J. MATER. CHEM., 1991,1(3), 483-484 Simple and Convenient Method for Preparing Functionalised Network Organopolysilanes Hamao Watanabe,* Minoru Abe, Katsumi Sonoda, Morihiko Uchida, Yuko lshikawa and Makoto lnomiya Department of Chemistry, Faculty of Engineering, Gunma Universitx Kiryu, Gunma 376, Japan A new type of organosilicon polymer, network organopolysilanes bearing methoxy functional groups on the polysilane framework, has been produced via the catalytic redistribution polymerisation of methoxydisilanes which were prepared using the 'pot-residue' disilane fraction in direct synthesis. Keywords: Organosilicon polymer; Functionalised network; Catalytic redistribution polymerisation Much attention has been focused on polysilanes which are accessible via Wurtz-type coupling reactions, homo- and co-polymerisation, of a variety of dichlorodialkyl- and/or di- chloroalkylaryl-silanes.These polysilanes, despite having only limited variety of structure owing to the linear backbone, have recently been shown by many workers to have versatile properties useful for functional materials in high-technology as photoresists, organic photo- and semi-conductors, ceramic precursors, non-linear optical materials, etc. Polysilanes con- sisting of functionalised and/or network structures can be expected to show a variety of unique physical and chemical properties different from those of the linear polysilanes. How- ever, only a few reports on such polysilane structures have appeared so far.' Previously, we have reported that the reactions of sym-methoxymethyldisilanes, (MeO),Me6 -,,Siz (n=4, 2),2 with sodium methoxide gave the first functionalised silanide anions, (Me0)'MeSi-and (MeO)Me2Si-.3 Also, we fond that sym-dimethoxydisilane (n=2) undergoes a catalytic redistribution reaction, giving a series of a,o-dimethoxypermethylpoly-silanes, from which, in the presence or absence of certain reagents, various products, such as a-hydro-o-methoxypoly- ~ilanes,~cyclopolysilanes,5 tetrasilacyclo- and disilacyclo-hexane6 derivatives, trisilacyclo-pentene6 and -pentane7 derivatives, were formed.It has been unequivocally demon- strated that these products can be produced through the reaction of methoxypermethylpolysilanide anion intermedi- ates, MeO(MezSi),Me2Si-, derived from a,o-dimethoxyper- methylpolysilanes by the action of an NaOMe cataly~t.~ As a continuing study of the series of the reactions men- tioned above, we report here the first simple method for preparing a new type of organopolysilane having func- tionalised network systems by using methoxylated disilanes as the starting materials, (MeO),,Me6-nSi (n=4, 3 and a mixture of the two).' Simultaneously, in view of the effective utilisation of disilane resources formed as the by-products in the direct synthesis of methylchlorosilanes, we were able to convert successfully the disilane fraction in the 'pot-residue' (C1,,Me6-,Siz; b.p.150-160 "C) into more usable materials in high-technology fields. The catalytic redistribution reaction of these disilanes was exothermic and proceeded readily in a no-solvent system or in tetrahydrofuran (THF) (Scheme 1).This produced polysilanes as a white or pale-yellow solid which is soluble in the usual organic solvents as has been generally shown in linear polysilanes. Typically, a mixture of la (5 g, 24mmol) and NaOMe (2 mol% relative to la) was stirred under nitrogen for 24 h, during which time the mixture was kept at 40 "C after the end of its exothermic reaction. Addition of a catalyst quencher (an excess amount of 1-chloro-2,3-epoxypropane) and then 'pot-residue' CI,Me,-.si, "Si,-CI,Me,-(n=4+3) (n= 4 and 3) methoxylation (MeO),Me,-,Si, 1 a n=4 b n=3 c n=4+3 Scheme 1 polysilanes catalyst A MeONa B Bu'OK C H,NLi D BuLi E Na toluene (15 cm3) gave a light green-yellow mixture, from which the insoluble material was separated by centrifugation to leave a toluene solution.The solution was evaporated to dryness in U~CUOto give a pale green-yellow powder of 2a (0.77 g, 16% relative to la employed). The toluene-insoluble material was mixed with absolute methanol (15 cm3) and centrifuged to give a white powder, on drying in U~CUO(0.16 g, Table 1 Catalytic polymerisation of disilanes polymer disilane" catalyst (mol%)b solvent' time/h quencherd no. %' ~~ i 24 ClEP 2a(l) 16 11 4 BrEP 2a(2) 14 i 24 BzCl 2a(3) 11 1 24 ClEP 2a(4) 15 1 24 ClEP 2a(5) 10 i 24 ClEP 2a(6) 20 11 4 ClEP 2a(7) 15 i 24 ClEP 2a(8) 19 11 2 ClEP 2a(9) 16 1 24 ClEP 2a(10) 11 11 4 BzCl 2a(ll) 12 i 24 BzCl 2b(12) 23 11 24 BzCl 2b(13) 20 i 24 BzCl 2c(14) 30 11 24 BzCl 2c(15) 24 "About 5 g (24 mmol).'Relative to the disilane employed. 'i, None; ii, THF (15 cm3). dCIEP, I-chloro-2,3-epoxypropane;BrEP, l-bromo- 2,3-epoxypropane; BzCI, benzyl chloride. 'Relative to the disilane employed. See ref. 6. BPrepared by methoxylation of Clz MeSiSiMe,Cl obtained from a disilane fraction, see ref. 8 [scheme (l)]. hA mixture of (MeO),MeSiSiMe(OMe),: (MeO)Me,SiSiMe(OMe), =63 :37 (b.p. 38-49 "C at 0.1 mmHg) prepared from a disilane fraction (b.p. 150-160 "C), see ref. 2. J. MATER. CHEM., 1991, VOL. 1 Table 2 Characteristics of selected samples of polysilanes polymer appearance M," MWIM" MeSi :0Meb pale- yellow powder 56 700 7.5 3: 1 72 200 9.3 3: 1 48 500 9.5 3: 1 71 300 10.3 e pale- yellow viscous liquid I100 1.2 10: 1 1600 1.3 6: 1 1300 1.3 3: 1 1500 1.3 8: 1 ceramic yield (%)f 80 75 70 e e e e e "GPC method; polystyrene standards.*Methyl hydrogen ratio by 'H NMR method. 'After heating from 40 to 1000 "C at a rate of 10 "C min-' in N,. dPolymer 2a sometimes changes insoluble in organic solvents after standing for several weeks. 'Not determined. 3.2% of 3a). Similarly, the reactions to produce the poly- silanes were carried out in THF solution, removal of the sol- vent in uucuo was made after quenching the catalyst and the subsequent treatment for the resulting mixture was similar to that of the above reaction.Thus, three types of polysilane, 2a, 2b, and 2c, were produced in the presence of catalysts from the corresponding starting materials, (MeO)2MeSiSiMe(OMe)2(la), (MeO)2MeSiSiMe2(OMe)(lb), and a mixture of la: lb=63 :37 (lc) (Table 1). The characterisation of the products was carried out in the usual manner. A sample of 2a, for example, showed IR absorption bands at ca. 1080(SiOMe) and 1250(SiMe) cm- ', 'H NMR broad peaks at 3.5 (centre, OCH,) and 1.0-O.l(SiCH,)ppm in a ratio of 1 :3, "Si NMR signals of several unresolved peaks near -80 ppm, and UV-VIS band rising from near 400 nm, which increases in intensity with decreasing wavelength.? These results suggest that the struc- ture of the sample is a network systemIb to which the methoxy groups are attached (Table2).Also, the polymer was found to be amorphous by X-ray diffraction. Thermogravimetric analyses of polysilane 2a (40-1000 "C; heating rate, 10 "C min-' in N2) were performed and the weight losses were <30% in all samples tested. With respect to the reaction pathway for the formation of the polymers, e.g. for 2a, it is likely that polysilanyl anions arising from the scission of permethoxymethylated polysilanes by the catalyst play an important role in the propagation leading to the network structure, chain elongation, branching and bridging between chains, accompanied by the regener- ation of metal methoxide in the catalytic cycle.4 t Absorptions in the region of ,I=350-250 nm increased by a factor of E =ca.103-10" (cyclohexane solution) per (MeSi),(OMe) unit. Finally, it should be emphasised that the present study opens up the way for the simple and convenient conversion of the disilane 'pot-residue' into more valuable forms; in particular, new types of organopolysilane with versatile properties as functional materials were produced. In addition, the polysilanes thus formed could have their structures and properties modified by replacing the methoxy or methyl groups in OMe substituents with others via the use of nucleo-philes (Grignard reagents and alkyl metals) or electrophiles (alkyl halides, etc.). References 1 (a) R. H. Baney, J. H. Gaul Jr.and T. K. Hilty, Organometallics, 1983,2,859;(b) R. A. Bianconi, F. C. Shilling and T. W. Weidman, Macromolecules, 1987, 22, 1697; (c) K. Furukawa, M. Fujino and N. Matsumoto, Macromolecules, 1990, 23, 3424. 2 H. Watanabe, M. Kobayashi, Y. Koike, S. Nagashima, H. Matsumoto and Y. Nagai, J. Organomet. Chem., 1977, 128, 173. 3 H. Watanabe, K. Higuchi, M. Kobayashi, M. Hara, Y. Koike, T. Kitahara and Y. Nagai, J. Chem. SOC., Chem. Commun., 1977, 534. 4 H. Watanabe, K. Higuchi, T. Goto, T. Muraoka, J. Inose, M. Kageyama, Y. Iizuka, M. Nozaki and Y. Nagai, J. Organomet. Chem., 1981, 218, 27. 5 H. Watanabe, K. Higuchi, M. Kobayashi, T. Kitahara and Y. Nagai, J. Chem. SOC., Chem. Commun., 1977, 704. 6 H. Watanabe, J. Inose, T. Muraoka, M. Saito and Y. Nagai, J. Organomet. Chem., 1983, 244, 329. 7 H. Watanabe, J. Inose, M. Kameyama, M. Saito and Y. Nagai, J. Chem. SOC., Chem. Commun., 1982, 1366. 8 H. Matsumoto, T. Motegi, M. Hasegawa and Y. Nagai, J. Organomet. Chem., 1977, 142, 149. Communication 1/01414E; Received 25th March, 1991