Self‐organized micropatterns of high aspect ratio polymer nanofibers by wetting of nanopores

The self‐organized micropatterns of high aspect ratio polymer nanofibers were prepared via a facile nanoporous wetting strategy. Various micropatterns with labyrinth‐like or honeycomb‐like topography can be formed in a controllable manner by adjusting the nanoporous template's nanochannel characteristic (deep‐hole or through‐hole), the size of nanopores, and the wetting time. The honeycomb‐like micropattern shows a little higher hydrophobicity than labyrinth‐like micropattern when the diameters of their nanofibers are similar. The formation of various self‐organized micropatterns is mainly dependant on the dilation stress and interaction between nanofibers during the template's removal and solvent evaporation process. The confining or free conditions of unreleased nanofibers' tips in nanopores determine the topography of the resultant self‐organized micropattern, i.e., labyrinth‐like or honeycomb‐like. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1280–1289, 2008     

Effect of Nonsolvent on the Formation of Polymer Nanomaterials in the Nanopores of Anodic Aluminum Oxide Templates

We study the effect of nonsolvent on the formation of polymer nanomaterials in the nanopores of porous templates. Water (nonsolvent) is added into a poly (methyl methacrylate) (PMMA) solution in dimethylformamide (DMF) confined in the nanopores of an anodic aluminum oxide (AAO) template. Water forms a wetting layer on the pore wall and causes the PMMA solution to be isolated in the center of the nanopore, resulting in the formation of PMMA nanospheres or nanorods after the solvent is evaporated. The formation of the polymer nanomaterials induced by nonsolvent is found to be driven by the Rayleigh‐instability‐type transformation. Without adding the nonsolvent, PMMA chains precipitate on the walls of the nanopores after the solvent is evaporated, and PMMA nanotubes are obtained.     

Fine tuning of SAP properties via epoxy‐silane surface modification

Using 3‐[(2,3‐epoxypropoxy)‐propyl]‐trimethoxysilane as a surface modifier, superabsorbent polymers with improved gel strength in their swollen state and saline absorbency under load are synthesized. The products are characterized using attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR), rheometry, scanning electron microscopy–energy dispersive X‐ray analysis, contact angle, thermogravimetric analysis, water absorbency and gel content. The temperature and the duration effect of the surface‐treatment process on residual monomer content are also investigated by high performance liquid chromatography. The gel strength (as shown by storage modulus) and absorbency under load are improved up to 3500–4000 Pa, and 30–40 g/g, respectively. It is suggested that the surface of the superabsorbent polymer particles has been modified by two mechanisms: i.e. interpenetrating polymer network and cross‐linking. Moreover, the surface modification has enhanced thermo‐stability and prohibited undesirable gel blockage. Depending on the post‐treatment method used, the wetting behavior of particles is also altered. Copyright © 2017 John Wiley & Sons, Ltd.     

Regio‐ and stereoselective cyclopolymerization of 1,2 : 4,5‐dianhydro‐3‐O‐methyl‐xylitol leading to a novel polycarbohydrate of (2→5)‐1,4‐anhydro‐3‐O‐methyl‐pentitol

(2→5)‐1,4‐Anhydro‐3‐O‐methyl‐pentitol, which is a novel carbohydrate polymer without an anomeric linkage, was synthesized by cationic cyclopolymerization of 1,2 : 4,5‐dianhydro‐3‐O‐methyl‐xylitol. When BF₃·OEt₂ was used as the initiator, soluble polymers were obtained in 28 to 50% yield. These polymers have number‐average molecular weights of 1 150 to 2 340 corresponding to an average degree of polymerization of 8.8 to 18.0. It was confirmed by ¹³C NMR that the resulting polymer mainly consists of 1,4‐anhydro‐3‐O‐methyl‐D L ‐arabinitol units.     

Mean‐field‐theory for polymers in mixed solvents. Thermodynamic and structural properties

Theoretical aspects of polymers in mixed solvents are considered using the Edwards Hamiltonian formalism. Thermodynamic and structural properties are investigated and some predictions are made when the mixed solvent approaches criticality. Both the single and the many chain problems are examined. When the mixed solvent is near criticality without solute, addition of a small amount of polymers shifts the criticality towards either enhanced compatibility or induced phase separation depending upon the value of the parameter describing the interaction asymmetry of the solvents with respect to the polymer. The polymer‐solvent effective interaction parameter increases strongly when the solvent mixture approaches criticality. Accordingly, the apparent excluded volume parameter decreases and may vanish or even become negative. Consequently, the polymer undergoes phase transition from a swollen state to an unperturbed state or even takes a collapsed configuration. The effective potential acting on a test chain in strong solutions is calculated and the concept of Edwards screening discussed. Structural properties of ternary mixtures of polymers in mixed solvents are investigated within the Edwards Hamiltonian model. It is shown that the effective potential on a test chain in strong solutions could be written as an infinite series expansion of terms describing interactions via one chain, two chains etc. This summation can be performed following a similar scheme as in the Ornstein‐Zernike series expansion.     

Solution‐crystallization and related phenomena in 9,9‐dialkyl‐fluorene polymers. II. Influence of side‐chain structure

Solution‐crystallization is studied for two polyfluorene polymers possessing different side‐chain structures. Thermal analysis and temperature‐dependent optical spectroscopy are used to clarify the nature of the crystallization process, while X‐ray diffraction and scanning electron microscopy reveal important differences in the resulting microstructures. It is shown that the planar‐zigzag chain conformation termed the β‐phase, which is observed for certain linear‐side‐chain polyfluorenes, is necessary for the formation of so‐called polymer‐solvent compounds for these polymers. Introduction of alternating fluorene repeat units with branched side‐chains prevents formation of the β‐phase conformation and results in non‐solvated, i.e. melt‐crystallization‐type, polymer crystals. Unlike non‐solvated polymer crystals, for which the chain conformation is stabilized by its incorporation into a crystalline lattice, the β‐phase conformation is stabilized by complexation with solvent molecules and, therefore, its formation does not require specific inter‐chain interactions. The presented results clarify the fundamental differences between the β‐phase and other conformational/crystalline forms of polyfluorenes. © 2015 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1492–1506     

Three‐Dimensional Block Copolymer Nanostructures by the Solvent‐Annealing‐Induced Wetting in Anodic Aluminum Oxide Templates

Block copolymers have been extensively studied over the last few decades because they can self‐assemble into well‐ordered nanoscale structures. The morphologies of block copolymers in confined geometries, however, are still not fully understood. In this work, the fabrication and morphologies of three‐dimensional polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) nanostructures confined in the nanopores of anodic aluminum oxide (AAO) templates are studied. It is discovered that the block copolymers can wet the nanopores using a novel solvent‐annealing‐induced nanowetting in templates (SAINT) method. The unique advantage of this method is that the problem of thermal degradation can be avoided. In addition, the morphologies of PS‐b‐PDMS nanostructures can be controlled by changing the wetting conditions. Different solvents are used as the annealing solvent, including toluene, hexane, and a co‐solvent of toluene and hexane. When the block copolymer wets the nanopores in toluene vapors, a perpendicular morphology is observed. When the block copolymer wets the nanopores in co‐solvent vapors (toluene/hexane = 3:2), unusual circular and helical morphologies are obtained. These three‐dimensional nanostructures can serve as naontemplates for refilling with other functional materials, such as Au, Ag, ZnO, and TiO₂.

     

The preparation of 3,6‐bis(3‐hexylthien‐2‐yl)‐s‐tetrazine and its conjugated polymers

We demonstrated, for the first time, that 3,6‐bis(3‐hexylthien‐2‐yl)‐s‐tetrazine (TTz) with hexyl group at the 3‐position of thiophene rings can be prepared using a modified sulfur‐assisted Pinner synthesis. Although the hexyl group creates large steric hindrance to the tetrazine ring formation reaction, and the reaction under a traditional condition only produces trace amount of the target product, the yield of this reaction under a modified reaction condition using anhydrous hydrazine at 68 °C can reach 65%. Two new copolymers of the resulting TTz and hexyl‐ or 2‐ethylhexyl‐substituted cyclepentadithiophene have been prepared. The polymers show a broader light absorption in film than in solution attributing to the large distribution of effective conjugation length of polymer chain due to the existence of both cis‐ and trans‐orientations of the 3‐hexylthiophene units in the planar polymer chain in solid state. Although the polymers show a narrow band gap and a deep HOMO level, which are desirable for generating an efficient light absorption and a larger open circuit voltage (V_oc) of the resulting solar cell devices, the device performance is not as good as expected. It is attributed to the random distribution of the cis‐ and trans‐conformations along the polymer chain. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Thiocarbonylthio end group removal from RAFT‐synthesized polymers by a radical‐induced process

The removal of thiocarbonylthio end groups by radical‐addition‐fragmentation‐ coupling from polymers synthesized by RAFT polymerization has been studied. We found that a method, which involves heating the polymer with a large excess (20 molar equivalents) of azobis(isobutyronitrile) (AIBN), while successful with methacrylic polymers, is less effective with styrenic or acrylic polymers and provides only partial end group removal. This is attributed to the propagating radicals generated from the latter polymers being poor radical leaving groups relative to the cyanoisopropyl radical. Similar use of lauroyl peroxide (LPO) completely removes the thiocarbonylthio groups from styrenic or acrylic polymers but, even with LPO in large excess, produces a polymer with a bimodal molecular weight distribution. The formation of a peak of double molecular weight is indicative of the occurrence of self‐termination and ineffective radical trapping. We now report that by use of a combination of LPO (2 molar equivalents) and AIBN (20 molar equivalents) we are able to completely remove thiocarbonylthio end groups of styrenic or acrylic polymers and minimize the occurrence of self termination. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6704–6714, 2009     

Dewetting instability during the formation of polymersomes from block-copolymer-stabilized double emulsions

We investigate the formation of polymer vesicles, or polymersomes, of polystyrene-block-poly(ethylene oxide) diblock copolymers using double emulsion droplets of controlled architecture as templates. To engineer the structure of the polymersomes, it is important to consider the concentration of diblock copolymer in the middle phase of the double emulsion. We describe how the presence of excess polymer can induce a transition from complete wetting to partial wetting of the middle phase, resulting in polymer shells with inhomogeneous thicknesses.     

Highly Hydrophilic Copolymers of N,N‐Dimethylacrylamide,Acrylamido‐2‐methylpropanesulfonic acid,and Ethylenedimethacrylate: Nanoscale Morphology in the Swollen State and Use as Exotemplates for Synthesis of Nanostructured Ferric Oxide

The polymer framework of water‐swollen copolymers of N,N‐dimethylacrylamide, acrylamido‐2‐methylpropanesulfonic acid, and ethylenedimethacrylate (nominal cross‐linking degrees of 4, 8, and 20 mol %) is composed of highly expanded domains, with “pores” not less than 6 nm in diameter. When the 4 % cross‐linked copolymer (DAE 26‐4) is swollen with a 10^?4 M solution of 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPOL) in water, MeOH, EtOH, or nBuOH, the molecules of the paramagnetic probe rotate rapidly (τ<1000 ps) and as fast as in the bulk liquid in the case of water. The swelling degree of DAE 26‐4 is related to the Hansen solubility parameters of a number of liquids, including linear alcohols up to n‐octanol. It is also found that the rotational correlation time of TEMPOL in the copolymer swollen by water and the lightest alcohols increases with decreasing specific absorbed volume. Time‐domain NMR spectrometry of water‐swollen DAE 26‐4 shows that sorption of only 14 % of the liquid required for its complete swelling is enough for full hydration of the polymer chains. Accordingly, in fully swollen DAE 26‐4 the longitudinal relaxation time of water closely approaches the value of pure water. {¹³C} CP‐MAS NMR on partially and fully water swollen samples of DAE 26‐4 shows that swelling increases the mobility of the polymer chains, as clearly indicated by the narrowing of the best‐resolved peaks. DAE 26‐4 was used as an exotemplate for the synthesis of nanocomposites composed of the polymer and nanostructured Fe₂O₃ through a series of ion‐exchange/precipitation cycles. After the first cycle the nanoparticles are 3–4 nm in diameter, with practically unchanged size after subsequent cycles (up to five). In fact, the nanoparticle size never exceeded the diameter of the largest available pores. This suggests that the polymer framework controls the growth of the nanoparticles according to the template‐controlled synthesis scheme. Selected‐area electron diffraction, TEM, and high‐resolution electron microscopy show that the nanostructured inorganic phase is composed of hematite.     

Lipase‐Catalyzed Ring‐Opening Polymerization of β‐Butyrolactone: End‐Group Analysis of Poly(3‐hydroxybutanoate) Using Supercritical Fluid Chromatography

The ring‐opening polymerization of (R,S)‐β‐butyrolactone (BL) in bulk was analyzed with respect to the polymer structure of the resulting poly[(R,S)‐3‐hydroxybutanoate)] [P(3HB)] by isolation of the pure form using preparative supercritical CO₂ fluid chromatography. It was confirmed that the four‐membered BL was polymerized in bulk by lipase to yield the corresponding cyclic, hydroxy‐ and crotonate‐terminated P(3HB)s. The relative ratios of the three types of polymers depended on the lipase concentration as well as on the monomer conversion. It was also confirmed that both cyclic and linear P(3HB) polymer species were subject to hydrolysis, and inter‐ and intramolecular transesterification by lipase to produce two series of polymers having linear and cyclic structures with higher and lower molecular weight. The formation of the cyclic P(3HB) iss regarded as the characteristic feature of the lipase‐catalyzed polymerization of BL.     

Synthesis of Responsive Two‐Dimensional Polymers via Self‐Assembled DNA Networks

Despite a growing interest in two‐dimensional polymers, their rational synthesis remains a challenge. The solution‐phase synthesis of a two‐dimensional polymer is reported. A DNA‐based monomer self‐assembles into a supramolecular network, which is further converted into the covalently linked two‐dimensional polymer by anthracene dimerization. The polymers appear as uniform monolayers, as shown by AFM and TEM imaging. Furthermore, they exhibit a pronounced solvent responsivity. The results demonstrate the value of DNA‐controlled self‐assembly for the formation of two‐dimensional polymers in solution.     

Mechanically Initiated Bulk‐Scale Free‐Radical Polymerization

Mechanical initiation of polymerization offers the chance to generate polymers in new environments using an energy source with unique capabilities. Recently, a renewed interest in mechanically controlled polymerization has yielded many techniques for controlled radical polymerization by ultrasound. However, other types of polymerizations induced by mechanical activation are rare, especially for generating high‐molecular‐weight polymers. Herein is an example of using piezoelectric ZnO nanoparticles to generate free‐radical species that initiate chain‐growth polymerization and polymer crosslinking. The fast generation of high amounts of reactive radicals enable the formation of polymer/gel by ultrasound activation. This chemistry can be used to harness mechanical energy for constructive purposes in polymeric materials and for controlled polymerizations for bulk‐scale reactions.     

Self‐assembly phenomena of the brush‐like amphiphilic organopolysiloxanes in aqueous solution

A series of brush‐like amphiphilic organopolysiloxanes with varying hydrophilic side‐chains was prepared, and the assembly behavior of these promising polymers was investigated in aqueous solution using a combination method of surface tension, steady‐state fluorescence, dynamic light scattering, and transmission electron microscopy. An increasing number of side‐chains could lead a higher surface tension of the polymer solution. The polymers formed regular “micelle‐like” spherical multipolymer assemblies in aqueous solution with the size distributed from the scale of hundreds to that of tens of nanometer, and the polymers that possessed more of the side‐chains would form comparatively loose and swollen assemblies with slightly higher micropolarities and bigger dimensions. The interesting discovery in this report was that the visible clearness of the solution could be improved by increasing the hydrophilicity of the assemblies in the solution. Copyright © 2014 John Wiley & Sons, Ltd.     

Silicon surface modification with trialkoxysilyl‐functionalized star‐shaped polymers

The synthesis of trimethoxysilane end‐capped linear polystyrene (PS) and star‐branched PS and subsequent silicon (Si) surface modification with linear and star polymers are described. Trimethoxysilane terminated PS was synthesized using sec‐butyl lithium initiated anionic polymerization of styrene and subsequent end‐capping of the living anions with p‐chloromethylphenyl trimethoxysilane (CMPTMS). ¹H and ²⁹Si NMR spectroscopy confirmed the successful end‐capping of polystyryllithium with the trimethoxysilane functional group. The effect of a molar excess of end‐capper on the efficiency of functionalization was also investigated, and the required excess increased for higher molar mass oligomers. Acid catalyzed hydrolysis and condensation of the trimethoxysilane end‐groups resulted in star‐branched PS, and NMR spectroscopy and SEC analysis were used to characterize the star polymers. This is the first report of core‐functionalized star‐shaped polymers as surface modifiers and the first comparative study showing differences in surface topography between star and linear polymer modified surfaces. Surface‐sensitive techniques such as ellipsometry, contact angle goniometry, and AFM were used to confirm the attachment of star PS, as well as to compare the characteristics of the star and linear PS modified Si surfaces. The polymer film properties were referenced to polymer dimensions in dilute solution, which revealed that linear PS chains were in the intermediate brush regime and the star‐branched PS produced a surface with covalently attached chains in the mushroom regime. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3655–3666, 2005     

Precise Size‐Selective Sieving of Nanoparticles Using a Highly Oriented Two‐Dimensional Supramolecular Polymer

The development of size‐selective membranes with well‐defined nanopores towards the precise separation of nanometer‐sized substances is a challenging task to achieve. Here a supramolecular membrane is presented that comprises a highly oriented, honeycomb‐like, 2D supramolecular polymer on a polycarbonate filter support. It enables precise size‐selective sieving of colloidal nanoparticles (NPs). Owing to the uniform parallel‐aligned nanocavities within the 2D supramolecular polymers, the composite membrane shows a high size‐selectivity with a sub‐nanometer accuracy in the cutoff size of about 4.0 nm. In principle, the species of size‐separable particles are unlimited, as demonstrated by quantum dots, noble metal, and metal oxide NPs. This supramolecular membrane combined with filtration advances the potential of NPs in terms of their monochromatic emission and size monodispersity, and also enables rapid removal of small magnetic NP adsorbents that are otherwise difficult to capture.     

Polystyrene-based blend nanorods with gradient composition distribution

The polystyrene-based polymer blends, partially miscible poly(bisphenol A carbonate)/polystyrene (PC/PS) and completely miscible poly(2,6-dimethylphenylene oxide)/polystyrene (PPO/PS), in nanorods with gradient composition distribution were discussed. The polymer blend nanorods were prepared by infiltrating the polymer blends into nanopores of anodic aluminum oxide (AAO) templates via capillary action. Their morphology was investigated by micro-Fourier transform infrared spectroscopy (micro-FTIR) and nano-thermal analysis (nano-TA) with spatial resolution. The composition gradient of polymer blends in the nanopores is governed by the difference of viscosity and miscibility between the two polymers in the blends and the pore diameter. The capillary wetting of porous AAO templates by polymer blends offers a unique method to fabricate functional nanostructured materials with gradient composition distribution for the potential application to nanodevices.     

Surface pattern formation on soft polymer substrate through photo‐initiated graft polymerization

Techniques for large‐area pattern formation on polymeric substrates are important for fabricating a large variety of functional devices, such as flexible electronics, tunable optical devices, adhesives, and so on. The present study demonstrates a method for pattern formation on poly(dimethylsiloxane) that involves grafting methacrylate polymers through photo‐initiated polymerization. The influence of substrate stiffness and monomers type on pattern formation was investigated. Firstly, the stiffness of the substrate was found to affect the topology of the patterns produced. The gap width of convex regions of the pattern was enlarged with decreasing stiffness. It was found that the gap width trended in a manner that was consistent with previous reports, but in this study, relatively large gap widths were observed compared with those from previous studies. Secondly, it was revealed that the solubility of the monomer in the poly(dimethylsiloxane) precursor was the dominant factor in determining whether or not pattern formation occurred. When using insoluble monomers (glycidyl methacrylate and benzyl methacrylate), characteristic patterns were observed. It is speculated that intermolecular attractive forces between the grafted polymers induce lateral aggregation on the substrate, resulting in buckling instability of the grafted polymer layer caused by a mismatch in the equilibrium between the grafted polymer layer and the substrate. Copyright © 2017 John Wiley & Sons, Ltd.