Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c02147
Julia T. Early, Alison Block, Kevin G. Yager, and Timothy P. Lodge
https://ift.tt/3eT4AOt
DOI: 10.1021/acs.macromol.0c02169
https://pubs.acs.org/doi/abs/10.1021/acs.macromol.0c02169
Micrometer‐scale spiral structures with clear handedness are obtained through self‐assembly of liquid crystalline block copolymer, poly(ethylene oxide)‐b‐poly(methyl methacrylate) bearing azobenzene mesogen side chains, with the aid of enantiopure tartaric acid as chiral additive. The formation of spiral structures can be reversibly controlled by ultraviolet light and heat treatment.
Abstract
The spiral is a fundamental structure in nature and spiral structures with controllable handedness are of increasing interest in the design of new chiroptical materials. In this study, micrometer‐scale spiral structures with reversible chirality were fabricated based on the assembly of a liquid crystalline block copolymer film assisted by enantiopure tartaric acid. Mechanistic insight revealed that the formation of the spiral structures was closely related to the liquid crystalline properties of the major phase of block copolymer under the action of chiral tartaric acid. The chiral spiral structures with controllable handedness were easily erased under ultraviolet light irradiation and restored via thermal annealing. This facile thermal treatment method provides guidance for fabrication of chiral micrometer‐scale spiral structures with adjustable chiral properties.
https://ift.tt/3vMxA0x
Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c01571
Yifan Zhang, Huda Shaikh, Alexander J. Sneyd, Jia Tian, James Xiao, Arthur Blackburn, Akshay Rao, Richard H. Friend, and Ian Manners
https://ift.tt/3eFdihA
Polymerization‐induced self‐assembly (PISA) can produce lyotropic phases of block copolymer nano‐objects. Time‐resolved SAXS studies confirm that reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate in n‐dodecane initially produces spheres exhibiting long‐range order that subsequently evolve to form hexagonally packed worms. Serial dilution leads to disordered worms.
Abstract
We report that polymerization‐induced self‐assembly (PISA) can be used to prepare lyotropic phases comprising diblock copolymer nano‐objects in non‐polar media. RAFT dispersion polymerization of benzyl methacrylate (BzMA) at 90 °C using a trithiocarbonate‐capped hydrogenated polybutadiene (PhBD) steric stabilizer block in n‐dodecane produces either spheres or worms that exhibit long‐range order at 40 % w/w solids. NMR studies enable calculation of instantaneous copolymer compositions for each phase during the BzMA polymerization. As the PBzMA chains grow longer when targeting PhBD80–PBzMA40, time‐resolved small‐angle X‐ray scattering reveals intermediate body‐centered cubic (BCC) and hexagonally close‐packed (HCP) sphere phases prior to formation of a final hexagonal cylinder phase (HEX). The HEX phase is lost on serial dilution and the aligned cylinders eventually form disordered flexible worms. The HEX phase undergoes an order–disorder transition on heating to 150 °C and a pure HCP phase forms on cooling to 20 °C.
https://ift.tt/38NoSFE
Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c02395
Shaofei Song, Xuemin Liu, Ehsan Nikbin, Jane Y. Howe, Qing Yu, Ian Manners, and Mitchell A. Winnik
https://ift.tt/3x0E5xu
Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c01088
Liying Kang, Albert Chao, Meng Zhang, Tianyi Yu, Jun Wang, Qi Wang, Huihui Yu, Naisheng Jiang, and Donghui Zhang
https://ift.tt/3wAOcIY
Unexpected excited‐state conjugation was observed in a series of copolymers derived from ladder silsesquioxane, vinyl(Me/Ph)Si(O0.5)2[PhSiO1.5]4(O0.5)2Si(Me/Ph)vinyl, which exhibited 30–60 nm red‐shifted emission relative to double‐decker derived analogues with equal or larger degrees of polymerization. Further studies hint at their potential application as semiconducting polymers.
Abstract
Multiple studies have explored using cage silsesquioxanes (SQs) as backbone elements in hybrid polymers motivated by their well‐defined structures and physical and mechanical properties. As part of this general exploration, we report unexpected photophysical properties of copolymers derived from divinyl double decker (DD) SQs, [vinyl(Me)Si(O0.5)2][PhSiO1.5]8[(O0.5)2Si(Me)vinyl] (vinylDDvinyl). These copolymers exhibit strong emission red‐shifts relative to model compounds, implying unconventional conjugation, despite vinyl(Me)Si(O‐)2 siloxane bridges. In an effort to identify minimum SQ structures that do/do not offer extended conjugation, we explored Heck catalyzed co‐polymerization of vinyl‐ladder(LL)‐vinyl compounds, vinyl(Me/Ph)Si(O0.5)2[PhSiO1.5]4(O0.5)2Si(Me/Ph)vinyl, with Br‐Ar‐Br. Most surprising, the resulting oligomers show 30–60 nm emission red‐shifts beyond those seen with vinylDDvinyl analogs despite lacking a true cage. Further evidence for unconventional conjugation includes apparent integer charge transfer (ICT) between LL‐co‐thiophene, bithiophene, and thienothiophene with 10 mol % F4TCNQ, suggesting potential as p‐type doped organic/inorganic semiconductors.
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Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c00561
Michael L. McGraw, Ryan W. Clarke, and Eugene Y.-X. Chen
https://ift.tt/3pYIqfW
Hey everyone, I'm doing a 6 months Co-Op in a polymer company that handles production of a wide variety of polymers. This last week I was given my very first real challenge that just left me dumb-founded. The engineers told me they just very recently found out about a non-desired byproduct that was gettting bigger and bigger inside the equipments. They were worried because they didn't know the cause.
In a copolymer plant where they use MVA (vinyl acetate monomer) and VCM (vinyl chloride monomer) as raw materials in one stage of their production process, they strip the copolymer resin (undry product) to remove the unreacted MVC/MVA. During the stripping they inject caustic soda to help react the unreacted MVA.
However, it is believed that this NaOH with the MVA is generating side reactions to produce acetaldehyde,how is it possible that this can happen? So far I haven't been able to find a reaction pathway that leads to acetaldehyde from our substances.
The way the engineers found out about the acetaldehyde is because we take daily samples from the reactor and strippers and take them to a lab to pin-point the composition using Gas chromatography.
Porous organic frameworks provide the suitable hydrocarbon cavities for anionic polymerization and copolymerization of isoprene and methylmethacrylate, forming core–shell nanostructured materials. Lithiation reaction on the frameworks generated multiple anion initiators which promoted the growth of anchored chains.
Abstract
An anionic mechanism is used to create polymers and copolymers as confined to, or anchored to, high‐surface‐area porous nanoparticles. Linear polymers with soft and glassy chains, such as polyisoprene and polymethylmethacrylate, were produced by confined anionic polymerization in 3D networks of porous aromatic frameworks. Alternatively, multiple anions were generated on the designed frameworks which bear removal protons at selected positions, and initiate chain propagation, resulting in chains covalently connected to the 3D network. Such growth can continue outside the pores to produce polymer‐matrix nanoparticles coated with anchored chains. Sequential reactions were promoted by the living character of this anionic propagation, yielding nanoparticles that were covered by a second polymer anchored by anionic block copolymerization. The intimacy of the matrix and the grown‐in polymers was demonstrated by magnetization transfer across the interfaces in 2D 1H‐13C‐HETCOR NMR spectra.
https://ift.tt/3qktbiy
The poly(phenylacetylene)s block copolymers PPA‐b‐PsmNap with the dynamic helical backbone were synthesized to mimic the allosterical nature of proteins. The copolymers can sequentially evolve from vesicles to nanobelts to helical strands during the process of conformation transformation.
Abstract
Allostery can regulate protein self‐assembly which further affects biological activities, and achieving precise control over the chiral suprastructures during self‐assembly remains challenging. Herein, to mimic the allosterical nature of proteins, the poly(phenylacetylene) block copolymers PPA‐b‐PsmNap with the dynamic helical backbone were synthesized to investigate their conformational‐transition‐induced self‐assembly. As the helical conformation of the block PsmNap spontaneously transforms from cis‐transiod to cis‐cisoid, the decreasing solubility of PsmNap blocks in THF induced self‐assembly of PPA‐b‐PsmNap. The self‐assembly structures of copolymers can sequentially evolve from vesicles to nanobelts to helical strands during the process of conformation transformation. The screw sense of final helical strands was strictly correlated to the helicity of the block PsmNap. This is helpful to understand the mechanism of allostery‐modulated self‐assembly.
https://ift.tt/3ttEDcC
Copolymers of acrylic acid (AA) and butyl acrylate (BA) with constant overall composition (1:1 AA:BA) and controlled composition profiles (gradient, asymmetric diblock and asymmetric triblock) show dynamic pH‐responsive self‐assembly behavior, with reversible changes in size and formation of sphere, worm and vesicle morphologies, in contrast to the frozen micelles formed by poly(AA‐block‐BA) block copolymers.
Abstract
A series of copolymers containing 50 mol % acrylic acid (AA) and 50 mol % butyl acrylate (BA) but with differing composition profiles ranging from an AA‐BA diblock copolymer to a linear gradient poly(AA‐grad‐BA) copolymer were synthesized and their pH‐responsive self‐assembly behavior was investigated. While assemblies of the AA‐BA diblock copolymer were kinetically frozen, the gradient‐like compositions underwent reversible changes in size and morphology in response to changes in pH. In particular, a diblock copolymer consisting of two random copolymer segments of equal length (16 mol % and 84 mol % AA content, respectively) formed spherical micelles at pH >5, a mix of spherical and wormlike micelles at pH 5 and vesicles at pH 4. These assemblies were characterized by dynamic light scattering, cryo‐transmission electron microscopy and small angle neutron scattering.
https://ift.tt/3l1ViQd
Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c12538
Daniel Sharon, Peter Bennington, Michael A. Webb, Chuting Deng, Juan J. de Pablo, Shrayesh N. Patel, and Paul F. Nealey
https://ift.tt/3btinYP
Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c12478
Jianchun Wang, Tao Cheng, Aidan Q. Fenwick, Turki N. Baroud, Alonso Rosas-Hernández, Jeong Hoon Ko, Quan Gan, William A. Goddard III, and Robert H. Grubbs
https://ift.tt/3d5pmJR
Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c10588
Huong Dau, Anthony Keyes, Hatice E. Basbug Alhan, Estela Ordonez, Enkhjargal Tsogtgerel, Anthony P. Gies, Evelyn Auyeung, Zhe Zhou, Asim Maity, Anuvab Das, David C. Powers, Dain B. Beezer, and Eva Harth
https://ift.tt/2K2t0b6
Allostery can regulate protein self‐assembly which further affects biological acitivities, and achieving precise control over the chiral suprastructures during self‐assembly remains challenging. Herein, to mimic the allosterical nature of proteins, the poly(phenyacetylene)s block copolymers PPA‐ b ‐PsmNap with the dynamic helical backbone were synthesized to investigate their conformational‐transition‐induced self‐assembly. As the helical conformation of the block PsmNap spontaneously transforms from cis‐transiod to cis‐cisoid, the decreasing solubility of PsmNap blocks in THF induced self‐assembly of PPA‐ b ‐PsmNap. The self‐assembly structures of copolymers can sequentially evlove from vesicles to nanobelts to helical strands during the process of conformation transformation. The screw sense of final helical strands was closely correlated to the helicity of the block PsmNap. This is helpful to understand the mechanism of allostery‐modulated self‐assembly.
https://ift.tt/3s3db4T
Polymerizations in confining systems provide a strategy to form materials with hierarchical constructions of linear polymers and 3D architectures. However, in this field, anionic polymerization is almost unexplored: we have filled the gap by implementing an anionic mechanism to create polymers and copolymers as confined to, or anchored to, high surface area porous nanoparticles. Far diverse linear polymers with soft and glassy chains, such as polyisoprene and polymethylmethacrylate, were produced by confined anionic polymerization in 3D networks of porous aromatic frameworks. Alternatively, multiple anions were generated on the designed frameworks which bear removal protons at selected positions, and initiate chain propagation, resulting in chains covalently connected to the 3D network. Such growth can continue outside the pores to produce polymer‐matrix nanoparticles coated with anchored chains. Sequential reactions were promoted by the living character of this anionic propagation , yielding nanoparticles that were covered by a second polymer anchored by anionic block‐copolymerization. The intimacy of the matrix and the grown‐in polymers was demonstrated unconventionally by magnetization transfer across the interfaces in 2D 1 H‐ 13 C‐HETCOR NMR spectra. The present achievements open intriguing perspectives for the use of versatile anionic polymerization to finely control interdigitated nanocomposites.
https://ift.tt/3qktbiy
Polymerizations in confining systems provide a strategy to form materials with hierarchical constructions of linear polymers and 3D architectures. However, in this field, anionic polymerization is almost unexplored: we have filled the gap by implementing an anionic mechanism to create polymers and copolymers as confined to, or anchored to, high surface area porous nanoparticles. Far diverse linear polymers with soft and glassy chains, such as polyisoprene and polymethylmethacrylate, were produced by confined anionic polymerization in 3D networks of porous aromatic frameworks. Alternatively, multiple anions were generated on the designed frameworks which bear removal protons at selected positions, and initiate chain propagation, resulting in chains covalently connected to the 3D network. Such growth can continue outside the pores to produce polymer‐matrix nanoparticles coated with anchored chains. Sequential reactions were promoted by the living character of this anionic propagation , yielding nanoparticles that were covered by a second polymer anchored by anionic block‐copolymerization. The intimacy of the matrix and the grown‐in polymers was demonstrated unconventionally by magnetization transfer across the interfaces in 2D 1 H‐ 13 C‐HETCOR NMR spectra. The present achievements open intriguing perspectives for the use of versatile anionic polymerization to finely control interdigitated nanocomposites.
https://ift.tt/3qktbiy
Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c04202
https://ift.tt/3jEljFk
