Herein, we report a high-yield click synthesis and self-assembly of conjugated amphiphilic block copolymers of polythiophene (PHT) and polyethylene glycol (PEG) and their superstructures. A series of different length PHT(m)-b-PEG(n) with well-defined relative block lengths was synthesized by a click-coupling reaction and self-assembled into uniform and stably suspended nanofibers in selective solvents. The length of nanofibers was controllable by varying the relative block lengths while keeping other dimensions and optical properties unaffected for a broad range of f(PHT) (0.41 to 0.82), which indicates that the packing of PHT dominates the self-assembly of PHT(m)-b-PEG(n). Furthermore, superstructures of bundled and branched nanofibers were fabricated through the self-assembly of PHT(m)-b-PEG(n) and preformed PHT nanofibers. The shape, length, and density of the hierarchical assembly structures can be controlled by varying the solvent quality, polymer lengths, and block copolymer/homopolymer ratio. This work demonstrates that complex superstructures of organic semiconductors can be fabricated through the bottom-up approach using preformed nanofibers as building blocks.
Recent advances in the growing field of nanoemulsions are opening up new applications in many areas such as pharmaceuticals, foods, and cosmetics. Moreover, highly controlled nanoemulsions can also serve as excellent model systems for investigating basic scientific questions about soft matter. Here, we highlight some of the most recent developments in nanoemulsions, focusing on methods of formation, surface modification, material properties, and characterization. These developments provide insight into the substantial advantages that nanoemulsions can offer over their microscale emulsion counterparts.
A new form of controlled growth free radical polymerization leading to narrow polydispersity polymers and/or block copolymers is described. The process is based on the polymerization of monomers in the presence of macromonomers of general structure CH2=C(Z)CH2(A)n [(A)n= radical leaving group, Z = activating group] and displays many of the characteristics of living polymerizations. The process is most suited to methacrylic monomers but with the appropriate choice of reaction conditions (high temperatures and/or low conversions) it can also be applied to acrylic and styrenic monomers. The macromonomers are conveniently prepared by catalytic chain transfer to alkyl cobalt(III) complexes or by addition‐fragmentation chain transfer. The factors which determine the efficiency of cobalt complexes for molecular weight reduction in free radical emulsion and solution polymerization of methyl methacrylate are also discussed.
Vinyl acetate polymerization initiated by azo radical sources in the presence of cobalt(II) tetramesitylporphyrin ((TMP)CoII) shows an induction period followed by an organo-cobalt mediated living radical polymerization (LRP). The induction period corresponds to converting (TMP)CoII to an organo-cobalt porphyrin derivative (organo-Co(TMP)). Living character at low vinyl acetate conversion is demonstrated by a linear increase in molecular weight with conversion, relatively low polydispersity homopolymers, and formation of block copolymers with methyl acrylate ((TMP)Co-PVAc-b-PMA). Deviations from ideal LRP occur by radical termination and chain transfer events at moderate conversion of vinyl acetate (VAc). Mechanistic studies demonstrate that the VAc radical polymerization is controlled by a degenerative transfer mechanism that utilizes organo-cobalt complexes as the transfer agent. Kinetic studies are utilized in comparing radical polymerization of vinyl acetate and methyl acrylate that are mediated by organo-cobalt complexes.
(Tetramesitylporphyrinato)cobalt(II)
((TMP)Co•) and the octabromo derivative
((Br8TMP)Co•) mediate an effective living radical polymerization of
acrylate monomers through the formation of
dormant organocobalt complexes ((por)Co−PA) with the growing
acrylate polymer radical (•PA).
Radical
polymerization of methyl acrylate controlled by
(Br8TMP)Co• is substantially faster
than that for (TMP)Co• because of the higher concentration of radicals
resulting from greater dissociation of the dormant
organocobalt complex. Unusually large molecular weight low
polydispersity acrylate homopolymers and
block copolymers have been obtained by this method. Kinetic
studies for the conversion of methyl acrylate
(MA) to poly(methyl acrylate) (PMA) initiated and controlled by
(TMP)Co−PMA are fully compatable
with a living radical process mediated by the metallo radical
((TMP)Co•). Overall apparent
activation
parameters for the polymerization process
(Δ
= 28 ± 2 kcal mol-1;
Δ
= 4 ± 1 cal K-1
mol-1) are
interpreted as sums of the activation parameters for radical
propagation
(Δ
∼ 4 kcal mol-1;
Δ
∼ 25
cal K-1 mol-1) and
thermodynamic values for homolytic dissociation of (TMP)Co−PMA
(ΔH° ∼ 24 kcal
mol-1; ΔS° ∼ 29 cal
K-1
mol-1).
We report a novel class of amphiphilic conjugated block copolymers composed of poly(3-octylthiophene) and poly(ethylene oxide) (POT-b-PEO) that exhibit highly tunable photoluminescence colors spanning from blue to red. POT-b-PEO self-assembles into various well-defined core/shell-type nanostructures as a result of its amphiphilicity. The self-assembly structure can be readily controlled by altering the solvent composition or by other external stimuli. The color change was completely reversible, demonstrating that the strategy can be used to manipulate the light-emission properties of conjugated polymers in a highly controllable manner without having to synthesize entirely new sets of molecules.
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