Langmuir 1990,6, 1807-1809
1807
Notes Polymerization of a Chemically Adsorbed Monolayer of a n Acetylene Derivative
SA-NTS IHdlaSi-C~C-lC~lll-SiCU
-
Kazufumi Ogawa,' Norihisa Mino, Hideharu Tamura, and Motoyoshi Hatadat
OH OH OH OH OH
Central Research Laboratories, Matsushita Electric Industrial Co., Ltd., 3-15, Yakumo-Nakamachi, Moriguchi, Osaka, 570 Japan, and Osaka Laboratory for Radiation Chemistry, Japan Atomic Energy Research Institute, 25-1 Mii-minamimachi,Neyagawa, Osaka, 572 Japan
Receiued Nouember 14,1989. In Final Form: March 2,1990 Polyacetylene, which consists entirely of conjugated double bonds, exhibits a number of interesting features with regard to optical, electronic, or magnetic properties such as a nonlinear optical effect,' electrical conductivity,2 or fer~omagnetism.~ Especially, synthesis of polyacetylene films with few sp2 defects has been the subject of many efforts to prepare organic polymer films of high electrical cond~ctivity.~ This paper reports that a monolayer of polyacetylene type can be prepared from (19-(trimethylsilyl)-18Figure 1. Schematic view of the preparation process of polynonadecyny1)trichlorosilane ( ( C H ~ ) ~ S ~ C ~ C ( C H ~ ) I acetylene ? S ~ - monolayers using a catalyst or an EB irradiation. CIS: SA-NTS) adsorbed monomolecularly on a silicon substrate by a chemical adsorption (CAI technique decane, 12% carbon tetrachloride, and 8%chloroform as developed by Sagi- followed by polymerization initiated recommended by Netzer e t aL'0 The CA process was either by (1)catalysts or by (2) high-energy electron beam investigated in detail by Netzer et aL7and Pomerantz et (EB) irradiation. al.I4 This procedure was carried out in a nitrogen SA-NTS was selected as film substance in this study, atmosphere, where solid particles above 0.2-wm diameter because the polymerization process of (silylmethy1)were removed by filtration. The substrate taken out from acetylene derivatives was studied in detail.'"13 the solution was washed with chloroform to remove excess Synthesized SA-NTS was characterized by NMR, IR, substance and then with water to convert the remaining and mass spectrometry. The purity of the compound was Si-CI bonds to Si-OH bonds in the deposited monodetermined to he 94.4% by gas chromatography. The layer. The surface of the substrate turned strongly method of synthesis will be published elsewhere. The hydrophobic by this procedure. substrate on which the SA-NTS monolayer was deposited Catalytic polymerization was carried out in a toluene was a Si wafer covered with SiOZ/Al prior to use for the solution of TaCls (Wako Pure Chemical Industries Ltd., measurement of IR spectra or a quartz plate for the UV 2.5 x mol/L) in a dry nitrogen atmospere at 30 OC spectra. Other chemicals used, unless otherwise noted, for 10 min. After being taken out from the catalyst were obtained from Aldrich Chemicals Co., in pure grade, solution, the substrate was washed with methanol to and used without further purification. remove excess catalyst that may remain on the surface. The experimental procedure is summarized in Figure Polymerization of the SA-NTS monolayers on the 1. SA-NTS was adsorbed monomolecularly by immersing substrate by EB irradiation was carried out in helium the substrate in the solution of SA-NTS (concentration: atmosphere (content of 0 2 less than 20 ppm) a t the dose 7 X l W mol/L) in a mixed solvent containing 80% n-hexarate of 0.02 Mrad/s. The dose absorbed by the monolayer was estimated by using a CTA film dosimeter. The 7 Osaka Laboratory. details of the EB irradiation are reported el~ewhere.'~ (1) Heeger, A. J.; Moses, D.; Sinclair, M.Synth. Met, 1981,17,343. (2)Shirakawa.H.:Louis.E.J.:Maediarmid.A.G.:Chiane.C.K.:Hee". . The monolayers thus polymerized by either of the two ger; A. J. J. Chem. Sac.. Chem. Commun. 1971,516. methods were subjected to infrared (IR) spectroscopy on (3) Ovchinnikov, A. A. Theor. Ckim. Acto 1918,47,297. a Shimadzu FTIR-4000 spectrometer with a multiple (4)Bnwscu, N.; Liu, 2. X.; Moses, D.; Heeger, A. J.; Nsarmann. H.; Theoohdou. N. Nature 1987.327. 403. external reflection (MER) attachment and to UV and (5fSaeiv. J. J . Am. Chem. Soe. 1980,102.92. visible spectrometry on an Otsuka Electronics spectro(6) Poiymeropoulos, E. E.; Sagk, J. J . Chem. pi'lye. 1918,69,1836. photometer MCPD-11OA. The MER IR spectra were ( I ) Netzer, L.: Sagiv, J. J. Am. Chem. Soe. 1983,105, 614. ( 8 ) Netzer. L.: Iscoviei. R.:Sack. J. Thin Solid Films 1983. I W . 67. measured with the incidence angle of 73" which resulted I: J. Tkrn Soltd Ftlms 1983.99.235. in seven external reflections. Seven-thousand interfero(IO) Voronkov, m. G.: Pukharivich. V. B.; Sushchinskaya, S. P.; Angrams had to be accumulated to obtain a spectrum. nenkova. V. 2.;Annenkova, V.M.; Andreeva, N. J. J. Polym. Sei., Polym. Ckem. Ed. 1980,16, 53. Assignments of the IR and UV spectra were made in (ll)Maauda,T.;Isobe,E.;Higashimura,T.;Tsksda,K.J.Am.Chem.
Sac. 1983, 105,7413. (12) Masuda, T.; Isobe, E.;Higashimura,T. Macromolecules 1985,18, 841. (13) Masuda, T.; Isobe, E.; Hgaahimura, T. J. Polym. Sei.,Polym. Ckem. Ed. 1986.24, 1839.
0743-7463/90/2406-1807$02.50/0
(14) Pomerantz,M.;Segmuller, A,; Nstzer, L.; Sagiv, J. Thin SolidFilms 1985,132,153. (15) Ogawa, K.;Tamurs, H.; Hstada, M.; Ishihsra, T. Colloid Polym. Sci.1988,266, 525.
0 1990 American Chemical Society
Notes
1808 Langmuir, Vol. 6, No. 12, 1990
- 1 S!r
I
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I
!
I
m
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Q
L
roo
I 2000
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cm-
Wovenumber 1cm-l)
Figure 2. IR spectra of the CA monolayers of SA-NTS before (A) and after (B) polymerization by the catalyst solution of TaCb (a);before EB irradiation (A) and after the irradiation in He gas atmosphere (B-D) (h). Irradiation dose: A, 0, B, 2, C, 5; D, 10 Mrad. All spectra reported here were the results of subtraction of the curves measured with the clean Si02/Al/Si platea from those measured after reflectingthe respective films on the same plates. I
Fmure 4. CPK model of SA-NTS pol er monolayer havi trans-polyacetylene conjugated bonradsorbed on a sol# substrate: (a) top view, (h) side view, (c) bottom view, and (d) schematic view of the atom positions projected to the substrate. I
stretching vibration of the C=C bond in a conjugated system, since it was reported that a conjugated doublebond system gives a peak at 1630 cm-' and a theoretical Figure 3. UV spectra of the CA monolayers of SA-NTS before calculation predicts that the conjugated double bond gives and after polymerizationby the catalyst solution of TaCb (a)and a band in the region between 1610 and 1470 by the EB irradiation of 5 Mrad in He gas atmosphere (b). Similarchange was observed for electron beam initiated polymerization, as shown in Figure 2b (A through D).The reference to the reports by Takeuchi et al.16 and Masuda intensity of the peak due to the C%C bond at 2175 cm-' et a).:* respectively. decreased, and the peak at 1640 cm-' aseigned to the C=C Figure 2a shows the IR spectra of the monolayers before stretching vibration appeared by the irradiation and (A) and after (B)the polymerization initiated by catalyst. increased in intensity with increasing dose. The peak at It is noted that the band due to the C=C stretching 1640 cm-I seemed to move slightly to a higher wavenumvibration observed at 2175 cm-I in the spectra taken before ber, possibly due to decrease of the length of the conpolymerization (spectrum A) disappeared by the polyjugation during irradiation. merization, and a new peak appeared at 1620 cm-', as The band that appeared at 1720 cm-I by the electron shown in spectrum B. The new band is assigned to the beam irradiation is assigned to the stretching vibration of (16)TTakeuehi,H.;AraLewa,T.;FuruLawa,Y.;Harada,L.;ShraLaara,a carbonyl group (vc-0) formed by the reaction of H.J. Mol. Strut. 1987,158,119. hydrocarbon chaii with oxygen that exists in helium as 250
YK)
350
4w
Wovelenpth l n m l
450
500
Notes
contaminant, since the band was only observed in the spectra of polymerized CA films by the EB irradiation but not in the spectrum (Figure 2a, spectrum B)of catalytically polymerized CA film. The band due to CH2 stretching vibrations ( u ~ 2930 , cm-1; us, 2860 cm-1) slightly decreased with increasing EB irradiation dose as shown in Figure 2b. This indicates that the radiation-induced oxidation, decomposition, and/or cross-linking of hydrocarbon chains occurred during the irradiation. No decrease of the CH2 band was observed by the catalytic polymerization (Figure 2a, spectrum B). The band that appeared at 1460 cm-l was also assigned to the scissoring vibration due to CHz groups (CH2,6). Another band was observed at about 1420 cm-' in the spectra of polymerized LB films and increased with dose as shown in spectrum B of Figure 2a and in spectra B, C, and D of Figure 2b. This band may be due to the same origin as the unassigned band at 1420 cm-' in the spectrum reported by Masuda et a1.12 in the polymerization of acetylene derivatives, but it is not assigned at present. The UV spectra of the monolayer before and after polymerization procedures are shown in Figure 3a and 3b for catalytic and E B initiations, respectively. T h e absorption peak is observed at 255 nm in the spectrum before polymerization. The intensity of the absorption increased and a shoulder appeared at 275 nm by the catalytic polymerization as shown in Figure 3a. Subtraction of the spectrum of the monomer from that of the polymer reveals that a new absorption appeared at 275 nm which agrees well with the data A(, 273 nm; Mn, 1.3 X lo5) reported by Masuda et a1.12 In the case of the EBof the peak that appeared by initiated polymer, A,, polymerization was 265 nm, which is shorter than that
Langmuir, Vol. 6,No. 12, 1990 1809
observed for the catalytically initiated polymer (275 nm). These results indicate that the polymers having conjugated double bonds were formed, and the length of conjugation in the catalytically initiated polymer was a little longer than that in the polymer obtained by EB initiation. A possible structure of the monolayer having a conjugated system built up by a CPK model is shown in Figure 4a (top), 4b (side), and 4c (bottom). The conjugated double-bond system (shown in Figure 4a) is located behind bulk Si-CH3 groups, and only a part of the system can be recognized. However, one can understand t h a t the projected length along the axis of the main chain of the conjugated double-bond repetition unit (C=C-C=C-) is close to that of Si-O-Si-0- and that of the distance between adjacent hydrocarbon chains (Figure 4c and also the illustration in Figure 4d). By this method, it is to be expected that the longer conjugated double bonds can be prepared by the irradiation of a monolayer with a particular orientation, because the molecules in the monolayer before polymerization are chemically bonded to the substrate so that the triple bonds are arranged in the position which is favorable for the formation of conjugated double bonds, and the conjugated bonds formed by the polymerization are protected from being twisted by molecular agitation.
Acknowledgment. The authors are grateful to Dr. T. Nitta, director of the Central Research Laboratories of the Matsushita Electric Industrial Co., Ltd., for his support and encouragement of this study. Registry No. SA-NTS (homopolymer), 127613-09-6;SiOz, 7721-01-9; TaClS, 7631-86-9.
