides to undergo polymerization with
diamines (Scheme 2) to produce processable poly(ether imide)s
which might have useful properties for specific applications.
Here we describe the results of these studies and report on the
glass-transition temperatures, molecular weights, solubilities,
thermal stabilities and colour of these polymers.
There has, over many years, been considerable interest in
polymers containing moieties derived from adamantane and
the literature has been reviewed.9 Recent papers have reported
polyimides,10 poly(ether ketone)s,11 polyphenylenes12 and
polybenzoxazoles.13 One reason for interest in such polymers
is the inherent thermal and chemical stability of the ada-
mantane unit. This report includes the synthesis of poly(ether
imide)s with main-chain adamantane-1,3-diyl units and their
preliminary characterization. More recently we prepared a
series of poly(ether imide)s with pendant adamantyl units, and
the properties of these polymers and a comparison with
polymers with main-chain units will be reported separately.14
Experimental
Diols (and their sources) used to prepare bis(ether anhydride)s
One of the main potential applications of poly(ether imide)s
is as membranes for gas separation, which requires the poly-
mers to be soluble for fabrication into hollow-fibre, asymmetric
membranes. Two factors are important in producing optimum
membrane properties. The polymers must show good per-
meability of gases and good selectivity in gas separation. It
has long been recognised that bulky groups enhance gas
permeability.7 Amongst other studies by various groups, we
have demonstrated a pattern of substituent type on selec-
tivity.5,8 We found that groups which were bulky enhanced
gas permeability while substituents which reduced main-chain
rotation enhanced selectivity. These factors together probably
decrease the efficiency of chain packing and bulky, stiff units,
which are probably difficult to pack in an efficient manner,
appear to impart favourable properties.
were: 4,4∞-(adamantane-1,3-diyl)diphenol 2a (Aldrich), 6,6∞-
dihydroxy-4,4,4∞,4∞,7,7∞-hexamethyl-2,2∞-spirobichromane
2b
(TCI), 1,1∞-bi-2-naphthol 2c (Aldrich), 4,4∞-bicyclo[2.2.1]hep-
tane-2,2-diyldiphenol 2d and 4,4∞-tricyclo[5.2.1.02,6]decane-
8,8-diyldiphenol 2e; the latter two diols were gifts from
Kodak Ltd. 4-Nitrophthalodinitrile was obtained from TCI,
4,4∞-oxydianiline was an ultrapure sample from BP. m-
Phenylenediamine (Fluka) was sublimed prior to use. Other
solvents and reagents used were obtained from sources specified
previously and were used as supplied.
Diols were reacted with 4-nitrophthalodinitrile in dimethyl
sulfoxide (DMSO) solution in the presence of anhydrous
potassium carbonate at room temperature to produce bis(ether
dinitrile)s 3a–e,15 exactly as described in previous publi-
cations.5,6 Reactions were typically performed using 10 mmol
of diol and 20 mmol of 4-nitrophthalodinitrile and were con-
tinued for 24 h. Products were isolated by pouring reaction
mixtures into water and washing the products with methanol.
Similarly, the bis(ether dinitrile)s were hydrolysed to bis(ether
diacid)s 4a–e with potassium hydroxide, isolated and then
dehydrated to bis(ether anhydride)s 5a–e with glacial acetic
Because a combination of bulky units and chain rigidity
might enhance both permeability and selectivity in gas
separation, we have investigated the possibilities of introducing
† This paper was presented, in part, at the International Polymer
Symposium, Gliwice, Poland, September 1995.
J. Mater. Chem., 1997, 7(4), 589–592
589

Scheme 1
Elmer Series 7 instruments. Measurements were made under
nitrogen at The Leverhulme Centre for Innovative Catalysis,
University of Liverpool, with a heating rate of 40°C min−1,
samples were annealed for 6 h at 170°C in vacuo, and in air
at The University of Sussex with a heating rate of 10 °C min−1.
Results and Discussion
All diols 2a–e satisfactorily underwent nitro displacement
reaction with 4-nitrophthalodinitrile according to Scheme 1 to
give pure bis(ether dinitrile)s 3a–e in good yield. The elemental
analysis data for the bis(ether dinitrile)s are given in Table 1.
Each bis(ether dinitrile) was readily hydrolysed by potassium
hydroxide to its corresponding bis(ether acid) 4 which was
isolated. The bis(ether acid)s were not characterized but were
directly dehydrated to the bis(ether anhydride). The bis(ether
anhydride)s 5a–e were characterized by elemental analyses and
melting points, supported by spectrocopy; details of elemental
analyses, yields and melting points, together with the solvents
used for recrystallization, are reported in Table 2.
Scheme 2
In order to test the feasibility of preparing poly(ether imide)s
from the several bis(ether anhydride)s, each bis(ether anhy-
dride) was reacted with one or two aromatic diamines [usually
m-phenylenediamine (MPD) and 4,4∞-oxydianiline (ODA)] in
NMP or DMAC, to prepare poly(amic acid)s which were then
chemically imidized with an acetic anhydride–pyridine mixture.
After precipitation into methanol, the poly(ether imide)s were
boiled with methanol in order to remove residual NMP. Where
soluble in NMP–1  LiCl, the molecular weights of the
poly(ether imide)s were determined and in all cases the glass-
transition temperatures of the polymers were measured by
differential scanning calorimetry. The results are reported
in Table 3.
acid and acetic anhydride as described previously; these pro-
cedures are summarized in Scheme 1. Elemental analysis data
for the bis(ether dinitrile)s and bis(ether anhydride)s, together
with their melting points and yields, are given in Tables 1 and
2, respectively.
Poly(ether imide)s were prepared from the bis(ether anhy-
dride)s in a two-stage process involving initial formation
of poly(amic acid) by reaction with diamine in N-methylpyr-
rolidone (NMP) or N,N-dimethylacetamide (DMAC) and
subsequent chemical imidization with an acetic anhydride–
pyridine mixture (151, v/v) as described in previous
publications and summarized in Scheme 2.5,6
It is noticeable that the glass-transition temperatures (T )
g
Molecular weights were determined by gel-permeation
chromatography using DMF–1  LiCl as eluent, PL-gel
polystyrene columns and polystyrene standards (both from
Polymer Laboratories) with refractive index detection (Knauer
detector). Glass-transition temperatures were determined using
of the polymers are almost independent of the diamine used
and are dominated by the bis(ether anhydride) structure; in
several series of poly(ether imide)s, derived from various
diphenols or dihydroxyphenylenes, those based on ODA have
glass-transition temperatures about 10°C lower than those
based on MPD. We previously noted a reduced dependance
a
Perkin-Elmer DSC2 differential scanning calorimeter.
Thermogravimetric analysis (TGA) was undertaken on Perkin-
of T on diamine structure in poly(ether imide)s based on
g
590
J. Mater. Chem., 1997, 7(4), 589–592

Table 1 Synthesis of bis(ether dinitrile)s
elemental analysis
yield (%)
bis(ether
dinitrile)
recrystallization
C
H
N
solvent
pure
87
87
79
78
crude
mp/°C
3a
3b
3c
3d
3e
Calc.
79.72
79.68
75.46
74.60
80.28
80.18
78.93
79.00
79.60
79.66
4.89
4.86
5.19
5.30
3.36
3.36
4.54
4.51
4.92
4.92
9.79
MeCN
MeCN
MeCN–MeOH
MeCN–MeOH(152)
MeCN
96
98
99
91
—
188–189
276–277
253–254
197–198
143–145
Found
Calc.
9.84
9.02
Found
Calc.
9.02
10.03
10.08
10.51
10.56
9.78
Found
Calc.
Found
Calc.
95
Found
9.75
Table 2 Synthesis of bis(ether anhydride)s
elemental analysis
bis(ether
recystallization
anhydride)
C
H
solvent
yield (%)
mp/°C
5a
5b
5c
5d
5e
Calc.
74.50
74.53
70.90
70.27
74.73
73.64
73.42
73.33
74.50
74.60
4.60
4.59
4.88
4.80
3.13
3.05
4.54
4.22
4.60
4.59
Ac O
73
87
88
95
85
184–186
290–291
221–222
111–112
168–169
2
Found
Calc.
Ac O–MeCN
2
Found
Calc.
Ac O
2
Found
Calc.
Ac O
2
Found
Calc.
Ac O–MeCN
2
Found
Table 3 Properties of polymers
Ar∞
Ar
Mw/kg mol−1
T /°C
g
119
255
106
83
253
271
268
122
—
254
—
98
250
248
52
70
255
253
J. Mater. Chem., 1997, 7(4), 589–592
591

naphthalene-derived bis(ether anhydride)s.16 When used for
practical gas separation membranes it is necessary for
polymers to operate at high temperatures and the glass-
transition temperatures of the polymers based on bulky
anhydrides are consistent with use for this purpose. It is
anticipated that polymers with significantly higher glass-
transition temperatures could be prepared by polymerization
of the bis(ether anhydride)s with rigid diamines, especially
those with hindering substituents ortho to the phthalimide
unit; we anticipate that glass-transition temperatures in excess
of 300 °C can readily be achieved.
poly(ether imide)s. Loss of 30% does not correspond to loss
of the total diol unit or to its central aliphatic structure.
Rather, the weight loss corresponds approximately to loss of
one substituted chromane unit per repeat, which might be
eliminated following scission of an aryl ether linkage adjacent
to the phthalimide unit.
Conclusions
It has been demonstrated that 4,4∞-(adamantane-1,3-
diyl)diphenol 2a, 6,6∞-dihydroxy-4,4,4∞,4∞,7,7∞-hexamethyl-2,2∞-
spirobichromane 2b, 1,1∞-bi-2-naphthol 2c, 4,4∞-bicyclo-[2.2.1]-
heptane-2,2-diyldiphenol 2d and 4,4∞-tricyclo- [5.2.1.02,6]-
decane-8,8-diyldiphenol 2e all undergo nitro displacement with
4-nitrophthalodinitrile to give bis(ether dinitrile)s which can
be converted to bis(ether anhydride)s. The bis(ether anhy-
dride)s react with aromatic diamines to give poly(ether imide)s
with bulky main-chain units which are soluble in chloroform
and are processable from solution in chloroform or aprotic
solvents. Where soluble in DMF–1  LiCl, the molecular
weights of the polymers were determined and the polymers
were shown to have high molecular weight; molecular weights
of polymers based on 5c and ODA and 5d and MPD were
not determined because of their insolubility in the medium
used. The polymers have little colour and those based on
MPD are virtually colourless. Glass-transition temperatures
are in the range 240–270 °C and the polymers based on MPD
show good thermal stability.
In general the polymers had little colour. Those based on
MPD were essentially colourless and did not discolour when
heated in air to temperatures up to 250°C. In addition, all
polymers were soluble in chloroform and, when prepared from
such solutions, solvent-cast films were creasable and did not
fracture and hence had useful mechanical properties; mechan-
ical properties have not yet been determined. The low colour
is consistent with reduced interchain interactions between N-
phenylphthalimide units which, in turn, is indicative of less
efficient chain packing, due to the bulky nature of the units
close to the phthalimide residues. The units could prevent
close approach of phthalimide units and could give rise to
high permeability for gas separation membranes.
Of relevance to potential applications is the thermal stabilit-
ies of the polymers. Thermal stabilities of the polymers pre-
pared from the bis(ether anhydride)s 5a, b, d and e with MPD
by DTA have been examined under a nitrogen atmosphere by
TGA. The results are presented in Fig. 1 which shows that all
the polymers have good thermal stability. The data in Fig. 1
exaggerate the true stabilities of the polymers beause the
heating rate used was 40 °C min−1. In comparison, data
obtained with the same polymer based on 2a (in air) at a
heating rate of 10 °C min−1 showed the same shape of thermo-
gram but initial decomposition started at 405 °C. Nevertheless,
the data in Fig. 1 provide comparative data for the samples
investigated and show the patterns of behaviour on thermal
decomposition. Initial decomposition of all samples occurs at
a similar temperature with decomposition of the polymer based
on adamantane starting to decompose at a slightly lower
temperature; similar initial decomposition temperatures prob-
ably indicate a common mode of chain scission, e.g. at the
ether linkage to the phthalimide; polyimides which do not
have such ether linkages, e.g. Kapton, are more stable. All
samples show decomposition in two stages, in common with
many other data on related polymers. Decomposition of the
polymer based on spirobichromane is somewhat distinctive in
showing a rapid loss of 30 wt% over a relatively small tempera-
ture rise; this step is probably indicative of a mode of decompo-
sition associated with the spirobichromane moiety rather than
the aromatic structures common to all the polymers and other
The authors wish to thank Dr M. R. H. Siddiqui of the
Leverhulme Centre for Innovative Catalysis, University of
Liverpool, for undertaking the TGA measurements under
nitrogen, Dr N. C. Billingham, University of Sussex, for those
undertaken in air, Kodak Ltd for the gift of two diols and the
EPSRC for providing financial support.
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Fig. 1 Thermogravimetric analysis data for poly(ether imide)s based
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heating rate 40 °C min−1, nitrogen atmosphere
Paper 6/07709I; Received 13th November, 1996
592
J. Mater. Chem., 1997, 7(4), 589–592