Kinetic Modeling of the Synthesis of Poly(4-vinylpyridine) Macro-Reversible Addition-Fragmentation Chain Transfer Agents for the Preparation of Block Copolymers

Reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the most common controlled polymerization techniques to prepare well-defined, rather narrow dispersed polymers due to reduced demands in reactant preparation. Despite these advantages, RAFT polymerization was so far primarily utilized on small laboratory scales. This study presents a first step to a scaled-up RAFT polymerization by developing and experimentally validating a kinetic model on the example of the polymerization of 4-vinylpyridine (4VP), which to date is not described in the literature. With the implementation of the results from modeling, the synthesis process was extended to a medium scale (from 6 to 36 g), while the same high conversions, molar mass, and low dispersity as in the smaller scale were achieved. The process is also optimized regarding the high degree of livingness necessary for using the 4VP polymers as a macro-RAFT agent in the subsequent reaction step for the synthesis of poly(4-vinylpyridine)-b-polystyrene diblock copolymers by RAFT dispersion polymerization

Direct Visualization of Order–Order Transitions in Silicon-Containing Block Copolymers by Electron Tomography

Here, we aim to comprehend the mechanism of the order–order transition (OOT) from nonequilibrium, metastable phase to equilibrium phase. Polystyrene-block-polydimethylsiloxane (PS-PDMS) block copolymer (BCP) bulks with metastable cylinder (C) and double gyroid (G) phases can be obtained from lamellae (L) forming PS-PDMS by simply tuning the selectivity of casting solvent. The recovery of the intrinsic L phase can be achieved by thermal annealing through OOT. Time-resolved small-angle X-ray scattering (SAXS) experiments are carried out to reveal the variation of the structural evolution in reciprocal space during annealing. The structural evolution in real space is directly visualized by using electron tomography (i.e., 3D transmission electron microscopy (TEM)). As a result, combining the time-resolved scattering experiments and the morphological observations from electron tomography offers new insights into the phase behaviors of the OOT of BCPs

Postfunctionalization of Nanoporous Block Copolymer Membranes via Click Reaction on Polydopamine for Liquid Phase Separation

In this work, an azido-modified dopamine derivative was synthesized and subsequently used to postfunctionalize the surface of nanoporous poly­(styrene)-<i>block</i>-poly­(4-vinylpyridine) diblock copolymer membranes. On the basis of this layer a continuative modification was realized by performing a “Click” reaction, namely, the Cu­(I)-catalyzed 1,3-dipolar cycloaddition, with different alkynes. While the Click reaction was monitored by X-ray photoelectron spectroscopy, the morphology of the membranes in the different states of modification was examined with scanning electron microscopy and atomic force microscopy. The membrane properties were characterized by measurements of contact angle and clean water permeance, retention tests, and protein adsorption. Independent from the alkyne applied during the Click reaction, the clean water permeance is approximately 1200 L m^–2 bar^–1 h^–1 and therefore slightly below the permeance of the pristine membrane. While the sharp molecular weight cutoff of the pristine membrane and all modified membranes is similar, antifouling properties as studied on the interaction of two model proteins (bovine serum albumin, hemoglobin) with the membranes turned out to be best for the membranes modified with 1-nonyne

Robust Block Copolymer Mask for Nanopatterning Polymer Films

The formation of well-oriented cylinders with perpendicular morphology for polystyrene-b-polydimethylsiloxane (PS-PDMS) thin films was achieved by spin coating. The self-assembled PS-PDMS nanostructured thin films were used as templates for nanopatterning; the PDMS blocks can be oxidized as silicon oxy carbide microdomains, whereas the PS blocks were degenerated by a simple oxygen plasma treatment for one-step oxidization. As a result, freestanding silicon oxy carbide thin films with hexagonally packed nanochannels were directly fabricated and used as masks for pattern transfer to underlying polymeric materials by oxygen reaction ion etching (RIE) to generate topographic nanopatterns. By taking advantage of robust property and high etching selectivity of the SiOC thin films under oxygen RIE, this nanoporous thin film can be used as an etch-resistant and reusable mask for pattern transfer to various polymeric materials. This approach demonstrates a simple, convenient, and cost-effective nanofabrication technique to create the topographic nanopatterns of polymeric materials

Phase Transitions of Polystyrene‑<i>b</i>‑poly(dimethylsiloxane) in Solvents of Varying Selectivity

A simple method to create a variety of nanostructures via the self-assembly of a single composition silicon-containing block copolymer (BCP) is developed. By using selective solvents for the self-assembly of polystyrene-block-poly­(dimethylsiloxane) (PS–PDMS), the phase behavior of intrinsic BCP can be enriched due to the strong segregation of the PS–PDMS enabling the diversity of the phase behavior of PS–PDMS/solvent mixtures and clear-cut phase transitions upon solvent evaporation. The solution-state phase behaviors of the strong segregation BCP system in different solvents are systematically studied using temperature-resolved and time-resolved SAXS experiments. A variety of phases, such as sphere, cylinder, gyroid, lamellar phases and even inverted phases, can be acquired by simply tuning the selectivity of solvent for casting. Meanwhile, owing to the high etching contrast of the silicon-containing block versus the PS block, various nanostructured SiOC can be fabricated by using one-step oxidation. This approach suggests an easy way to create inorganic oxide nanostructures for various applications

Orienting Block Copolymer Thin Films via Entropy

Controlling the orientation of nanostructured thin films of block copolymers (BCPs) is essential for next-generation lithography using BCPs. According to conventional wisdom, the orientation of BCP thin films is mainly determined by molecular interactions (enthalpy-driven orientation). Here, we show that the entropic effect can be used to control the orientation of BCP thin films. Specifically, we used the architecture of star-block copolymers consisting of polystyrene (PS) and poly­(dimethylsiloxane) (PDMS) blocks to regulate the entropic contribution to the self-assembled nanostructures. The study unequivocally demonstrate that for star-block copolymers with the same volume fractions of PS and PDMS, perpendicularly oriented BCP nanostructures could be induced via an entropic effect regulated by the number of arms. Also, the feasibility of using the star-block copolymer thin films for practical applications is demonstrated by using the thin film as a mask for nanolithography or as a template for the fabrication of nanoporous monolith

Influence of Poly(ethylene glycol) Segment Length on CO₂ Permeation and Stability of PolyActive Membranes and Their Nanocomposites with PEG POSS

Three grades of PolyActive block copolymers are investigated for CO₂ separation from light gases. The polymers are composed of 23 wt % poly­(butylene terephthalate) (PBT) and 77 wt % poly­(ethylene glycol terephthalate) (PEGT) having the poly­(ethylene glycol) segments of 1500, 3000, and 4000 g/mol, respectively. A commercial PEG POSS (poly­(ethylene glycol) functionalized polyoctahedral oligomeric silsesquioxanes) is used as a nanofiller for these polymers to prepare nanocomposites via a solvent casting method. Single gas permeabilities of N₂, H₂, CH₄, and CO₂ are measured via the time-lag method in the temperature range from 30 to 70 °C. The thermal transitions of the prepared membranes are studied by differential scanning calorimetry (DSC). It is found that the length of PEG segment has a pronounced influence on the thermal transition of the polymers that regulates the gas separation performance of the membranes. The stability of the nanocomposites is also correlated with the thermal transition of the polyether blocks of the polymer matrices