“Uncontrolled” Preparation of Disperse Poly(lactide)-block-poly(styrene)-block-poly(lactide) for Nanopatterning Applications

Diblock and Triblock Copolymers as Nanostructured Precursors to Functional Nanoporous Materials: From Design to Application

Block copolymers have gained tremendous interest from the scientific community in the last two decades. These macromolecular architectures indeed constitute ideal nanostructured precursors for the generation of nanoporous materials meant for various high added value applications. The parallel emergence of controlled polymerization techniques has notably enabled to finely control their molecular features to confer them with unique structural and physicochemical properties, such as low dispersity values (Đ), well-defined volume fractions, and controlled functionality. The nanostructuration and ordering of diblock or triblock copolymers, which can be achieved through various experimental techniques, including channel die processing, solvent vapor or thermal annealing, nonsolvent-induced phase separation or concomitant self-assembly, and nonsolvent-induced phase separation, allows for the preparation of orientated microphase-separated copolymers whose morphology is dictated by three main factors, i.e., Flory-Huggins interaction parameter between constitutive blocks, volume fraction of the blocks, and polymerization degree. This review article provides an overview of the actual state of the art regarding the preparation of functional nanoporous materials from either diblock or triblock copolymers. It will also highlight the major applications of such peculiar materials.

Novel Well-defined Polystyrene-block-Poly(lactide-co-glycolide) Block Copolymers

A facile preparation of polystyrene-block-poly(lactide-co-glycolide) PS-b-PLGA block copolymers was reported in detail. Well-defined PS-b-PLGA block copolymers were successfully obtained via living anionic polymerization and ring-opening polymerization. First, hydroxyl-terminated linear polystyrenes were prepared by living anionic polymerization. The resulting polymers were used as macroinitiators for ring-opening copolymerization of lactide and glycolide in the presence of the 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst in dichloromethane at ambient temperature. Transesterification and formation of DBU-initiated polymers were minimized by optimizing the catalyst concentration. Three block copolymers were synthesized in various molecular weights from 5000 g/mol to 33600 g/mol with low polydispersity. The formation of well-defined PS-b-PLGA block copolymers was followed by nuclear magnetic resonance spectroscopy and size-exclusion chromatography. Thermal properties of the block copolymers were investigated by thermal gravimetric analysis and differential scanning calorimetry. The morphology of the block copolymers was investigated using small-angle X-ray scattering in the bulk and via grazing incidence small-angle X-ray scattering as well as atomic force microscopy in thin film demonstrating organized nanostructures with uniform domain sizes. Overall, this manuscript describes an expanded polymer toolbox for PLGA-based polymers for next-generation lithography applications.

Multifunctional Structured Platforms: From Patterning of Polymer-Based Films to Their Subsequent Filling with Various Nanomaterials

There is an astonishing number of optoelectronic, photonic, biological, sensing, or storage media devices, just to name a few, that rely on a variety of extraordinary periodic surface relief miniaturized patterns fabricated on polymer-covered rigid or flexible substrates. Even more extraordinary is that these surface relief patterns can be further filled, in a more or less ordered fashion, with various functional nanomaterials and thus can lead to the realization of more complex structured architectures. These architectures can serve as multifunctional platforms for the design and the development of a multitude of novel, better performing nanotechnological applications. In this work, we aim to provide an extensive overview on how multifunctional structured platforms can be fabricated by outlining not only the main polymer patterning methodologies but also by emphasizing various deposition methods that can guide different structures of functional nanomaterials into periodic surface relief patterns. Our aim is to provide the readers with a toolbox of the most suitable patterning and deposition methodologies that could be easily identified and further combined when the fabrication of novel structured platforms exhibiting interesting properties is targeted.

Downsizing feature of microphase-separated structures via intramolecular crosslinking of block copolymers

A novel strategy for downsizing the feature of microphase-separated structures was developed via the intramolecular crosslinking reaction of block copolymers (BCPs) without changing the molecular weight. A series of BCPs consisting of poly[styrene-st-(p-3-butenyl styrene)] and poly(rac-lactide) (SBS-LA) was subjected to Ru-catalyzed olefin metathesis under highly diluted conditions to produce intramolecularly crosslinked BCPs (SBS(cl)-LAs). Small-angle X-ray scattering measurement and transmission electron microscopy observation of the SBS(cl)-LAs revealed feature size reduction in lamellar (LAM) and hexagonally close-packed cylinder (HEX) structures in the bulk state, which was surely due to the restricted chain dimensions of the intramolecularly crosslinked SBS block. Notably, the degree of size reduction was controllable by varying the crosslink density, with a maximum decrease of 22% in the LAM spacing. In addition, we successfully observed the downsizing of the HEX structure in the thin film state using atomic force microscopy, indicating the applicability of the present methodology to next-generation lithography technology.

Computational Design of High-χ Block Oligomers for Accessing 1 nm Domains

Molecular dynamics simulations are used to design a series of high-χ block oligomers (HCBOs) that can self-assemble into a variety of mesophases with domain sizes as small as 1 nm. The exploration of these oligomers with various chain lengths, volume fractions, and chain architectures at multiple temperatures reveals the presence of ordered lamellae, perforated lamellae, and hexagonally packed cylinders. The achieved periods are as small as 3.0 and 2.1 nm for lamellae and cylinders, respectively, which correspond to polar domains of approximately 1 nm. Interestingly, the detailed phase behavior of these oligomers is distinct from that of either solvent-free surfactants or block polymers. The simulations reveal that the behavior of these HCBOs is a product of an interplay between both "surfactant factors" (headgroup interactions, chain flexibility, and interfacial curvature) and "block polymer factors" (χ, chain length N, and volume fraction f). This insight promotes the understanding of molecular features pivotal for mesophase formation at the sub-5 nm length scale, which facilitates the design of HCBOs tailored toward particular desired morphologies.

CuAAC click chemistry: a versatile approach towards PVDF-based block copolymers

Functionalized benzoyl peroxide-initiated polymerization of vinylidene fluoride allows straightforward preparation of PVDF-based block copolymers with an appealing crystallization behavior.

A novel copper catalyst containing a hydroxyl functional group: a facile strategy to prepare block copolymers of vinyl monomer and ε-caprolactone via tandem reverse ATRP and ROP

A facile hydroxyl-functionalized catalyst was first accessed to prepare block copolymers of vinyl and cyclic ester monomers via tandem reverse ATRP/ROP.