US007399.504B2 (12) United States Patent (10) Patent No.: US 7,399,504 B2 Dibbs et al. (45) Date of Patent: Jul. 15, 2008 (54) METHOD OF PREPARING AN INSOLUBLE (56) References Cited POLYMERFILM ON A SUBSTRATE FROMA SOLUBLE POLYMER CONTAINING LABLE U.S. PATENT DOCUMENTS SOLUBLIZING GROUPS 5,708, 130 A 1/1998 Woo et al. ................... 528/397 (75) Inventors: Mitchell Gene Dibbs, Midland, MI 6,169,163 B1 1/2001 Woo et al. ................... 528/397 (US); Michael Inbasekaran, Midland, 7,095,044 B2 * 8/2006 Brown et al. .................. 257/40 MI (US); Paul Henson Townsend, III, 2004/0266207 A1* 12/2004 Sirringhauss et al. ....... 438,725 Mesa, AZ (US); Kenneth L. Foster, Brighton, MI (US); Shaoguang S. Feng, Midland, MI (US); David J. Brennan, Midland, MI (US); Q. Jason Niu, (Continued) Midland, MI (US); James P. Godschalx, Midland, MI (US); Dean M. Welsh, OTHER PUBLICATIONS Midland, MI (US); Ray E. Drumright, Midland, MI (US) Brown, A.R., et al., “Field-effect transistors made from solution processed organic semiconductors.” Synthetic Metals. 1997. vol. 88, (73) Assignee: Dow Global Technologies Inc., pp. 37-55. Midland, MI (US) (Continued) (*) N' SEE", Primary Examiner Erma Camerson p S.C. 154(b) by 386 dy (74) Attorney, Agent, or Firm Sughrue Mion, PLLC (21) Appl. No.: 10/936,010 (57) ABSTRACT (22) Filed: Sep. 8, 2004 (65)65 PriorOla Publication DatJaa The present invention relates to a method for preparing poly US 2005/0106324 A1 May 19, 2005 meric films, preferably electroactive films, with enhanced O O physical properties by the steps of applying to a Substrate a Related U.S. Application Data Solution of a polymer containing pendant labile solubilizing (60) Provisional application No. 60/503.229, filed on Sep. groups, then removing the solvent and a Sufficient concentra 16, 2003. tion of the labile solubilizing groups render the polymer less soluble in the solvent than before the labile groups were (51) 5.MO2 2006.O1 removed. It is believed that the removal of pendant soluble B05D3/6 6. O groups a) permits optimization of the semiconducting back B05D 3/10 30 6. 8: bone for charge transport performance, b) allows direct con trol of microstructure in the final film, and c) renders the final (52) U.S. '575,4372. E.E. film more robust during Subsequent process steps needed to (58) Field of Classification Search ................. is construct multilayer devices. 427/553,557,558, 226,337,340, 341 See application file for complete search history. 16 Claims, 1 Drawing Sheet 3.3 O. 200 400 US 7,399,504 B2 Page 2 OTHER PUBLICATIONS Sirringhaus, S., et al. “High-Resolution Inkjet Printing of All-Poly mer Transistor Circuits.” Science. 2000. Volument 290, pp. 2123 Gaup, C.L., et al., “Poly(3,4-ethylenedioxypryole): Organice Elec 2126. trochemistry of a Highly Stable Electrochromic Polymer.” Macro Skotheim, T.A., Elsenbauner, R. L. & Reynolds, J.R. (eds.), Hand molecules. 2000. vol. 33, pp. 1132-1133. book of Conducting Polymers. 2" ed. 1998. Chapter II, pp. 197-422 (and references therein). Leadbeater, N.E., et al., “Transition-Metal-Free Suzuki-Type Cou Tsuie, B. et al., “Electroactive and luminescent polymers: new pling Reactions; Scope and Limitations of the Methodology.” J. Org. fluorene-herterocycle-based hybrids.” Journal of Materials Chemis Chem. 2003. vol. 68, No. 14, pp. 5660-5667. try. 1999. vol. 9, pp. 2189-2200. Liu, J., et al., “Polythiophene Containing Thermally Removable Yu, J., et al., “Structural Order in Conjugated Organic Films Prepared Solubilizing Groups Enhances the Interface and the Performance of by Catalytic Deprotection of Self-Assembled Polymers.” Chem. Polymer Titania Hybrid Solar Cells,” J. Am. Chem. Soc. 2004. vol. Mater. 2001. vol. 13; pp. 526-529. 126, pp. 9486-9487. * cited by examiner U.S. Patent Jul. 15, 2008 US 7,399,504 B2 F.G. 1 | 2OO 3OO 4OO 5OO 6OO 7OO 8 OO US 7,399,504 B2 1. 2 METHOD OF PREPARING AN INSOLUBLE than before the removal or conversion of the labile solubiliz POLYMERFILM ON A SUBSTRATE FROMA ing groups, wherein the polymer contains structural units SOLUBLE POLYMER CONTAINING LABLE selected from the group consisting of fluorene-2,7-diyls and SOLUBLIZING GROUPS triarylamine-diyls. CROSS-REFERENCE STATEMENT BRIEF DESCRIPTION OF DRAWINGS This application claims the benefit of U.S. Provisional application No. 60/503.229 filed Sep. 16, 2003. FIG. 1 is an illustration of the visible spectra of solvent 10 washings of substrates coated with thermally treated copoly BACKGROUND OF THE INVENTION mers of dioctylfluorene-bithiophene. The present invention relates to a method of preparing a DETAILED DESCRIPTION OF THE INVENTION polymer with reduced solubility in an organic Solvent from a polymer that is soluble in the solvent by virtue of the presence 15 In a first aspect, the present invention relates to a method of of solubilizing groups which, when removed or converted to forming an insoluble film on a Substrate comprising the steps nonsolubilizing groups, form the polymer that has reduced of applying a polymer dissolved in a solvent onto the Sub solubility in the solvent. strate, then removing the solvent and Subjecting the polymer Electroactive polymers such as conjugated polymers con to conditions that render the polymer less soluble, preferably taining structural units of a fluorene monomer are useful as virtually or totally insoluble in the solvent. The polymer, thin films in electronic devices such as organic light emitting which is preferably conjugated and electroactive, is charac diode displays (OLEDs) or transistors. Typically, a solution terized by containing pendant labile solubilizing groups that, of an electroactive polymer such as poly(9,9-dioctyl fluo on the one hand, facilitate the dissolution of the polymer in a rene-alt-bithiophene) dissolved in Xylenes is applied to a solvent and, on the other hand, are selectively removable or Substrate by techniques such as spin coating or inkjet print 25 convertible so as to inhibit redissolution of the polymer. The ing, whereupon solvent is removed to form a thin film of the labile groups are removable or convertible by any of a number soluble polymer with desirable electroactive properties. The of means including thermally, chemically, or optically. presence of the octyl groups on the fluorene structural units of the polymer imparts Solubility and improves the handling As used herein, the term “insoluble film’ means that suf characteristics of the polymer, but may disadvantageously 30 ficient pendant groups have been removed (or converted) degrade the transport characteristics and prevent the forma from the polymer backbone to render the film significantly tion of ordered microstructure in the final film. less soluble in the solvent the polymer was originally dis Although polymer films containing ordered microstructure solved in. Preferably, the film has less than 50% the solubility, are clearly desired, polymers that intrinsically develop Such more preferably less than 10% the solubility, most preferably structure tend to be insoluble in precursor ink solutions. 35 less than 1% the solubility of the polymer prior to removal or Therefore, applying these preferred polymers to substrates by conversion of labile pendant groups. Solution processing is impractical if not impossible. While it The labile solubilizing group preferably contains a) a is possible to apply an insoluble polymer onto a substrate by C-Cso hydrocarbyl group or b) a C-Cso hydrocarbyl group means such as evaporation, Sputtering, or plasma enhanced and one or more heteroatoms of S. N. Si, P. or O or c) an chemical vapor deposition, these techniques are slow and 40 aralkyl group and optionally one or more heteroatoms of S, N, expensive. Si, P. or O. As used herein, the term “hydrocarbyl group' Consequently, it would be desirable to prepare an insoluble refers to a group that contains carbon and hydrogenatoms and electroactive organic film on a Substrate from a material that optionally other atoms. The term “aralkyl group' is used can be easily and reproducibly applied to the substrate. herein to refer to aromatic and aliphatic groups that may 45 optionally contains other atoms. More preferably, the labile SUMMARY OF THE INVENTION solubilizing group includes C-C alkyl groups such as n-hexyl, 2-ethylhexyl, n-octyl, n-decyl, or n-dodecyl groups, The present invention addresses a need in the art by pro or C-C alkyl groups that contain ether or thioether groups viding in a first aspect a method comprising the steps of a) Such as tertiary alkyl ether or tertiary alkylthioether groups, applying to a Substrate a solution of a solvent and a polymer 50 or ester or thioester groups such as methyl ort-butyl esters of containing labile solubilizing groups; b) removing the solvent carboxylic acids, as illustrated: from the solution to form a soluble polymer film; and c) removing or converting a sufficient amount of the labile solu bilizing groups from the soluble polymer film to form a film on the substrate that is less soluble in the solvent than before 55 R"-CXCCHCH the removal or conversion of the labile solubilizing groups, wherein the polymer contains structural units selected from R" the group consisting of fluorene-2,7-diyls and triarylamine diyls. In a second aspect, the invention is an electronic device 60 where each R" is independently Hor C-C alkyl; preferably comprising a coated Substrate prepared by the steps of a) each R is independently H. methyl or ethyl: more preferably applying to the Substrate a solution of a solvent and an elec each R" is methyl or ethyl;