Synthesis, characterization and gas transport properties of cardo bis(phenylphenyl)fluorene based semifluorinated poly(ether amide)s

Article abstract of DOI:10.1039/c4ra00920g

Here we report the synthesis and properties of a series of processable poly(ether amide)s (PAs) having the bis(phenylphenyl)fluorene moiety prepared from a new diamine monomer, 9,9-bis-[3-phenyl-4-{2′-trifluoromethyl- 4′-(4′′-aminophenyl) phenoxy}phenyl]fluorene. Analogous PAs having the bis(phenyl)fluorene moiety have also been prepared from the diamine 9,9-bis-[4-{2′-trifluoromethyl-4′-(4′′-aminophenyl) phenoxy} phenyl]fluorene for comparative purposes. The synthesized PAs exhibited high thermal stability (up to 517°C and 539°C in air and nitrogen respectively, for 10% weight loss), high glass transition temperature (272-299°C) and high tensile strength up to 117 MPa. The optically transparent membranes (λ_cut-off ≥ 368 nm) from these PAs showed high gas permeability in barrer (PCO₂ up to 67.42 and PO ₂ up to 15) and high permselectivity (PCO₂/PCH₄ up to 88.37 and PO₂/PN₂ up to 10.84); especially for the O₂/N₂ gas pair the PAs surpass or touch the present upper boundary limit of 2008 drawn by Robeson. The effect of the bis(phenylphenyl) fluorene moiety and diacid moieties in PAs on the dielectric values, thermal, mechanical, optical and gas transport properties were correlated. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra00920g

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PAPER
Synthesis, characterization and gas transport
properties of cardo bis(phenylphenyl)fluorene
based semifluorinated poly(ether amide)s
Cite this: RSC Adv., 2014, 4, 28078
*
Parthasarathi Bandyopadhyay, Debaditya Bera, Sipra Ghosh and Susanta Banerjee
Here we report the synthesis and properties of a series of processable poly(ether amide)s (PAs) having the
bis(phenylphenyl)fluorene moiety prepared from a new diamine monomer, 9,9-bis-[3-phenyl-4-{20-
trifluoromethyl-40-(400-aminophenyl) phenoxy}phenyl]fluorene. Analogous PAs having the bis(phenyl)-
fluorene moiety have also been prepared from the diamine 9,9-bis-[4-{20-trifluoromethyl-40-(400-
aminophenyl) phenoxy} phenyl]fluorene for comparative purposes. The synthesized PAs exhibited high
thermal stability (up to 517 ꢀC and 539 ꢀC in air and nitrogen respectively, for 10% weight loss), high glass
transition temperature (272–299 ꢀC) and high tensile strength up to 117 MPa. The optically transparent
membranes (lcut-off $ 368 nm) from these PAs showed high gas permeability in barrer (PCO up to 67.42
2
Received 1st February 2014
Accepted 14th June 2014
and PO up to 15) and high permselectivity (PCO /PCH up to 88.37 and PO /PN up to 10.84); especially for
2
2
4
2
2
the O2/N2 gas pair the PAs surpass or touch the present upper boundary limit of 2008 drawn by
Robeson. The effect of the bis(phenylphenyl)fluorene moiety and diacid moieties in PAs on the dielectric
values, thermal, mechanical, optical and gas transport properties were correlated.
DOI: 10.1039/c4ra00920g
www.rsc.org/advances
separation membranes have been used for the capture of
carbon dioxide from power plant ue gases.6,7
1. Introduction
Till now, many polymers have been considered as potential
membrane materials but actually few of them found real appli-
cation in industrial scale.7 The suitable gas separation
membranes for industrial gas separating plants should have
sufficiently good mechanical and lm-forming properties, with a
good chemical and thermal stability under the conditions of the
separation process.6 The membrane should have sufficient
resistance to plasticization and absence of aging i.e., reduction of
permeability with respect to time.6 In gas separation application,
a tradeoff generally exists between permeability and permse-
lectivity i.e., any improvement in permeability accompanied with
a decrease of permselectivity, and vice versa.8 Therefore, the
primary aim is to improve gas permeation by overcoming the
“tradeoff” behavior between permeability and permselectivity of
polymers. Gas permeation through polymer membrane proceeds
by solution diffusion mechanism.9 In this process gas molecules
get absorbed on the polymeric surface aer that move through
the polymeric membrane by jumping through the adjacent holes
(FFV i.e., fractional free volume) in the polymer due to disruption
of the interchain packing. The jump occurs by the transient
opening of the leap channels of effective size.
Amorphous polyamides have several applications in the area of
membrane based gas separation, coatings, engineering plastics,
polymer blends, and composites. Aromatic polyamides (high
Tg) can be utilized as promising membrane materials in the gas
permeation eld because of their excellent thermal, mechanical
and solvent resistance properties.1–4 There is enormous possi-
bility of preparing a large variety of polyamide structures by
suitably designing the diacids or diamine monomers.1–4
However, rigidity of their backbone and interchain hydrogen
bonding between polymer repeat unit structures result in very
poor processability, high soening temperatures and low gas
permeability.1–4 Hence, the major challenge is to synthesize
processable PAs without affecting their excellent properties and
to improve the permeability and permselectivity. Over the past
two decades, membrane based gas separation is an economi-
cally and environmentally attractive alternative to the cryogenic
or pressure swing adsorption processes.5 The membrane based
gas separation processes have gained wide acceptance due to
carbon dioxide capture and separation, natural gas purication,
and separation of CO2/N2 and produce N2 from air.2,3,5 At
present, global warming has been identied as one of the
world's major environmental worry. Capture of CO2 especially
attained a great importance because of the environmental
protection i.e., global warming.6,7 Recently, polymeric gas
Therefore, the polymer chain mobility (rigidity), inter-chain
distance and FFV are the important factors in determining gas
transport properties in the solution–diffusion mechanism for
the glassy polymers.8 The chain rigidity increases the permse-
lectivity and lowers the permeability. The greater interchain
distance between polymer repeat unit structures imparts higher
Material Science Centre, Indian Institute of Technology, Kharagpur – 721302, India.
E-mail: susanta@matsc.iitkgp.ernet.in; Fax: +91 3222 255303; Tel: +91 3222 283972
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permeability but lower permselectivity.8 Therefore; chain stiff- using CDCl3 (deuterated chloroform) or DMSO-d6 (deuterated
ness should be coupled with an increase in interchain separa- dimethyl sulfoxide) or pyridine-d5 (deutered pyridine) as
tion in order to get simultaneously higher permeability and solvents. FTIR spectra of the polymer membranes were recorded
permselectivity.8 The cardo group, bulky pendant groups, kinks with a NEXUS Nicolet Impact-410 spectrophotometer. Gel
and bends in the polymeric structures inhibit the close packing, permeation chromatography (GPC) was done with a Waters
leading to higher fractional free volume (FFV) which, in turn, instrument (Waters 2414). Tetrahydrofuran (THF) was used as
improve the processability and gas permeability.1–5,10,11
eluent (ow rate 0.5 mL minꢁ1, polystyrene was used as stan-
New classes of partially uorinated polymers are of special dard and RI detector was used to record the signal) and Styragel
interest because of their possible use as gas permeation HR-4 columns were employed. NETZSCH DSC 200PC differen-
membranes and their enhanced ame resistance, low dielectric tial scanning calorimeter (DSC) was used (heating rate of 20 ꢀC
constant, and remarkably low water absorption values.10–12 minꢁ1) to measure the glass transition temperature of the
Peruorinated polymeric membranes showed low tendency of polymers in nitrogen. Glass transition temperatures (Tg) were
plasticization in the presence of hydrocarbon vapors, common taken at the midpoint of the step transition in the second
impurities in gas mixtures in gas permeation study.6 The tri- heating run. Thermal decomposition behavior of these poly-
uoromethyl groups (–CF3) in the polymer backbone improve mers was investigated using a NETZSCH TG 209 F1 instrument
ꢁ1
ꢀ
the polymer solubility which is known as uorine effect without at a heating rate of 10 C min under synthetic air (N2–O2 is
penalty of thermal stability.12 The bulky –CF3 group also serves 80 : 20) and nitrogen. Tensile strength and elongation at break
to increase the free volume and rigidity of the polymer, thereby of the thin polyamide membranes were measured with the help
improving gas permeabilities and permselectivity values of UTM-INSTRON, PLUS, Model no. 8800. Test samples with
simultaneously.12
dimension of 10 ꢂ 25 mm2 and a thickness around 80–85 mm
The bis(phenyl)uorene-based cardo polymers have a struc- were used for the measurement of tensile strength and
ture in which a bulky uorene moiety projects vertically from the percentage of elongation at break. Tests were done using a cross-
polymer main chain.5 The four phenyl rings connected to a head speed of 5% minꢁ1 of the specimen length. Ultra violet
quaternary carbon centre in cardo bis(phenyl)uorene moiety spectra of the polymer lms were recorded at room temperature
experience severe rotational hindrance. Therefore, the cardo using detector SD-2000 (Ocean Optics Inc.) and source lamp DH-
moiety must reduce the packing as well as increase the rigidity 2000. The dielectric constant values of the polyamide lms were
of main chains which, in turn, improve the gas permeability and determined by the parallel plate capacitor method with HIOKI
permselectivity values.5,11 In recent years, polymers containing 3532-50 LCR Hi Tester at 1 MHz at a temperature of 30 ꢀC and a
uorene moieties have been extensively studied because of their relative humidity of 45. Wide angle X-ray diffractograms were
potential applications as photoelectronic materials and show recorded by Rigaku, Ultema III X-ray diffractometer using a Cu
high thermal stability, enhanced solubility, low refractive index, Ka (0.154 nm) source. The Cu Ka source operated at 40 kV and 40
high optical transparency with low dielectric constant.5,11,13–15
mA and the range of 2 theta for XRD measurement was 10–40ꢀ.
Bis(phenylphenyl)uorene based polymers are expected to be The densities of the membranes were measured using a Wallace
highly sterically hindered due to two additional pendant phenyl High Precision Densimeter-X22B (UK) (isooctane displacement)
rings in comparison to the analogous bis(phenyl)uorene based at 30 ꢀC. The gas transport properties of the PA membranes were
ꢀ
polymers. Therefore, the study of gas separation properties for studied at 3.5 bar of applied gas pressure and at 35 C using
such analogous polymers having bis(phenylphenyl)uorene and automated Diffusion Permeameter (DP-100-A) manufactured by
bis(phenyl)uorene moieties and comparison of their properties Porous Materials Inc., USA. Ultrahigh pure (99.99%) gases
will be interesting. Therefore in continuation of our investiga- (methane, nitrogen, oxygen, and carbon dioxide) from BOC
tion on new polymeric membranes for superior gas separation Gases, India, were used for the permeation study. The perme-
performance, in the present investigation we would like to ability coefficient, ideal perm selectivity (a), diffusion coefficient
report the synthesis, characterization and gas transport study of (D), ideal diffusivity selectivity (aD), solubility coefficient (S), and
a series of new poly(ether amide) (PA) membranes containing ideal solubility selectivity (aS) were determined according to
bis(phenylphenyl)uorene moiety. Besides, this work focused to reported procedure.3,10 The reproducibility of the measurements
understand the relationship between the structural variations in was checked from three independent measurements using the
the repeat unit of the PAs and their physical properties and gas same membrane and it was better than ꢃ5%.
permeability/selectivity. Finally, the gas transport properties of
these polyamides have been compared with structurally
analogues polymers having bis(phenyluorene) moiety.
2.2. Starting materials
9-Fluorenone, 3-mercaptopropionic acid, 2-phenylphenol, 4,40-
(hexauoroisopropylidene)bis(benzoic acid), 5-tert-butyl-iso-
phthalic acid, isophthalic acid, terephthalic acid, naphthalene-
2,6-dicarboxylic acid and tetrakis (triphenyl phosphine) palla-
2. Experimental
2.1. Equipments
Carbon, hydrogen and nitrogen content of the compounds were dium(0) (99%) were purchased from Sigma Aldrich (USA) and
determined by pyrolysis method by Vario EL elemental analyzer. triphenyl phosphite (TPP), (DMAc), sulfuric acid (96%), were
1H-NMR and proton decoupled 13C-NMR spectra were recorded purchased from E. Merck, India and were used as received.
on a Bruker 200, 400 and 600 MHz instrument (Switzerland) 1-Methyl-2-pyrrolidinone (NMP) (E. Merck, India) was puried
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by stirring with NaOH and distilled from P2O5 prior to use. (symmetric and asymmetric NO2 stretch) 1138 (C–F), 1048
Toluene (E. Merck, India) was dried by reuxing over sodium (symmetric COC), 899 (CN stretch for aromatic NO2), 825
1
metal. Pyridine (E. Merck, India) was puried by stirring with (aromatic CH bend out of plane). H-NMR: dH(ppm) (200 MHz;
NaOH and distilled under reduced pressure. CaCl2 (E. Merck, CDCl3; Me4Si): 8.28 (d, J ¼ 8.6 Hz, 4H, H1), 7.85–7.81 (m, 4H, H4,
India) and anhydrous K2CO3 (E. Merck, India) were dried for H15), 7.65–7.54 (m, 6H, H2, H3), 7.47–7.37 (m, 8H, H12, H14, H9),
12 h at 120 ꢀC prior to use. Methanol (Rankem, India) was used 7.33–7.27 (m, 12H, H7, H8, H13, H10, H11), 6.98 (d, J ¼ 8.6 Hz, 2H,
for precipitation of polymers. The compound 4-uoro-40-nitro- H6), 6.80 (d, J ¼ 8.6 Hz, 2H, H5).
3-triuoromethyl-biphenyl (3) was prepared according to the
2.3.2. Synthesis of 9,9-bis-[3-phenyl-4-{20-triuoromethyl-
procedure reported earlier.16 The 9,9-bis(4-hydroxy-3-phenyl- 40-(400-aminophenyl) phenoxy}phenyl]uorene (5). The dinitro
phenyl)uorene (2) was synthesized starting from 9-uorenone compounds (4) (10 g, 9.68 mmol), Pd–C (Pd content 1%, 0.35 g),
(1) and 2-phenylphenol, in presence of H2SO4, toluene and 3- and THF (120 mL) were taken in a three-necked 500 mL round
mercaptopropionic acid, according to procedure reported in bottom ask equipped with a stirring bar, dropping funnel and
literature.17
condenser. To this mixture, hydrazine monohydrate (120 mL)
was added dropwise over a period of 1 h at 75 C. The mixture
ꢀ
was heated to reux for 48 h under N2 atmosphere.
The completion of the reaction was monitored by thin layer
chromatography (TLC) and the reaction mixture was ltered at
hot condition to remove catalyst. THF was distilled off from the
reaction mixture by rotary evaporator. Remaining mixture was
poured into 1 L deionised water to precipitate a yellowish solid
product. Precipitate was ltered and washed with deionised
water to remove entrapped hydrazine. The crude product was
dried under vacuum at 60 ꢀC. Pure amine was obtained aer
purication by silica gel column chromatography using
dichloromethane as eluent.
The di(ether amine) ‘5’ monomer was prepared from 9,9-
bis(4-hydroxy-3-phenylphenyl)uorene monomer and depicted
in Scheme 1.
2.3. Monomer synthesis
2.3.1. Synthesis of 9,9-bis-[3-phenyl-4-{20-triuoromethyl-
40-(400-nitrophenyl) phenoxy}phenyl]uorene (4). In a round
bottom ask tted with a Dean–Stark apparatus, a nitrogen
inlet and a magnetic stirrer, 9,9-bis(4-hydroxy-3-phenylphenyl)
uorene monomer (2) (5 g, 9.95 mmol), 4-uoro-40-nitro-3-tri-
uoromethyl-biphenyl (3) (5.67 g, 19.90 mmol), anhydrous
potassium carbonate (K2CO3) (4.12 g, 29.85 mmol) were dis-
solved into a dry solvent mixture of NMP and toluene (1 : 1, v/v,
80 mL each). At rst, the reaction mixture was heated for 4 h at
140 ꢀC followed by heating at 170 ꢀC for another 2 h. Aer
cooling to the room temperature the reaction mixture was
poured slowly into large excess of water. The obtained precipi-
tate was ltered, washed with water for several times and dried
Yield: 7 g (ꢄ74%). Anal. calcd for C63H42F6N2O6 (972.32 g
molꢁ1): C, 77.77%; H, 4.35%; N, 2.88%; found: C, 77.70%; H,
4.40%; N, 2.84%. FTIR (KBr, cmꢁ1): 3469, 3382 (NH stretching),
1621 (aromatic C]C ring stretching), 1480, 1326 (asymmetric
COC), 1240, 1130 (CF), 1052 (symmetric COC), 818 (aromatic CH
bend out of plane). 1H-NMR: dH(ppm) (400 MHz; DMSO-d6;
Me4Si): 7.92 (d, J ¼ 7.2 Hz, 2H, H15), 7.71 (s, 2H, H3), 7.62–7.58
(m, 4H, H4, H12), 7.40–7.33 (m, 6H, H8, H9), 7.29–7.27 (m, 10H,
H10, H11, H13, H14), 7.24–7.23 (m, 6H, H7, H2), 6.97–6.95 (m, 2H,
H6), 6.80 (d, J ¼ 8.4 Hz, 2H, H5), 6.62 (d, J ¼ 8.4 Hz, 4H, H1). 13C-
NMR: dC(ppm) (150 MHz; DMSO-d6; Me4Si): 153.12, 151.67,
150.95, 149.42, 142.71, 140.24, 137.27, 136.42, 133.28, 131.42,
130.74, 129.80, 129.42, 128.94, 128.71, 128.26, 127.85, 126.81,
125.92, 125.06, 124.08, 123.25, 121.44, 120.64, 119.98 (q, J ¼
30 Hz), 119.20, 114.97, 64.79. 19F-NMR: dF(ppm) (376 MHz;
DMSO-d6,; CFCl3): ꢁ61.29 (s).
ꢀ
under vacuum at 80 C for overnight.
2.4. Polymerization and membrane preparation
Yield: 9 g (ꢄ87%). Anal. calcd for C63H38F6N2O6 (1032.98 g The di-amine monomer (5) was polymerized with ve different
molꢁ1): C, 73.25%; H, 3.71%; N, 2.71%; found: C, 73.20%; H, aromatic diacids in molar ratio of 1 : 1 using NMP as solvent
3.76%; N, 2.66%. FTIR (KBr, cmꢁ1): 1606 (aromatic C]C ring in the presence of triphenyl phosphite (TPP), CaCl2 and pyri-
stretching), 1482, 1341 (asymmetric COC), 1517, 1341 dine (Scheme 2). A representative polymerization reaction of
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Scheme 1 Synthesis of the bis(ether amine) monomer, ‘5’.
diamine monomer with 4,40-(hexauoroisopropylidene)bis- traces of solvent and CaCl2. The off-white brous polymer was
ꢀ
(benzoic acid) is as follows:
dried overnight at 80 C in a vacuum oven. The same method
a mixture of diamine (5), 9,9-bis-[3-phenyl-4-{20-triuoro- was used for the preparation of other PAs.
methyl-40-(400-aminophenyl) phenoxy}phenyl]uorene (0.712547
g, 0.73283 mmol), 4,40-(hexauoroisopropylidene)bis(benzoic monomer
The analogous ve PAs were prepared from the diamine
9,9-bis-[4-{20-triuoromethyl-40-(400-aminophenyl)
acid) (0.287453 g, 0.73283 mmol), calcium chloride (0.36 g), phenoxy} phenyl]uorene on reaction with ve different
NMP (5 mL), pyridine (1.4 mL), and TPP (1.4 mL, 5.34 mmol) aromatic dicarboxylic acids by similar phosphorylation reac-
were taken in a 50 mL round bottom ask equipped with reux tion. The PAs prepared from this diamine monomer with 5-tert-
condenser. The mixture was heated with continuous stirring butyl-isophthalic acid, isophthalic acid and terephthalic acid
(using magnetic stirrer) at 110 ꢀC for 6 h under nitrogen respectively were reported earlier.18–20
atmosphere. The reaction mixture became highly viscous
during this period.
The polymeric membranes were prepared by casting 10–15%
(w/v) homogeneous polymer solutions in DMAc solvent onto
The mixture was poured in methanol (500 mL) with constant clean glass Petri dishes according to our previous reported
stirring and obtained a precipitate off white brous polymer. protocol.2,3
The polymer was washed thoroughly with distilled water (hot
The thicknesses of the membranes were between 75–80 mm.
and cold) followed by methanol for complete removal of any The membranes were employed for elemental analyses,
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Scheme 2 Synthesis of the poly(ether amide)s (PA‘A’–‘E’).
solubility tests, density determination, thermal analyses, tensile
tests, X-ray diffraction measurements, gas permeability
measurements and to record the ATR-FTIR and NMR spectra.
The specic density values were used to determine the frac-
tional free volume (FFV) of the polymers for each gas, using
group contribution method developed by Park and Paul.21 The
polymer/membrane properties are reported in Tables 1–3.
2.4.1. Poly(ether amide) ‘A’. Anal. calcd for C75H52F6N2O4
(1159.22 g molꢁ1): C, 77.71%; H, 4.52%; N, 2.42%; found: C,
77.65%; H, 4.46%; N, 2.47%. FTIR (KBr, cmꢁ1): 3305 (NH), 3053,
2965 (aromatic CH), 2965 (aliphatic CH), 1665 (CO), 1234, 1124
2.4.2. Poly(ether amide) ‘B’. Anal. calcd for C80H48F12N2O4
(1329.23 g molꢁ1): C, 72.29%; H, 3.64%; N, 2.11%; found: C,
72.33%; H, 3.70%; N, 2.06%. FTIR (KBr, cmꢁ1): 3304 (NH), 3059,
2923 (aromatic CH), 1667 (CO), 1241, 1134 (CF). 1H-NMR:
dH(ppm) (400 MHz; pyridine-d5; Me4Si): 11.38 (s, 2H, amide
protons), 8.26–8.25 (m, 8H, H1, H16), 8.02–8.00 (m, 2H, H15),
7.97 (s, 2H, H3), 7.91–7.89 (m, 4H, H2), 7.72–7.62 (m, 12H, H4,
H17, H12, H9), 7.55 (d, J ¼ 7.6 Hz, 4H, H8, H14), 7.48–7.40 (m, 4H,
H10), 7.35–7.32 (m, 4H, H13, H11), 7.26–7.24 (m, 4H, H7, H6), 6.96
(d, J ¼ 8.4 Hz, 2H, H5). 19F-NMR: dF(ppm) (376 MHz; pyridine-d5;
CFCl3): ꢁ62.77 (s), ꢁ64.69 (s).
1
(CF). H-NMR: dH(ppm) (400 MHz; pyridine-d5; Me4Si): 11.48 (s,
2.4.3. Poly(ether amide) ‘C’. Anal. calcd for C71H44F6N2O4
(1103.11 g molꢁ1): C, 77.31%; H, 4.02%; N, 2.54%; found: C,
77.26%; H, 4.07%; N, 2.60%. FTIR (KBr, cmꢁ1): 3304 (NH), 3060,
2923 (aromatic C–H), 1662 (CO), 1234, 1123 (CF). 1H-NMR:
dH(ppm) (400 MHz; pyridine-d5; Me4Si): 11.30 (s, 2H, amide
protons), 9.11 (s, 1H, H16), 8.37 (d, J ¼ 7.2 Hz, 2H, H17), 8.23 (d,
J ¼ 8 Hz, 4H, H1), 8.01 (d, J ¼ 7.2 Hz, 2H, H15), 7.96 (s, 2H, H3),
7.89 (m, 4H, H2), 7.71 (d, J ¼ 7.6 Hz, 4H, H4, H12), 7.68–7.62
2H, amide protons), 9.03 (s, 1H, H16), 8.45 (s, 2H, H17), 8.27 (d, J
¼ 8.4 Hz, 4H, H1), 8.01 (d, J ¼ 8 Hz, 2H, H15), 7.95 (s, 2H, H3),
7.90–7.88 (m, 4H, H2), 7.71–7.59 (m, 12H, H4, H14, H8, H9, H12),
7.45–7.41 (m, 4H, H10), 7.35–7.31 (m, 4H, H13, H11), 7.25 (m, 4H,
H7, H6), 6.96 (d, J ¼ 8.4 Hz, 2H, H5), 1.14 (s, 9H, H18). 19F-NMR:
dF(ppm) (376 MHz; pyridine-d5; CFCl3): ꢁ62.88 (s).
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(m, 6H, H9, H14), 7.48–7.42 (m, 6H, H10, H13), 7.35–7.32 (m, 5H, (m, 4H, H10), 7.37–7.33 (m, 4H, H8, H13), 7.27–7.25 (m, 6H, H11,
H8, H11, H18), 7.26–7.24 (m, 4H, H6, H7), 6.97 (d, J ¼ 8.4 Hz, 2H, H6, H7), 6.99 (d, J ¼ 7.6 Hz, 2H, H5). 19F-NMR: dF(ppm) (376 MHz;
H5). 19F-NMR: dF(ppm) (376 MHz; pyridine-d5; CFCl3): ꢁ62.69 (s). pyridine-d5; CFCl3): ꢁ62.88 (s).
2.4.4. Poly(ether amide) ‘D’. Anal. calcd for C71H44F6N2O4
2.4.6. Poly(ether amide) ‘B0’. Anal. calcd for C68H40F12N2O4
(1103.11 g molꢁ1): C, 77.31%; H, 4.02%; N, 2.54%; found: C, (1177.04 g molꢁ1): C, 69.39%; H, 3.43%; N, 2.38%; found: C,
77.36%; H, 3.99%; N, 2.50%. FTIR (KBr, cmꢁ1): 3288 (NH), 2921, 69.34%; H, 3.48%; N, 2.34%. FTIR (KBr, cmꢁ1): 3335 (NH), 3039
2851 (aromatic CH), 1659 (CO), 1233, 1123 (CF). 1H-NMR: (aromatic CH), 1670 (CO), 1237, 1124 (CF). 1H-NMR: dH(ppm) (400
dH(ppm) (400 MHz; pyridine-d5; Me4Si): 11.33 (s, 2H, amide MHz; DMSO-d6; Me4Si): 10.57 (s, 2H, amide protons), 8.08 (d, J ¼
protons), 8.38 (s, 4H, H16), 8.23 (d, J ¼ 8.8 Hz, 4H, H1), 8.01 (d, J 8.6 Hz, 4H, H12), 7.98–7.89 (m, 10H, H1, H3, H4, H11), 7.72 (d, 4H,
¼ 7.2 Hz, 2H, H15), 7.95 (s, 2H, H3), 7.91–7.89 (m, 4H, H2), 7.70 J ¼ 8.2 Hz, H2), 7.57–7.49 (m, 6H, H8, H13), 7.44–7.36 (m, 4H, H9,
(d, J ¼ 8 Hz, 6H, H4, H12, H14), 7.64 (d, J ¼ 8.8 Hz, 6H, H9, H8), H10), 7.24–7.20 (m, 4H, H7), 7.13–7.01 (m, 6H, H5, H6). 19F-NMR:
7.45–7.41 (m, 4H, H10), 7.35–7.31 (m, 4H, H11, H13), 7.26–7.22 dF(ppm) (376 MHz; DMSO-d6,; CFCl3): ꢁ62.83 (s), ꢁ64.76 (s).
(m, 4H, H6, H7), 6.95 (d, J ¼ 8 Hz, 2H, H5). 19F-NMR: dF(ppm) (376
MHz; pyridine-d5; CFCl3): ꢁ62. 49 (s).
2.4.7. Poly(ether amide) ‘E0’. Anal. calcd for C63H38F6N2O4
(1000.98 g molꢁ1): C, 75.59%; H, 3.83%; N, 2.80%; found: C,
2.4.5. Poly(ether amide) ‘E’. Anal. calcd for C71H44F6N2O4 75.54%; H, 3.79%; N, 2.85%. FTIR (KBr, cmꢁ1): 3334 (NH), 3037
(1153.17 g molꢁ1): C, 78.12%; H, 4.02%; N, 2.43%; found: C, (aromatic CH), 1654 (CO), 1234, 1124 (CF). 1H-NMR: dH(ppm)
78.07%; H, 4.07%; N, 2.48%. FTIR (KBr, cmꢁ1): 3302 (NH), 3059, (400 MHz; pyridine-d5; Me4Si): 11.44 (s, 2H, amide protons),
2922 (aromatic CH), 1659 (CO), 1233, 1123 (CF). 1H-NMR: 8.82 (s, 2H, H12), 8.42–8.36 (m, 6H, H1, H13), 8.09 (s, 2H, H3),
dH(ppm) (400 MHz; pyridine-d5; Me4Si): 11.39 (s, 2H, amide 8.00–7.96 (m, 4H, H11, H14), 7.80–7.78 (m, 6H, H2, H4), 7.69 (d,
protons), 8.79 (s, 2H, H16), 8.39 (d, J ¼ 7.6 Hz, 2H, H17), 8.32 (d, J ¼ 7.6 Hz, 2H, H8), 7.51–7.41 (m, 8H, H7, H9, H10), 7.19–7.10 (m,
J ¼ 7.2 Hz, 4H, H1), 8.03–7.97 (m, 6H, H3, H15, H18), 7.92–7.90 6H, H6, H5). 19F-NMR: dF(ppm) (376 MHz; pyridine-d5; CFCl3):
(m, 4H, H2), 7.73–7.64 (m, 10H, H4, H9, H12, H14), 7.47–7.43 ꢁ62. 55 (s).
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compound (4) was formed by aromatic nucleophilic substitution
reaction between the dihydroxy compound (2) and 4-uoro-40-
nitro-3-triuoromethyl-biphenyl (3).16 Finally, the dinitro
compound was reduced to diamine compound (5) using
hydrazine monohydrate and Pd/C as catalyst and THF as solvent.
The crude diamino compund was puried through silica gel
column chromatography using dichloromethane as eluent.
3. Results and discussion
3.1. Monomer synthesis
The uorinated bis(ether amine) monomer (5) was synthesized
starting from 9-uorenone (1) as shown in Scheme 1. The
compound 9,9-bis(4-hydroxy-3-phenylphenyl)uorene (2) was
prepared from 9-uorenone as reported earlier.17 The dinitro
Table 1 Physical properties of the poly(ether amide)s
Mn (g molꢁ1
)
PDIb
l0 (nm)
UV-transmittanced (%)
Dielectric constant (1 MHz)
dsp (A)
a
c
e
˚
Polymer
PA ‘A’
PA ‘B’
PA ‘C’
PA ‘D’
PA ‘E’
PA ‘A0’
PA ‘B0’
PA ‘C0’
PA ‘D0’
PA ‘E0’
106 000
122 000
102 000
98 500
172 000
80 000
83 700
75 000
78 000
93 850
2.2
2.1
2.5
2.0
2.7
2.8
2.5
2.5
2.7
2.3
371
374
378
399
403
368
381
382
403
407
68
79
64
67
41
68
70
61
62
40
2.41
2.20
2.59
2.55
2.65
2.51
2.40
3.31
2.96
2.80
5.99
6.13
5.89
5.82
5.55
5.95
6.08
5.84
5.58
5.41
a
b
c
d
Number average molecular weight; polystyrene calibration. Polydispersity index. Cut-off wave length. UV-transmittance at 500 nm (%).
dsp: intersegmental distance between the polymer chain obtained from the Bragg equation.
e
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Table 2 Fractional free volumes, N–H group density and observed density of the polymers
Polymer
Densitya
N–H group density (%)
FFV (CH4)
FFV (N2)
FFV (O2)
FFV (CO2)
PA ‘A’
PA ‘B’
PA ‘C’
PA ‘D’
PA ‘E’
PA ‘A0’
PA ‘B0’
PA ‘C0’
PA ‘D0’
PA ‘E0’
1.22
1.17
1.24
1.27
1.29
1.26
1.21
1.27
1.31
1.32
2.59
2.26
2.72
2.72
2.60
2.98
2.55
3.15
3.15
3.85
0.188
0.195
0.164
0.159
0.133
0.179
0.179
0.161
0.153
0.131
0.171
0.190
0.151
0.146
0.125
0.164
0.177
0.150
0.142
0.126
0.176
0.191
0.154
0.149
0.129
0.168
0.177
0.153
0.145
0.130
0.178
0.194
0.159
0.154
0.133
0.167
0.178
0.155
0.147
0.130
a
Density (g cmꢁ3) measured at 30 ꢀC.
appeared at around 166.5 ppm. A representative 13C-NMR
spectrum of PA ‘A’ in pyridine-d5 is shown in Fig. 2.
3.2. Polymer synthesis and their properties
The polyamides having bis(phenylphenyl)uorene moiety (PA
‘A’–‘E’) were synthesized by the polycondensation reaction of
the diamine monomer, 9,9-bis-[3-phenyl-4-{20-triuoromethyl-
40-(400-aminophenyl) phenoxy}phenyl]uorene with ve di-
fferent aromatic diacids. Similarely, the analogous PAs (PA ‘A0’–
‘E0’) having bis(phenyl)uorene moiety were prepared using the
diamine monomer, 9,9-bis-[4-{20-triuoromethyl-40-(400-amino-
phenyl) phenoxy} phenyl]uorene. All polyamides (PA ‘A’–‘E’)
were readily dissolved (10% w/v) at room temperature in NMP,
DMF, DMAc, THF and Pyridine. The rate of dissolution in
different solvents of bis(phenylphenyl)moiety containing PAs
were relatively higher than the analogous bis(phenyl)uorene
moiety containing PAs. This is attributed to the two phenyl
groups which reduce the interchain packing in bis(phenyl-
phenyl) uorene based PAs. Transparent and exible
membranes from these PAs obtained from their DMAc solution.
The chemical structures of the polymer repeat units were
The PAs showed a singlet for quaternary carbon centre in
cardo uorene moiety at around 65.4 ppm. The peaks corre-
sponds to the aliphatic primary (31 ppm) and tertiary(35 ppm)
carbons were found in case of PA ‘A’. All the structural charac-
terization conrmed high conversion of diamine and diacid to
polyamide. High molecular weight of the PAs from the GPC
results (Mn ¼ 98 500–172 000 g molꢁ1) also established the
above fact.
UV-visible spectroscopic studies of the PA ‘A’–‘E’ membranes
indicated high optical transparency (upto 79% at 500 nm) and a
lower cut-off wavelength between 371–403 nm [Table 1]. The
lower cut-off wavelength values and high optiacl transparecy
(except PA ‘E’) values might be due to the bis(phenylphenyl)-
uorene moiety, ether linkages and bulky –CF3 groups in the
diamine moiety which reduce the intermolecular interaction
between the polymer chains.5,22,23 Highest optical transparency
and lower cutoff wavelength (except PA ‘A’) of PA ‘B’ was
attributed to the weak intermolecular cohesive interaction
between polymer chains due to its hexauoroisopropylidene
group (higher uorine loading).22,23 The two phenyl groups in
bis(phenylphenyl)uorene moiety undergo steric hindrance
and disturbed the conjugation along the backbone. Therefore
these polymers showed higher optical transparency and lower
cut-off wavelength than analogous polymers. The dielectric
constant values of the PA ‘A’–‘E’ membranes were measured at 1
1
conrmed by means of elemental analysis, FTIR-ATR, and H-
NMR spectroscopy. FTIR-ATR spectra of the poly(ether amide)s
displayed characteristic absorption bands for amide group in
the range of 3305–3288 cmꢁ1 (N–H stretching) and 1656–1665
cmꢁ1 (carbonyl group stretching). The absence of free amine
absorption peak above 3400 cmꢁ1 supported high conversion of
diamines to polyamides. The results of the elemental analysis
(C, H, and N) of the PAs were in good agreement with polymer
repeat unit structures.
ꢀ
MHz and at a temperature of 30 C with a relative humidity of
The repeat unit structures of the polymers were conrmed by
the 1H-NMR and 13C-NMR spectra. The PAs showed exact
45%. The PAs showed low dielectric constant values [Table 1].
The very low polarizability of C–F bonds of triuoromethyl
group with cardo group resulted in higher fractional free
volume of the polymers. Therefore, the PAs showed low
dielectric constant values.23 The lower dielectric constant values
of PA ‘B’ and PA ‘A’ might be due to the packing disruptive
hexauoroisopropylidene linkage and tert-butyl groups in
comparison to the other polymers. These polymers showed
lower dielectric constant value than the analogous bis (phenyl)
uorene based polymers. The fact is attributed to the higher
fractional free volume of the bis(phenypheny)uorene based
polymers. The dielectric constant values of these polyamides
have been co-related with their gas transport properties [3.3].
1
number of desired H and 13C signals corresponding to their
structures. A representative 1H-NMR spectrum of PA ‘A’ in
pyridine-d5 is shown in Fig. 1. The PAs showed a singlet above at
11 ppm corresponding to the amide proton and all the other
magnetically different protons, their splitting pattern and
relative peak intensities were in accordance to the chemical
structure of the polymers.
In proton decoupled 13C-NMR spectra the C–F (–CF3)
coupling constant values for each quartet for one bond coupling
(1JC–F) were around 271 Hz and for the two bonds coupling
(2JC–F) were around 31 Hz. The peak (d) for carbonyl carbon
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Table 3 Thermal and Mechanical properties of the poly(ether amide)s
b
ꢀ
Td10
(
C)
In N2
TSc (Mpa)
Modd (GPa)
EBe (%)
5.60
a
ꢀ
–Ar–
–R–
Polymer
Tg
(
C)
In air
PA ‘A’
274
477
517
83
2.02
Do
Do
PA ‘B’
PA ‘C’
274
272
505
505
520
527
90
79
2.12
1.74
6.0
6.0
Do
Do
PA ‘D’
PA ‘E’
273
278
517
506
536
539
103
107
2.29
2.34
8.6
7.4
PA ‘A0’
PA ‘B0’
273f
297
448f
497
481
522
69f
92
1.30f
1.74
9.0f
Do
11.0
Do
Do
PA ‘C0’
PA‘D0’
285g
294h
465g
477h
437
440
71g
99h
1.8g
2.2h
10g
12.9h
Do
PA ‘E0’
299
468
442
117
2.2
11.0
a
b
Glass transition temperature determined by DSC, heating rate at 20 ꢀC minꢁ1
.
10% degradation temperature measured by TGA under air and
nitrogen, heating rate at 10 ꢀC minꢁ1
.
Tensile strength. d Young's modulus. e Percent of elongation at break. f Values taken from ref. 18. g Values
c
taken from ref. 19. h Values taken from ref. 20.
Fig. 3 shows WAXD patterns of the polymers (PA ‘A’–‘E’). The show a clear shoulder on the high-angle side for all the PAs at
broad peaks indicating the amorphous nature of the polymers. similar 2 theta value. The shoulder peak at the larger 2 theta
The amorphous nature is due to the bulky cardo uorene value might be due to the stacking of the aromatic connector
moiety and triuoro methyl groups which restrict their inter- group in adjacent polymer chains.5 The peak (halo maxima)
chain interaction and free rotation of their molecular struc- observed at lower 2 theta (higher dsp) might be due to loose
tures.2,3,5 Two broad peaks in WAXD patterns have been stacking in polymer matrices exhibited by the enlarging effect
reported earlier for cardo polyamides, polyimides, poly- cardo bis(phenylphenyl)uorene moiety.5 It is known that the
carbonates and Polyarylates.2,5,24 The WAXS patterns of PAs position of the halo maximum can be considered as an
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Fig. 1 1H-NMR spectrum of PA ‘A’ in pyridine-d5 (* signals at 8.74, 7.59, and 7.22 ppm are for pyridine).
indicator of the most probable intersegmental distance (dsp) FFV.5 In general, the bis(phenylphenyl)uorene based PAs
between the chains, as calculated from Bragg equation. The showed lower density, higher FFV and dsp in comparison to
decreasing order of dsp values at peak corresponding to lower 2q their analogous PAs [Table 2].
value follows the order as PA ‘B’ > PA ‘A’ > PA ‘C’ > PA ‘D’ > PA ‘E’
Two phenyl groups reduces the H-bonding and it is evident
[Table 1]. Introduction of packing disruptive groups –C(CF3)2 from their N–H group density25 values in comparison to the
(PA ‘B’) and –CMe3 (PA ‘A’) in acid containing moiety of these analogous bis(phenyl)uorene based PAs [Table 2]. It is evident
two PAs increases the dsp than the other unsubstituted analogs that the openness of the polymer matrix is likely to increase due
(PA ‘C’, PA ‘D’ and PA ‘E’).23–25
to the reduced intermolecular hydrogen-bonding.
The lower dsp values of PA ‘D’ and PA ‘E’ might be attributed
The TGA thermograms for the polymers are shown in Fig. 4A
to the more symmetric nature and ordered structures of their and B under air and nitrogen respectively. TGA thermograms
backbones. The dsp value can be used as a measure of openness indicated that all the PAs in the series have high thermal
of the polymer chains and it is evident from Tables 1 and 2 that stability with 10% weight loss in the range of 477–517 ꢀC under
the decreasing order of FFV is nicely matching with decreasing air and 517–539 ꢀC under nitrogen [Table 3]. The least thermal
order d-spacing for all the polymers. The PA ‘B’ (hexa- stability of PA ‘A’ compared to the other PAs in the series is due
uoroisopropylidene group) has higher FFV than PA ‘A’ (–CMe3 to presence of easily oxidizable pendant tert-butyl groups.25
group) although both of them have bulky substituent. The
The PA ‘B’ also showed 10% weight loss at lower temperature
above observation attributed to the hexauoroisopropylidene compared to other polymers in these series except PA ‘A’. The
group is more effective to increase the FFV than tert-butyl added exibility in PA ‘B’ at hexauoroisopropylidene group
group.25 The more triuoromethyl groups in PA ‘B’ are more might be responsible for lower degradation temperature at 10%
effective to reduce cohesive energy density and increase the weight loss. The analogous PAs with bis(phenyl)uorene moiety
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Fig. 2 13C-NMR spectrum of PA ‘A’ in pyridine-d5 (* signals at 150.2, 135.8, and 123.7 ppm are for pyridine).
Fig.
3 Wide-angle X-ray diffraction plots of poly(ether amide)
membranes.
showed lower thermal stability than these PAs (except PA ‘B’ vs.
PA ‘B0’). The above observation might be due to the presence of
two thermally stable phenyl groups in bis(phenylphenyl)uo-
rene moiety. PA ‘C0’ PA ‘D0’ and PA ‘E0’ showed higher thermal
stability in air than in nitrogen. Similar observation also found
for PAs in some earlier publications.26,27 It is interesting to note
that all the PA ‘A’–‘E’ showed almost same Tg values (274–278
ꢀC) and there was no indication of melting or crystallization
temperature up to 350 ꢀC in DSC plots (Fig. 5).
Therefore, the acidic counter part of the PAs have no
signicant role in manipulating the Tg values of the polymers
due to the extreme bulky nature of the diamine moiety. In
Fig. 4 TGA thermograms of the poly(ether amide)s under (A) air and
(B) under nitrogen atmosphere (heating rate 10 ꢀC minꢁ1).
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3.3. Gas transport properties
3.3.1. Effect of chemical structures on gas transport prop-
erties of bis(phenylpheyl)uorene based PAs. Gas permeability
coefficients and permselectivity values of the PAs are depicted
in Table 4. The diffusion coefficient, solubility coefficient,
solubility and diffusivity selectivity values have been presented
in Table 5. The gas permeability of four different gases through
these PA membranes follow the order as P(CO2) > P(O2) > P(N2) >
P(CH4); which is typically in the reversed order of their respec-
˚
˚
˚
tive kinetic diameter, CO2 (3.3 A) < O2 (3.46 A) < N2 (3.64 A) <
˚
CH4 (3.8 A). The order of gas permeability coefficients of the PAs
follows the order as PA ‘B’ > PA ‘A’ > PA ‘C’ > PA ‘D’> PA ‘E’.
Fig. 5 DSC curves of the poly(ether amide)s (heating rate: 20 ꢀC
minꢁ1).
comparison to the analogous poly(ether amide)s, surprisingly
these polymers showed lower Tg value (except PA ‘A’ vs. PA ‘A0’).
The two substituted pendant phenyl groups in bis(phenyl-
phenyl)uorene moiety containing PAs reduce N–H group
density (H-bonding) and thus favour slight polymer chain
motion. Therefore two phenyl groups increase the space
between polymer chains as it is evident from their higher FFV
values (less cohesive energy density) which resulted in lower Tg
compared to the analogous PAs. Wang et al. also reported
similar observation for alkyl-substituted cardo poly(aryl ether
sulfone)s with unsubstituted analog.28
The PA ‘A’–‘E’ membranes showed tensile strengths of 83–
107 MPa, elongations at break of 5.6–8.6% and Young's
modulus of 1.74–2.34 Gpa [Table 3]. The highest tensile
strength and modulus of PA ‘E’ is attributed to the rigid
naphthalene moiety (fused). These PAs showed lower elonga-
tion at break in comparison to the analogoues PAs. The differ-
ence is attributed to the steric hindrance of the two pendant
phenyl rings in bis(phenylphenyl)uorene moiety.
The order of fractional free volume of the polymers for all the
gases are PA ‘B’ > PA ‘A’ > PA ‘C’ > PA ‘D’ > PA ‘E’. The decreasing
order of permeability coefficients of the different gases through
these PA membranes is nicely matching with their decreasing
order of FFV values of different gases through these polymers.
The above decreasing trend of permeability also nicely matches
with their decreasing order of dsp [Table 1]. The relation
between gas permeability and FFV can be described by the
following equation:
P ¼ Ae(ꢁB/FFV)
where, A and B depend on temperature and gas type.29,30 For
amorphous polymers, the logarithm of permeability decreases
about linearly with increasing reciprocal fractional free
Table 4 Gas permeability coefficients (P) measured at 35 ꢀC (3.5 bar) and permselectivities (a) values of the synthesized poly(ether amide)s and
their comparison with other reported polymers
Polymer
P (CO2)
P (O2)
P (N2)
P (CH4)
a (CO2/CH4)
a (O2/N2)
a (CO2/N2)
a (CO2/O2)
Reference
PA ‘A’
PA ‘B’
PA ‘C’
PA ‘D’
PA ‘E’
PA ‘A0’
PA ‘B0’
PA ‘C0’
PA ‘D0’
PA ‘E0’
FBP/TBIAa
FBP/IAa
3gb
60.32
67.42
40.38
38.00
32.00
52.00
60.23
21.53
19.76
15.92
36.80
12.40
35.30
31.20
13.55
15.00
9.05
7.37
6.22
12.15
12.92
5.70
4.93
4.18
9.55
3.03
7.35
7.23
1.25
1.70
1.11
0.80
0.69
1.19
1.46
0.70
0.59
0.51
2.37
0.62
1.36
1.30
1.00
1.33
0.93
0.43
0.40
0.86
1.28
0.50
0.32
0.29
1.93
0.57
0.91
0.90
60.32
50.69
43.42
88.37
80.00
60.47
47.05
43.06
61.75
54.90
15.50
20.10
39
10.84
8.82
8.15
9.21
9.01
10.21
8.85
8.14
8.36
8.20
4.95
5.32
5.40
5.50
48.26
39.66
36.38
47.50
46.38
43.70
41.25
30.76
33.49
31.22
15.53
20
4.45
4.49
4.46
5.16
5.14
4.28
4.66
3.78
4.01
3.81
3.85
4.09
4.80
4.32
From this study
Do
Do
Do
Do
Do
Do
Do
Do
Do
29
29
1
26
24
3hb
35
1
a
b
Gas permeability coefficient (P) values taken from ref. 29. Gas permeability coefficient (P) values taken from ref. 1. P ¼ gas permeability
coefficient in barrer. 1 barrer ¼ 10ꢁ10 cm3 (STP) cm cmꢁ2 sꢁ1 cm Hg.
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Table 5 Gas diffusion coefficients (D) expressed in 10ꢁ8 cm2
s
ꢁ1, solubility coefficients (S) in 10ꢁ2 cm3 (STP) cmꢁ3 cm Hg, diffusivity selectivity
(aD) and solubility selectivity (aS) values of the poly(ether amide)s at 35 ꢀC and 3.5 bar
CO2
O2
N2
CH4
(CO2/CH4)
(O2/N2)
Polymer
D
S
D
S
D
S
D
S
aD
aS
aD
aS
PA ‘A’
PA ‘B’
PA ‘C’
PA ‘D’
PA ‘E’
PA ‘A0’
PA ‘B0’
PA ‘C0’
PA ‘D0’
PA ‘E0’
5.17
9.38
4.28
3.08
2.71
4.40
5.54
2.51
2.00
1.80
11.67
7.19
9.43
12.34
11.81
11.81
10.87
8.58
9.49
1.43
1.26
1.44
1.50
1.58
2.28
2.23
1.81
1.97
2.22
1.95
2.77
1.95
1.34
1.21
1.45
1.55
1.29
1.24
1.17
0.64
0.61
0.57
0.60
0.57
0.82
0.94
0.54
0.48
0.44
1.82
2.02
1.77
1.75
1.20
1.33
1.37
1.26
1.18
1.08
0.55
0.66
0.53
0.25
0.33
0.65
0.93
0.40
0.27
0.27
2.84
4.64
2.42
1.76
2.26
3.31
4.04
1.99
1.69
1.67
21.22
10.89
17.79
49.36
35.79
18.17
11.69
21.45
36.59
32.74
4.87
4.29
3.23
3.68
3.26
3.68
3.74
2.44
2.02
1.61
2.23
2.07
2.41
2.50
2.77
2.78
2.37
3.35
4.10
5.05
11.89
6.30
4.93
3.94
5.34
5.80
3.15
2.5
9.88
8.84
1.88
volume.31 Fig. 6 depicts the relationship between logarithm of gas permeability values for the different gases for PA ‘B’ were in
permeability coefficient values and reciprocal fractional free accordance with its highest FFV and dsp values compared to all
volume for the PA ‘A’–‘E’ for the four different gases.
the other PAs. The difference in the gas permeability coefficient
The diffusion coefficients decrease in the order D(O2) > values of the polymers mainly comes from diffusivity coefficient
D(CO2) > D(N2) > D(CH4) [Table 5]. For gases like O2, N2, and values, rather than the solubility coefficient values of
CH4; the gas diffusivity values decrease with the increase of gas these polymers. Generally, the introduction of hexauoroi-
molecule size.28 The diffusivity coefficient value of CO2 was sopropylidene group increases gas diffusivity.5 PA ‘A’ and PA ‘B’
smaller than that of O2 although CO2 has smaller kinetic showed higher diffusion coefficient values than the less
diameter than O2.
permeable other three polymers. The incorporation of tert-butyl
The quadrupolar interaction of CO2 with the amide linkages group (PA ‘A’) and hexauoroisopropylidene linkage (PA ‘B’) in
in the PA backbone reduces its diffusivity coefficient value. acid containing part increases the diffusivity, FFV as well as
˚
Further, CO2 molecule has a “kinetic diameter” of 3.3 A and its permeability coefficient values compared to the other PAs. The
˚
collision diameter of 3.94 A. Thus, CO2 molecule might have a higher permeability coefficient values PA ‘A’ and PA ‘B’ are
larger effective size than O2 and as a result D(O2) > D(CO2).32
attributed to the reduction in chain packing density (H-
The decreasing order diffusivity coefficient values of the bonding) as observed from their higher d-spacing and FFV and
different gases through these PA membranes is PA ‘B’ > PA ‘A’ > lower N–H group density values [Table 2]. PA ‘B’ (hexa-
PA ‘C’ > PA ‘D’ > PA ‘E’. The above order actually relates with the uoroisopropylidene group) exhibited higher permeability and
openness of the polymeric materials as similar decreasing order lower selectivity for different gas pairs than PA ‘A’ (tert-butyl
also observed for dsp and FFV values for the PAs.
group). Hexauoroisopropylidene linkage brings an additional
The apparent diffusion coefficients can be governed by the exibility at the bridged carbon centre of the acidic counterpart
FFV and the free volume size distribution and polymer chain of PA ‘B’. Therefore this PA is comparatively non-selective for
mobility.5 X-ray patterns suggest the difference of the free the size based separation of the penetrant molecules as well as
volume distribution among the cardo polymers.5 The highest higher –CF3 content in PA ‘B’ compared to the other PAs
increases the permeability coefficient for all the gases in a large
extent rendering this PA little lower selective. S. C. Kumbharkar
et al. also reported lower permselectivity values of poly-
benzimidazoles based on 4,40-(hexauoroisopropylidene)bis-
(benzoic acid) compared to the 5-tert-butyl-isophthalic acid for
CO2/CH4 and O2/N2 gas pairs.25 The PA ‘C’ showed higher
permeability than PA ‘D’. The above observation was attributed
to the more symmetrical terephthalic acid connector group has
high chain packing density as it is observed from its lower FFV
and dsp values. Similar results were also found in our previous
publications.2,3,33 PA ‘E’ exhibited very low permeability for all
the gases due to its higher chain packing density as it is
observed from its lowest dsp and lowest FFV [Tables 1 and 2]
values. It was in accordance with our previous publication that
the compact and rigid naphthalene connector group reduces
the permeability.2,33 Ding et al. also observed the lower perme-
ability values for naphthalene acid containing PAs.1 The PA ‘D’
Fig. 6 Correlation of permeability coefficient (P in cm3 (STP) cm cmꢁ2
sꢁ1 cm Hg.) with fractional free volume.
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and PA ‘E’ exhibited higher permselectivity values for CO2/CH4
gas pair. The above observation attributed to their more
compact structure and these polymers might provide smaller
average size free volume elements which are suitable for the
diffusion of smaller gas molecules than larger gas molecules.
CO2 showed higher solubility coefficient because of its high
critical temperature and it induces some sort of interaction with
the carbonyl or amide linkage of the polyamides.2,3 The higher
permeability of CO2 for individual polymers resulted from its
higher solubility coefficient value. The order of permselectivity
for CO2/CH4 gas pair follows as PA ‘D’ > PA ‘E’ > PA ‘A’ > PA ‘B’ >
PA ‘C’ and for O2/N2 is PA ‘A’ > PA ‘D’ > PA ‘E’ > PA ‘B’ > PA ‘C’.
According to the “solution–diffusion” mechanism, gas
permeability solely depends on gas diffusivity coefficient (D)
and solubility coefficient (s). Hence, the contribution of both
the terms should be considered for individual gases in order
to understand the changes in permeability and permse-
lectivity values of the individual polymers.28 The diffusivity
selectivities of uncondensable gas pairs (O2/N2) in the ve PAs
varied from 3.23 to 4.87, whereas its solubility selectivities
were from 2.07 to 2.77. Therefore, the O2/N2 permselectivity
values might be governed by the diffusivity selectivity values.
Therefore higher permselectivity value for O2/N2 gas pair of PA
‘A’ comes from its higher diffusivity selectivity (4.87) value for
this gas pair and lower permselectivity of PA ‘C’ comes from
its lower diffusivity selectivity value (3.23) for this gas pair.
The gas diffusivity selectivity values of CO2/CH4 gas pair
varied from 1.76 to 4.64 and the solubility selectivities were
from 10.89 to 49.36. Thus, the solubility selectivity values have
an important contribution in CO2/CH4 permselectivity values.
Therefore, the overall permselectivity values for CO2/O2, CO2/
N2 and CO2/CH4 are mainly due to the solubility selectivities
as diffusivity selectivities were comparatively small for
these gas pairs [Table 5]. The higher permselectivity for CO2/
CH4 gas pair of PA ‘D’ comes from its higher solubility
selectivity value for this gas pair. In this scenario PA ‘B’
behave differently.
Fig. 7 The dependence of gas permeability vs. dielectric constant of
all the PA membranes for CO2, O2, N2, and CH4 gases.
respectively. All the PAs under this investigation exhibited
excellent gas separation performance. Particularly, for O2/N2 gas
pairs, their data points exceeded or touched the upper bound
limit drawn by Robeson35 in 2008.
In general, these bis(phenylphenyl)uorene based PAs
showed high permeability with higher selectivity than the
analogous bis(phenyl)uorene based polyamides. The higher
permeabilty coefficient values of the bis(phenylphenyl)uorene
based PAs might be due to the steric hindrance between two
phenyl groups that reduces H-bonding (lower N–H group
density), increases the FFV and dsp values compared to the
bis(phenyl)uorene based polyamides [Table 2]. These results
are consistent with the higher diffusion coefficient values
observed for the PA ‘A’–‘E’ [Table 5]. A. Singh et al. reported that
polymers having phenyl substituent were more permeable than
their unsubstituted analogs to all gases.36 The higher permse-
lectivity values of PA ‘A’–‘E’ for O2/N2 and CO2/CH4 gas pairs
attributed to their higher diffusivity selectivity and solubility
selectivity (except PA ‘B’ vs. PA ‘B0’) values respectively in
comparison to the analogous PA ‘A0’–‘E0’.
The possible reason of extremely high permeability and
selectivity of these new PAs might be due to the increase of
chain rigidity and FFV simultaneously.
The dielectric constant values of the PAs varied from 2.20 to
2.65 in 1 MHz at 30 ꢀC (Table 1). The dielectric constant
depends on free volume and polarity factor.34 Matsumoto et al.
showed a linear relationship between carbon dioxide and
methane permeability coefficient values with dielectric constant
values for several polyimides.34 They concluded that correlation
of dielectric constant with permeability is much more satisfac-
tory than that with fractional free volume. The PAs showed a
linear relationship between permeability coefficient values
for different gases with their dielectric constant values as
shown in Fig. 7.
3.3.2 Comparison of the gas transport properties. The gas
permeability and permselectivity values of the analogous
bis(phenyl)uorene based polyamides, bis(phenyl)uorene
based polyarylates (FBP/TBIA and FBP/IA)29 and phenylindane
based polyamides (3g and 3h)1 have been reported along with
bis(phenylphenyl)uorene based polyamides in Table 4. For a
better comparison, the permselectivity of CO2/CH4 versus CO2
permeability and permselectivity of O2/N2 versus O2 perme-
Fig. 8 Robeson plot35 for a comparison of O2/N2 selectivity vs. O2
permeability coefficients of the PAs under this investigation and some
ability of all these polymers have been plotted in Fig. 8 and 9 other reported polymers.1,29
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References
1 Y. Ding and B. Bikson, Polymer, 2002, 43, 4709.
2 P. Bandyopadhyay, D. Bera, S. Ghosh and S. Banerjee,
J. Membr. Sci., 2013, 417, 413.
3 D. Bera, P. Bandyopadhyay, B. Dasgupta and S. Banerjee,
J. Membr. Sci., 2012, 407–408, 116.
4 J. Espeso, A. E. Lozano, J. G. de la Campa and J. de Abajo,
J. Membr. Sci., 2006, 280, 659.
5 S. Kazama, T. Teramoto and K. Haraya, J. Membr. Sci., 2002,
207, 91.
6 Y. Yampolskii, Macromolecules, 2012, 45, 3298.
7 E. Favre, J. Membr. Sci., 2007, 294, 50.
8 Y. Dai, M. D. Guiver, G. P. Robertson, Y. S. Kang, K. J. Lee and
J. Y. Jho, Macromolecules, 2004, 37, 1403.
Fig. 9 Robeson plot35 for a comparison of CO2/CH4 selectivity vs. CO2
permeability coefficients of the PAs under this investigation and some
other reported polymers.1,29
9 G. Maier, Angew. Chem., Int. Ed., 1998, 37, 2960.
10 S. K. Sen and S. Banerjee, J. Membr. Sci., 2010, 365, 329.
11 B. Dasgupta and S. Banerjee, J. Membr. Sci., 2010, 362, 58.
12 Y. Dai, M. D. Guiver, G. P. Robertson and Y. S. Kang,
Macromolecules, 2005, 38, 9670.
4. Conclusions
A series of organo soluble new polyamides were prepared from
a
new
diamine
monomer,
9,9-bis-[3-phenyl-4-{20-tri-
phenoxy}phenyl]uorene
13 Z. Xu, C. Dannenberg, J. Springer, S. Banerjee and G. Maier,
Chem. Mater., 2002, 14, 3271.
uoromethyl-40-(400-aminophenyl)
14 V. Kute and S. Banerjee, J. Appl. Polym. Sci., 2007, 103, 3025.
15 M. Redecker, D. D. C. Bradley, M. Inbasekaran, W. W. Wu
and E. P. Woo, Adv. Mater., 1999, 11, 241.
16 V. Kute and S. Banerjee, Macromol. Chem. Phys., 2003, 204, 2105.
17 T. Shimura, M. Watanabe and K. Miyatake, RSC Adv., 2012, 2,
5199.
18 S. Maji and S. Banerjee, J. Appl. Polym. Sci., 2008, 108, 1356.
19 S. Maji and S. Banerjee, J. Membr. Sci., 2010, 360, 380.
20 S. Maji and S. Banerjee, J. Membr. Sci., 2010, 349, 145.
21 J. Y. Park and D. R. Paul, J. Membr. Sci., 1997, 125, 23.
22 Z. Ge, S. Yang, Z. Tao, J. Liu and L. Fan, Polymer, 2004, 45, 3627.
23 L. Tao, H. Yang, J. Liu, L. Fan and S. Yang, Polymer, 2009, 50, 6009.
24 M. R. Pixton and D. R. Paul, J. Polym. Sci., Part B: Polym.
Phys., 1995, 33, 1135.
when reacted with several substituted and non-substituted
diacids. The incorporation of bulky bis(phenylphenyl) uorene
moiety, –CF3 group and aryl ether linkage improve the proc-
essability, thermal stability, optical and gas permeation prop-
erties and reduce dielectric constant values of the polymers.
High thermal and mechanical stability of these polymers made
them suitable candidates for gas permeation measurements.
The gas transport studies revealed that such a designed struc-
ture remarkably improved both the gas permeability and
permselectivity of these polymers. PA ‘B’ having hexa-
uoroisopropylidene linkages showed highest permeability in
barrer (PCO ¼ 67.42 and PO ¼ 15) for all the gases whereas PA
2
2
‘A’ having tert-butyl moiety exhibited the highest permse-
lectivity towards O2 relative to N2 (10.84) and PA ‘E’ containing
naphthalene moiety showed the highest permselectivity
towards CO2 over CH4 (88.37) among the series. The compar-
ison of these PAs with analogous bis(phenyl)uorene PAs
revealed that, the phenyl groups in bis(phenylphenyl)uorene
based PAs improves the thermal stability, optical transparency,
permeability and permselectivity and lowers the dielectric
constant values. All the reported cardo uorene based PAs
showed excellent separation performance for O2/N2 gas pair
and their data points exceeded or touched the latest upper
boundary limit drawn by Robeson while for CO2/CH4 gas pair
the data points laid very close to the upper boundary.
25 S. C. Kumbharkar, P. B. Karadkar and U. K. Kharul, J. Membr.
Sci., 2006, 286, 161.
26 H. Yagci and L. J. Mathias, Polymer, 1998, 39, 3779.
27 S.-H. Hsiao, C.-P. Yang, M.-H. Chuang and H.-C. Hsiao, J. J.
Polym. Sci., Part A: Polym. Chem., 2000, 38, 247.
28 Z. Wang, T. Chen and J. Xu, Macromolecules, 2001, 34, 9015.
29 M. R. Pixton and D. R. Paul, J. Polym. Sci. Part B: Polym.
Physics., 1995, 33, 1135.
30 J. S. McHattie, W. J. Koros and D. R. Paul, Polymer, 1992, 33,
1701.
31 W. M. Lee, Polym. Eng. Sci., 1980, 20, 65.
32 S. A. Stern, Y. Liu and W. A. Feld, J. Polym. Sci., Part B: Polym.
Phys., 1993, 31, 939.
33 P. Bandyopadhyay, D. Bera and S. Banerjee, Sep. Purif.
Technol., 2013, 104, 138.
34 K. Matsumoto, P. Xu and T. Nishikimi, J. Membr. Sci., 1993,
81, 15.
35 L. M. Robeson, J. Membr. Sci., 2008, 320, 390.
36 A. Singh, K. Ghosal, B. D. Freeman, A. E. Lozano, J. G. de la
Campa and J. de Abajo, Polymer, 1999, 40, 5715.
Acknowledgements
P. Bandyopadhyay acknowledges CSIR, New Delhi, for providing
him a research fellowship to carry out this work. The authors
thank AvH Foundation for donation of the GPC instrument
used in this work and Department of Science and Technology
(DST), India for nancial support as project sponsor (Grant no.
SR/S3/ME/0008/2010) for this work.
28092 | RSC Adv., 2014, 4, 28078–28092
This journal is © The Royal Society of Chemistry 2014