RECENT ADVANCES IN SYNTHESIS OF MONOSUBSTITUTED ACETYLENE POLYMERS RAZVOJ NA PODROČJU SINTEZE MONOSUBSTITUIRANIH ACETILENSKIH POLIMEROV JIM VOHLIDAL1, J. SEDLAČEK1, M. ŽIGON2 'Department of Physical and Macromolecular Chemistry Faculty of Science, Charles University Albertov 2030, CZ-128 40 Prague 2 Czech Republic 2National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 During the last three years, a considerable progress has been achieved in deveiopment of catalyst systems for living polymerization of various substituted acetylenes. Nowadays, there are available single-component catalysts of this type based on stable carbene complexes and multicomponent catalysts based on MoOCU and WOCU, both operating in metathesis mode, as well as Rh(diene) complexes operating in the ZN mode. VVithin that time period, similar progress has been attained in polymerization of novel substituted acetylene monomers, including those bearing functional groups like -NO2, -NRi, -C=N, etc. and those bearing ionic or zwitterionic pendant groups. These advancements provide an improved basis for more systematic study of functional properties of these electrically and fotonically active polymers and a better comprehension of relations between the covalent structure and functional properties of this class of polymers. Key words: substituted acetylene polymers, living polymerization, functional polymers V obdobju zadnjih treh let je bil dosežen znaten napredek pri razvoju katalizatorskih sistemov za živo polimerizacijo različnih substituiranih acetilenov. Danes so tako na razpolago enokomponentni katalizatorji te vrste na osnovi stabilnih karbenskih kompleksov in večkomponentni katalizatorji na osnovi M0OCI4 in WOCU, ki delujejo po metateznem načinu, ter Rh(dienski) kompleksi, ki delujejo po načinu Ziegler-Natta (ZN). Za isto obdobje je značilen tudi napredek na področju polimerizacije novih substituiranih acetilenskih monomerov, vključno z monomeri s funkcionalnimi skupinami, kot so npr. -NO2, -NR2 ali -C=N, in z ionskimi ali zvvitterionskimi stranskimi skupinami. Razvoj na tem področju zagotavlja boljšo osnovo za sistematičen študij funkcionalnih lastnosti teh električno in fotonsko aktivnih polimerov ter za boljše razumevanje povezav med kovalentno strukturo in funcionalnimi lastnostmi te skupine polimerov. Ključne besede: substituirani acetilenski polimeri, živa polimerizacija, funkcionalni polimeri 1 INTRODUCTION For at least two decades, conjugated polytners attract significant interest of both academics and industry due to their potential applicability as functional materials for future electronic devices'"8. One class of these materials are substituted acetylene polymers, SAP, that are insula-tors in native state and do not show metallic conductivity neither after doping. However, they exhibit other useful functional properties like photoconductivity, electrolumi-nescence, nonlinear optical properties, etc. originating from their ability to capture, transport and mediate rau-tual conversions of charge and energy and from their inereased higher-order optical susceptibility. Besides, they are candidates for molecular wires transporting the charge and/or energy (signals) through membranes of su-pramolecular systems, see, e.g. ref.9. Actually, carotenoid pigments like carotenes and zeaxanthines, serving as molecular wires in living systems, are oligomers of the SAP type. It can be thus said that the research on synthesis and properties of substituted acetylene polymers really meets material demands of future electronics based on the molecular and supramolecular devices. There are a few published revievvs and book chapters summarizing the state of art in the field of synthesis of substituted acetylene polymers until 19952-3-5-8. In this pa- per a brief survey of recent developments in the field of living polymerization systems and synthesis of novel substituted acetylene polymers is presented. 2 LIVING POLYMERIZATION OF SUBSTITUTED ACETYLENES Living polymerization systems provide: (i) the most efficient control of the polymer molecular weight, and (ii) possibility to synthesize block copolymers of substituted acetylenes that can show some new interesting properties originated from their domain interfaces. First living metathesis polymerizations of substituted acetylenes have been reported in 1987 for o-Me3Si-phenylacetylene51(, n and tert-butylacetylene12. Most ef-fort has been paid to systems with phenylacetylenes bearing bulky ortho substituents and MoOCL/B^Sn/ EtOH catalyst that give polymers with polydispersity I„<1.10. Analogous systems without ethanol or bulky substituents do not show living polymerization. Monomers with medium-size substituents yield only living-like systems providing In values about 1.2 to 1.3 and m-and p-substituted phenylacetylenes provide systems in which a termination takes plače5 '314. An exception is 1-chloro-l-octyne that also provides living polymerization system15. In 1994, Schrock et al.16 reported of the living metathesis poIymerization of o-trimethylsilyl phenylace-tylene induced by (l-adamantyl-N=)[OCH(CF3)2]2(2,4-lutidine)-Mo=CH-CMe2Ph carbene complex (In = 1.05). They found that other carbene initiators with bulkier li-gands do not provide living polymerization systems. Buchmeiser and Schrock have reported of the living stereoregular polymerization of three organometallic acetylenes, ethynylferrocene and ethynylruthenocenen and 4-(ferrocenylethynyl)-4'-ethynyltolan (tolan is a triv-ial name for diphenylacetylene)18 induced by another Mo-carbene complex: (2,6-Me2-CsH3-N=) [OCH(CF3)2]2Mo=CH-CMe2Ph in THF and toluene. Recently, Masuda et al. reported living poIymeriza-tion of o-CFj-phenyl-acetylene in anisole induced by WOCl/Bu4Sn/t-BuOH catalyst (I„<1.1)19. Again, alcohol vvas found to be essential for the living polymerization to be achieved. Similar behaviour has been observed for the systems MoOClVE^Al/EtOH (1:1:4), MoOCVEfeZn/ EtOH (1:1:4) and MoOCVBuLi (vvithout alcohol) for vvhich polymer polydispersities about I„=1.02 to 1.03 are reported19. Rh!(diene) complexes represent another class of living polymerization initiators because, unlike the previ-ous, they operate in the Ziegler-Natta mode and induce living polymerization of sterically uncrovvded acetylenes including unsubstituted phenylacetylene, PA. Kishimoto, Nyori et al. reported20 of the living polymerization of PA induced by [Rh(nbd)(PPh3)2(-C=CPh)] and the synthesis of block copolymers of PA vvith p-methoxy-PA. Living system is only obtained if a strong base like 4-(dimethy-lamino)pyridine, DMAP, is added into polymerization mixture. Later on, the same authors reported of the living polymerization of PA and p-(0CH2CH2CH20-Ph-Ph-OCH3)-PA by bridged binuclear Rh1 complex [Rh(nbd)(OCH3)]2 in apresence of DMAP21. In ali cases, stereoregular head-to-tail cis-transoid structure is reported for polymers prepared on catalysts derived from Rh(diene) complexes. In summary, it can be said that a development of living polymerization systems has achieved considerable advances in recent years and further progress in this field seems quite promising. Besides, the catalysts forming living polymerization systems often give stereoregular polymers vvhich is promising for a progress in analysis of microstructure of substituted acetylene polymers. 3 NEW SUBSTITUTED ACETYLENE POLYMERS Functional properties of SAPs depend on their struc- ture that, in the first plače, is predetermined by pendant groups attached to their main chains. Great attention is, therefore, paid to design and synthesis of nevv polymers vvith more sophisticated structure that are expected to possess better functional properties. In addition, the investigation of these nevv polymers brings up nevv knovvl-edge improving our general understanding of the rela- tions betvveen the polymer structure and functional properties that is rather poor till now. Some interesting, re-cently prepared substituted acetylene polymers are pre-sented in the next survey. HCsCH§) i Me X X = Y = H 2 X = Y = Me 3 X = Me Y = tBu 4 Demonstration of positive effect of bulky ortho sub-stituents on the molecular vveight, thermal stability, UV/vis absorption and other properties of PPA22. Rate of polymerization decreases from 1 to 4. Tert-butyl group improves polymer solubility: poly(3) is insoluble vvhereas poly(4) is soluble and provides free standing films. Copolymers of 4 vvith 1 and 2 vvere prepared. Gas permeability and dark conductivity measurements are reported. Hc=e—5 i First polymerization of iodophenylacetylenes by various Mo, W and Rh based catalysts. Poly(5)s formed on MoC15 based catalysts are insoluble, on Rh catalyst partly soluble, and on WOCl4 based catalyst soluble. Di-oxane cosolvent increases MW of polymers prepared on WOCl4 based catalyst. Unusual, negative effects of com-mon cocatalysts like Ph4Sn and Bu4Sn have been observed. Content of cis-units decreases in the follovving order: Rh>Mo>W/dioxane>W/benzene. Poly(7) is stable in solutions exposed to air vvhereas poly(5) and poly(6) are not. Photoconductivity of soluble polymers prepared by WOCI4 based catalyst is reported23"25. HteCHjo)-W02 8 1 j. vohlidal et al.: recent advances in synthesis of First polymerization of 8 and its copolymerization with PA by WOCl4/Me4Sn in dioxane/benzene and [Rh(nbd)(PPh3)2(-C=CPh)]. WOCl4 by itself does not transform 8 to any oligomer or polymer. Homopolymers of 8 are insoluble. Photoconductivity measurements on the copolymer of 8 with PA are reported. Nitro group was found to act as a trap for photogenerated charge car-riers25-26. HteC-^) 1 HteC-/OV-Me 9 Polymerizations in vvater, THF, Et3N and toluene in-duced by various Rh'(nbd) and Rh'(cod) complexes: other ligands: tosyl, H20, Cl, piperidine, o-phenyle-nediamine, N-methylimidazole, bis(4-tBu)-2-pyridyl-methanethiolate, tBuNH2, NH3. [Rh(cod)(tosyl)(H20)] complex yields all-cis polymers. Acetylenes of aliphatic type (l-octyne, l-butyne-4-ol, 5-hexyne carboxylic acid and 2-butyne dicarboxylic acid) do not polymerize on this Rh catalyst27. OCONH-X HfeCHg^ where X = : (R,)-CH(CH )-Ph m- 10 3 1 « p- 11 00-CH(CH )-a-naphtyl 3 p- 12 -0-SiMe -tBu m- 13 2 p- 14 -0-SiPh -tBu p- 15 z PA 1 4-ethynylbiphenyl 16 a-ethynylnaphtalene 17 Homopolymerization of phenylacetylenes with bulky, optically active groups linked to phenyl ring and their copolymerization with non-chiral monomers. [Rh(nbd)Cl]2 in THF solvent vvas found to be efficient initiator yielding high cis-transoidal polymers vvhereas WCyPh4Sn and MoCl5/Ph4Sn systems have provided oligomers and/or low-MW polymers only. Upfield shifts of olefinic protons' NMR signal up to 0.25 ppm are cor-related to increasing co-monomer bulkiness resulting in tvvisting up of the main chain. Polymers of 10,11 and 12 as vvell as their copolymers vvith achiral acetylenes 1 and 13 to 17 shovv circular dichroism, CD, in 300 to 500 nm range. Stereoregularity of main chains vvas found to be essential for CD activity (non stereoregular polymers of chiral monomers do not shovv significant CD bands). Computational study of the polymers' helical structure is presented28. HfeC-^O)-000-(ch2 }n" -o-©-©-« 18 n = 6, 12 Successful transformation of both monomers 18 into cis-transoid stereoregular PPAs vvith pendant polar mesogenic groups by using [Rh(nbd)Cl]2 catalyst. WCls/Ph4Sn yields either cyclotrimers (in THF) or their mixture vvith lovv MW polymer (in toluene). MoCl5/Ph4Sn catalyst has not shown activity in any solvent. DSC records as vvell as slovv polymer dissolving prove to a formation of mesogenic structures29. HC=C-^^y-C=C-SiIPr3 19 where X = CsC-SiJPr 20 3 Selective polymerization of 19 and 20 by Mo, W and Rh based initiators taking plače on terminal ethynyl group is reported. Polymer formed by WOCl4/Ph4Sn catalyst in benzene involves a small amount of soluble high-MW fraction. Dioxane cosolvent suppresses this fraction formation and increases content of cis units in poly(19) and poly(20). Content of cis units increases in order: W/benzene-C=C—Fc 22 (Fc is ferrocenyl). TaCl5 quantitatively cyclotrimer-izes 21 to 1,2,4- and l,3,5-triferrocenylbenzenes (mole ratio 3:2). Solid state structure of 1,3,5-isomer vvas es-tablished: up-up-down arrangement of Fc groups. 21 vvas copolymerized vvith 1 to a soluble statistical copolymer. 22 vvas selectively polymerized on terminal ethynyl group by using W and Rh based catalysts to partly soluble polymers3233. HC=C-^ HCsC-/ 23 P NO NO x = cooch ch ooc—(o NO The first reported polymerization of acetylene bear-ing nitro group. Cyclopolymerization of dipropargylic monomer induced by MoCyPh4Sn and PdCl2 catalysts. The former yields only partly soluble (solubility depends on the solvent used in polymerization), whereas the latter eompletely soluble poly(23). W-based catalysts were found as inactive. Polymer shows UV/vis absorption up to ca 650 nm34. V hc=c-\ O hc=c-^ r = h r = Me r'= h r2= pentyl 26 rj = Me r2= ph 27 R1= R2= cyclohexyl 28 hc=c-ch hc=c-ch hc=c-ch N 30 31 [0 32 MoOCIVMejSn and MoCl5/EtAlCl2 polymerize 30 to insoluble polymer, 31 to insoluble polymer and metha-nol-soluble fraction, and 32 to soluble, high-MW polmer (W value up to 480 000) and methanol soluble fraction. Methanol soluble fractions formed on M0OCI4 consist of oligomers only (MW below 1000), whereas in those formed on MoCl5 involve polymers of „ value up to 35000. The former catalyst is more active than the latter one. WOCl4/Me4Sn system in dioxane/benzene (highly active in polymerization of nitroPA, 8) shovvs lovv activity at room temperature (only methanol soluble polymer is reported) but no activity at 60°C 37. b c h2" 9 2 11 hc=c-ch -s co 2 \ 3+ 33 b c h2" 9 2 U Cyclopolymerization of series of dipropargyl ethers. MoC15 based catalysts (EtAlCl2 and Bu4Sn cocatalysts) vvere found to be most active providing high yields of medium-MW polymers. WC16 based catalysts are almost inefficient and PdCl2 gives only 25% yield of poly(27). Poly(24) is insoluble. Solubility of poly(25) and poly(26) depends on the monomer concentration in po-lymerization mixture (above [M] = 0.5 mol/L, the formed polymers are insoluble). On the contrary, poly(27) and poly(28) are vvell soluble. Bulky a-substi-tuents are suggested to support intramolecular cycliza-tion and suppress intermolecular crosslinking, thus en-suring good polymer solubility. UV/vis absorption up to 600 nm and dark conductivity in both native and iodine doped state are reported35. O. OEt V HC=C-CH CH7 XOEt 2 ^COOEt 29 By itself M0CI5 and WC16 do not induce polymeriza-tion of 29 but together vvith EtAlCl2 or Ph4Sn cocatalysts provide good yields of low-to-medium-MW yellow polymers (W belovv 10000). PdCl2 gives only lovver yield of brovvn poly(29). UV/vis absorption up to 500 nm is reported36. First preparation of polyacetylene vvith deltahedral sandvvich carborane pendant groups is reported. WOCl4/Ph4Sn catalyst induces polymerization of 33 to a polymer partly soluble in DMSO. Strong intermolecular interactions of zvvitterionic carborane groups (dipole moment 17.7x10"30 Cm) are perhaps responsible for lovv solubility. The same catalyst copolymerizes 33 vvith 1 to a soluble statistical copolymer38. HC^O) h c7 + 37 18 34 , Br Quaternization of 2-vinylpyridine vvith 1-bromooc-tadecane is accompanied by a spontaneous polymeriza-tion of formed 34. Poly(34) vvas also prepared by quaternization of thermally prepared poly(2-vinylpyrid-ine). Multilayers thin films of poly(34) vvere prepared by LB technique and their properties vvere investigated. Electrical conductivity of native and iodine doped polmer and oxygen and nitrogen permeation of membranes deposited on Nafion as substrate are reported. The multi-layer membranes have shovvn excellent long term stabil- ity39,40 N-/ ,Br 34 h t/ + 37 18 HC=C—>,+ R HC=C-^ ^Bu iK SO 3 SO R = Et 35 R = Bu 36 R = hexyl 37 R = octyl 38 Synthesis of amorphous, conjugated polybetaines by cyclopolymerization of 35 to 38 induced by M0CI5, WC16 and PdCl2 catalysts. Negative effect of cocatalysts (EtAlCl2 and Bu4Sn) has been observed for the first two catalysts (viz. also polymerization of iodophenylacety-lene 5). Solubility of polymers in various solvents, UV/vis absorption up to 600 nm, dark conductivity in native and iodine doped state are reported41. 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