Optimization of Photorefractivity Based on Poly(N‐vinylcarbazole) Composites: An Approach from the Perspectives of Chemistry and Physics

The optimization of photorefractivity (PR) based on a poly(N‐vinylcarbazole) (PVCz) composite devise is proposed from the perspectives of chemistry and physics. The device's PR chemistry (dependence of PVCz's molecular weight) and physics (dependence of grating periodicity and laser wavelength) are studied. Increasing the molecular weight of PVCz from 23 000 to 1 270 000 g mol^?1 significantly increases diffraction efficiency, grating build‐up speed (inverse of response time), and sensitivity. Narrowing grating period from 5.1 to 1.1 μm gives faster response time and larger optical gain. Shorter wavelength of writing laser from 633 to 532 nm provides higher diffraction efficiency, faster response time, and larger optical gain.

     

The Effect of PEG Crystallization on the Morphology of PEG/Peptide Block Copolymers Containing Amyloid β‐Peptide Fragments

Ordered nanostructures are observed in the melt and solid state for a series of three peptide/PEG conjugates containing fragments of amyloid β‐peptides. These are conjugated to PEG with = 3 300 g · mol^?1 and a melting temperature T_m = 45–50 °C. The morphology at room temperature is examined by AFM and POM. This shows spherulite formation for the weakly fibrillizing KLVFF‐PEG sample but fibril formation for FFKLVFF‐PEG. The fibrillization tendency of the latter is enhanced by multiple phenylalanine residues. Simultaneous SAXS and WAXS was used to investigate the morphology as a function of temperature. The secondary structure is probed by FTIR.

     

Amphiphilic Block Copolymers Containing Regioregular Poly(3‐hexylthiophene) and Poly(2‐ethyl‐2‐oxazoline)

Poly(3‐hexylthiophene)‐block‐poly(2‐ethyl‐2‐oxazoline) amphiphilic rod–coil diblock copolymers have been synthesized by a combination of Grignard metathesis (GRIM) and ring‐opening cationic polymerization. Diblock copolymers containing 5, 15, and 30 mol‐% poly(2‐ethyl‐2‐oxazoline) have been synthesized and characterized. The synthesized rod–coil block copolymers display nanofibrillar morphology where the density of the nanofibrills is dependent on the concentration of the poly(2‐ethyl‐2‐oxazoline) coil segment. The conductivity of the diblock copolymers was lowered from 200 to 35 S · cm^?1 with an increase in the content of the insulating poly(2‐ethyl‐2‐oxazoline) block. By contrast, the field‐effect mobility decreased by 2–3 orders of magnitude upon the incorporation of the poly(2‐ethyl‐2‐oxazoline) insulating segment.

     

Full‐Color Processible Electrochromic Polymers Based on 4,4‐Dioctyl‐Cyclopentadithiophene

Three soluble electrochromic copolymers based on 4,4‐di‐octyl‐cyclopentadithiophene (DOCPDT): PDOCPDT‐OT, PDOCPDT‐PT, and PDOCPDT‐Cz were synthesized and the electrochromic properties were investigated. Colorimetric analysis revealed that red‐colored PDOCPDT‐OT, green‐colored PDOCPDT‐PT and their blue mother polymer PDOCTDT are cathodic coloration polymers. PDOCPDT‐Cz is yellow in its neutral state and shows an anodic electrochromism. The structural flexibility, color diversity, processibility and good electrochromic performance make octyl‐cyclopentadithiophene‐containing polymers prominent candidates for electrochromic applications.

     

Microwave‐Assisted Synthesis of Poly(L‐lactic acid) via Direct Melt Polycondensation Using Solid Super‐Acids

A microwave‐assisted method of synthesizing high‐molecular‐weight PLA using SSA as green catalyst was developed. Yellowish PLA with above 2.0 × 10⁴ g · mol^?1 was obtained when the reaction was run at 260 °C within 60 min under microwave irradiation with 0.4 wt.‐% SSA. This method used only 10% of the energy consumption necessary for conventional heating, and the catalyst could be used five times without losing catalytic activity. The improvement in and the decrease in the energy consumption under microwave irradiation suggested that selective heating and hot spots effects played a crucial role. The method was shown to be a time‐saving, green and a promising way to lower the cost and spread the application of PLA.

     

Synthesis and Optical Properties of Poly[2‐{N‐Methyl‐N‐(4‐(4‐ethynylphenylazo)phenyl)amino}ethyl butyrate]

Summary: The high‐molecular‐weight functional polyacetylene that contain a para‐aminoazobenzene chromophore, poly[2‐{N‐Methyl‐N‐(4‐(4‐ethynylphenylazo)phenyl)amino}ethyl butyrate] [poly(EAPAB)], was synthesized in moderate yield and characterized by FT‐IR, ¹H NMR, UV‐vis, TGA, and GPC. The nonlinear optical and optical limiting properties were performed with 8 ns pulse width at 532 nm wavelength. The results show that the introduction of the flexible amino group effectively improved the solubility of polymer [poly(EAPAB)] in common organic solvent, such as CHCl₃, THF, and dioxane, while poly(4‐ethynylazobenzene) [poly(4EAB)] without the flexible amino group shows poor solubility in common organic solvent. Simultaneously, poly(EAPAB) still shows good thermal stability, large third‐order nonlinear optical property, and novel optical limiting property owing to the functionalization of the para‐aminoazobenzene chromophore.

Polymerization of EAPAB by Rh(nbd)Cl₂‐Et₃N to poly(EAPAB).     

Synthesis and pH/Temperature‐Responsive Behavior of PLLA‐b‐PDMAEMA Block Polyelectrolytes Prepared via ROP and ATRP

Well‐defined diblock poly(L ‐lactide)‐block‐poly(dimethylamino‐2‐ethyl methacrylate) (PLLA‐b‐PDMAEMA) copolymers were synthesized by combining ROP of LLA and ATRP of DMAEMA, from a dual‐initiator 2‐hydroxylethyl 2‐bromoisobutyrate. The molecular characterization of these diblock copolymers was performed using ¹H NMR, FT‐IR, and GPC‐MALLS analysis. The responsive behavior of these diblock copolymers in aqueous solutions at different pH and temperatures were investigated using DLS. Results show that both higher pH and temperature result in a higher degree of neutralization, weaker hydrogen bonding, and micellar aggregation. As observed by TEM, changes in micellar morphology are in accordance with DLS results.

     

Click‐Chemistry: An Alternative Way to Functionalize Poly(2‐methyl‐2‐oxazoline)

CROP has been used to synthesize well‐defined POXZ with a monofunctional (iodomethane) or a bifunctional (1,3‐diiodopropane) initiator. POXZ has been functionalized with an azido group at one (α‐azido‐POXZ, = 3.58 × 10³ g · mol^?1) or both ends (α,ω‐azido‐POXZ, = 6.21 × 10³ g · mol^?1) of the macromolecular chain. The Huisgen 1,3‐dipolar cycloaddition has been investigated between azido‐POXZ and a terminal alkyne on a small or larger molecule (PEG). In each case, the click reaction has been successful and quantitative. In this way, different telechelic polymers (polymers bearing different functions such as acrylate, epoxide, or carboxylic acid) and block copolymers of POXZ and PEG have been prepared. The polymers have been characterized by means of FTIR, ¹H NMR, and SEC.

     

Acrylic‐Based Polyurethane/Silica Hybrids Prepared by Acid‐Catalyzed Sol–Gel Process: Structure and Mechanical Properties

Summary: Silica sols were first prepared based on different ratios of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) by an acid‐catalyzed sol–gel process, and then incorporated into acrylic‐based polyurethanes. The structures and morphologies of silicone‐oxo clusters were studied by ²⁹Si NMR, SAXS, and scanning electron microscopy (SEM), whereas the mechanical properties of polyurethane/silica hybrids were characterized by DMA and tensile tests. The silicone‐oxo clusters in both silica sol and polyurethane hybrids became denser and larger at a higher molar ratio of TEOS/MTES and higher silica content, and the silica‐oxo clusters of polyurethane/silica hybrids even became more compact and larger than those of silica sols, increasing the elastic modulus and tensile strength of polyurethane/silica hybrids.

Typical structure of silica sol prepared from the hydrolysis and condensation of TEOS and MTES with acid as the catalyst.     

Synthesis of a Polyphenol with a Mesoionic 6‐Oxo‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate as Pendant Group and Its Photochemical Behavior

This study deals with the synthesis of a polyphenol bearing photosensitive groups, and its photochemical behavior upon UV irradiation. Mesoionic 5‐(4‐hydroxybenzyl)‐6‐oxo‐1,2,3‐triphenyl‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate was prepared by condensation of 4‐benzyloxybenzylmalonic acid with N,N′‐diphenylbenzamidine using dicyclohexylcarbodiimide as condensing agent, followed by deprotection of the benzyl group. The monomer was polymerized by an iron‐salen complex to give a polymer with a mesoionic 6‐oxo‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate moiety as the pendant group. Spin coated polymer films were prepared and characterized. It was shown by IR spectroscopy that irradiation with UV light converted the mesoionic structure to a bis(β‐lactam) structure. Waveguide spectroscopy showed a large decrease in the film thickness without refractive index changes during irradiation.

Time development of the refractive index and the film thickness measured with p‐polarized light.     

Synthesis,Characterization and Field‐Effect Transistor Performance of Poly[2,6‐bis(3‐alkylthiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]diselenophene]s

Benzo[1,2‐b:4,5‐b′]diselenophene (BDS) has been incorporated for the first time in a polymer. bis(Stannyl)‐functionalized BDS was copolymerized with 3,3′‐bis(alkyl)‐5,5′‐bithiophenes (dodecyl and tetradecyl side chains) through Stille copolymerization, to yield p‐type polymer semiconductors for organic field‐effect transistor application. The electronic and structural effect of the selenium atoms, compared to sulphur atoms in analogous copolymers, is described. The molecular weight has a decisive influence on the photophysical properties and supramolecular ordering, expressed in field‐effect transistor measurements. Saturation mobilities around 10^?2 cm² · V^?1s^?1 are obtained on standard silicon substrates.

     

Preparation of Carboxyl‐Functionalized Polystyrene/Silica Composite Nanoparticles

Summary: This paper describes the synthesis of carboxyl‐functionalized polystyrene/silica (PS/SiO₂) composite nanoparticles with various contents of poly(methacrylic acid) (PMAA) on the surface by post‐addition of methacrylic acid (MAA) via emulsion polymerization. High yields and binding efficiencies (around 90%) are achieved by an optimal procedure mainly involving the appropriate addition of MAA and amounts of surfactant and silica. The kinetics investigated indicates that the polymerization follows a mechanism different than that found in some earlier studies. The amount of grafted PMAA was determined by titration and FT‐IR, and altered in a wide range (1–40 wt.‐% to PS). Transmission electron microscopy (TEM) photographs show that the composite nanoparticles are about 60 nm in spherical shape and have a multi‐layered core‐shell structure with a cluster of primary silica beads as the core and PMAA as the outmost shell. There are approximately 4 to 21 primary silica beads in one composite nanoparticle, depending on the amount of silica added.

Preparation of carboxyl‐functionalized polystyrene(PS)/silica composite nanoparticles.     

“One‐pot” Synthesis of 1‐Vinyl‐2‐pyrrolidone with Protic Functional Groups in 3‐Position

A synthetic route that allows modification of 1‐vinyl‐2‐pyrrolidone with an alcohol or thiol group in its 3‐position in a one‐pot reaction without using protecting groups is described. The strategy used to achieve this goal is the reaction of the carboxamide anion of 1‐vinyl‐2‐pyrrolidone with cyclic precursors of these functionalities. It is furthermore shown that VP‐monomers functionalized with OH groups are suitable for the preparation of the corresponding copolymers with pure VP. As a second application of the new compounds, we also describe the synthesis of the first asymmetric crosslinker based on VP.

     

Semicontinuous Emulsion Polymerization of Butyl Methacrylate and 1, 3‐Butadiene in the Presence of Cyclodextrins and Cytocompatibility of Dicarboxylic Acid Telechelic Oligo(butyl Methacrylate)s Derived from Ozonolysis of the Latexes

Ozonolysis of unsaturated polymers produced useful telechelic oligomers that can form building blocks for networks and block copolymers. The unsaturated polymers can be prepared by semicontinuous emulsion polymerization with dienes, and here it is shown that the addition of cyclodextrins enhanced the incorporation of these comonomers. Both α‐ and β‐cyclodextrin provide copolymers with higher fractions of butadiene (BD) incorporated into the chain but α‐cyclodextrin had the highest levels of incorporation. Oxidative work up after ozonolysis produced latexes of carboxylic acid oligomers of different molar masses. A clear effect of polymer size on toxicity was observed with the oligomers with < 2 700 g · mol.^?1 proving to have similar cytotoxic effects to lactic acid. However, oligomers with above 2 700 g · mol.^?1 were cytocompatible and gave similar results to a polylactide control material.

     

Double‐Gyroid Morphology of a Polystyrene‐block‐Poly(ferrocenylethylmethylsilane) Diblock Copolymer: A Route to Ordered Bicontinuous Nanoscale Architectures

A polystyrene‐block‐poly(ferrocenylethylmethylsilane) diblock copolymer, displaying a double‐gyroid morphology when self‐assembled in the solid state, has been prepared with a PFEMS volume fraction ?_PFEMS = 0.39 and a total molecular weight of 64 000 Da by sequential living anionic polymerisation. A block copolymer with a metal‐containing block with iron and silicon in the main chain was selected due to its plasma etch resistance compared to the organic block. Self‐assembly of the diblock copolymer in the bulk showed a stable, double‐gyroid morphology as characterised by TEM. SAXS confirmed that the structure belonged to the Ia d space group.

     

Polyhedral Oligomeric Silsesquioxane‐ and Fullerene‐End‐Capped Poly(ε‐caprolactone)

Novel fullerene‐ and polyhedral oligomeric silsesquioxane‐ (POSS) double end‐capped poly(ε‐caprolactone) (PCL) were successfully synthesized. The crystallization behavior of the fullerene‐ and POSS‐ double end‐capped PCL and the effect of aggregation of the POSS and fullerene moieties on the crystallization of PCL were thoroughly studied. The aggregation of the fullerene moieties has much larger confinement effect on the crystallization of PCL than that of POSS. The successful incorporation of two nano‐sized objects, that is, fullerene and POSS, into the PCL matrix may introduce their merits, so that PCL can attain multi‐functional properties.

     

Cyclodextrins in polymer synthesis: Steric retardation of the free‐radical polymerization in aqueous medium of 4‐vinylbenzaldehyde/methylated β‐cyclodextrin complex

4‐Vinylbenzaldehyde ( 3 ) was complexed with methylated β‐cyclodextrin ( 4 ) (me‐β‐CD) yielding the water soluble host‐guest complex ( 5 ). Radical polymerization was initiated with K₂S₂O₈/Na₂S₂O₅ in water at room temperature and also at 70 °C. The polymerization tendency of this complex ( 5 ) is lower compared to the styrene/me‐β‐CD‐complex ( 7 ). Also copolymerizations of 5 and complexed styrene ( 6 ) at these two temperatures were carried out and the results are discussed in respect to the behavior of the homopolymerization. The resulting polymers ( 8a‐k , 9a , 9b ) were characterized by SEC‐measurements and ¹H NMR spectroscopy. TEM‐measurements of the homopolymers 8f and 8k show differences in the particle size depending on the amount of me‐β‐CD.

TEM recordings of the polymers 8f (left) and 8k (right).     

Aniline‐Based Disulfide/Aniline Copolymers as a High Energy‐Storage Material

Aniline‐based disulfide, 5‐amino‐1,4‐dihydrobenzo[d]‐1′,2′‐dithiadiene (DTAn), was synthesized through a new route. The DTAn/aniline copolymers [P(DTAn‐co‐An)] were prepared by chemical oxidative polymerization. The results show that the polymerization activity of the DTAn is obviously lower than that of aniline, and the degree of polymerization increases with the increasing feed ratio of aniline and oxidant dosage. The cyclic voltammograms of the copolymers indicate that intramolecular self‐catalyzed effects occurred between the conducting backbone and the S‐S side chain. The charge–discharge tests of Li/P(DTAn‐co‐An) cell show an initial specific capacity of 262 mAh · g⁻¹, which suggests that P(DTAn‐co‐An) may be a promising cathode material in secondary lithium batteries.

     

Fluorene‐Based Single‐Chain Copolymers for Color‐Stable White Light‐Emitting Diodes

Fluorene‐based single‐chain copolymers with a white light emitter consisting of a blue and an orange chromophore have been synthesized and their photophysical and electroluminescent properties are investigated. The experimental results suggest that only a relatively small fraction of the orange‐emitting units incorporated into the fluorene is needed to achieve efficient white light emission by controlled incomplete energy transfer. A device from a copolymer with 0.02% DDQ content showed the highest external quantum efficiency of 2.64% with a luminance efficiency of 4.06 cd · A^?1 with CIE coordinates (0.28, 0.24). The EL emissions are extremely stable over a wide range of current densities.