Exploring the limits of the geometric copolymerization model

The geometric copolymerization model is a recently introduced statistical Markov chain model. Here, we investigate its practicality. First, several approaches to identify the optimal model parameters from observed copolymer fingerprints are evaluated using Monte Carlo simulated data. Directly optimizing the parameters is robust against noise but has impractically long running times. A compromise between robustness and running time is found by exploiting the relationship between monomer concentrations calculated by ordinary differential equations and the geometric model. Second, we investigate the applicability of the model to copolymerizations beyond living polymerization and show that the model is useful for copolymerizations involving termination and depropagation reactions

Computational mass spectrometry of linear binary synthetic copolymers

The accurate characterization of synthetic polymer sequences represents a major challenge in polymer science. We present a computational approach to quantify the abundances of all sequences in a measured copolymer sample. The first step in our workflow is transforming mass spectra into copolymer fingerprints. Our method is based on linear programming and is capable of automatically resolving overlapping isotopes and isobaric ions. Peak intensities in matrix-assisted laser desorption/ionization spectra are influenced by mass and composition-dependent ionization. We demonstrate a method to correct the abundance bias. The second step in our workflow is interpreting the computed copolymer fingerprints using new Markov chain models for copolymerization kinetics: The Bernoulli and Geometric models. In contrast to previous Markov chain approaches to copolymerization, both models take variable chain lengths and time-dependent monomer probabilities into account and allow computing sequence likelihoods and copolymer fingerprints. We find that computing the models is fast and memory efficient. Then, we focus on the Geometric copolymerization model with reactivity parameters. First, several approaches to identify the optimal model parameters from observed fingerprints are evaluated using Monte-Carlo simulated data. A compromise between robustness and running time is found by exploiting the relationship between ordinary differential equations and the Geometric model. Second, we show that the model is also useful for copolymerizations involving termination and depropagation reactions. We then compute several copolymer statistics and compared them to the statistics obtained from Monte-Carlo simulations. Last but not least, we present our software framework COCONUT, which implements all algorithms presented in this thesis. Our software is freely available and provides a graphical user interface. COCONUT represents a step towards comprehensive computational support in polymer science

Engineering block copolymers for advanced lithography

Block copolymer (BCP) nanoimprint lithography is an attractive possible solution for manufacturing hard disk drives with information densities greater than 1 Tbit/in². At these densities, individual bits must be smaller than 10 nm, and BCPs can be engineered to spontaneously self-segregate into features on this size scale. In addition to small feature sizes, industrially relevant BCPs should have simple orientation strategies and possess good etch contrast and resistance. Several silicon-containing BCPs were investigated due to the increased etch contrast and resistance imparted by silicon. The synthesis, characterization, and thin film studies of three silicon-containing BCPs are detailed. Due to the surface energy mismatch between the silicon-containing block and the organic block, solvent annealing and top coats were needed to perpendicularly orient these materials. While these materials possess many advantages, they each have shortcomings that prevent them from being ideal industrial materials. A derivative of poly(styrene-block-methyl methacrylate) was engineered to take advantage of its simple orientation procedure while decreasing the smallest achievable feature size. The synthesis and characterization, including determination of the [chi] parameter, of this BCP are detailed. The thin film assembly of this BCP was also successfully demonstrated, and this dissertation concludes with several ideas for future studies.Chemical Engineerin

Copolymers of amorphous polystyrene and crystallizable hydrogen bonding units

Copolymers are macromolecules composed of linear or non-linear arrangements of chemically different polymeric chain parts. In most cases the different constituting blocks are incompatible, giving rise to a rich variety of well-defined self-assembled structures both in bulk and in selective solvents. These self-assembled structures may form the basis for applications ranging from thermoplastic elastomers to information storage, drug delivery and photonic materials. As a result, there is a continuous investigation of the self-assembly process as well as of the response of these materials to external stimuli. Therefore, it is not surprising that these materials play an important role in contemporary macromolecular science, covering the full spectrum of polymer chemistry, polymer physics and applications. In the present thesis, copolymers of amorphous polystyrene and aliphatic or aromatic polyamide units, having various structures (diblock, multiblock and graft copolymers) were synthesized and their structure-properties relationships were investigated. These copolymers were applied in order to verify a so-called "sticky-blocks" concept, which aims at designing materials with improved processabilty as compared to high molecular weight industrially used polystyrenes. The principle of "sticky-blocks" lies in decreasing the molecular weight of polystyrene (thus improving melt flow) and compensating for the loss of entanglements per individual macromolecule, by creating hydrogen-bonded, semi-crystalline polymeric networks, which would have similar properties as the high molecular weight homo-polystyrenes. Polyamides we chosen to function as "sticky-blocks" due to their relatively low melt viscosity (200-400 Pas) and optimal mechanical and thermal properties at relatively low molecular weights (20,000-30,000 g/mol), inherent in the presence of relatively strong hydrogen-bond interactions. We demonstrated in this thesis that, by using aromatic polyamides (T6T6T) of (reported) high crystallinity and stability of the crystalline phase, segmented multiblock copolymers of polystyrene and T6T6T with molar masses up to around 40,000 g/mol can be relatively easily prepared. However, due to the very high incompatibility of the two phases, the synthesized multiblock copolymers displayed rather weak crystals and premature phase separation (presumed via liquid-liquid demixing), and the desired semi-crystalline network structure could not be obtained. Nevertheless, the thermal stability and moduli improved considerably, not only compared to neat PS of similar molecular mass (50,000 g/mol), but also compared to commercial PS with Mw ˜ 200,000 g/mol. Aliphatic polyamides (polyamide-6) were also used as "sticky blocks" in the preparation of diblock and graft copolymers. The diblock copolymers of polystyrene and polyamide-6 had a maximum molecular weight of 20,000 g/mol and were prepared via anionic polymerization of e-caprolactam, starting from PS end-functionalized macroinitiators. These semi-crystalline materials were presumed to be well-flowing (lack of entanglements), but were too brittle to possess measurable mechanical properties. Therefore, for achieving less brittle copolymers, graft copolymers of higher molecular weight (Mn up to 100,000 g/mol) were made via combined ATRP and reactive processing. The graft copolymers seemed the most promising materials to be used for achieving the goal of this thesis. As revealed by thermo-mechanical analyses (DMTA) and rheology, relatively stable crystalline polymeric networks can be formed. Moreover, the graft copolymers had a lower viscosity in the melt under injection moulding shear conditions, while maintaining and even improving some properties of commercial PS. Summarizing, by using this approach, the goal set for decreasing the molecular weight of the PS (thereby improving its flow properties) and compensating for the loss of entanglements per PS macromolecule by introducing "sticky blocks", can most probably be achieved when some further improvements suggested in this thesis can be realized

Patternable materials for next-generation lithography

One of the salient truths facing the microelectronics industry today is that photolithography tools are unable to meet the resolution requirements for manufacturing next-generation devices. In the past, circuit feature sizes have been minimized by reducing the exposure wavelength used for patterning. However, this strategy failed with the worldwide dereliction of 157 nm lithography in 2003. Extreme ultraviolet (EUV) lithography still faces many technical challenges and is not ready for high volume manufacturing. How will the microelectronics industry continue to innovate without regular advances in photopatterning technology? Regardless of which paradigm is adopted, new materials will probably be required to meet the specific challenges of scaling down feature sizes and satisfying the economic ultimatum of Moore’s Law. In the search for higher resolution patterning tools, device manufacturers have identified block copolymer (BCP) lithography as a possible technique for next-generation nanofabrication. BCP self-assembly offers access to sub-5 nm features in thin films, well beyond the resolution limits of photolithography. However, BCP materials must be carefully designed, synthesized, and processed to create lithographically interesting features with good etch resistance for pattern transfer. In this dissertation, we describe a pattern transfer process for 5 nm BCP lamellae and a directed self-assembly (DSA) process for aligning 5 nm structures in thin films. To achieve defect-free alignment, the interfacial interactions between the BCP and pre-patterned substrate must be precisely controlled. We also discuss a new process for selectively modifying oxidized chromium films using polymer brushes, which could further improve the aforesaid DSA process. To facilitate better pattern transfer of BCP structures, several new BCPs with “self-developing” blocks were synthesized and tested. These materials depolymerize and evaporate in strongly acidic environments, leading to developed BCP features without the need for etching or solvent. “Self-developing” polymers may also be useful materials for traditional photolithography. Chemically amplified resists used in manufacturing today are fundamentally limited by a trade-off between sensitivity and pattern quality. To overcome this problem, we present a new type of photoresist that relies on depolymerization, rather than catalysis, to achieve amplification without producing significant roughness or bias in the final patternChemical Engineerin

Effect of interfaces on thermophysical properties and block copolymer self-assembly in polymer thin films

When materials are tailored for use at the nanoscale, thermophysical properties can deviate from their bulk values, and these phenomena are broadly referred to as nanoconfinement effects. In thin films, one of the critical factors of nanoconfinement effects is interfacial interactions; as the film thickness decreases, the interfacial area to volume ratio increases dramatically, often causing interfacial effects to dominate the properties of the entire film. As polymers continue to be leveraged in nanotechnology, from nanocomposites to lithography, understanding the effects of interfaces is highly desired. While numerous studies have revealed how thermophysical properties, (e.g., glass transition temperature (Tg), self-diffusion coefficient (D), and effective viscosity (η [subscript eff]) change with film thickness, correlations between these parameters are still unclear. Herein, the Tg, D, and η [subscript eff] are measured for a model system of unentangled poly (isobutyl methacrylate) (PiBMA, 16-300 nm thick) supported by SiOx. The non-bulk-like correlation between Tg, D, and η [subscript eff] is successfully explained using a three-layer model. To further investigate the effect of confining interfaces, the Tg and D of PiBMA are studied for four multilayer geometries, where the interfacial interactions are varied from strong to weak. The Tg-D relationship of thin films deviates from bulk behavior, and the magnitude of the deviations depends on the polymer-substrate interactions. A friction analysis reveals that this deviation originates from heterogeneous dynamics near the confining interfaces. Engineering interfaces between polymers and substrates is also crucial for BCP lithography, especially on non-traditional substrates (e.g. flexible or 2D materials). In particular, precise control of the surface energy of the underlying substrate is required to produce lithographically useful structures, such as lamellar domains oriented perpendicular to the substrate. In this study, polydopamine is first exploited as a universal adhesive to enable BCP nanopatterning on a variety of flexible materials. In addition, we developed a potentially scalable graphene nanoribbon fabrication method using wetting-transparency assisted BCP lithography. Lastly, inspired by the wetting transparency phenomenon, possible techniques to control the microdomain orientations of BCPs through thin layers are explored using a model bi-layer substrate made from homopolymers of each block, along with a theoretical model based on van der Waals forces.Chemical Engineerin