Rudy J. Wojtecki

Supramolecular motifs in dynamic covalent PEG-hemiaminal organogels

Dynamic covalent materials are stable materials that possess reversible behaviour triggered by stimuli such as light, redox conditions or temperature; whereas supramolecular crosslinks depend on the equilibrium constant and relative concentrations of crosslinks as a function of temperature. The combination of these two reversible chemistries can allow access to materials with unique properties. Here, we show that this combination of dynamic covalent and supramolecular chemistry can be used to prepare organogels comprising distinct networks. Two materials containing hemiaminal crosslink junctions were synthesized; one material is comprised of dynamic covalent junctions and the other contains hydrogen-bonding bis-hemiaminal moieties. Under specific network synthesis conditions, these materials exhibited self-healing behaviour. This work reports on both the molecular-level detail of hemiaminal crosslink junction formation as well as the macroscopic behaviour of hemiaminal dynamic covalent network (HDCN) elastomeric organogels. These materials have potential applications as elastomeric components in printable materials, cargo carriers and adhesives.

Computational and experimental investigations of one-step conversion of poly(carbonate)s into value-added poly(aryl ether sulfone)s.

Significance This work describes a convenient, quantitative, and robust one-step transformation of polycarbonates into high-value poly(aryl ether sulfone)s in the presence of a carbonate salt and bis(aryl fluorides). This strategy has important implications for the repurposing of plastic waste into value-added materials by the use of carefully controlled depolymerization conditions. Computational studies used to support these findings show how carbonate salts decompose organic carbonates and form the poly(aryl ether sulfone) products. Determining the role of the metal salt in the depolymerization/repolymerization process will enable future design for economic recycling and synthesis methods. It is estimated that ∼2.7 million tons poly(carbonate)s (PCs) are produced annually worldwide. In 2008, retailers pulled products from store shelves after reports of bisphenol A (BPA) leaching from baby bottles, reusable drink bottles, and other retail products. Since PCs are not typically recycled, a need for the repurposing of the PC waste has arisen. We report the one-step synthesis of poly(aryl ether sulfone)s (PSUs) from the depolymerization of PCs and in situ polycondensation with bis(aryl fluorides) in the presence of carbonate salts. PSUs are high-performance engineering thermoplastics that are commonly used for reverse osmosis and water purification membranes, medical equipment, as well as high temperature applications. PSUs generated through this cascade approach were isolated in high purity and yield with the expected thermal properties and represent a procedure for direct conversion of one class of polymer to another in a single step. Computational investigations performed with density functional theory predict that the carbonate salt plays two important catalytic roles in this reaction: it decomposes the PCs by nucleophilic attack, and in the subsequent polyether formation process, it promotes the reaction of phenolate dimers formed in situ with the aryl fluorides present. We envision repurposing poly(BPA carbonate) for the production of value-added polymers.

Development of polycarbonate-containing block copolymers for thin film self-assembly applications

Access to well-defined materials is one of the key requirements for successful implementation of block copolymer-based lithography for advanced semiconductor nodes. We report on the development of polystyrene-b-polytrimethylene carbonate (PS-b-PTMC) block copolymer (BCP) using organocatalytic ring opening polymerization of trimethylene carbonate (TMC) from hydroxyl-functional polystyrene macroinitiator as a materials candidate for directed self-assembly applications. The impact of organocatalyst choice and the extent of TMC conversion on the quality of PS-b-PTMC BCP were studied using gel permeation chromatography and nuclear magnetic resonance (NMR) spectroscopy techniques. As a direct method to identify PTMC homopolymer content in the resulting BCPs, a new NMR-based technique was developed. Finally, the influence of BCP purity on the thin film morphology was studied using atomic force microscopy and grazing incidence small angle X-ray scattering techniques. Our results indicate that the PTMC homopolymer impurity negatively impacts the thin film morphology, which is extremely important for lithographic applications.

Developments in Dynamic Covalent Chemistries from the Reaction of Thiols with Hexahydrotriazines

Dynamic covalent chemistries have garnered significant attention for their potential to revolutionize technologies in the material fields (engineering, biomedical, and sensors) and synthetic design strategies as they provide access to stimuli responsiveness and adaptive behaviors. However, only a limited number of molecular motifs have been known to display this dynamic behavior under mild conditions. Here, we identified a dynamic covalent motif-thioaminals-that is produced from the reaction of hexahydrotriazines (HTs) with thiols. Furthermore, we report on the synthesis of a new family of step-growth polymers based on this motif. The condensation efficiently proceeds to quantitative yields within a short time frame and offers versatility in functional group tolerance; thus, it can be exploited to synthesize both small molecule thioaminals as well as high molecular weight polymers from the step-growth polymerization of HTs with dithiols. Careful evaluation of substituted HTs and organic thiols supported by DFT calculations led to a chemically diverse library of polymers based on this motif. Finally, dynamic substitution reactions were employed toward the facile preparation of functional oligomers and macromolecules. This dynamic covalent motif is particularly attractive for a range of applications that include material design and drug delivery due to the economic feasibility of synthesis.

Facile carbohydrate-mimetic modifications of poly(ethylene imine) carriers for gene delivery applications

Commercially-available linear and branched PEIs (LPEI and BPEI) were chemically-modified with carbohydrates and carbohydrate-mimetics to improve biocompatibility. Hydroxyl moieties were installed in a close proximity via reaction of PEIs amines with paraformaldehyde (pF) or glycidol. Mixing PEI with pF led to the formation of hemiaminal moieties as well as N-methylation of the backbone through an Eschweiler–Clarke-type rearrangement. The amount of attached hydroxyl groups depended on the initial amount of pF and the results were in agreement with NMR studies on model reactions with primary and secondary amines. The primary amines of BPEI triggered the ring-opening of glycidol and sugar-containing epoxides, in methanol and at room temperature. PEI chains modified with pF displayed the same cytotoxicity as the parent polymer, unless a sufficient amount of pF was added to trigger N-methylation of the backbone. In contrast, glycidol and sugar-functionalized BPEIs exhibited lower toxicity but similar (if not higher) transfection efficiency as compared to unmodified BPEI.

Study of resist hardmask interaction through surface activation layers

At IBM, one of the focus items for EUV patterning development is to enable the fullest extent of scaling to a second EUV node while maintaining single-exposure levels. The challenge for the next node of EUV patterning has been with attaining acceptable defectivity levels that can enable electrical yield at pitches 32nm and below. For single-expose EUV, the primary detractors to sub-32nm pitch yield are typically microbridging and line break defects, which have different root causes but can exist in the same dose range. Since the etch strategies for mitigating one of these defect types will result in exacerbating the other, the burden to improve defectivity cannot be placed solely on the pattern transfer process. Resist scumming, which is the root cause of microbriging, can be modulated through interactions with the resist-hardmask interface. The lack of acid at the substrate interface causes resist scumming, and therefore increasing the acidity at the resist hardmask interface can be expected to mitigate post-litho microbridge defects. As the number of EUV photons are significantly less compared to DUV exposures due to the high energy contained in each photon, an extra acid boost can also help to address the stochastics failures that dominate EUV patterning. This paper will demonstrate the concept of modulating the resist-hardmask interaction through surface activation layers, and show the subsequent effects on patterning process window and microbridging defectivity toward yield at pitches <32nm.

Contrast enhanced diffusion NMR: quantifying impurities in block copolymers for DSA

Block-copolymers (BCPs) offer the potential to meet the demands of next generation lithographic materials as they can self-assemble into scalable and tailorable nanometer scale patterns. In order for these materials to find wide spread adoption many challenges remain, including reproducible thin film morphology, for which the purity of block copolymers is critical. One of the sources of impurities are reaction conditions used to synthesize block copolymers that may result in the formation of homopolymer as a side product, which can impact the quality and the morphology of self-assembled features. Detection and characterization of these homopolymer impurities can be challenging by traditional methods of polymer characterization. We will discuss an alternate NMR-based method for the detection of homopolymer impurities in block copolymers – contrast enhanced diffusion ordered spectroscopy (CEDOSY). This experimental technique measures the diffusion coefficient of polymeric materials in the solution allowing for the ‘virtual’ or spectroscopic separation of BCPs that contain homopolymer impurities. Furthermore, the contrast between the diffusion coefficient of mixtures containing BCPs and homopolymer impurities can be enhanced by taking advantage of the chemical mismatch of the two blocks to effectively increase the size of the BCP (and diffusion coefficient) through the formation of micelles using a cosolvent, while the size and diffusion coefficient of homopolymer impurities remain unchanged. This enables the spectroscopic separation of even small amounts of homopolymer impurities that are similar in size to BCPs. Herein, we present the results using the CEDOSY technique with both first generation BCP system, poly(styrene)-b-poly(methyl methacrylate), as well as a second generation high-χ system.