27 research outputs found
Hyper-cross-linked polymers with controlled multiscale porosity: Via polymerization-induced microphase separation within high internal phase emulsion
We report the preparation of hierarchically porous polymers containing fully interconnected and controlled micro-, meso-, and macropores, where a hyper-cross-linked microporous polymer skeleton forms a reticulating mesoporous wall that supports a highly porous macropore framework. These materials provide high specific surface area and >90% porosity, useful for rapid sorption of organic molecules. © 2018 The Royal Society of Chemistr
Photoinitiated Polymerization-Induced Microphase Separation for the Preparation of Nanoporous Polymer Films
We report on the
use of photoinitiated reversible additionâfragmentation
chain transfer (RAFT) polymerization for the facile fabrication of
cross-linked nanoporous polymer films with three-dimensionally (3D)
continuous pore structure. The photoinitiated polymerization of isobornyl
acrylate (IBA) in the presence of 2-(dodecylthiocarbonothioylthio)-2-methylpropionic
acid (CTA) and 2,2-dimethoxy-2-phenylacetophenone as a photoinitiator
proceeded in a controlled manner, yet more rapidly compared to thermally
initiated polymerization. When polylactide-macroCTA (PLA-CTA) was
used, PLA-<i>b</i>-PIBA with high molar mass was obtained
after several minutes of irradiation at room temperature. We confirmed
that microphase separation occurs in the PLA-<i>b</i>-PIBA
and that nanoporous PIBA can be derived from the PLA-<i>b</i>-PIBA precursor by selective PLA etching. To fabricate the cross-linked
nanoporous polymer, IBA was copolymerized with ethylene glycol diacrylate
(EGDA) in the presence of PLA-CTA to produce a cross-linked block
polymer precursor consisting of bicontinuous PLA and PÂ(IBA-<i>co</i>-EGDA) microdomains, via polymerization-induced microphase
separation. We demonstrated that nanoporous PÂ(IBA-<i>co</i>-EGDA) monoliths and films with 3D continuous pores can be readily
obtained via this approach
Synthesis of Heterograft Copolymers with a Semifluorinated Backbone by Combination of Grafting-through and Graftingfrom Polymerizations
International audienceWe report that an alternating semifluorinated copolymer of chlorotrifluoroethylene (CTFE) and vinyl ether (VE) is an attractive platform for the synthesis of heterograft copolymers consisting of two distinct side chains. The radical terpolymerization of CTFE with PLA-tethered vinyl ether (PLAVE) synthesized by ring-opening polymerization and isobutyl vinyl ether (IBVE) as a spacer produced PLA-grafted fluorinated copolymer via a âgrafting-throughâ manner. Two PLAVEs with different molar masses (2 and 10 kg molâ1) were successfully incorporated, and the grafting density could be controlled by varying the [PLAVE]/[IBVE] initial molar ratio. From the chlorine atoms in the CTFE repeating units, atom transfer radical polymerization (ATRP) of styrene was further employed to grow PS side chains following a âgrafting-fromâ mechanism per each (CTFE-alt-VE) repeating unit dyad. First-order kinetics was observed for the styrene polymerization and supported controlled growth of PS. The resulting heterograft copolymers possessed regularly spaced PS chains and statistically distributed PLA chains on the backbone, generating a nanoscopic disordered morphology via microphase separation driven by incompatibility between PLA and PS. By copolymerization of styrene and divinylbenzene (DVB) in neat ATRP condition, a cross-linked polymer monolith with the disordered bicontinuous morphology could be also prepared via polymerization-induced microphase separation. The cross-linked precursor was converted into a mesoporous polymer with pore size of 3.7â10.4 nm by removal of PLA. The mesopore size was tunable by adjusting the PLA molar mass and styrene/DVB molar ratio
Synthesis and Thermo-Responsive Behavior of Poly(<i>N</i>-isopropylacrylamide)-<i>b</i>-Poly(<i>N</i>-vinylisobutyramide) Diblock Copolymer
Thermo-responsive diblock copolymer, poly(N-isopropylacrylamide)-block-poly(N-vinylisobutyramide) was synthesized via switchable reversible additionâfragmentation chain transfer (RAFT) polymerization and its thermal transition behavior was studied. Poly(N-vinylisobutyramide) (PNVIBA), a structural isomer of poly(N-isopropylacrylamide) (PNIPAM) shows a thermo-response character but with a higher lower critical solution temperature (LCST) than PNIPAM. The chain extension of the PNVIBA block from the PNIPAM block proceeded in a controlled manner with a switchable chain transfer reagent, methyl 2-[methyl(4-pyridinyl)carbamothioylthio]propionate. In an aqueous solution, the diblock copolymer shows a thermo-responsive behavior but with a single LCST close to the LCST of PNVIBA, indicating that the interaction between the PNIPAM segment and the PNVIBA segment leads to cooperative aggregation during the self-assembly induced phase separation of the diblock copolymer in solution. Above the LCST of the PNIPAM block, the polymer chains begin to collapse, forming small aggregates, but further aggregation stumbled due to the PNVIBA segment of the diblock copolymer. However, as the temperature approached the LCST of the PNVIBA block, larger aggregates composed of clusters of small aggregates formed, resulting in an opaque solution
Circularly Polarized Light-Driven Supramolecular Chirality
Introduction of asymmetry into a supramolecular system via external chiral stimuli can contribute to the understanding of the intriguing homochirality found in nature. Circularly polarized light (CPL) is regarded as a chiral physical force with right- or left-handedness. It can induce and modulate supramolecular chirality due to preferential interaction with one enantiomer. Herein, this review focuses on the photon-to-matter chirality transfer mechanisms at the supramolecular level. Thus, asymmetric photochemical reactions are reviewed, and the creation of a chiral bias upon CPL irradiation is discussed. Furthermore, the possible mechanisms for the amplification and propagation of the bias into the supramolecular level are outlined based on the nature of the photochromic building block. Representative examples, including azobenzene derivatives, polydiacetylene, bicyclic ketone, polyfluorenes, C-n-symmetric molecules, and inorganic nanomaterials, are presented
Synthesis of Polypropylene via Catalytic Deoxygenation of Poly(methyl acrylate)
We propose the defunctionalization of vinyl polymers as a strategy to access previously inaccessible polyolefin materials. By utilizing B(C6F5)(3)-catalyzed deoxygenation in the presence of silane, we demonstrate that eliminating the pendent ester in poly(methyl acrylate) effectively leaves a linear hydrocarbon polymer with methyl pendants, which is polypropylene. We further show that a polypropylene-b-polystyrene diblock copolymer and a polystyrene-b-polypropylene-b-polystyrene triblock copolymer can be successfully derived from the poly(methyl acrylate)-containing block polymer precursors and exhibit quite distinct materials properties due to their chemical transformation. This unique postpolymerization modification methodology, which goes beyond the typical functional group conversion, can offer access to a diverse range of unprecedented polyolefin block polymers with a variable degree of functional groups. © 2019 American Chemical Society11sciescopu
Cross-Linked Nanoporous Materials from Reactive and Multifunctional Block Polymers
Polylactide-<i>b</i>-poly(styrene-<i>co</i>-2-hydroxyethylmethacrylate) (PLA-<i>b</i>-P(S-<i>co</i>-HEMA)) and polylactide-<i>b</i>-poly(styrene-<i>co</i>-2-hydroxyethylacrylate) (PLA-<i>b</i>-P(S-<i>co</i>-HEA)) were synthesized by combination of ring-opening polymerization and reversible additionâfragmentation chain transfer polymerization. <sup>1</sup>H nuclear magnetic resonance spectroscopy and size exclusion chromatography data indicated that the polymerizations were controlled and that hydroxyl groups were successfully incorporated into the block polymers. The polymers were reacted with 4,4âČ-methylenebis(phenyl isocyanate) (MDI) to form the corresponding cross-linked materials. The materials were annealed at 150 °C to complete the coupling reaction. Robust nanoporous materials were obtained from the cross-linked polymers by treatment with aqueous base to hydrolyze the PLA phase. Small-angle X-ray scattering study combined with scanning electron microscopy showed that MDI-cross-linked PLA-<i>b</i>-P(S-<i>co</i>-HEMA)/PLA-<i>b</i>-P(S-<i>co</i>-HEA) can adopt lamellar, hexagonally perforated lamellar, and hexagonally packed cylindrical morphologies after annealing. In particular, the HPL morphology was found to evolve from lamellae due to increase in volume fraction of PS phase as MDI reacted with hydroxyl groups. The reaction also kinetically trapped the morphology by cross-linking. Bicontinuous morphologies were also observed when dibutyltin dilaurate was added to accelerate reaction between the polymer and MDI
One-Step Synthesis of Cross-Linked Block Polymer Precursor to a Nanoporous Thermoset
Using a simultaneous block polymerization/in
situ cross-linking from a heterofunctional initiator approach, we
produced a nanostructured and cross-linked block polymer in a single
step from a ternary mixture of monomers and used it as a precursor
for a cross-linked nanoporous material. Using 2-(benzylsulfanylthiocarbonylsulfanyl)Âethanol
as a heterofunctional initiator, simultaneous ring-opening transesterification
polymerization of d,l-lactide in the presence of
tin 2-ethylhexanoate as a catalyst and reversible additionâfragmentation
chain transfer polymerization of styrene at 120 °C produced a
polylactide-<i>b</i>-polystyrene (PLA-<i>b</i>-PS) block polymer. Incorporation of divinylbenzene in the polymerization
mixture allowed in situ cross-linking during the simultaneous block
polymerization to result in the cross-linked block polymer precursor
in one step. This material was converted into cross-linked nanoporous
polymer by etching PLA in a basic solution
Polymeric Nanoparticles via Noncovalent Cross-Linking of Linear Chains
Novel polymeric nanoparticles were prepared through the chain collapse of linear polymers driven by noncovalent cross-linking of dendritic self-complementary hydrogen-bonding units (SHB). Random copolymers containing SHB units, poly[(methyl methacrylate)-r-2-((3,5-bis(4-carbamoyl-3-(trifluoromethyl)phenoxy)benzyloxy)carbonylamino)ethyl methacrylate] (A1, A2), were synthesized with various incorporation ratios by reversible additionâfragmentation chain transfer (RAFT) polymerization. Dramatically different behavior was observed depending on the level of incorporation of the supramolecular units. At high loadings of A2 (6% SHB incorporation), intramolecular chain collapse is favored, resulting in the formation of well-defined polymer nanoparticles, which were characterized by scanning force microscopy (SFM), dynamic light scattering (DLS), and viscosity studies. In contrast, analysis of copolymer A1 (1% SHB incorporation) revealed that chain collapse occurred primarily through intermolecular interactions leading to large aggregates
Semipermeable Microcapsules with a Block-Polymer-Templated Nanoporous Membrane
Microcapsules
with nanoporous membranes can regulate transmembrane
transport in a size-dependent fashion while protecting active materials
in the core from the surrounding, and are thereby useful as artificial
cell models, carriers for cells and catalysts, and microsensors. In
this work, we report a pragmatic microfluidic approach to producing
such semipermeable microcapsules with precise control of the cutoff
threshold of permeation. Using a homogeneous polymerization mixture
for the polymerization-induced microphase separation (PIMS) process
as the oil phase of water-in-oil-in-water (W/O/W) double emulsions,
a densely cross-linked shell composed of a bicontinuous nanostructure
that percolates through the entire thickness is prepared, which serves
as a template for a monolithic nanoporous membrane of microcapsules
with size-selective permeability. We demonstrate that the nanopores
with precisely controlled size by the block polymer self-assembly
govern molecular diffusion through the membrane and render manipulation
of the cutoff threshold