Well‐defined copolymers based on poly(vinylidene fluoride): From preparation and phase separation to application

Poly(vinylidene fluoride) (PVDF) has reached the second largest production volume of fluoropolymers in recent years, and its popularity can be ascribed to high thermal stability and chemical inertness combined with its ferroelectric behavior. Copolymerization of vinylidene fluoride with other monomers leads to a wide variety of products with modified or improved properties. Besides commercially available fluorinated random copolymers, well‐defined block‐, graft, and alternating copolymers based on PVDF received more attention in recent years. PVDF‐containing block copolymers that may self‐assemble into well‐ordered morphologies are of particular interest, being potential precursors for functional nanostructured materials applicable in membranes and electronics. This Highlight provides an overview of the routes developed towards these materials via conventional and controlled polymerization techniques. In addition, it discusses their nanoscopic phase behavior and current and potential applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2861–2877     

Reduction and pH dual‐responsive block copolymers containing pendent p‐nitrobenzyl carbamate functionalities: Synthesis and self‐assembly behavior

We report on the preparation of reduction‐responsive amphiphilic block copolymers containing pendent p‐nitrobenzyl carbamate (pNBC)‐caged primary amine moieties by reversible addition–fragmentation chain transfer (RAFT) radical polymerization using a poly(ethylene glycol)‐based macro‐RAFT agent. The block copolymers self‐assembled to form micelles or vesicles in water, depending on the length of hydrophobic block. Triggered by a chemical reductant, sodium dithionite, the pNBC moieties decomposed through a cascade 1,6‐elimination and decarboxylation reactions to liberate primary amine groups of the linkages, resulting in the disruption of the assemblies. The reduction sensitivity of assemblies was affected by the length of hydrophobic block and the structure of amino acid‐derived linkers. Using hydrophobic dye Nile red (NR) as a model drug, the polymeric assemblies were used as nanocarriers to evaluate the potential for drug delivery. The NR‐loaded nanoparticles demonstrated a reduction‐triggered release profile. Moreover, the liberation of amine groups converted the reduction‐responsive polymer into a pH‐sensitive polymer with which an accelerated release of NR was observed by simultaneous application of reduction and pH triggers. It is expected that these reduction‐responsive block copolymers can offer a new platform for intracellular drug delivery. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1333–1343     

Non‐self‐adjoint singular second‐order dynamic operators on time scale

In this study, maximal dissipative second‐order dynamic operators on semi‐infinite time scale are studied in the Hilbert space , that the extensions of a minimal symmetric operator in limit‐point case. We construct a self‐adjoint dilation of the dissipative operator together with its incoming and outgoing spectral representations so that we can determine the scattering function of the dilation as stated in the scheme of Lax‐Phillips. Moreover, we construct a functional model of the dissipative operator and identify its characteristic function in terms of the Weyl‐Titchmarsh function of a self‐adjoint second‐order dynamic operator. Finally, we prove the theorems on completeness of the system of root functions of the dissipative and accumulative dynamic operators.     

Versatile functional poly(3‐hexylthiophene) for hybrid particles synthesis by the grafting onto technique: Core@shell ZnO nanorods

We demonstrate an efficient strategy to anchor poly(3‐hexylthiophene) (P3HT) onto zinc oxide (ZnO) surfaces. Synthesis of a novel triethoxysilane‐terminated regioregular P3HT is herein reported and supported by thorough characterization. Three triethoxysilane‐terminated P3HTs of different molar masses were prepared via a hydrosilylation reaction from allyl‐terminated P3HT. MALDI‐TOF and ¹H NMR were performed to characterize the polymer and show that around 80% of the chains are end‐functionalized. These polymers were then grafted onto the ZnO nanorods to create a macromolecular self‐assembled monolayer. This versatile technique could be subsequently applied to different metal oxide surfaces, such as silicon, titanium, or indium‐tin oxide, and represents a new one‐pot strategy based on triethoxysilane coupling reaction. Importantly, the influence of the molar mass on the grafting density and the polymer shell thickness was studied via thermo gravimetric analysis and transmission electron microscopy. The optical properties of the hybrid materials were determined by UV–visible absorption and photoluminescence to show a quenching effect of P3HT fluorescence by ZnO when grafted. This electronic transfer associated with an improved miscibility of the ZnO@P3HT, makes these hybrid materials suitable candidates for photovoltaic applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 30–38     

Three‐Component Self‐Assembly of a Series of Triply Interlocked Pd12 Coordination Prisms and Their Non‐Interlocked Pd6 Analogues

Template‐assisted formation of multicomponent Pd₆ coordination prisms and formation of their self‐templated triply interlocked Pd₁₂ analogues in the absence of an external template have been established in a single step through Pd? N/Pd? O coordination. Treatment of cis‐[Pd(en)(NO₃)₂] with K₃tma and linear pillar 4,4′‐bpy (en=ethylenediamine, H₃tma=benzene‐1,3,5‐tricarboxylic acid, 4,4′‐bpy=4,4′‐bipyridine) gave intercalated coordination cage [{Pd(en)}₆(bpy)₃(tma)₂]₂[NO₃]₁₂ ( 1 ) exclusively, whereas the same reaction in the presence of H₃tma as an aromatic guest gave a H₃tma‐encapsulating non‐interlocked discrete Pd₆ molecular prism [{Pd(en)}₆(bpy)₃(tma)₂(H₃tma)₂][NO₃]₆ ( 2 ). Though the same reaction using cis‐[Pd(NO₃)₂(pn)] (pn=propane‐1,2‐diamine) instead of cis‐[Pd(en)(NO₃)₂] gave triply interlocked coordination cage [{Pd(pn)}₆(bpy)₃(tma)₂]₂[NO₃]₁₂ ( 3 ) along with non‐interlocked Pd₆ analogue [{Pd(pn)}₆(bpy)₃(tma)₂](NO₃)₆ ( 3′ ), and the presence of H₃tma as a guest gave H₃tma‐encapsulating molecular prism [{Pd(pn)}₆(bpy)₃(tma)₂(H₃tma)₂][NO₃]₆ ( 4 ) exclusively. In solution, the amount of 3′ decreases as the temperature is decreased, and in the solid state 3 is the sole product. Notably, an analogous reaction using the relatively short pillar pz (pz=pyrazine) instead of 4,4′‐bpy gave triply interlocked coordination cage [{Pd(pn)}₆(pz)₃(tma)₂]₂[NO₃]₁₂ ( 5 ) as the single product. Interestingly, the same reaction using slightly more bulky cis‐[Pd(NO₃)₂(tmen)] (tmen=N,N,N′,N′‐tetramethylethylene diamine) instead of cis‐[Pd(NO₃)₂(pn)] gave non‐interlocked [{Pd(tmen)}₆(pz)₃(tma)₂][NO₃]₆ ( 6 ) exclusively. Complexes 1 , 3 , and 5 represent the first examples of template‐free triply interlocked molecular prisms obtained through multicomponent self‐assembly. Formation of the complexes was supported by IR and multinuclear NMR (¹H and ¹³C) spectroscopy. Formation of guest‐encapsulating complexes ( 2 and 4 ) was confirmed by 2D DOSY and ROESY NMR spectroscopic analyses, whereas for complexes 1 , 3 , 5 , and 6 single‐crystal X‐ray diffraction techniques unambiguously confirmed their formation. The gross geometries of H₃tma‐encapsulating complexes 2 and 4 were obtained by universal force field (UFF) simulations.     

Novel Capsular Aggregates from Flexible Tripodal Triureas with Cs Symmetry

Tris(2‐ and 3‐ureidobenzyl)amines with C_s symmetry self‐assemble in solution forming mixtures of regioisomeric capsular aggregates, one of which is chiral and the other centrosymmetric. Under certain conditions, a predominance of the centrosymmetric regioisomer is found before equilibrium, that is, a mixture close to the statistical ratio of the two species is reached. In the solid state, there is a preference for the centrosymmetric capsules. Molecular models of both regioisomeric aggregates have been built and analyzed for comparison. Guests inside capsules formed by self‐assembly of desymmetrized tris(3‐ureidobenzyl)amines feel different magnetic environments, depending on whether they are inside a chiral or an achiral regioisomeric container. Of special significance are the experiments with a more flexible triurea endowed with an ureidopropylic arm, which self‐assembles with the same efficiency as the more rigid tris(ureidobenzyl)amines.     

Criss‐cross amphiphilic polymers and analogous model systems

A new class of amphiphilic polymers carrying two pendant docosyl (C22) chains, located at periodic intervals that are separated by PEG chains of varying lengths, was synthesized via a simple melt‐transesterification polymerization, using dimethyl, 2,5‐didocosyloxyterephthalate as one of the monomers. DSC, variable temperature FT‐IR, and WAXS studies demonstrated that immiscibility between the pendant docosyl units and the backbone PEG segments drives their self‐segregation; this results in the crystallization of the pendant docosyl segments and the generation of a lamellar morphology with the alkyl segments and the PEG chains occupying alternate layers. Based on the study of model criss‐cross amphiphiles that resemble the polymer repeat unit, it is postulated that the chains reconfigure such that both the docosyl chains fold to one side of the terephthalate unit while the PEG segments form a loop on the other side; these chains then organize in a bilayer to form the lamellar structure. The simplicity of the synthesis and the rather unique properties of these polymers suggests that such a design could be translated to develop other interesting functional materials that could exploit the immiscibility‐driven microphase separation for the generation of sub‐10 nm domains; these could have potential applications, such as in membranes, solid polymer electrolyte formulations, and so forth. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1554–1563     

Brush macro‐RAFT agent mediated dispersion polymerization of styrene in the alcohol/water mixture

Dispersion RAFT polymerization of styrene in the alcohol/water mixture mediated with the brush macro‐RAFT agent of poly[poly(ethylene oxide) methyl ether vinylphenyl‐co‐styrene] trithiocarbonate [P(mPEGV‐co‐St)‐TTC] with similar molecular weight but different chemical composition is investigated. Well‐controlled RAFT polymerization including an initial slow homogeneous polymerization and a subsequent fast heterogeneous polymerization at almost complete monomer conversion is achieved. The molecular weight of the synthesized block copolymer increases linearly with the monomer conversion, and the polydispersity is relatively narrow (PDI < 1.3). The RAFT polymerization kinetics is dependent on the chemical composition in the brush macro‐RAFT agents, and those with high content of hydrophobic segment lead to fast RAFT polymerization. The growth of the block copolymer nano‐objects during the RAFT polymerization is explored, and various block copolymer nano‐objects such as nanospheres, worms, vesicles and large‐compound‐micelle‐like particles are prepared. The parameters such as the chemical composition in the brush macro‐RAFT agent, the chain length of the solvatophobic block, the concentration of the feeding monomer and the solvent character affecting the size and morphology of the block copolymer nano‐objects are investigated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3177–3190