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Synthesis and Self-Assembly of Organometallic Semiconducting PMMA-b-PFS-b-PS-b-PFS-b-PMMA Pentablock Copolymers

Datta, Uttam (2005)
Synthesis and Self-Assembly of Organometallic Semiconducting PMMA-b-PFS-b-PS-b-PFS-b-PMMA Pentablock Copolymers.
Technische Universität Darmstadt
Ph.D. Thesis, Primary publication

Abstract

It was the goal of the present work to synthesize a series of well-defined pentablock copolymers of styrene (S), [1]dimethylsilaferrocenophane (FS) and methyl methacrylate (MMA) by sequential addition of monomers. Lithium naphthalide was used as difunctional initiator and a 1,1-dimethylsilacyclobutane (DMSB) mediated 1,1-diphenylethylene (DPE) end-capping technique was applied to ensure high block efficiency. The PMMA-b-PFS-b-PS-b- PFS-b-PMMA systems have molecular weights of Mn = 50,000 g/mol, polydispersity indices of PDI ≤ 1.12 and PFS volume fractions of around φ PFS=0.15. First, the difunctional middle block of PS was formed, followed by triblock PFS-b-PS-b-PFS, which then - after appropriate end-capping - was employed as a macroinitiator to polymerize MMA, leading to the final pentablock copolymer. The block copolymers were characterized by SEC and NMR. Under optimum reaction conditions - i.e. when chain termination during DPE/DMSB end-capping is minimized - the pentablock copolymer was obtained in approximately 75 % purity: the crude product contained - in addition to the pentablock - some tetrablock (20%) and triblock (5%) copolymers. This raw material, however, could be purified by selective precipitation procedures which addressed the differences in polarity of the constituents. By that method, almost quantitative removal of the triblock was possible whereas a small amount of the tetrablock remained in the pentablock fraction. Fortunately the presence of such small amounts of tetrablock copolymers did not influence the pentablock copolymer micromorphologies in an irreproducible way. Thus, profound investigations were possible to analyze the bulk properties of the materials. The pentablock copolymers were examined with the help of TEM and SAXS for their microphase behavior. The self-assembly was studied starting from dichloromethane, tetrahydrofuran and toluene solutions, after taking into consideration the solubility parameters. The formation of thermodynamically stable micromorphologies was forced by storing the solvent cast films in the saturated atmosphere of the corresponding solvent for 3-4 weeks followed by annealing at elevated temperatures 180 DegC - 220 DegC. Prior to this, it was ensured by TGA and DSC analysis that the pentablock copolymers are of sufficient thermal stability for this treatment. Annealing under various conditions followed by TEM analysis revealed good phase separation and the formation of highly ordered microstructures, such as spheres-on/in-spheres, spheres on lamellar interface, biphasic lamellar, cylinders and spheres on cylinders micromorphologies. These morphologies were further verified and supported by SAXS scattering profiles. Conductivity measurements on original and doped samples (I2 and TCNE) of PFS containing homo and block copolymers with/without microphase separation were carried out by dielectric spectroscopy (DRS). The maximum conductivity observed for the doped PFS sample (10-7 S/cm) decreased to 10-10 S/cm on dilution by domains of PS and PMMA in the block copolymers of various architectures.

Item Type: Ph.D. Thesis
Erschienen: 2005
Creators: Datta, Uttam
Type of entry: Primary publication
Title: Synthesis and Self-Assembly of Organometallic Semiconducting PMMA-b-PFS-b-PS-b-PFS-b-PMMA Pentablock Copolymers
Language: English
Referees: Gruber, Prof. Dr. Erich
Advisors: Rehahn, Prof. Dr. Matthias
Date: 29 July 2005
Place of Publication: Darmstadt
Publisher: Technische Universität
Refereed: 27 June 2005
URL / URN: urn:nbn:de:tuda-tuprints-5880
Abstract:

It was the goal of the present work to synthesize a series of well-defined pentablock copolymers of styrene (S), [1]dimethylsilaferrocenophane (FS) and methyl methacrylate (MMA) by sequential addition of monomers. Lithium naphthalide was used as difunctional initiator and a 1,1-dimethylsilacyclobutane (DMSB) mediated 1,1-diphenylethylene (DPE) end-capping technique was applied to ensure high block efficiency. The PMMA-b-PFS-b-PS-b- PFS-b-PMMA systems have molecular weights of Mn = 50,000 g/mol, polydispersity indices of PDI ≤ 1.12 and PFS volume fractions of around φ PFS=0.15. First, the difunctional middle block of PS was formed, followed by triblock PFS-b-PS-b-PFS, which then - after appropriate end-capping - was employed as a macroinitiator to polymerize MMA, leading to the final pentablock copolymer. The block copolymers were characterized by SEC and NMR. Under optimum reaction conditions - i.e. when chain termination during DPE/DMSB end-capping is minimized - the pentablock copolymer was obtained in approximately 75 % purity: the crude product contained - in addition to the pentablock - some tetrablock (20%) and triblock (5%) copolymers. This raw material, however, could be purified by selective precipitation procedures which addressed the differences in polarity of the constituents. By that method, almost quantitative removal of the triblock was possible whereas a small amount of the tetrablock remained in the pentablock fraction. Fortunately the presence of such small amounts of tetrablock copolymers did not influence the pentablock copolymer micromorphologies in an irreproducible way. Thus, profound investigations were possible to analyze the bulk properties of the materials. The pentablock copolymers were examined with the help of TEM and SAXS for their microphase behavior. The self-assembly was studied starting from dichloromethane, tetrahydrofuran and toluene solutions, after taking into consideration the solubility parameters. The formation of thermodynamically stable micromorphologies was forced by storing the solvent cast films in the saturated atmosphere of the corresponding solvent for 3-4 weeks followed by annealing at elevated temperatures 180 DegC - 220 DegC. Prior to this, it was ensured by TGA and DSC analysis that the pentablock copolymers are of sufficient thermal stability for this treatment. Annealing under various conditions followed by TEM analysis revealed good phase separation and the formation of highly ordered microstructures, such as spheres-on/in-spheres, spheres on lamellar interface, biphasic lamellar, cylinders and spheres on cylinders micromorphologies. These morphologies were further verified and supported by SAXS scattering profiles. Conductivity measurements on original and doped samples (I2 and TCNE) of PFS containing homo and block copolymers with/without microphase separation were carried out by dielectric spectroscopy (DRS). The maximum conductivity observed for the doped PFS sample (10-7 S/cm) decreased to 10-10 S/cm on dilution by domains of PS and PMMA in the block copolymers of various architectures.

Alternative Abstract:
Alternative abstract Language

Ziel der vorliegenden Arbeit war die Synthese einer Serie wohldefinierter Pentablockcopolymeren aus Styrol (S), [1]Dimethylsilaferrocenophan (FS) und Methylmethacrylat (MMA) durch sequentielle anionische Polymerisation. Als bifunktioneller Initiator wurde Lithium-naphthalid verwendet. Um hohe Blockausbeuten zu gewährleisten, wurden Endcapping-Reaktionen mit 1,1-Diphenylethylen (DPE) in Anwesenheit von 1,1-Dimethylsilacyclobutan (DMSB) durchgeführt. Die zahlenmittleren Molekulargewichte (Mn) der so erhaltenen PMMA-b-PFS-b-PS-b- PFS-b-PMMA-Pentablockcopolymeren betrugen etwa 50.000 g/mol. Die Polydispersitäts-Indices (PDI) lagen unterhalb von 1,12, der Volumenbruch des PFS (φ PFS) um 0,15. Im Zuge der Synthese wurde zuerst der Polystyrolblock als mittlerer Block hergestellt, woraus dann die PFS-b-PS-b-PFS-Dreiblockcopolymere gebildet wurden. Nach geeigneter Endcapping-Reaktion dienten diese dann als bifunktionelle Makroinitiatoren für das MMA. So wurden schließlich die gewünschten Pentablockcopolymeren erhalten. Die Blockcopolymeren wurden mit Größenausschlusschromatographie (SEC) und Kernresonanzspekroskopie (NMR) charakterisiert. Bei optimalem Reaktionsverlauf, d.h. bei minimalem Abbruch während der DPE/DMSB-Endcappingreaktion, konnte das Pentablockcopolymere aus der Synthese in einer Reinheit von etwa 75 % erhalten werden. Das so erhaltene Rohprodukt enthielt weiterhin ca. 20 % Tetrablock- und ca. 5 % Triblock Copolymeres. Im Anschluß an die Synthese gelang durch fraktionierte Fällung eine Aufreinigung. Dabei wurden die unterschiedlichen Polaritäten der Blöcke genutzt. So war die vollständige Abtrennung der Dreiblockcopolymeren möglich, während eine kleine Menge des Tetrablocks mit vertretbarem Aufwand nicht aus dem Pentablockcopolymeren zu entfernen war. Die Anwesenheit dieser geringen Mengen an Tetrablock-Copolymerer hatte jedoch keinen unreproduzierbaren Einfluss auf die Mikrophasenmorphologie des Pentablockcopolymeren. Deshalb konnten hiermit detaillierte Untersuchungen zu den Eigenschaften im Festkörper durchgeführt werden. Das Mikrophasen-Separationsverhalten der Pentablockcopolymeren wurde mit Hilfe der Transmissionselektronenmikroskopie (TEM) und der Röntgenkleinwinkelstreuung (SAXS) untersucht. Konkret wurde die Selbstorganisation in Filmen studiert, die aus Polymerlösungen in Dichlormethan, Tetrahydrofuran und Toluol gebildet wurden. Die Auswahl dieser Lösungsmittel war unter Berücksichtigung der Löslichkeitsparameter erfolgt. Um thermodynamisch stabile Mikrophasenmorphologien zu erhalten, wurden die gegossenen Filme unter gesättigter Atmosphäre des entsprechenden Lösungsmittels drei bis vier Wochen gelagert und anschließend bei 180 DegC - 220 DegC getempert. Zuvor war die thermische Stabilität der Proben mittels TGA und DSC sichergestellt worden. Die unter verschiedenen Bedingungen getemperten Copolymere zeigen im Transmissionselektronenmikroskop gut separierte Phasen und unterschiedlich geordnete Mikrostrukturen wie beispielsweise Kugeln in/auf Kugeln, Kugeln in lamellaren Grenzflächen, zweiphasige Lamellen, Zylinder und Kugeln auf Zylindern. Diese Mikrostrukturen wurden zusätzlich mit Hilfe von Röntgenkleinwinkelstreukurven verifiziert. Leitfähigkeitsmessungen an unveränderten sowie an oxidativ dotierten (mit I2 und TCNE) PFS-haltigen Homo- und Blockcopolymeren, die sowohl phasensepariert als auch einphasig vorlagen, wurden mit Hilfe der dielektrischen Spektroskopie (DRS) durchgeführt. Hierbei zeigte sich, dass die höchste beobachtete Leitfähigkeit von 10-7 S/cm bei einem dotierten Ho-mo-PFS bei Verdünnung durch PMMA- und PS-Domänen in Blockcopolymeren bis auf 10-10 S/cm abnahm.

German
Uncontrolled Keywords: Anionic polymerization, Self-assembly, pentablock copolymers, organometallic polymers, functional polymers, semiconducting, microphase separation, Small Angle X-ray Scattering (SAXS), Dielectric Relaxation Spectroscopy (DRS), Ferrocene
Classification DDC: 500 Science and mathematics > 540 Chemistry
Divisions: 07 Department of Chemistry
Date Deposited: 17 Oct 2008 09:22
Last Modified: 26 Aug 2018 21:25
PPN:
Referees: Gruber, Prof. Dr. Erich
Refereed / Verteidigung / mdl. Prüfung: 27 June 2005
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