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New liquid crystalline columnar poly(epichlorohydrin-co-ethylene oxide) derivatives leading to biomimetic ion channels.


Proton transport and transfer phenomena have been the object of extensive research from rather different points of view by materials scientists, chemists, physicists, and biologists (1), (2). Over the past three decades, most research in the field of proton conductivity has been undertaken by the materials science community, mainly for the development of new proton-conducting materials to be used in electrochemical cells (e.g., fuel cells, batteries, sensors). Perfluorosulfonic acid (PFSA) membranes, such as Nafion[R] (marketed by DuPont), have aroused great interest in recent years for their proton-conducting properties (3). To achieve optimum performance for these materials, it is essential to control properties such as proton conductivity, water management, relative affinity of methanol and water in direct methanol fuel cells (DMFCs), mechanical, thermal, and oxidative stability, etc. This is a challenge for Nafion " materials, in which the possible chemical variations are quite limited; furthermore, PFSA membranes are expensive. Another serious drawback of membranes of this sort is their environmental inadaptability. For this reason, more than 200 patents and papers have been recently published on the preparation of new proton-conducting membranes (4-8). One of the possible approaches is to design materials containing ion transport channels, in which the channels localize the permeation path and simultaneously protect the transport process against the environment, like an ion-transporting molecular cable (9-12). Percec and coworkers (13-17) have comprehensively investigated the self-organization of supramolecular monodendrons and styrene-, methacrylate-, or oxazoline-based polymers for the design of ion-active nanostructured supramolecular systems. The polyethers like poly(oxy-1-chloro methylethylene (PECH) and its copolymer with ethylene oxide P(ECH-co-E0) have chloromethyl units, which can be easily nucleophili-cally substituted (18-20). These polyethers are of low cost and commercially easily available materials. In a very recent paper, we have reported on the preparation of oriented membranes based on a novel liquid crystalline poly-ether (21). This polyether was obtained by chemical modification of commercial PECH with the dendron potassium 3,4,5 -tris [4-(n-dodecan-l-yloxy)benzyloxy]benzoate (22). As we reported, this polymer self-assembles into a columnar structure, due to an exo-recognition of the side-chain dendrons. In the resulting structure, the polyether main chain forms a channel in the inner part of the columns, while the hydrophobic side-chain dendrons lie in the outer part. The presence of the polar ether linkages in the inner channel favors the interaction with proton and other cations, in the same way as crown ethers would do (23). For this reason, the inner polyether chain could work as an ion channel. Satisfactory orientation of the polymer was achieved by sandwiching the polymer solution between a water layer and a wet glass layer to induce unfavorable surface interactions between the outer, hydrophobic portion of the columns and their surroundings. The presence of oriented channels in the polymeric membrane resulted in remarkable proton permeability, around 2 X [10.sup.-6] c[m.sup.2] [s.sup.-1] s, comparable to that of Nafion N117.

In this article, we modified P(ECH-co-E0) with the dendron potassium 3,4,5-tris[4-(n-dodecan-1-yloxy)benzy-loxy]benzoate, to obtain liquid crystalline columnar polyethers. According to our previous experience, the formation of a stable columnar mesophase should lead to a continuous ion channel along the column axis. A degree of modification from 57 to 69% was achieved and all the modified copolymers exhibited a liquid crystalline columnar mesophase. Therefore, these polyethers are suitable candidates for the preparation of small cation transporting membranes.



All organic and inorganic reagents were supplied by Fluka or Aldrich and used as received. Tetrahydrofuran (THF) was freshly distilled from sodium benzophenone ketyl under argon. P(ECH-co-E0) with PECH/PEO 1:1 ([M.sub.w]= 5.01 X [10.sup.5], [M.sub.n] 1.08 x [10.sup.5] determined by gel permeation chromatography) was used as received. Tetra-butylammonium bromide (TBAB) [greater than or equal to] 99% (Fluka) was dried at 50[degrees]C in vacuo for 24 h.

Synthesis of Dendritic Mesogenic Groups

The potassium carboxylate (potassium 3,4,5-tris[4-(n-dodecan-l-yloxy)benzyloxy]benzoate) (2) was prepared from methyl 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]-benzoate (1) as described elsewhere (Scheme 1) (22). The reported procedure was slightly modified, to convert (1) directly to (2), instead of converting it before to 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoic acid, as follows: a solution of 6 N KOH in [C.sub.2][H.sub.5]OH (34.3 g potassium hydroxide in 102 mL ethyl alcohol) was added to methyl 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]ben-zoate (10.2 g, 0.01 mol) in a 500-mL round bottom flask. The reaction mixture was heated at 100[degrees]C on oil bath. After 1 h, the reaction mixture was poured into ice cold water (500 mL). A yellow solid material was filtered and vacuum dried at room temperature. It was recrystallized twice from hot absolute ethanol with active charcoal to yield a light yellow solid (yield 85%). Its structure was confirmed by [.sup.1] H and [.sup.13]C NMR spectroscopy.

Copolymer Modification: Synthesis of Copolymers CPI, CP2, CP3, CP4, and CP5

About 0.5 g (0.0036 mol) of P(ECH-co-E0) was dissolved in a 125-mL round bottom flask under argon in freshly prepared dried THF (60 mL) by stirring overnight at room temperature (Scheme 2). A viscous solution was obtained. The necessary amounts of potassium carboxy-late and tetrabutylammonium bromide (TBAB) were added under argon atmosphere, with inert atmospheric techniques. The reaction mixture was heated under magnetic stirring to the desired temperature. It was heated to 60[degrees]C in THF, and in case of N-methyl-2-pyrrolidone (NMP), it was heated to 80[degrees]C. In experiment CP3, THF/ DMF were used in equal ratio and heated to 80[degrees]C. After 8 days, the reaction mixture was poured into ~500 mL of ice cold water.

The modified copolymer obtained after filtration was redissolved in 125 mL of hot THF and precipitated again in 96% ethanol twice (about 400 mL [g.sup.-1] of copolymer). After the second precipitation, the rubbery modified copolymer was collected by filtration and dried at 60[degrees]C under vacuum for 48 h. Table 1 shows the experimental conditions, the yield and degree of modification for the various experiments.

TABLE 1. The modification degree and copolymer yield obtained in
the modification of P(ECH-co-EO).

Experiment   RCOOK  P(ECH-co-EO)/COOK  Solvent    Time  Modification
               (a)                              (days)       (b) (%)

CP1            5.4              1:1.0  THF           8            67

CP2            7.3              1:1.2  THF           8            58

CP3            3.6              1:1.2  THF/DMF       8            64

CP4            3.6              1:1.2  NMP           8            60

CP5            5.4              1:1.5  THF           8            56

Experiment  Modification  Yield
                 (c) (%)    (d)

CP1                   69     83

CP2                   59     88

CP3                   65     85

CP4                   62     87

CP5                   57     82

(a.) Stoichiometric amounts of TBAB referred to chlorine
were used in each case.

(b.) Average value determined by [.sup.1]H NMR.

(c.) Determined by chlorine elemental analysis.

(d.) Calculated from the average degree of modification.

Characterization and Measurements

Elemental analyses were carried out on a Carlo Erba EA1106 device. The chlorine content was determined with Schoninger's method, which involves the combustion of the sample in a platinum closed vessel and the poten-tiometric measurement of the HCI evolved.

Average molecular weights were determined in THF by size exclusion chromatography (SEC); analyses were carried out with an Agilent 1200 series system with PLgel 3 pm MIXED-E, PLgel 5 [micro]pm MIXED-D, and PLgel 20 pm MIXED-A columns in series, and equipped with an Agilent 1100 series refractive-index detector. Calibration curves were based on polystyrene standards having low polydispersities. THF was used as an eluent at a flow rate of 1.0 mL [min.sup.-1], the sample concentrations were 5-10 mg [mL.sup.-1], and injection volumes of 100 [micro]L were used.

[.sup.1]H NMR and [.sup.13]C NMR spectra were recorded at 400 and 100.4 MHz, respectively, on a Varian Gemini 400 spectrometer with proton noise decoupling for [.sup.13]C NMR. The [.sup.13]C NMR spectra of the polymers were recorded at 30[degrees]C, with a flip angle of 45[degrees], and the number of transients ranged from 20,000 to 40,000 with 10-20% (w/v) sample solutions in CD[C1.sub.3]. The central peak of CD[C1.sub.3]. was taken as the reference, and the chemical shifts were given in parts per million from TMS with the appropriate shift conversions.

HR-MAS spectra were recorded on a Bruker Avance III 500 Spectrometer operating at a proton frequency of 500.13 MHz. The instrument was equipped with a 4-mm triple resonance ([.sup.1]H, [.sup.13]C, [.sup.31]P) gradient HR-MAS probe. A Bruker Cooling Unit (BCU-Xtreme) was used to keep the sample temperature at 293 or 323 K. Samples conveniently prepared with CD[C.sub.13] were spun at 6 kHz to keep the rotation sidebands out of the spectral region of interest. One-dimensional (1D) [.sup.13]C spectra were acquired using power gate decoupling (zgpg Bruker[R] pulse program) and inverse gate decoupling (zgOig Bruker[R] pulse program) with 4096 scans. The spectral width of 250 ppm was acquired in 64 K points at different temperatures (293 or 323 K). These sets of parameters for 13C were used for longitudinal relaxation ([T.sub.1]) calculation experiments. For [T.sub.1] calculation, a relaxation time of 8 s (dl) was left between scans and an inversion recovery experiment (t1irpg Bruke[R] pulse) was performed sampling points at 0.0125, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.9, 1.2, 2.4, and 4.8 s. The following equation was used for curves fitting the magnetization recovery (24):

In([M.sub.o] - M([tau])) = In 2 + ln[M.sub.o] - [tau/[T.sub.1]) (1)

where [tau] is the decay time of the experiment and M([tau]) = -[M.sub.0] at [tau] = 0

If relaxation was due to a single component, then experimental data resulted in a straight line; if this was not the case, multicomponent analysis by computer-aided nonlinear least squares method had to be performed.

Densities were determined by gas pycnometry using Micrometritics AccuPyc 1330 machine at 30[degrees]C.

Thermal transitions were detected with a Mettler-Toledo differential scanning calorimeter model 822 in dynamic mode at a heating or cooling rate of 10[degrees]C [min.sup.-1]. Nitrogen was used as the purge gas. The calorimeter was calibrated with an indium standard (heat flow calibration) and an indium-lead-zinc standard (temperature calibration).

Clearing temperature were roughly estimated using polarized optical microscopy (POM); textures of the samples were observed with an Axiolab Zeiss optical microscope equipped with a Linkam TP92 hot stage.

For X-ray experiments, the polymers were mechanically oriented by shearing below clearing temperature on a glass plate. Measurements were made using a Bruker-AXS D8-Discover diffractometer equipped with parallel incident beam (Gobel mirror), vertical [[theta]]-[theta] goniometer, XYZ motorized stage. The GADDS detector was a HI-STAR (multiwire proportional counter of 30 X 30 [cm.sup.2] with a 1024 X 1024 pixel). Samples were placed directly on the sample holder for transmission mode. An X-ray collimator system allowed to analyze areas of 100 and 500 pm. The X-ray diffractometer was operated at 40 kV and 40 mA to generate Cu K[alpha] radiation. The GADDS detector was 30 X 30 [cm.sup.2] with a 1024 X 1024 pixel CCD sensor placed at 30 and 9 cm from the sample. Two analytical conditions were used to measure the sample.

For low 20 range: collimator, 100 pm; distance sample-detector, 30 [micro]m. The collected frame (2D XRD pattern) covers a range from 0.9 up to 9.2[degrees] 2[theta]. The diffracted X-ray beam travelled through a He-filled chamber (SAXS attachment) to reduce the air scattering at low angles. The direct X-ray beam was stopped by a beam stop placed directly on the detector face. The exposition time was of 1800 s per frame and it was first chi-integrated to generate the conventional 2[theta] vs. intensity dif-fractogram and after it was 2[theta]-integrated to generate a Chi vs. intensity diffractogram.

Medium 2[theta] range: collimator, 500 pm; distance sample-detector, 9 cm. The collected frame (2D XRD pattern) covers a range from 3.0 up to 25.5[degrees] 2[theta]. The direct X-ray beam is stopped by a beam stop placed behind the sample with and aperture of 4[degrees]. The exposition time was of 300 s per frame and it was first chi-integrated to generate the conventional 2[theta] vs. intensity diffractogram and after it was 2[theta]-integrated to generate a Chi vs. intensity diffractogram.


As mentioned previously, the aim of this work was to obtain polyethers bearing the dendron 3,4,5-tris[4-(n-dodecan-l-yloxy)benzyloxy]benzoate so that the formation of hexagonal columnar mesophases could be induced. The bimolecular substitution of the chlorine atom in P(ECH-co-E0) with the appropriate dendritic potassium carboxylate should give the desired polymer with no substantial modification in either the backbone size or the polymer microstructure (Scheme 2).

The chemical modification of PECH under phase-transfer catalyst conditions with carboxylates has been used by several researchers [25, 261, but few studies have focused on obtaining anisotropic materials [27, 28]. Because we obtained good modification degrees and detected no dehy-drochlorination side reactions in the chemical modification of PECH [29, 30], we were encouraged to use the same strategy and reaction conditions for chemically modifying P(ECH-co-E0). The given reactions were performed for 8 days in different solvents like THF, THF/ DMF, and NMP. As previously stated, the temperature ranged from 60 to 80[degrees]C, depending on the solvent. These conditions were selected on the basis of our previous experience, various substrates and nucleophiles, as they gave high and almost quantitative modification degrees (25), (31). In this way, the P(ECH-co-E0) solutions in different solvents were heated with different ratios of potassium carboxylate in the presence of a stoichiometric amount of TBAB. Table 1 summarizes the OC[H.sub.2]C1/Nu ratio used, the modification degrees and polymer yields obtained in these experiments.

In this case, the modification degree could not be further improved by increasing the nucleophile/C[H.sub.2]C1 ratio beyond the stoichiometric (see comparison of experiments CP1, CP2, and CP5). Nor could we get higher modification degrees by increasing solvent polarity (compare experiments CP2, CP3, and CP4). In this case, the modification degree reached a plateau value around 69%. This plateau seems to be related to a progressive compaction of the conformational coil which is induced by the gradual displacement of chlorine: this would finally lead to a decrease in the percentage of accessible reactive sites (32).

Average molecular weights were determined in THF on a SEC system with polystyrene as a reference sample. All values of molecular weights and polydispersity are reported in Table 2. One could expect an increasing trend of the molecular weight with modification degree, since considerably heavy dendritic groups were introduced: however, one should keep in mind that molecular weight values are obtained under the assumption that the copolymer behaves like polystyrene in THF. The introduction of dendrons into the P(ECH-co-E0) is expected to greatly modify the hydrodynamic volume of the system. For this reason, it is not easy to predict a trend of the molecular weight with the modification degree, since the introduction of the dendritic groups can lead to significant changes in the hydrodynamic volume with respect to the starting polymer. Density values of modified polymers (Table 2) greatly decrease with respect to the starting P(ECH-co-E0), that suggests a considerable change in polymer conformation after modification.

TABLE 2. Molecular weight and densities of the
synthesized copolymers.

Polymer          Modification (a) [M.sub.n] *  [M.sub.w] *
                             (%)   10(-4b) (g   10(-5b) (g
                                     mol(-1))     mol(-1))

CP1                           69        15.40         7.00

CP2                           59         9.70         3.85

CP3                           65         5.59         2.33

CP4                           62         5.88         2.02

CPS                           57         5.67         2.03

P(ECH-co-EO) (d)              --        10.80         5.01

Polymer          [M.sub.w]/[M.sub.n.sup.b]  [[rho].sub.c]

CP1                                   4.55          1.053

CP2                                   3.97          1.058

CP3                                   4.17          1.074

CP4                                   3.44          1.057

CPS                                   4.16          1.059

P(ECH-co-EO) (d)                      4.61          1.308

(a.) Determined by chlorine elemental analysis.

(b.) Determined by SEC.

(c.) Determined at 30[degress]C. Error: [+ or -] 3%.

(d.) Starting copolymer.

The microstructure and composition of the copolymer were characterized by NMR spectroscopy. Figure 1 reports the [sup.1]H NMR spectrum of CP1 copolymer as an example. All [sup.1]H NMR spectra are characterized by broad signals in three regions. The aromatic region shows three partially overlapped signals at 7.20, 6.75, and 6.62 ppm. Considering the relative integration areas and by comparison with the spectrum of methyl 3,4,5-tris(n-dodecan-l-yloxy)benzoate, the signal at 7.20 (8H) can be assigned to the protons of the benzoate group plus the benzylic protons ortho to the--C[H.sub.2]0--. The signals at 6.75 and 6.62 ppm (4H+2H) correspond to the benzylic protons meta to the--C[H.sub.2]0--of the lateral and central alkyloxybenzyloxy substituents. The characteristic signals, corresponding to most protons of the dodecyloxy alkyl chains in the dendron, can be observed in the high-field region at 1.7, 1.4, 1.2, and 0.8 ppm. The most interesting region lies between 5 and 3.4 ppm in which five signals can be observed. The two signals centered at 4.42 and 4.24 ppm correspond to the two methylenic carbon c' protons in the modified monomeric unit; the signal centered at 3.90 ppm corresponds to the methylene attached to the oxygen in the alkyl chains of the mesogenic unit and to the methynic proton b'. The partially overlapped broad signal between 3.9 and 3.4 ppm corresponds to the methylenic and methynic protons a, a', b, and c in the modified and unmodified monomeric units, as well as to the methylenic protons a" of the ethylene oxide unit. Finally, the signal centered at 4.82 ppm can be assigned to the benzylic methylenes of the dodecyloxybenzyloxy substituent.

Figure 2 shows the [sub.13]C NMR spectrum of copolymer CPI with the corresponding assignments. The aromatic carbons and the carbonyl of the benzoate moiety introduced appear between 166 and 108 ppm, whereas carbons 2-12 of the aliphatic alkyl chains appear at the expected displacements in the region between 32 and 14 ppm. The carbons of the main chain units appear in the central region of the spectra. The methine and side methylenic carbons of the modified and unmodified monomeric units appear at different chemical shifts. Therefore, b and b' appear at 78.6 and 77.4 ppm, respectively, and c and c' appear at 43.5 and 63.8 ppm. The chemical shift of b' was deduced from reported spectra of modified PECH in TCE-[d.sub.2] (22), since in our case it appears overlapped with the CD[Cl.sub.3] signal. The carbons a, a', and a" appear as a broad signal at 69.2 ppm. Carbon 1 of the alkyl chains appears as a wide peak at 67.8 ppm. The chemical shifts of the benzylic methylenes depend on their relative position in the aromatic ring. Those in position 3 and 5 appear at 70.7 ppm, whereas the same carbon in position 4 appears downfield at 74.7 ppm. Neither [sub.1]H NMR nor [sub.13]C NMR spectra showed detectable amounts of any of the signals corresponding to unsaturated vinylether units (33). This indicates that the dehydrohalogenation reaction does not take place under our experimental conditions. The copolymer composition was calculated by NMR spectroscopy because this methodology gave accurate results (as compared with elemental chlorine analysis) in previous studies. Quantification was carried out from the [sub.1]H NMR spectra by comparing the areas of the aromatic peaks between 7.4 and 6.8 ppm, the benzylic proton signal at 4.8 ppm, and the methylenic protons c' at 4.4 ppm with the broad signal between 4.0 and 3.5 ppm (see Fig. 1). The results agreed with those of the comparative elemental analysis.

The characterization of the mesomorphic phases was performed on the basis of DSC, POM, and X-ray diffraction experiments. Table 3 shows the results of POM and DSC characterization. Before DSC and POM experiments, all copolymers were annealed for 2 h in between [T.sub.g] and clearing temperature (Table 3). Glass-transition temperatures ([T.sub.g]) were estimated from the second heating on DSC scans in case of all copolymers and ranged between--12 and 3[degrees]C.

TABLE 3. Phase transitions and annealing temperature
of the copolymers CP1--CP5.

Sample  Modification  [T.sub.g.sup.a]  [T.sub.m.sup.a]     Annealing
             (a) (%)     ([degrees]C)     ([degrees]C)   temperature

CP1               69              -12               50           100

CP2               59                2               34            70

CP3               65                0               27            90

CP4               62                3               26            80

CP5               57                3               29            70

Sample  [T.sub.c.sup.b]

CP1             115-118

CP2               85-90

CP3              95-100

CP4             100-115

CP5               87-90

(a.) Determined by DSC from the second heating scan.

(b.) Clearing range determined by POM.

In all copolymers, DSC analysis put into evidence an endotherm which ranged between 26 and 50[degrees]C, which suggested the existence of a crystalline portion in the modified copolymers. XRD experiments performed at room temperature did not put into evidence any peaks attributable to crystallinity in the samples. Nevertheless, we performed HR-MAS NMR experiments on CP2 copolymer at 20 and 50[degrees]C, that is, below and above the transition detected by DSC. HR-MAS 13C NMR spectra of CP2 are reported in Fig. 3a and b. We focused our attention on the following peaks: 43.5 ppm, corresponding to the side methylenic carbon (c) of the unmodified unit; 63.8 ppm, corresponding to the side methylenic carbon (c') of the modified unit; 78.6 ppm, corresponding to the methine (b) of the unmodified unit. We did not take into account the peak at 77.4 ppm, corresponding to the methine (b') of the modified unit, because it was partially overlapped with the chloroform signal.

We therefore determined [T.sub.1cs] by the inversion-recovery pulse sequence as described in the Experimental part. The results are reported in Table 4. In the case of the methylene of the modified unit (63.8 ppm), two components of [T.sub.1c] were found at 20[degrees]C, which reduced to one when temperature was raised to 50[degrees]C. In the case of methylene and methine of the unmodified units, only one component was found at 20[degrees]C, whose value also decreased on increasing the temperature. In semi-crystalline polymers, double exponential have been observed and they are commonly interpreted by assigning one relaxation process to the crystalline domains and the other relaxation process to the amorphous portion. The longer Tic value found for c' corresponded to 1.4 s. For the crystalline phase of PEO at room temperature, [T.sub.1cs] of 14-16 s were reported (34), which are considerably longer than in our case. Taking into consideration that a strict similarity between PEO and CP2 structures should not be sought, there are also several aspects which could further justify such differences in the Tics: first, the [T.sub.1cs] reported for PEO refer to methylene and methine in the main chain, while in our case the relaxation time refers to a side methylene; second, they were determined about 40[degrees] below melting temperature, while in our case the relaxation experiment was performed only 14[degrees] below the observed transition; third, given the XRD results, in our case it is reasonable to suppose that the amount of crystalline portion in CP2 is quite low when compared to PEO samples reported in the literature. This could also affect the value of [T.sub.1c], as explained below. Therefore, we attributed the two components of [T.sub.1c] to the presence of amorphous and crystalline portions in copolymer CP2. Finally, we concluded that the endotherms centered round 40[degrees]C could be attributed to main-chain crystallinity for the whole set of polymers. As an approximation, under this assumption, we roughly estimated the degree of crystallinity [X.sub.c], in our modified copolymers from the experimental melting enthalpy value and taking as a reference the reported melting enthalpy for 100% crystalline PEO (35). The obtained values, together with melting temperatures and melting entropies, are reported in Table 5. As expected, [X.sub.c] values resulted extremely low, being 1.71.8%; in the case of CP1, which has the highest modification degree (i.e., 69%), higher melting temperature, melting entropy, and crystallinity degree were found. This suggests that the presence of the side dendrons, which are responsible for the mesogenic columnar ordering, is also able to induce some crystalline order in the copolymer main chain. In all cases, such low values of [X.sub.c]. presumably correspond to a great contact surface between the crystalline and amorphous regions, which determines that the crystal carbons can migrate quickly into the noncrystalline regions and relax. This could explain the short relaxation time found for the crystalline component of methylene c'.

TABLE 4. Carbon spin-lattice relaxation Limes of selected
peaks of CP2 copolymer at 20 and 50[degrees]C.

Peak (ppm)       [T.sub.1c] at       [T.sub.1c] at
               20[degrees] (s)      50[degrees](s)

43.5        1.75 [+ or -] 0.09  0.30 [+ or -] 0.02

63.8         0.39 [+ or -]0.01,  0.22 [+ or -] 0.01
              1.4 [+ or -] 0.4

78.6         0.70 [+ or -] 0.01  0.57 [+ or -] 0.03

TABLE 5. Characteristics of the crystalline phase
of copolymers CP1-CP5.

Sample  Modification       Melting       Melting      Melting
          degree (%)   temperature  enthalpy (a)  entropy (a)
                      ([degrees]C)          (kJ      (J K(-1)
                                       mol(-1))      mol(-1))

PEO               --            62         8.67          25.8

CP1               69            50         0.32          0.99

CP2               59            34         0.16          0.50

CP3               65            27         0.16          0.42

CP4               62            26         0.16          0.55

CP5               57            29         0.15          0.49

Sample  [X.sub.c.sup.b](%)

PEO                    100

CP1                    3.7

CP2                    1.8

CP3                    1.8

CP4                    1.8

CP5                    1.7

(a.) Per mol repetitive unit.

(b.) Degree of crystallinity calculated with respect
to 100% crystalline PEO.

All copolymers exhibited liquid-crystalline behavior, as shown by POM and confirmed by XRD. By DSC, we could evaluate neither the clearing temperature nor the clearing enthalpy, since only a very small variation of heat flow signal with respect to the baseline could be observed, even after annealing. The clearing temperature ranges were therefore determined by POM: they were found to depend on the modification degree achieved, as expected, but were all around 90-100cC. For instance, the change in the optical texture of CP1 in the clearing range is shown in Fig. 4a-c.

Table 6 shows the results of X-ray diffraction experiments performed at room temperature on the samples oriented by shearing in the rubbery state. As an example, Fig. 5 shows the X-ray diffraction pattern of CP5 in the low 2[theta] range (0.9-9.2[degrees]) (a) and in the medium 2[theta] range (3-25.5[degrees]) (b). In the case of all copolymers, the XRD pattern showed a sharp reflection at 2[theta] = ~2.0[degrees], and a broad halo at 20 = ~20[degrees]. This diffractogram is compatible with a columnar mesophase, the lower spacing corresponding to the planar distance between disks and the higher one corresponding to the lateral distance between columns. The former 2[theta] value corresponded to the [d.sub.100] plane of a columnar phase and allowed to calculate the dimensions of the unit cell, while the latter corresponded to [d.sub.001] plane and could be referred to the distance between dendrons (36).

TABLE 6. X-ray patterns of oriented samples ot copolymers
CPl--CP5 at room temperature.

Polymer  Modification  [d.sub.100] (a)  [d.sub.001] (a)  [a.sub.b]
                  (%)              (A)              (A)        (A)

CP1                69               42              4.7         49

CP2                59               45              4.7         52

CP3                65               46              4.7         53

CP4                62               47              4.7         54

CP5                57               45              4.7         53

Polymer  [[delta].sup.c]

CP1                  5.1

CP2                  6.0

CP3                  6.0

CP4                  6.4

CP5                  6.0

(a.) Planes of the hexagonal prism.

(b.) Dimension of the hexagonal unit cell.

(c.) Number of disks per unit cell.

For a hexagonal mexophase, and given the experimental densities [rho], we can calculate the number of repeat units of copolymer [mu] that are present in a hexagonal prism layer of height c from the following equation:

[rho] = 2[micro]/[square root of (term)]3[N.sub.A][a.sup.2]c (2)

where M is the molecular weight of the repeat unit, NA is Avogadro's number, a = <d100>1/[square root of (term)]3 is the dimension of the hexagonal unit cell, and c = [d.sub.ool]cos x, and x are the angles between the prism height and the distance between disks calculated from the XRD pattern of oriented samples. By considering the experimental modification degree of the copolymer [alpha], we can finally find the number of disks contained in a unit cell, [delta] = [mu] x [alpha]. The same calculation can also be applied to columnar samples because geometrical considerations make it possible to assume that in a columnar mesophase the columns self-assemble in a compact hexagonal packing where statistical fluctuations in the column positions do not produce any of the additional reflections that are expected in a [PHI]h phase: that is, the instantaneous positions of the columns fit a hexagonal organization even if the average positions do not (22).

Figure 6 shows the XRD pattern on flat film of an oriented CP5 sample, in the low 2[theta] range (0.9-9.2[degrees]) (a) and in the medium 2[theta] range (3-25.5[degrees]) (b). It can be seen that the reflection at 2[theta] = 1.9[degrees], corresponding to the [d.sub.100] plane, is polarized in the meridian, while the halo at ~2[theta] = 20[degrees], corresponding to dm plane, exhibits polarization at the equator. This experimental evidence showed that dendrons are approximately perpendicular to the column axis and was found in the XRD pattern of oriented samples of the whole copolymer series CP1--CP5. The estimated average number of dendrons per unit cell ranged from 5 to 6. The self-assembling of CP1--CP5 copolymers into columns is schematized in Fig. 7. In the case of the copolymers obtained by chemical modification of PECH with the same dendron, the unit cell had dimensions in the same range, but it was found that the number of dendrons contained in a unit cell ranged between 3 and 6, with a tilt angle comprised between 23[degrees] and 45[degrees] (36). This difference can be ascribed to the higher flexibility of the ethylene oxide unit, which allowed the unit cell to accommodate more dendrons in the case of our copolymers.


A new family of liquid crystalline columnar polyethers was obtained by modification of P(ECH-co-EO) with the dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]ben-zoate. In agreement with our previous experience, the modification degree could not be further improved by increasing either the nucleophile/C[H.sub.2]C1 ratio beyond the stoichiometric one, or solvent polarity, and was found to reach a plateau value around 69%. NMR characterization indicated that side reactions, such as dehydrohalogenation, did not take place under our experimental conditions. All copolymers exhibited liquid-crystalline columnar behavior, as shown by POM and confirmed by XRD. Moreover, DSC analysis and HR-MAS experiments suggested that the presence of the side dendrons, which are responsible for the mesogenic columnar ordering, is also able to induce small crystalline order in the copolymer main chain. The clearing temperature ranges were determined by POM: they depended on the modification degree, as expected, and were all around 90-100[degrees]C. X-ray diffraction experiments on oriented samples showed that the dendrons are approximately perpendicular to the column axis and that their average number per unit cell ranged from 5 to 6. Therefore, these copolymers can be used to prepare oriented membranes for small cation transport, in agreement with the results that we obtained by using PECH modified with dendrons (21). In the case of the membranes based on modified P(ECH-co-E0), the higher flexibility of the EO moiety and the different modification degrees achieved, could vary the characteristics of the ion channel in the inner part of the columns.


The authors are grateful to Dr. Miguel Angel Rodriguez for HR-MAS NMR experiments.

Correspondence to: M. Giamberini; e-mail: Contract grant sponsor: Ministerio de Ciencia e Innovacion; contract grant number: MAT2008-00456/MAT.

DOI 10.1002/pen.23240

Published online in Wiley Online Library (

[C] 2012 Society of Plastics Engineers


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Suryakant Vilasrao Bhosale, (1) Muhammad Azam Rasool, (2) Jose Antonio Reina, (1) Marta Giamberini (2)

(1) Departament de Quimica AnaRica i Quimica Organica, Universitat Rovira i Virgili, Carrer Domingo sln, Campus Sescelades, 43007 Tarragona, Spain

(2) Departament de Enginyeria Quimica, Universitat Rovira i Virgili, Av. Paisos Catalans, 26 Campus Sescelades, 43007 Tarragona, Spain
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Author:Bhosale, Suryakant Vilasrao; Rasool, Muhammad Azam; Reina, Jose Antonio; Giamberini, Marta
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:4EUSP
Date:Jan 1, 2013
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