isocyanate)/Polyaniline Polyblend
Yu-Jen Li,1Ko-Shan Ho,1 Wan-Ting Lo,1Shin-Shiao Yang,1 Liang Chao,2 Yu-Chen Chang,3 Yu-Kai Han,1 Tar-Hwa Hsieh,1 Ying-Jie Huang4
1Department of Chemical and Materials Engineering, National Kaohsiung University of Applied Sciences,
Kaohsiung 807, Taiwan
2Center for General Education, Technology and Science Institute of Northern Taiwan, Peito, Taipei 11202, Taiwan 3Institute of Materials Science and Engineering National Sun Yat-Sen University, Kaohsiung, Taiwan
4Institute of Nanotechnology, National Chiao Tung University, Hsinchu, Taiwan
Received 7 May 2008; accepted 8 November 2008 DOI 10.1002/app.29727
Published online 2 March 2010 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Poly(n-undecyl isocyanate) (PUDIC)/
n-dodecylbenzenesulfonic acid (DBSA)-doped polyaniline (PANIDBSA) polyblend was prepared and the effect of the H-bonding between these two polymers on the compat-ibility, conjugation chain length of PANIDBSA, and helixity of PUDIC in the polyblend system were studied. The monomer and polymer were characterized by NMR spectra and the polyblend was analyzed by FTIR, UV–vis spectra, and wide-angle X-ray diffraction. It was found when the blend composition of the PUDIC was higher than 10%, the WAXD patterns demonstrated lower angle shifting for the peaks at around 2y ¼ 2–2.5, referring to the distance
between the layers of the layered structure of PANIDBSA crystalline with increasing PUDIC, indicating the
expan-sion of the layered structure of PANIDBSA. The FTIR spectra illustrated the presence of an absorption peak at 1700 cm1shift to higher wave number with PUDIC due to its H-bonding with PANIDBSA. The UV–vis spectra of PANIDBSA described a blue-shift of thekmaxwith PUDIC,
indicating that the presence of PUDIC in the polyblend sys-tem can interrupt and decrease the conjugation chain length of PANIDBSA. The optical activity of the helical PUDIC decreased notably with the presence of PANIDBSA, resulting from the reversed helical effect (de-nature) of H-bonding.VVC 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 1–7, 2010
Key words:blends; chiral; conducting polymers
INTRODUCTION
Intrinsically conducting polymers (ICP) are useful for a large number of applications: conducting paints and glues, electromagnetic shielding, anti-static formulations, sensors and actuators, electronic devices, and corrosion protection are a few exam-ples.1,2ICP included polyparaphenylene (PPP), poly-pyrrole (PPy), polythiophene (PTh), and polyaniline (PANI) etc. Su and Kuramoto3report the use of long alkyl organic acid (ex: n-dodecylbenzenesulfonic acid (DBSA) to be the dopant3–5 can avoid polyani-line chain curl and increase its solubility on common organic solvents.
Shashoua et al.6–8 reported the using of NaCN as the initiator in preparing a helical poly(alkyl isocya-nate) (nylon 1) in N,N-dimethylformamide (DMF) via the low temperature (100C to 40C) anionic
poly-merization. These kind of polymers own rigid back-bones of length 40 nm,9,10due to the conjugation of the carbonylp electrons to CAN bonding. Goodman11 synthesized poly(alkyl isocyanates) having optical
activity due to the helical conformation at78C but the product has low yield and broad molecular weight distribution. Muller and Zental12,13 describe the synthesis of seven new types of copolymer series prepared by copolymerization of hexyl isocyanate with seven new chiral azo chromophores with an iso-cyano functionality. The resulted copolyisocyanates (Nylon 1) have a good solubility but the yield is still low. The above methods were concerned about the synthesis of various nylon 1 to study either their solu-bility in common organic solvents or the chirality of their solution. This research is to synthesize one of the nylon 1, poly(n-undecyl isocyanate) (PUDIC) to study the possibility of destroying its helical conforma-tion through the formaconforma-tion H-bonding between its carbonyl groups and other H-donating polymer by polyblend. Once the H-bonding through the carbonyl group is formed, its p electron will not be able to conjugate with backbone CAN group. The loss of backbone conjugation (rigidity) can reduce the possi-bility for nylon 1 to create a helical conformation or even become a random-coiled polymer. The removal of its helical conformation can be checked from the decrease of its chirality in the solvent and is similar to the so-called de-nature (disappearance of helical conformation) behavior of a biopolymer when its
Journal of Applied Polymer Science, Vol. 117, 1–7 (2010) V
VC 2010 Wiley Periodicals, Inc.
intramolecular H-bonding was destroyed at high tem-perature (i.e. frying).
To increase the probability of the formation of H-bonding, we used DBSA-doped polyaniline (PAN-IDBSA) which also has long alkyl side chains and H-donating amine group to blend with PUDIC. Therefore, we can analyze the conformational change of the PUDIC with the effect of the formation H-bond and its compatibility with PANIDBSA. It would be very interesting if the chirality of the PUDIC in the blend can be sensed simply by measuring the conduc-tivity orkmaxof the blend, which is also related to the
composition.
And, on the PANIDBSA part, we can study the change of its length of conjugation by the red or blue shift of its kmax, which is also related to the
degree of extension (random-coil or extended) of its backbone before and after mixing with PUDIC.
EXPERIMENTAL Preparation of PANIDBSA by emulsion polymerization
The 0.13 mol of aniline monomer was mixed in a solution of 0.0027 mol SLS, 0.0644 mol DBSA, and 160 g of deionized (DI) water in four-necked flask equipped with a mechanical stirrer and stirred for 1 h to allow the formation of an emulsion solution. The 20 mL of fuming sulfuric acid was added slowly to the previous solution to obtain an emulsion solu-tion of anilinium salt monomer. APS (0.01 mol) was dissolved in 30 mL of water and was added to the solution to carry out the emulsion polymerization overnight. The micelle droplets with obtained poly-mers were destroyed to release the enclave polypoly-mers by the addition of n-butylacetate and kept stirring for 20 min. The organic phase with PANIDBSA was then separated from water by a funnel. Large amount of methanol was poured into the organic phase to precipitate the PANIDBSA from n-butylace-tate. The mixture was filtered to obtain the filter cake which was then washed with methanol mixed until the filtrate became colorless. The cake was then dried at 60C for 24 h in an oven.
Synthesis ofn-undecylisocyanate
n-undecylisocyanate was prepared as follows: 0.1 mol distilled lauroyl chloride (Aldrich, USA, ACS grade) was mixed with 0.12 mol sodium azide (Aldrich) in 250 mL dry toluene (dried with sodium and collected followed by distillation) and refluxed overnight. The unreacted sodium azide and the by-product sodium chloride were separated by vacuum distilling the n-undecylisocyanate out. A distillate with a bp at
80–85C (vacuumed to 800 Pa) was collected and the yield is estimated to be around 29%.
Polymerization of PUDIC14,15
250 mL of Dimethylformamide (DMF, Aldrich, ACS grade) was placed into a 500-mL three-necked flask with 1 g phosphorous pentoxide (P2O5) for
over-night and then distilled with a bp at 38C and 400 Pa. Sodium cyanide was dried in vacuum with P2O5
for 4 h, dissolved in the dry DMF (in a 10-mL volu-metric flask) to make a saturated solution. A 100-mL flask was dried on flame and inert gas (Argon) was purged through the system. The temperature was kept at 36C by a dry ice/acetone bath. Thirty milliliters of DMF was injected into the flask and 1 mL of undecylisocyanate, 10 min later. After 20 min, one drop of the saturated sodium cyanide solution of DMF was injected into the batch, a white cluster of polymer suddenly appeared in the solution. Excess methanol was poured into the mixture to terminate the polymerization.
The polymer was isolated by filtration and about 0.3 g of white powder was obtained. This product was further purified by dissolution in chloroform, precipitation by methanol, and drying in vacuum. 0.23 g of PUDIC was obtained with a yield of 23%. Preparation of PUDIC/PANIDBSA
2.5 wt % PANIDBSA and 0.5 wt % PUDIC were pre-pared in xylene solution individually by dissolving the dry polymers in the solvent and was stirred for at least 24 h. PUDIC/PANIDBSA with various per-centages of PUDIC (0.5, 1, 2, 5, 10, and 20%) were prepared by mixing these two different solutions together in various proportions. Some of the solution was kept to be analyzed by UV–vis and optical activity meter, the rest was dried at 60C for 24 h for other measurements.
Characterization
Nuclear magnetic resonance (NMR)
1H-NMR spectrum of n-undecylisocyanate monomer
was obtained from its deuterated chloroform solution using a Bruker MSL-300 spectrometer operated at 300 MHz. And PUDIC dissolved in the deuterated chloroform (conc. 1 mg/1 mL) was used to obtain its
13C-NMR spectrum from a Varian Gemini 300 MHz
NMR spectrometer. Chemical shifts were referenced to13C signals of the deuterated solvent.
Fourier transform infrared spectroscopy (FTIR) The IR spectra of all the samples were obtained from a Bio-Rad FTS 165 FTIR with a resolution of 4 cm1
and 16 scanning mixed and stapled into tablet with dry KBr powders. The scanning wave numbers ranged from 4000 to 400 cm1. The IR spectra of lauroyl chloride, n-undecylisocyanate, PUDIC, and PANIDBSA were recorded.
Optical activity
The optical activities of neat PUDIC and PUDIC/ PANIDBSA were obtained from a Polax-D Type optical meter.
UV–vis spectroscopy
The UV–vis spectra of the various polyblend in solu-tion were obtained from a Hitachi U-2000 at 200 nm/ min. The scanning wave length ranged from 1100 nm to 600 nm.
Wide-angled X-ray diffraction (WAXD)
A Phillips X-ray generator was used for the X-ray diffraction studies. Samples were cast on the slide or just placed on the slide. The samples were exposed to a Cu/Ni targeted radiation with 45 kV and 35 mA from 2to 40, the exposure time of 50 s in every 0.04 was used.
RESULTS AND DISCUSSION NMR spectra
1H-NMR spectrum of the synthesized product from
the reaction of azide with acyl chloride in refluxing toluene proved to be n-undecylisocyanate as shown in Figure 1 which demonstrates several types of
methylene ACH2A, and methyl ACH3groups of the
alkyl n-undecyl chain. 13C-NMR spectrum shown in Figure 2 was used to characterize the PUDIC in d-CHCl3. The assignment of the resonance peaks of
various carbons are illustrated in the attached chem-ical structure. The resonance peaks of the aliphatic carbons of n-undecyl side chain can be seen around 10–40 ppm from Figure 2 except the carbonyl carbon whose absorption peak is at 52 ppm and not demon-strated in the spectrum. From the characterization on the monomer and polymer by NMR spectra, a helical, rigid poly(alkylisocynate) is prepared. IR spectra
The IR spectrum of the lauroyl chloride which is the precursor of n-undecylisocyanate monomer was illus-trated in Figure 3(a) with a huge absorption at 1800 cm1assigned as the carbonyl group of the acyl chloride. It was converted into isocyanate by Curtis rearrangement after refluxing with sodium azide in dry toluene with nitrogen gas released during reac-tion. Then, it was found in Figure 3(b) that the acyl chloride group at 1800 cm1disappeared entirely and isocyanate groups at 2200 cm1 appeared after the formation of n-undeylisocyanate which was then polymerized by NaCN in DMF into PUDIC, demon-strating a strong carbonyl band at 1700 cm1in Figure 3(c). The n-undecyl side chain remained unchanged during the preparation of isocyanate and polymeriza-tion as seen from Figure 3(a–c). And Figure 3(d) revealed the presences of both the quinoid and benze-noid ring of neat PANIDBSA from the absorption peaks at 1559 and 1478 cm1, respectively. The absorption band at 1300 cm1of the CAN on both the
Figure 1 1H-NMR spectrum of n-undecyl isocyanate monomer.
PANIDBSA and PUDIC backbone is very significant, and the absorption peaks at 1005 and 1030 cm1 char-acterize the AS¼¼O belonged to the ASO3H group of
PANIDBSA. All assigned peaks were listed in Table I. The absorption peak at 1700 cm1representing the stretch mode of theAC¼¼O was used to monitor the interaction between PANIDBSA and PUDIC in the blends. In Figure 4, the carbonyl shifted to higher wave number due to the increase of the stretching strength of AC¼¼O bond after blending with small amount of PANIDBSA in toluene, indicating the
presence of the hydrogen bonding with the PUDIC as the H-acceptor (carbonyl) and PANIDBSA as the H-donator (amine). The strong H-bonding was able to induce the reversing of the helical conformation of PUDIC as depicted in Scheme 1 and effectively depressed the overall optical activity of PUDIC in toluene since the R (þ) and D () circulation will cancel each other.
X-ray diffraction patterns
The full span of WAXD patterns for all neat poly-mers and polyblends were shown in Figure 5 with a compact hexagonal cylindrical structure of the rigid rod packing.16
The hairy rod structure of rigid polymers with long alkyl side chains easily demonstrates a self-organized layer-to-layer structure with alkyl side
Figure 3 IR-spectra of (a) lauroyl chloride, (b) n-undecyl isocyanate, (c) PUDIC, (d) PANIDBSA.
TABLE I
Assignments of IR Spectrum of PANIDBSA Frequency
(cm1) Assignment
2958 m (ACH3)
2924 m (ACH2A)
1600 m (AC¼¼CA), benzene ring
1561 dopedm (AC¼¼NA) of quinoid
1467 dopedm (AC¼¼CA) of benzoid
1307 m (ACANA)
1178
1135 ABANHABA
1034 mas(AS¼¼O) of ASO3H
1006 msy(AS¼¼O) of ASO3H
801 m (CAH) para-substituted aromatic
out of plain bending
Figure 4 IR-spectra of PUDIC with increasing PANIDBSA in the blends.
Scheme 1 schematic diagram of H-bonding between PUDIC and PANIDBSA with reversing helical conformation of PUDIC.
chains interdigitized to each other and the layer-to-layer distance can be determined from the diffrac-tion angles (2y) around 2–5 from its WAXD pat-tern.16–22Both PANIDBSA and PUDIC demonstrated the layered structure with significant diffraction peaks at low angles (2–5) from which the layer-to-layer distance created from the extension of their nonpolar long alkyl side chains described in the upper right graph in Figure 5 can be obtained. To characterize the possible structural variation of the layered structure of PANIDBSA in the blend, the X-ray diffraction patterns of blends with various thermal compositions were taken and shown in the upper left graph in Figure 5. The distances between the layers were calculated from the diffraction peak at 2y ¼ 2.35 which is corresponding to 3.74 nm for neat PANIDBSA and 2y ¼ 3.26 corresponding to 2.71 nm for neat PUDIC, respectively. As there are only 11 carbons of n-undecyl side chain for neat PUDIC, illustrating a length of 2.71 nm which is shorter than 3.74 nm of phenyl-n-dodecyl side chains of PANIDBSA with a phenyl and twelve numbers of carbons. The PANIDBSA created a diffraction peak of (002) at smaller angle ( 2–2.5), representing the
layer distance of PANIDBSA were interfered by the introduction of small amount of PUDIC. When more and more PUDIC were incorporated into the poly-blend system, the diffraction peak shifted to lower angle, indicating the expansion of layer distance of PANIDBSA due to the insertion of PUDIC, resulting from the formation of H-bonding between these two polymers as described in Scheme 1. When the blend ratio were increased to be over 10%, the lower angle shifting was more significant due to the increase of the compatibility.
UV–vis spectra
Various compositions of PUDIC/PANIDBSA were taken by UV–vis spectroscopy and shown in Figure 6. Commonly, the doped polyaniline would produce a localized polaron, resulting in a kmax around 750–
850 nm, referring to the conjugation length of PAN-IDBSA backbone. Now, the PANPAN-IDBSA had a kmax
at 827 nm and the peak experienced a blue-shift with rising ratio of PUDIC. When the ratio of PUDIC was raised to 20%, thekmax shifted from 827
to 812 nm due to the gradually increasing
interruption on the conjugation length of PANIDBSA by PUDIC through the formation of the H-bonding between them.
The normalized conductivity (apparent conductiv-ity divided by composition) is provided to replace apparent one to remove the effect of dilution of non-conducting material of PUDIC in the blends. When normalized conductivities of various PUDIC/PAN-IDBA were calculated and listed with kmax in Table
II, it is found that the conductivities of PANIDBSA dropped with PUDIC composition as were the val-ues of kmax. The intermolecular H-bonding from
PUDIC did contribute to the decreasing conductivity through the re-coiling on the PANIDBSA, which also led to the blue shift ofkmax.
The H-bonding in the blends brought PUDIC closer to the PANIDBSA and the bulky alkyl side chain of PUDIC can cause the re-coiling of the PANIDBSA structure through the so-called reverse secondary doping effect, which enhanced the blue shift.20
Optical activity
The H-bonding can also change the degree of helical conformation of PUDIC itself, which can be monitored by comparing the optical activity of neat PUDIC and
polyblends. As both the conjugation chain length of PANIDBSA and optical activity of PUDIC depend strongly on the formation of H-bonding, in Figure 7 the optical activity andkmaxversus the composition of
PANIDBSA was plotted to illustrate their relationship. The optical activity of the helical PUDIC decreased notably with the presence of PANIDBSA, resulting from the H-bonding due to the reverse, (de-natured) helical effect on the helical conformation of the PUDIC as seen in Scheme 1. The helical, reverse effect came from the losing of conjugation along the PUDIC back-bone when the lone paired electrons of carbonyl groups were not able to conjugate with the main-chain CAN bonds after being occupied by the H-donating amine groups through the formation of the H-bonding.
CONCLUSIONS
This research was based on synthesizing PUDIC that has a long alkyl side chain attaching to a helical rod structure to blend with PANIDBSA. The interaction of the polyblend system was found to originate from the formation of the H-bonding between the car-bonyl groups of PUDIC and amine groups of PAN-IDBSA. The WAXD patterns indicated the distance of lamellar structure of PANIDBSA backbone and were expanded with PUDIC from the insertion of it due to the formation of H-bonding. The presence of H-bonding was illustrated by the higher wave num-ber shifting of the absorption peak at 1700 cm1 characteristic of theAC¼¼O of PUDIC with the intro-duction of PANIDBSA. The hydrogen bonding between PUDIC and PANIDBSA also contributed to the blue shift of the kmax of UV–vis spectra due to
the decreased conjugation length of PANIDBSA backbone. The optical activity of the helical PUDIC decreased notably with the presence of PANIDBSA, resulting from the de-naturing (reverse helix) effect of the helical conformation of the PUDIC.
Figure 7 Diagram of optical activity and max versus composition of PANIDBSA.
TABLE II
kmaxand Conductivity of Various PUDIC/PANIDBSA
PUDIC/ PANIDBSA kmax (nm) Apparent conductivity (s/cm) Normalized conductivity (apparent conductivity/ composition of PANIDBSA) (s/cm) 0/100 827 0.61 0.61 0.5/99.5 825 0.60 0.60 1/99 824 0.51 0.51 2/98 821 0.47 0.48 5/95 818 0.32 0.34 10/90 816 0.12 0.13 20/80 812 0.08 0.1
Figure 6 UV–vis spectra of PANIDBSA with increasing PUDIC in the blends.
The formation of intermolecular H-bonding effect on the component polymers with helical conforma-tion and high conjugaconforma-tion turns out to be very inter-esting. In the future, a nanorod polyaniline will be prepared and will be mixed with the helical rod PUDIC to study the compatibility, rigidity, helixity of the rigid polymer blend.
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