Academic literature on the topic 'Polymer Bürsten'

Die mechanische Oberflächenbearbeitung moderner Verbundwerkstoffe stellt mitunter sehr spezielle Anforderungen an die dafür eingesetzten Werkzeuge. Ein sehr aktuelles Beispiel dafür ist das Finishing der Oberflächen von Halbzeugen aus sogenannten Wood Polymer Composites. Hier haben sich technische Bürstensysteme bewährt.

Binäre Polymerbürsten bestehen aus zwei verschiedenen Polymertypen, die nebeneinander auf dem gleichen Trägermaterial verankert sind. Wenn diese Polymere unterschiedliche Benetzungseigenschaften haben, können damit schaltbare Oberflächen produziert werden. Abhängig vom Lösungsmittel, dem man die binäre Polymerbürste aussetzt, streckt sich entweder das hydrophile oder das hydrophobe Polymer zum Lösungsmittel hin, während die zweite Komponente nahe der Oberfläche verbleibt. Durch diese vertikale Phasenseparation kann temporär eine bestimmte Oberflächeneigenschaft erzeugt werden. Allerdings verschwindet diese sofort wieder, wenn ein anderes Lösungsmittel die binäre Bürste benetzt, sei es durch direkten Kontakt oder über die Gasphase. In der vorliegenden Arbeit wurde untersucht, ob es möglich ist, neuartige schaltbare binäre Polymerbürsten bestehend aus einem hydrophilen und einem hydrophoben Polymer angebunden auf Siliziumwafern herzustellen, deren Schaltfähigkeit durch photochemische Vernetzung unterbunden werden kann. Geprüft worden ist unter anderem, inwiefern sich hydrophober und hydrophiler Zustand der Schicht fixieren lassen und ob daraus resultierend, eine entsprechende Strukturierung der Oberfläche nach Bestrahlung durch eine geeignete Fotomaske oder durch fokussiertes Licht nachweisbar ist. Als hydrophobe Komponente wurden photovernetzbare Styren/2-(4’-Styryl)-inden-Copolymere verwendet, als hydrophile Komponente kam Polyvinylpyridin zum Einsatz. Mit einem speziellen Oberflächeninitiator konnten durch „Grafting from“ binäre Polymerbürsten mit bis zu 300 nm Schichtdicke erzeugt werden. Es ist gelungen, diese schaltbaren Schichten durch selektive photochemische Vernetzung einer der Bürstenkomponenten im hydrophilen oder im hydrophoben Zustand zu fixieren, was durch Kontaktwinkelmessung nachgewiesen werden konnte. Wie beabsichtigt, verlieren dabei die vernetzten Bereiche ihre Schaltfähigkeit. Es ließen sich feine Oberflächenstrukturen mittels Bestrahlung durch eine Fotomaske erzeugen, die sichtbar werden, wenn man sie mit Wasser benetzt bzw. Wasserdampf aussetzt.

Binäre Polymerbürsten bestehen aus zwei verschiedenen Polymertypen, die nebeneinander auf dem gleichen Trägermaterial verankert sind. Wenn diese Polymere unterschiedliche Benetzungseigenschaften haben, können damit schaltbare Oberflächen produziert werden. Abhängig vom Lösungsmittel, dem man die binäre Polymerbürste aussetzt, streckt sich entweder das hydrophile oder das hydrophobe Polymer zum Lösungsmittel hin, während die zweite Komponente nahe der Oberfläche verbleibt. Durch diese vertikale Phasenseparation kann temporär eine bestimmte Oberflächeneigenschaft erzeugt werden. Allerdings verschwindet diese sofort wieder, wenn ein anderes Lösungsmittel die binäre Bürste benetzt, sei es durch direkten Kontakt oder über die Gasphase. In der vorliegenden Arbeit wurde untersucht, ob es möglich ist, neuartige schaltbare binäre Polymerbürsten bestehend aus einem hydrophilen und einem hydrophoben Polymer angebunden auf Siliziumwafern herzustellen, deren Schaltfähigkeit durch photochemische Vernetzung unterbunden werden kann. Geprüft worden ist unter anderem, inwiefern sich hydrophober und hydrophiler Zustand der Schicht fixieren lassen und ob daraus resultierend, eine entsprechende Strukturierung der Oberfläche nach Bestrahlung durch eine geeignete Fotomaske oder durch fokussiertes Licht nachweisbar ist. Als hydrophobe Komponente wurden photovernetzbare Styren/2-(4’-Styryl)-inden-Copolymere verwendet, als hydrophile Komponente kam Polyvinylpyridin zum Einsatz. Mit einem speziellen Oberflächeninitiator konnten durch „Grafting from“ binäre Polymerbürsten mit bis zu 300 nm Schichtdicke erzeugt werden. Es ist gelungen, diese schaltbaren Schichten durch selektive photochemische Vernetzung einer der Bürstenkomponenten im hydrophilen oder im hydrophoben Zustand zu fixieren, was durch Kontaktwinkelmessung nachgewiesen werden konnte. Wie beabsichtigt, verlieren dabei die vernetzten Bereiche ihre Schaltfähigkeit. Es ließen sich feine Oberflächenstrukturen mittels Bestrahlung durch eine Fotomaske erzeugen, die sichtbar werden, wenn man sie mit Wasser benetzt bzw. Wasserdampf aussetzt.

In the past decade there has been a growing interest in one-dimensional (1D) nanostructures, such as nanowires, nanotubes and nanorods, owing to their size-dependent optical and electronic properties and their potential application as building blocks, interconnects and functional components for assembling nanodevices. One of the ways to obtain such architectures is a template-directed synthesis which is practically a straightforward route to 1D nanostructures. In this approach, the template simply serves as a scaffold, within (or around) which a different material is generated in situ and shaped into a nanostructure with its morphology complementary to that of the template. It is generally accepted that template-directed synthesis provides a simple, high-throughput, and cost-effective procedure that also allows the complex topology present on the surface of a template to be duplicated in a single step. In the current work, utilization of the molecular bottle brushes as templates is proposed for the fabrication of conductive nanorods. Their non-spherical macromolecular geometries and lengths up to a few hundred nanometers allow the application of these structures in nanowire synthesis. The variety of molecular bottle brush architectures and their composition enables the adjustment of appropriate conditions for the preparation of conductive materials. Moreover, the ability of the brushes to assemble on a surface under certain conditions provides their usage as building blocks for the preparation of complex conductive networks. Here, the preparation, characterization, and applications of molecular bottle brushes are discussed. Two main goals were pursued. First, to deepen the knowledge in the synthesis of molecular bottle brushes, and to investigate their behavior on the surface. Second, to explore the application of the brushes as templates or building blocks for the formation of conductive nanowires. For the purpose, new ways of molecular brush synthesis by using the “grafting to” approach had to be developed. It was found that the reaction of nucleophilic addition based on pentofluorophenol chemistry and a coupling “click chemistry” reaction can be used to fabricate molecular brushes. Both methods showed efficient results and demonstrated high reactivity of the backbone with the end groups of the side chains. The “click chemistry” approach, however, demonstrated better results considering higher thicknesses of the brushes and, therefore, higher grafting density of the side chains. The “grafting to” together with the “grafting from” methods are very powerful synthetic tools, which can be used in the fabrication of any desired molecular bottle brush architectures. Additionally, complexation of oppositely charged bottle polymer brushes at a single-molecule level using AFM and CryoTEM was experimentally investigated. It was found that polyelectrolyte complexes have “scrambled-egg” morphology, where oppositely charged polymer chains are not oriented parallel to each other but cross each other. Furthermore, molecular bottle brushes were used as templates for the preparation of conductive nanowires. Three approaches for their fabrication were tested. It was found that brushes could easily be covered with various conductive materials, for example conductive polymers or metals. It was showed that for very small, tiny objects as molecular bottle brushes, one can use FIB in order to build up electrodes at its ends. The electrodes could be sputtered with an accuracy of 500 nm and further be used in the determination of the conductivity. The molecular bottle brushes covered with palladium showed the resistance of 50 MΩ, which, regarding the size of the brush, corresponds to a conductivity of one single molecule being ~1 S*cm-1. The obtained conductivity data were in good correlation with the data found in literature. We believe that the molecular bottle brushes have high potential applicability for the building of complex conductive networks. Future refinement of the synthetic methods, combined with improvements in structuring and positioning of objects at the nanoscale, could lead to their implementation in the construction of high-performance electronic devices.

The aim of the present work was to screen the main methods for the synthesis of conjugated polymers for their suitability in the preparation of conductive polymer brushes. The main focus was put on the grafting of intrinsically soluble substituted regioregular polyalkylthiophenes because of their excellent optoelectronic properties. The resulting polymer films were characterized and their optoelectrical properties studied. For the first time, a synthesis of conductive polymer brushes on solid substrates using “grafting-from” method was performed. The most important, from my opinion, finding of this work is that regioregular head-to-tail poly-3-alkylthiophenes – benchmark materials for organic electronics - can be now selectively grafted from appropriately-terminated surfaces to produce polymer brushes of otherwise soluble polymers - the architecture earlier accessible only in the case of non-conductive polymers. In particular, we developed a new method to grow P3ATs via Kumada Catalyst Transfer Polymerization (KCTP) of 2-bromo-5-chloromagnesio-3-alkylthiophene. Exposure of the initiator layers to monomer solutions leads to selective chain-growth polycondensation of the monomers from the surface, resulting into P3AT brushes in a very economical way. The grafting process was investigated in detail and the structure of the resulting composite films was elucidated using several methods. The obtained data suggests that the grafting process occurs not only at the poly(4-bromstyrene) (PS-Br)/polymerization solution interface, but also deeply inside the swollen PS-Br films, penetrable for the catalyst and for the monomer The grafting process was investigated in detail and the structure of the resulting composite film was elucidated using ellipsometry, X-ray Photoelectron Spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), and Conductive atomic force microscopy (C-AFM). The obtained data suggests that the grafting process occurs not only at the poly(4-bromostyrene), PS-Br/polymerization solution interface, but also deeply inside the swollen PS-Br film, which is penetrable for the catalyst and the monomer. The process results in an interpenetrated PS-Br/P3HT network, in which relatively short poly(3-hexylthiophene), P3HT grafts emanate from long, cross-linked PS-Br chains. A further method investigated during our work was to covalently graft regioirregular P3HT to substrates modified by macromolecular anchors using oxidative polymerization of 3HT with FeCl3. P3HT layers with variable thicknesses from 30 nm up to 200 nm were produced using two steps of polymerization reaction. The P3HT obtained by oxidative polymerization had always an irregular structure, which was a result of the starting monomer being asymmetric, which is undesired for electronic applications. The third method for the production of conductive polymer brushes was to graft regioregular poly(3,3''-dioctyl-[2,2';5',2'']terthiophene) (PDOTT) by electrochemical oxidative polycondensation of symmetrically substituted 3,3''-dioctyl-[2,2';5',2'']terthiophene (DOTT). A modification of the supporting ITO electrode by the self-assembled monolayers (SAMs) of compounds having polymerizable head-groups with properly adjusted oxidative potentials was found to be essential to achieve a covalent attachment of PDOTT chains. The polymer films produced show solvatochromism and electrochromism, as well as the previous two methods. After polymerization, the next step towards building organic electronic devices is applying the methods obtained in nano- and microscale production. Block copolymers constitute an attractive option for such surface-engineering, due to their ability to form a variety of nanoscale ordered phase-separated structures. However, block copolymers containing conjugated blocks are less abundant compared to their non-conjugated counterparts. Additionally, their phase behaviour at surfaces is not always predictable. We demonstrated in this work, how surface structures of non-conductive block copolymers, such as P4VP-b-PS-I, can be converted into (semi)conductive P4VP-b-PS-graft-P3HT chains via a surface-initiated polymerization of P3HT (Kumada Catalyst Transfer Polymerization (KCTP) from reactive surface-grafted block copolymers. This proves that our method is applicable to develop structured brushes of conductive polymers. We believe that it can be further exploited for novel, stimuli-responsive materials, for the construction of sensors, or for building various opto-electronic devices. The methods developed here can in principle be adapted for the preparation of any conductive block copolymers and conductive polymers, including other interesting architectures of conductive polymers, such as block copolymers, cylindrical brushes, star-like polymers, etc. To this end, one needs to synthesize properly-designed and multi-functional Ni-initiators before performing the polycondensation.

The aim of the present work was to screen the main methods for the synthesis of conjugated polymers for their suitability in the preparation of conductive polymer brushes. The main focus was put on the grafting of intrinsically soluble substituted regioregular polyalkylthiophenes because of their excellent optoelectronic properties. The resulting polymer films were characterized and their optoelectrical properties studied. For the first time, a synthesis of conductive polymer brushes on solid substrates using “grafting-from” method was performed. The most important, from my opinion, finding of this work is that regioregular head-to-tail poly-3-alkylthiophenes – benchmark materials for organic electronics - can be now selectively grafted from appropriately-terminated surfaces to produce polymer brushes of otherwise soluble polymers - the architecture earlier accessible only in the case of non-conductive polymers. In particular, we developed a new method to grow P3ATs via Kumada Catalyst Transfer Polymerization (KCTP) of 2-bromo-5-chloromagnesio-3-alkylthiophene. Exposure of the initiator layers to monomer solutions leads to selective chain-growth polycondensation of the monomers from the surface, resulting into P3AT brushes in a very economical way. The grafting process was investigated in detail and the structure of the resulting composite films was elucidated using several methods. The obtained data suggests that the grafting process occurs not only at the poly(4-bromstyrene) (PS-Br)/polymerization solution interface, but also deeply inside the swollen PS-Br films, penetrable for the catalyst and for the monomer The grafting process was investigated in detail and the structure of the resulting composite film was elucidated using ellipsometry, X-ray Photoelectron Spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), and Conductive atomic force microscopy (C-AFM). The obtained data suggests that the grafting process occurs not only at the poly(4-bromostyrene), PS-Br/polymerization solution interface, but also deeply inside the swollen PS-Br film, which is penetrable for the catalyst and the monomer. The process results in an interpenetrated PS-Br/P3HT network, in which relatively short poly(3-hexylthiophene), P3HT grafts emanate from long, cross-linked PS-Br chains. A further method investigated during our work was to covalently graft regioirregular P3HT to substrates modified by macromolecular anchors using oxidative polymerization of 3HT with FeCl3. P3HT layers with variable thicknesses from 30 nm up to 200 nm were produced using two steps of polymerization reaction. The P3HT obtained by oxidative polymerization had always an irregular structure, which was a result of the starting monomer being asymmetric, which is undesired for electronic applications. The third method for the production of conductive polymer brushes was to graft regioregular poly(3,3''-dioctyl-[2,2';5',2'']terthiophene) (PDOTT) by electrochemical oxidative polycondensation of symmetrically substituted 3,3''-dioctyl-[2,2';5',2'']terthiophene (DOTT). A modification of the supporting ITO electrode by the self-assembled monolayers (SAMs) of compounds having polymerizable head-groups with properly adjusted oxidative potentials was found to be essential to achieve a covalent attachment of PDOTT chains. The polymer films produced show solvatochromism and electrochromism, as well as the previous two methods. After polymerization, the next step towards building organic electronic devices is applying the methods obtained in nano- and microscale production. Block copolymers constitute an attractive option for such surface-engineering, due to their ability to form a variety of nanoscale ordered phase-separated structures. However, block copolymers containing conjugated blocks are less abundant compared to their non-conjugated counterparts. Additionally, their phase behaviour at surfaces is not always predictable. We demonstrated in this work, how surface structures of non-conductive block copolymers, such as P4VP-b-PS-I, can be converted into (semi)conductive P4VP-b-PS-graft-P3HT chains via a surface-initiated polymerization of P3HT (Kumada Catalyst Transfer Polymerization (KCTP) from reactive surface-grafted block copolymers. This proves that our method is applicable to develop structured brushes of conductive polymers. We believe that it can be further exploited for novel, stimuli-responsive materials, for the construction of sensors, or for building various opto-electronic devices. The methods developed here can in principle be adapted for the preparation of any conductive block copolymers and conductive polymers, including other interesting architectures of conductive polymers, such as block copolymers, cylindrical brushes, star-like polymers, etc. To this end, one needs to synthesize properly-designed and multi-functional Ni-initiators before performing the polycondensation.

The synthesis and polymerization of macromonomers containing a polymerizable styrene head group and a tail of ethylene oxide derivatives of different character were investigated. The synthesis of macromonomers was based on living anionic polymerization of oxiranes. Two monomers were used: 1-ethoxyethyl glycidyl ether (glycidol acetal), which after hydrolysis forms hydrophilic glycidol blocks and glycidyl phenyl ether forming hydrophobic blocks. Polymerizable double bonds were introduced by terminating the living chain with p-(chloromethyl)styrene. However, MALDI-TOF-MS end group analysis showed that all synthesized macromonomers were a mixture of the macromonomer and the non-functionalized oligomer. The degree of functionalization varied from 55 to 75 %. The obtained macromonomers showed amphiphilic properties and formed micelles in water. The determined critical micellization (CMC) concentration for poly(glycidol) macromonomer (DP = 50) was ca. 10 g/L, while the poly(glycidol) block macromonomers with hydrophobic spacer showed CMC on the level 0,7 g/L. The conventional free radical and controlled free radical polymerisation (ATRP) were used for preparation of polymacromonomers with different properties. The radical polymerization of the macromonomers was carried out in water using AVA as initiator and in the mixture of water/benzene (10/1 v/v) using AIBN. Core-shell polymers of different character and molar masses with polydispersity indices from 1,4 -3,0 were obtained. The ATRP carried out in water using PEO macroinitiator led to polymacromonomers with polydispersity indices from 1,1 to 1,3 and desiried molecular weight. In all cases the conversion of macromonomer (able to polymerization) was close to 100%. The polymerization product could easily be separated from the unable to reaction residue.