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Synthesis, Characterization, and Properties of Tailored Functional Block Copolymers (2011)

Robin Pettau

This thesis covers the design, synthesis, characterization, and application of functional block copolymers (BCP) based on a polymer analogous approach and includes three main subjects. The first subject is the implementation of a specially constructed reactor setup for sequential anionic polymerization that allows parallel block copolymer synthesis based on one identical A-block on a lab scale. For this reason, this setup facilitates the preparation of block copolymer series in a combinatorial fashion. It consists of one main reactor and three secondary reactors with individual temperature control. The addition of monomers or additives to each reactor can be handled separately. AB diblock copolymer and ABC triblock copolymer series were prepared with different lengths of the final block as well as different chemical structures of the last block. The second subject covers the synthesis, characterization, processing and application of new liquid crystalline azobenzene-containing block copolymers designed as materials for holographic data storage. Therefore, these polymers contained an amorphous, optical inert poly(methyl methacrylate) (PMMA) or polystyrene (PS) matrix and a functional segment based on polyhydroxystyrene (PHS). Different lengths of flexible spacers and/or mixtures of two spacer lengths were employed to connect the mesogenic chromophores to the polymer backbone. The structure-property relation of functionalized BCPs and the resulting mesophase was investigated. Holographic experiments were conducted on selected examples of the photo-addressable polymers. Smectic annealed samples or amorphous quenched samples were obtained by different sample preparation methods to investigate the influence of the liquid crystalline order. While the initial sensitivity to light induced orientation of the polymer systems remained unaffected, the writing times and level of postdevelopment were improved for quenched samples. Variation in spacer lengths resulted in decreasing smectic order with decreasing spacer length as well as for mixtures of two different spacer lengths promoting lower writing times in the holographic experiments. Additionally, the temperature dependence of the temporal evolution of the refractive index modulation in the smectic polymers was studied. A significant decrease of writing times and an enhancement of the postdevelopment were revealed at elevated temperatures. Stable holographic gratings could be obtained even at 100 °C. 1.1 mm thick samples, that are a prerequisite for volume holographic data storage with a high data storage density, were prepared by injection molding of blends of photoaddressable BCPs with PMMA or PS. Preliminary results confirmed the long-term stability of inscribed holographic gratings and demonstrated angular multiplexing of holographic volume gratings. The third subject covers the synthesis and characterization of new cyanobiphenyl-containing ABA triblock copolymers and their application as BCP gelators for the low molecular weight liquid crystal (LC) 4-cyano-4’-(pentyl)biphenyl (5CB). Based on the selective solubility of the A and B blocks in the nematic solvent, ABA triblock copolymers can be used for the thermoreversible gelation of 5CB. To this end, ABA and ABA’ triblock copolymers comprised of PS A-blocks and a cyanobiphenyl-functionalized PHS B-block with a high degree of polymerization were prepared by the combination of anionic polymerization, using two different synthetic routes, and polymer analogous attachment of the mesogens. Series of linear gelators were prepared with variations in B-block length, A-block lengths and star shaped BCPs by coupling linear ABA’ triblock copolymers. Structure-property relations of the cyanobiphenyl-functionalized polymers regarding the mesophase characterization revealed a dependence of solubility in the nematic 5CB on spacer length. A comprehensive study was conducted to investigate the influence of the BCP backbone and architecture on the gelation of 5CB. Oscillating rheology measurements and thermal characterization were employed to investigate the thermoreversible LC gels. Most of the BCP gelators achieved gelation of 5CB at a mass concentration of 5 wt%. The properties of the different gels where compared at this fixed concentration. The influence of the gelator backbone on the gel properties was investigated by comparing different sets of triblock copolymers. While a short functionalized B-block resulted in high network density and, thus, a high elasticity of the gel the length of the A-blocks influenced the node stability. The LC gel using a star-shaped gealtor exhibited a significantly higher elasticity than with the respective linear block copolymer gelator.

Synthesis of reponsive homo- and block copolymers - application to the generation of inorganic-organic nanohybrids (2010)

Pierre-Eric Millard

Responsive homopolymers and multi-responsive block copolymers were prepared via reversible addition-fragmentation chain transfer (RAFT) and atom transfer radical polymerization (ATRP). Self-assembly in solution depending on environmental stimuli was investigated and exploited to create responsive micelles. New cross-linking strategies were thoroughly performed in aqueous solution to allow a controlled preservation and a high shape-persistence of the colloid particles, even when exposed to non-selective environmental conditions. The synthesis of poly(N-isopropylacrylamide) (PNIPAAm) was investigated by ATRP for subsequent polymer-protein nanohybrid generation. This temperature-responsive polymer was polymerized directly in pure water at a low temperature (4 ºC) by using a functional ATRP initiator which allows post-polymerization conjugation. Without the addition of Cu(II), the kinetics were extremely fast, typically less than one minute for a full conversion. By adjusting the ratio of Cu(I)/(Cu(II) and selecting a very active ligand, all polymerizations proceeded in a controlled fashion to near quantitative conversion without evidence of termination. N-isopropylacrylamide and acrylic acid (AA) were also homopolymerized by RAFT in aqueous media using a novel strategy. Instead of using a diazo-initiator, which generally decomposed at high temperatures, gamma-irradiation was used to initiate polymerization at ambient temperature. This type of radiation has many advantages. A very tiny and constant amount of radicals can be generated, which is perfect for the RAFT process. Moreover, the rate of initiation only has a low level of dependence on temperature and can be used in a wide range of temperatures. Finally, compared to UV-initiation, gamma-irradiation can penetrate the reaction solution deeper and without evidence of irreversible decomposition of the dithioester end group. Therefore, RAFT polymerizations of NIPAAm and AA were achieved with a very good level of control, even at high monomer conversions. This new process was then extended to many other water-soluble monomers for generating homopolymers and block copolymers. Among these, acrylamide, N,N-dimethylacrylamide, 2-hydroxyethyl acrylate and poly(ethylene glycol) methacrylate gave the best results. This technique proved to be very efficient at generating very long and narrowly distributed polymers (up to a degree of polymerization of 10,000) and at designing block copolymers. High molecular weight PNIPAAm-b-PAA copolymers, synthesized by RAFT polymerization under gamma-radiation, were used to generate multi-responsive cross-linked micelles. These block copolymers were self-assembled in water at pH 7 by increasing the temperature over the lower critical solution temperature. The PNIPAAm became hydrophobic and formed the micellar core and the hydrophilic PAA block generated the corona which prevented full aggregation of the system. Then, by amidification at elevated temperatures of the carboxylic moieties via a trifunctional primary amine, the structure was found to remain even after cooling down the system. The shell-cross-linked micelles formed were utilized to generate inorganic-organic nanohybrids by the in situ reduction of gold or silver salts to generate nanoparticles inside the nanocarrier. Another strategy of cross-linking was also investigated by using amino-functional silsesquioxane nanoparticles. In water around neutral pH values and room temperature, these particles interacted with the carboxylic groups of a high molecular weight PNIPAAm-b-PAA by hydrogen bonding and ionic interactions to generate an insoluble complex. Due to the presence of the hydrophilic PNIPAAm block, defined spherical micelles were obtained. The inorganic-organic particles were successfully cross-linked by subsequent amidification to preserve the structure, even at a high pH. Different temperature properties of the hybrids were observed depending on the pH value, due to the residual charge in the micellar core. At a neutral pH, shrinking of the corona was observed, while at a high pH (pH 13) a fully reversible aggregation of the system occurred.

Structural Analysis of Cylindrical Particles by Small Angle X-ray Scattering (2005)

Li Li

The objective of this work is to analyze nano-scaled cylindrical particles by small angle X-ray scattering (SAXS). Three systems with cylinder-shaped particles: (1) Laponite particles in aqueous solutions, (2) Poly(carbon suboxide) particles in binary water/DMF solutions, and (3) Suprastructural aggregates of coil-ring-coil block copolymers in cyclohexane, have been studied by SAXS performing either a Kratky-Compact-Camera in our laboratory or ID2 beamline of the European Synchrotron Radiation Facility (ESRF) in Grenoble. The synthetic clay particles, Laponite RD, have been chosen as ideal disc-shaped model particles. In combination of SAXS with static light scattering, the scattering intensities of a concentration serial (volume fraction from 0.0002 to 0.0016) were measured in almost three orders of magnitude of the scattering vector q. Through extrapolation of concentration the scattering intensity at vanishing concentration, i.e. the form factor P(q) of particles was achieved. It shows q-2 decay at intermediate q range, which indicates that the shape of single Laponite particle in aqueous solution is platelet. The plateau of the form factor at low q range implies that there is no aggregate or cluster structure, and the Laponite particles are dispersed completely under the investigated conditions. More detailed structural information was then obtained by fitting of P(q) with disc model. The radii of the discs exhibit a large polydispersity. A radius of 10.5 nm with Schulz-Zimm distribution of Rw/Rn = 1.5 (where Rw and Rn denote weight and number average radius, respectively) was found to fit the form factor perfectly. The thickness of one single platelet was determined to be 0.9 nm. The weight averaged molecular weight and radius of gyration were determined to be 930 kg/mol and 13.4 nm, respectively. The inter-particle interactions of Laponite particles were investigated by the structure factor S(q), from which the effective diameter of interparticle interactions deff was determined for the first time. The strong electrostatic Coulomb repulsion between charged Laponite particles was attributed to the much higher value of deff (= 46 nm), in comparison to 2Rg (= 27 nm). The recently developed multicomponent interaction site model was performed by Harnau to predict these experimental structure factors. An effective potential of interaction, which pays attention to a screened Coulomb interaction as well as an attractive interaction, leads to the best description of the model to the experimental data. By means of SAXS, the size of synthetic polymer carbon suboxide ((C3O2)n) dissolved in binary water/DMF solutions was determined for the first time with radius of gyration Rg = 1.7 nm and molecular weight Mw = 2760 g/mol, which corresponds to a polymerization’s degree of about 40. This value is much larger than literature one (5-10). The form factor of polymer carbon suboxide can be described by a semiflexible chain model. The radius of gyration in cross-section RC and molecular weight per unit length ML were obtained to be 0.3 nm and 350 g/(mol.nm), respectively, which can confirm the fact that the chemical structure of poly(carbon suboxide) is repeated pyronic ring, as suggested in most literatures. Thus the structure and size of polymer carbon suboxide were characterized completely by SAXS. Finally, SAXS was employed to analyze a suprastructural aggregation system derived by self-assembly of coil-ring-coil block copolymers. This is a newly synthesized subclass of rod-coil block copolymers composed of a nanometer-sized shape-persistent macrocycle and two covalently attached polystyrene (PS) coils. The solubility of the rigid ring is largely enhanced due to the attachment of the flexible side groups. With suitable length of the flexible side groups (Mw (PS) = 2500 g/mol) the block copolymers can form colloidal-sized aggregates in selected solvent cyclohexane, which were concluded to be of cylindrical shape with the rigid rings packing densely in a tubular way and the flexible side groups arranging outside of the ring. Such aggregated cylinder brushes can be further confirmed to exist as a mixture of cylinder bundles by analyzing the local structural parameter ML (= 25730 g/(mol.nm), molecular weight per nm length of cylindrical objects). In comparison of this value with M0 (= 6500 g/mol, molecular weight of single coil-ring-coil block copolymer) and d (= 0.6 nm, distance of adjacent densely packed rings), the number fraction of coexisted single cylinder, bi- and tri-cylinder bundles was resulted to be 1:1:2. Through fitting by using approximated circular cylinder model the radius of single cylinders was determined to be 2.6 nm (polydispersity 20 percent) with a hollow inside of radius of 1.2 nm.

Soft Compartmentalized Polymer Colloids: Janus Particles, Multicompartment Structures, Inorganic-Organic Hybrids and Applications (2008)

Andreas Walther

Compartmentalized polymer-based colloids with nanoscopic dimensions and different topologies were prepared based on various block copolymer architectures. The polymers were prepared via anionic polymerization or a controlled radical polymerization technique (RAFT). Self-assembly both in solution and in bulk were rigorously exploited to create the multicompartment architectures. Several new crosslinking strategies, in bulk and in solution, were thoroughly investigated to allow a controlled preservation and a high shape-persistence of the colloidal particles even when exposed to non-selective solvents. Cylindrical and disc-like Janus particles were investigated according to their self-assembly behavior into superstructures. The Janus discs undergo back-to-back stacking in organic solvent. In aqueous solution, a size-dependent aggregation was found. While the smaller Janus discs are unimolecularly dissolved with a significant polystyrene surface exposed to the water, the larger Janus sheets can shield the insoluble side by a large bending in an intramolecular fashion. Janus cylinders self-assemble on two hierarchical levels. Upon exposure to a selective solvent, they self-organize into fibers. The length of these fibers depends on the concentration and a critical aggregation concentration exists below which self-assembly is absent. Secondly, the Janus cylinders form fibrillar networks with tunable pore sizes when deposited from more concentrated solution. The surface-active properties of spherical Janus particle were exploited for the investigation of two possible applications of both academic and industrial relevance. In Pickering emulsion polymerization, extremely well-defined latexes with long-term stability could be prepared in a very facile fashion. A control of the particle size by changing the concentration of Janus particles could easily be achieved. Secondly, the nanostructuring of polymer blends was shown for a PS/PMMA model system. The system exhibits a control on two length scales. The first is the controlled decrease of the domains of the dispersed phase and the second is the controlled spacing between the particles at the interface. The particles are exclusively located at the interface and the nanostructuring can be obtained while matching macroscopic processing constraints, i.e. high-shear blending in a mini mixer. The self-assembly of bis-hydrophilic triblock terpolymers with two outer hydrophobic blocks was investigated for a variety of different hydrophilic end blocks. The overall architecture of the solution structures could be tailored by changing the hydrophobic-to-hydrophilic balance. Additionally, the interaction between the corona-forming blocks has an influence on the particle shapes as well. The micelles possess coronas with appealing and tunable properties, due to the presence of a hydrophobic core and hydrophilic biocompatible and stimuli-responsive segments. The self-assembly of miktoarm star terpolymers, bearing arms of polystyrene (PS), polybutadiene (PB) and poly(2-vinylpyridine) (P2VP), was analyzed both in solution as well as in the bulk state. In solution, the miktoarm star terpolymers form multicompartment micelles with a glassy (PS) and a soft compartment (PB), all rendered water-soluble by the P2VP corona. Strikingly, the soft PB compartments show hydrophobic bridges in aqueous medium which is of high interest as they can be used as a second motif for sensing, adhesion control or interaction with cellular membranes. The transfer of a hexagonally ordered cylindrical bulk phase via crosslinking of the PB domain of a bulk structure of a similar miktoarm star terpolymer allowed the preparation of novel multicompartment cylinders. The structures possess perfectly parallel aligned compartments. Two symmetric and opposing PS and P2VP compartments surround a central ribbon-like PB compartment. The P2VP compartments could be used to generate perfectly aligned bi-axial nanowires inside spatially separated compartments within close proximity. Due to the presence of an amphiphilic corona, the extent of the compartmentalization can be tuned from separated nanowires into one homogenous nanowire simply by exchanging the solvent. The complexity and high control of the structure of this multicompartment cylinder is unmatched and can most likely not be obtained by solution based self-assembly.

Shear-induced alignment in block copolymer solutions (2005)

Gabi Cantea

The alignment of the ordered microdomains of block copolymers in solution has been accomplished by using mechanical shear fields. Two pathways to monitore the achievement of aligned structures have been used: rheo-optical and in situ rheo-SAXS methods. The AC diblock copolymer and ABC triblock terpolymer with high molecular weights and different morphologies were synthesized via anionic polymerization and the alignment has been monitored from the solutions of neat AC diblock, ABC triblock and their blend in a non-volatile solvent. Before proceeding to the alignment protocols the thermodynamics of the diblock copolymer solutions has been studied by rheological means. The slightly asymmetric diblock copolymer polystyrene-b-poly(t-butyl methacrylate) (ST) as solutions at different concentrations was investigated by scanning of moduli over a range of temperatures and the morphological transitions were detected. This led us to conclude that dioctyl phthalate is a selective solvent for this diblock copolymer (ST) and a transition from the initially lamellar toward a cylindrical or spherical morphology takes place before order-disorder transition. A route to check the induced asymmetry due to the solvent selectivity was accomplished by applying the Leibler dilution approximation theory. While for the less asymmetric diblock copolymer ST(72K) the dilution approximation theory could be approached, for the higher asymmetric ST(117K) a failure of the theory has been encountered. For the system ST(72K) where the theory was still valid, as a result an expression for the interaction parameter has been developed. The alignment kinetics were performed first by making use of the rheooptical method and the monitored retardation was further used for calculation of birefringence. A perfectly symmetric diblock ST with high molecular weight (100K) as solution in dioctyl phthalate was used for the alignment protocols. Previous investigation of such system did not show any order-order transition, thus for this particular symmetric diblock the same lamellar morphology was preserved in the swollen state. Over a wide range of frequencies and strain amplitudes the monitored birefringence was always positive meaning a perpendicular alignment with the normals of lamellae along the vorticity axis and perpendicular on the plane formed between flow direction and gradient velocity axes. This prefered alignment has been explained due to the low viscoelastic contrast between the polystyrene and poly(t-butyl methacrylate) blocks which did not allow the sliding toward a parallel alignment found for systems with a large viscoelastic contrast. Thus, choosing an appropriate chemical sequence of blocks a selective type of macroscopic alignment by LAOS can be achieved. The introduction of the third elastomeric block between the thermoplastic outer blocks (S and T), namely SBT triblock terpolymer, lead to significant changes in terms of alignment in the sense of tunable intermediate (perpendicular and transverse) aligned states which finally led to the same final parallel orientation in the diluted state. The in situ rheo-SAXS method applied to the same system elucidated the intermediate mechanism leading to a final parallel aligned state such as a coexistence of parallel and perpendicular states which gave rise to a transverse alignment in rheooptical method. As a finally aligned state resulting from in situ rheo-SAXS in oscillatory mode the perpendicular one was found within a short time scale (1h), while the rheooptical method revealed a perpendicular state at short time scale (1h) and parallel state at long time scale (10h). Finally, the investigation of the lamellar non-centrosymmetric blend SBT:ST=60:40 allowed preferential parallel alignment above a critical strain amplitude instead below the critical strain amplitude only perpendicular alignment is achieved. While the rheooptical method applied to a bcc morphology of a solution of SBM triblock terpolymer in DOP did not give evidence for an induced morphological transition, in situ rheo-SAXS was a powerful tool to illustrate such a transition. Moreover, we have shown that more complicated morphologies like knitting pattern of SEBM (as cast film from chloroform) which reveals a bcc morphology as a solution in DOP could be investigated and macroscopically aligned via in situ rheo-SAXS while the rheooptical method could not be used due to the non transparent system. The induced columnar structure could be monitored in 2D SAXS patterns which have never been reported before. In summary, it was demonstrated that mechanical field alignment of block copolymer domains in solution allowed to generate highly anisotropic structures even for block copolymers with high molecular weights under ambient conditions and for a large variety of morphologies.

Self-Assembly of Block Copolymers in External Fields (2002)

Alexander Böker

The influence of external fields on the microdomain structure of block copolymers has been studied. Both surface fields and electric fields have been considered. External electric fields are used to create macroscopically oriented bulk samples. In order to circumvent limitations associated with the application of external fields to melts of high molecular weight block copolymers and multiblock copolymers of complex architecture, a new solvent-based procedure is introduced, i.e. the block copolymer microdomains are aligned by application of an electric field (E ~ 1 - 2 kV/mm) during solvent casting of bulk samples. In order to elucidate the dominating parameters and governing mechanisms, the microdomain orientation kinetics of concentrated block copolymer solutions exposed to a DC electric field is investigated by time-resolved synchrotron small-angle X-ray scattering (SAXS) at the ID02 beamline at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. As a first model system, a lamellar polystyrene-b-polyisoprene block copolymer dissolved in toluene is used. The orientation kinetics follows a single exponential behavior with characteristic time constants varying from a few seconds to some minutes depending on polymer concentration, temperature, electric field strength, and system size. Furthermore, two mechanisms governing the electric field alignment of a lamellar block copolymer from concentrated solutions are identified. It is shown that depending on the segregation power (c µ fP, c µ 1/T) a single mechanism dominates the orientation process, i.e. in a weakly segregated system (low concentration or high temperature) the migration of boundaries prevails, whereas a stronger phase separated system (high concentration or low temperature) predominantly exhibits rotation of grains. In addition, the orientation kinetics slows down with increasing polymer concentration, which can be correlated to the respective solution viscosity and the mechanism of orientation. Moreover, the influence of the electric field strength on the orientation kinetics is determined, including a threshold value below which no electric field induced orientation could be achieved on the time scale of the experiment. The time constants of the fastest processes were in the range of 0.5 sec, reaching a final orientation described by order parameters of up to P2 = -0.35. Finally, the variation of temperature yields control of the governing mechanisms at a fixed polymer concentration. In additional studies, the dielectric contrast of the block copolymer components was varied systematically (PS-b-PI, PS-b-PMMA, PS-b-PtBMA, PS-b-PHEMA-b-PMMA, PS-b-P2VP). It is found that a high dielectric contrast leads to faster alignment kinetics (e.g. the time constants of the fastest processes for a PS-b-P2VP diblock system in THF are in the range of 0.3 sec) and reduces the threshold field strength (around 200 V/mm for PS-b-P2VP). Furthermore, it could be shown that the interplay between degree of phase-separation, solution viscosity and dielectric contrast is crucial to decide if a given polymer/solvent system can be used for electric field-induced microdomain alignment. For example, it was found that PS-b-PtBMA shows electric field-induced orientation of the microdomains while PS-b-PMMA does not. This can be explained by the larger interaction parameter cST compared to cSM leading to a phase-separated solution at lower viscosities. In a similar way, the introduction of a high dielectric constant middle block (PHEMA) into a PS-b-PMMA, which additionally enhances phase separation, is shown to be the key to creating a well-performing methacrylate-based block copolymer system for electric field induced alignment from solution. Finally, we could show that the even more complex lamellar and core-shell cylindrical PS-b-P2VP-b-PtBMA high molecular weight triblock copolymer systems could be oriented by virtue of an electric field from solution. In summary, it was demonstrated that electric field alignment of block copolymer domains from solution is a powerful tool to generate highly anisotropic bulk block copolymer samples. The large variety of parameters which we can control allows us to further improve the preparation of macroscopically aligned melt samples via solvent casting in the presence of an electric field.

Polymeric Nanoparticles for the Modification of Polyurethane Coatings (2011)

Sandrine Tea

Rubber-based nanomodifiers were successfully synthesized following two different strategies and were used as impact modifiers in polyurethane (PU) automotive clearcoats to improve chip resistance. Various narrowly distributed polybutadiene-b-poly(methyl methacrylate) (B-M) block copolymers differing in composition and molecular weights were synthesized and studied with respect to their self-assembly in organic selective solvents. Dynamic light scattering and transmission electron microscopy measurements revealed that spherical micelles were obtained in acetonitrile for all block copolymers, independently of the polymer concentration. Their radii varied from 11 to 69 nm depending on the molecular weight of the initial linear block copolymer and their aggregation behavior in acetonitrile followed the model established by Förster and Antonietti for strongly segregated block copolymers. In DMF and acetone, block copolymers with 85 %wt PMMA were dissolved as unimers. For lower methacrylate contents, the sizes of the obtained spherical micelles were decreasing from DMF to acetone independently of the polymer concentration. The calculated interaction parameters confirmed acetonitrile as the best solvent for PMMA followed by DMF and acetone as the poorest one. The size of the spherical aggregates could be tuned by the molecular weight and/or by the nature of the selective solvent. Polybutadiene-b-poly(n-butly acrylate) (B-nBA), polybutadiene-b-poly(n-butyl methacrylate) (B-nBMA) and polybutadiene-b-poly(t-butyl methacrylate) (B-tBMA) did not show such a large choice in selective solvents and spherical micelles were obtained in DMF, DMAc and acetone respectively. Cross-linking of the polybutadiene core of the obtained micelles was performed in solution using two different methods: cold vulcanization and radical reaction upon the decomposition of a photo-initiator under UV radiation. Both methods allow retaining the spherical shape of the micelles leading to narrowly distributed non fusible nanospheres. In the case of B-M nanoparticles, the degree of cross-linking seemed independent of the amount of cross-linker used. Unlikely, B-nBMA and B-nBA nanoparticles exhibited increasing degrees of cross-linking with the amount of photo-initiator introduced. Their degrees of cross-linking were particularly lower than those of B-M nanoparticles. The hydrolysis of the t-BMA corona of the nanoparticles obtained from B-tBMA linear block copolymers self-assembly in selective solvent resulted in water soluble nanoparticles carrying acid functions and thus potentially exhibiting pH-responsive behavior. Various hyperstars consisting of a hyperbranched PB core and (meth)acrylate arms were synthesized by anionic self-condensing vinyl copolymerization (SCVCP) of divinylbenzene and butadiene followed by the anionic polymerization of the linear (meth)acrylate arms. The amount of hyperbranched products resulting from SCVCP could be enhanced by introducing additional DVB to the reaction while polymerizing. The topology of the hyperbranched PB cores was confirmed by viscosity measurements. All Mark-Houwink-Sakurada exponents were significantly below the value for linear PB. The initiation of (meth)acrylate arms was confirmed by NMR spectroscopy. Upon the arm-growth reaction, the branched topology was retained as witnessed by further viscosity measurements. The introduction of cross-linked nanoparticles based on linear block copolymers did not disturb the transparency of PU coatings. Even after curing reaction, the nanoparticles were well-dispersed into the coating. TEM observations confirmed this last result where neither aggregation nor flocculation of the cross-linked nanoparticles was observed. Hyperstar polymers were found to undergo self-assembly upon the curing reaction leading to “onion-like” structured aggregates, in the case of PMMA hyperstars, with sizes as large as 200 nm. Aggregates of the same size order were observed for the other hyperstars but no defined structures were found. For all hyperstar modified coatings, the transparency of the films was altered. In both cases, cross-linked nanoparticles and hyperstar modified coatings, improvements of chip resistance were observed. The improvements were even better with increasing amount of cross-linked nanoparticles but no effect was noticed on the hardness of the coatings. Similar trends were observed for the hyperstar modified coatings.

Phasenverhalten von Blockcopolymeren und deren Wechselwirkung mit normalen Kohlenwasserstoff-Tensiden (2005)

Elham Eghbali

Die Mizellbildung dreier Blockcopolymer-Systemen in Wasser und deren Wechselwirkungen mit normalen Kohlenwasserstoff-Tensiden wurden durch Messungen der Oberflächenspannung, Elektronenmikroskopie, Lichtstreuung und Kleinwinkelneutronenstreuung untersucht. Für das System PEO18-PEB64-PEO18 sind die wässrigen Lösungen der Blockcopolymere trüb und metastabil und trennen sich innerhalb von ein paar Wochen in zwei Phasen. Das Blockcopolymer ist oberflächenaktiv und erniedrigt die Oberflächenspannung von Wasser. Die elektronenmikroskopischen Aufnahmen einer 1% igen Lösung des Blockcopolymers in Wasser weisen auf eine Polymorphie der Aggregate und einen fehlenden Gleichgewichtszustand hin. Unilamellare und multilamellare Vesikel und fadenförmige Mizellen sind nebeneinander auf den Aufnahmen erkennbar. Mit der Zugabe eines anionischen Tensids, SDS, ändern sich die optischen Eigenschaften sowie die Nullviskosität der Lösung und die Morphologie der Aggregate. Unterhalb der cmc des Blockcopolymers wurde keine Wechselwirkung mit Tensiden erkannt. Oberhalb der cmc lagern sich die Tensidmoleküle an die Aggregate der Blockcopolymere an. Mit zunehmender Tensidkonzentration verschwinden die größeren Aggregate und Vesikel und die Trübung der Lösung nimmt ab. Die dominante Morphologie ändert sich mit der zunehmenden Tensidkonzentration von Vesikeln zu fadenförmigen Mizellen, zu großen Mischaggregaten und zu kleinen SDS-Mizellen in welche einzelne Polymerketten gelöst sind. Diese Mischmizellen befinden sich im Gleichgewicht mit reinen SDS-Mizellen. Bei Sättigung der Blockcopolymere mit Tensid bleibt die Oberflächenspannung konstant und bei einem Wert wie dem von reinem Tensid. Die Lösungen sind dann klar und haben eine niedrige Viskosität. Die Sättigungs-Tensidkonzentration nimmt linear mit der Polymerkonzentration zu. Für das System PnBA100-PAA150 sind die wässrigen Lösungen der Blockcopolymere trüb und trennen sich in zwei Phasen. Mit der Neutralisation der Polysäure-Gruppe nimmt die Trübung ab. Für dieses System wurden zwei interessante Eigenschaften beobachtet: 1- Keine Oberflächenaktivität 2-Abhängigkeit der Viskosität von dem alpha-Wert Auf den elektronenmikroskopischen Aufnahmen sind die Änderungen der Morphologie und der Teilchenanordnung mit dem alpha-Wert erkennbar. Bei alpha=0 koexistieren unterschiedliche Morphologien wie kugelförmige Mizellen und Stäbchen, deren Größe und Form darauf hinweisen, daß das System sich nicht in einem thermodynamischen Zustand befindet. Bei alpha>0.1 sind die Teilchen ausschließlich kugelförmig. Die Polymer-Moleküle aggregieren in kugelförmige Aggregate mit einer Kern-Schale Struktur. Mit zunehmendem alpha-Wert erkennt man eine hohe Ordnung der Aggregate und einen ziemlich gleichmässigen Abstand zwischen den Teilchen. Die Polyelektrolyt-Kette streckt sich mit zunehmendem alpha-Wert, bei alpha=0,5 hat sie die höchste Länge erreicht und die Mizellen besitzen die höchste Ordnung. Aus der SANS-Messung läßt sich zwischen den Teilchen ein Abstand von ca. 104 nm und ein Durchmesser von ca. 99 nm für die Teilchen berechnen. Dies entspricht einer dichten Packung der Aggregate, welche sich in der hohen Viskosität der Lösung wiederspiegelt. Sowohl kationische, anionische und zwitterionische Tenside lagern sich an das Blockcopolymer an. Das kationische Tensid bindet an die negativ geladenen Säuregruppen und bildet einen nicht löslichen Komplex, welcher sich bei niedrigeren Tensidkonzentrationen um den Kern der Blockcopolymere legt. Die Mizelle hat dann einen schalenförmigen Aufbau mit dem Butylacrylat-Block im Zentrum, der mit einer Schale von dem unlöslichen Komplex umgeben ist. Der Rest der Polyelektrolyt-Kette bildet die Corona.) Bei höheren Tensidkonzentrationen fällt der Komplex aus der Lösung. Das Tensid bindet sich kooperativ an die Polysäure und ist nicht gleichmäßig verteilt. Mit dem anionischen Tensid SDS dominieren hydrophobe Wechselwirkungen. Das Tensid dringt in den Kern der Mizelle hinein. Nach Absättigung der vorhandenen Grenzfläche und Auflösung der Blockcopolymermizellen aggregieren die Tensid-Moleküle in normale Mizellen. Mit dem zwitterionischen Tensid C14DMAO wird die Wechselwirkung bei niedrigen alpha-Werten durch Protonenübertragung und elektrostatische Kräfte und bei höheren alpha-Werten durch hydrophobe Kräfte beherrscht. Das Blockcopolymer PMMA60-PAA90 aggregiert in Wasser ohne die Oberflächenspannung zu erniedrigen. Die wässrigen Lösungen von PMMA60-PAA90 schäumen obwohl das Blockcopolymer die Oberflächenspannung des Wassers kaum ändert. Die Viskosität von 1 %igen Blockcopolymer-Lösungen ändern sich nur wenig mit dem alpha-Wert und bleiben für den ganzen Neutralisationsbereich niedrig. Auf der Kryo-TEM Aufnahme der Mizellen ist eine starke Ordnung erkennbar, die aber keine hohe Viskosität verursacht. Der Unterschied kann ebenfalls an der Länge der Polyelektrolyt-Ketten liegen.

Orientation and Phase Behavior of Block Copolymers in External Electric Fields (2007)

Kristin Schmidt

The influence of external electric fields on the microdomain structure of block copolymers has been studied. The results range from an analysis of the mechanism and kinetics of the reorientation process, via the discussion of the driving force, to first investigations on the influence of an electric field on the phase behavior. The electric field induced effects on concentrated block copolymer solutions were investigated by in-situ synchrotron small-angle x-ray scattering. The first part concerns the analysis of the mechanism and kinetics of the alignment of lamellar forming diblock copolymer solutions as well as a quantitative study of the reorientation kinetics of various block copolymers in order to clarify the driving force of reorientation in a DC electric field. The second part of this thesis describes the influence of an electric field on the phase behavior of block copolymers. It is shown that a gyroid phase (G) as well as a hexagonally perforated lamella phase (HPL) exposed to an electric field undergo a phase transition to cylinders (C) and lamellae (L), respectively. Furthermore, an anisotropic deformation of the chain conformation in various lamellar and cylindrical block copolymer solutions via electric fields is demonstrated.

Novel Semiconductor Block Copolymers for Organic Electronic Devices: Synthesis, Properties and Applications (2009)

Michael Sommer

Diese Arbeit beschreibt die Synthese und Charakterisierung von neuartigen, maßgeschneiderten Donor-Akzeptor (D-A) Blockcopolymeren mit elektronisch funktionellen Blöcken, sowie deren Anwendung in organischen Feldeffekttransistoren und organischen Solarzellen. Die hergestellten D-A Blockcopolymere können in zwei Klassen unterteilt werden: Blockcopolymere mit einem amorphen und einem kristallinen Block und Blockcopolymere mit zwei kristallinen Blöcken. Die Synthese dieser neuen Materialien verlangt die geschickte Kombination von klassischer organischer Chemie mit einer oder zwei Polymerisationsmethoden. Die Besonderheit solcher aufwendigen Blockcopolymere liegt in ihrer Fähigkeit zur Mikrophasenseparation. Die dadurch entstehenden Domänengrößen liegen im Bereich der Exzitonendiffusionslänge, wodurch D-A Blockcopolymere als äußerst vielversprechend für Ladungstrennung und Ladungstransport gelten. Die Selbstaggregation der D-A Blockcopolymere wird vom Zusammenspiel verschiedener Kräfte geleitet: Kristallisation eines oder zweier Blöcke und Mikrophasenseparation. Solche Materialien mit definierten Moleküleigenschaften sind bisher sehr wenig erforscht und ermöglichen es, die D-A Grenzfläche in dünnen Filmen präzise einzustellen. Um definierte Blockcopolymerarchitekturen herzustellen, wurden zwei verschiedene Polymerisationsmethoden mit lebendem Charakter verwendet, kombiniert und angepasst: Nitroxid-vermittelte radikalische Polymerisation (NMRP) und Grignard Metathese Polymerisation (GRIM). Die Grignard Metathese Polymerisation wurde erfolgreich optimiert und verwendet, um mehrere Poly(3-hexylthiophen)P3HT-Blöcke mit kontrolliertem Molekulargewicht und niedriger Polydispersität herzustellen. Weiterhin wurde eine einfache und zielgerichtete Eintopfreaktion entwickelt, um P3HT-Makroinitiatoren für die NMRP herzustellen. Ausgehend von diesen Makroinitiatoren wurden mehrere definierte Blockcopolymere mit P3HT und Perylen Bisimidacrylat PerAcr mit unterschiedlicher Komposition und unterschiedlichem Molekulargewicht synthetisiert. Die Besonderheit von P3HT-b-PPerAcr liegt in der kristallin-kristallinen Blockcopolymerarchitektur, wobei das erste Segment hauptkettenkristallin und das zweite Segment seitenkettenkristallin ist. Der kristallin-kristalline Charakter wurde mittels differentieller Wärmeflußkalorimetrie und Röntgenstreuung bestätigt, wobei eine Koexistenz von lamellaren P3HT- und eindimensionalen PPerAcr Stapeln festgestellt wurde. Die Koexistenz dieser Aggregate ist maßgeblich von der Komposition, dem Molekulargewicht, und der Vorbehandlung von P3HT-b-PPerAcr abhängig. Während thermisch vorbehandelte Proben eine verstärkte Ausbildung von kristallinen PPerAcr Domänen zeigen, fördert die Lösungsmitteldampfbehandlung die Aggregation von P3HT. Dieser Effekt wird übereinstimmend bei der Untersuchung der optischen, thermischen, morphologischen und elektrischen Eigenschaften gefunden. Die Herstellung von organischen Solarzellen mit P3HT-b-PPerAcr als aktiver Schicht ergab einen Rekordwert der externen Quantenausbeute von 31 %, was für die beiden Komponenten P3HT und Perylenbisimid den höchsten gemessenen Wert darstellt.

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