Polymerization Of N-vinylcarbazole Research Articles

Mechanistic Insights into the Stereoselective Cationic Polymerization of N-Vinylcarbazole.

The synthesis of stereoregular polymers through ionic mechanisms using asymmetric ion-pairing (AIP) catalysis is emerging as an effective strategy to achieve differentiated material properties from readily available building blocks. Stereoselective cationic polymerization in particular is primed for advancement using AIP by leveraging the breadth of Brønsted and Lewis acid small-molecule catalysis literature; however, mechanistic studies that address polymer-specific phenomena are scarce and, as a result, the lack of mechanistic understanding has limited catalyst design. In a recent study, we demonstrated the only example of a stereoselective and helix-sense-selective cationic vinyl polymerization of N-vinylcarbazole using chiral scandium-bis(oxazoline) Lewis acids. To better understand the mechanism of this highly stereoselective polymerization and elicit design principles for future advances, we present a combined experimental and computational study into the relevant factors that determine tacticity and helicity control. Key mechanistic experiments suggest two competing elementary steps-chain-end conformation equilibration and propagation-whose relative rates can be influenced by monomer concentration, isotope effects, and catalyst design to tune tacticity. In contrast, helicity is influenced by complex relationships between the stereoselectivity of the first monomer propagation and a time-dependent initiator-catalyst mixing time. The more complete understanding of stereoselective cationic polymerization through AIP developed herein provides insights into polymer-specific mechanisms for stereocontrol, which we believe will motivate continued catalyst discovery and development for stereoselective vinyl polymerization.

Redox-initiated polymerization of N-vinylcarbazole based on carbon dots for modification and beyond

Herein, carbon dots (CDs) and N,N-dimethylaniline (DMA) were designed as a redox couple for redox-initiated polymerization of N-vinylcarbazole (NVC) under mild conditions. Several ratios of CDs to DMA and various temperatures were adopted to prove the feasibilities of the redox-initiated polymerization. Meanwhile, the CDs as fillers were encapsulated, crosslinked and passivated by the resulting poly (N-vinylcarbazole) (PVK) to form red emissive PVK-CDs composites with a fluorescence quantum yield up to 28.75%, which is significantly higher than that of pristine CDs. In particular, the loading of CDs also enhanced the electron-transfer properties and thermostability of PVK. Hence, this work not only applied CDs to redox-initiated polymerization of NVC so as to prepare CDs modified PVK, but also illustrated the electron-transfer properties of CDs in polymerization and PVK modification. Expectedly, by taking advantages of electron-transfer properties of CDs, it is expectable for redox-initiated polymerization to synthesize more CDs modified polymers for promising applications.

Influence of ultrasound on multi-site phase transfer catalyzed polymerization of N-vinyl carbazole in two phase system

Carbazole—containing motifs are of most desired materials because of its wide range of applications due to π- extended systems, molecular and optical properties was easily tunable via diverse structural modifications. Herein, we reported an efficient and facile polymerization of N-vinyl carbazole (NVK) using multi-site phase transfer catalyst with and without ultrasound condition. The rate of polymerization (Rp) was effectively improved with ultrasound in short time on compare with silent condition. Role of different parameters such as variation of frequency, monomer, initiator, catalyst and temperature, solvents, aqueous and pH on the rate of polymerization of NVK was explored under silent and ultrasound condition (45 kHz/550 W). Activation energy of polymerization was supported for an enhancement of rate under ultrasound condition. From the experimental results, an appropriate kinetic model and role of various parameters in polymerization reaction was discussed. The obtained poly (N-vinyl carbazole) was confirmed and characterized by FT-IR, 1H NMR, TGA and XRD techniques.

Electrochemical, optical and morphological properties of poly (N-vinylcarbazole/TiO2) and (N-vinylcarbazole/aniline)/TiO2 copolymer prepared by electrochemical polymerization

AbstractPoly (N-vinylcarbazole) (PVK) and a new copolymer, PVK/polyaniline (PANI), have been successfully prepared by electrochemical polymerization of N-vinylcarbazole (NVK) and NVK/aniline from acetonitrile medium and LiClO4 supporting electrolyte. Composite thin films were studied by cyclic voltammetry (CV) in LiClO4/acetonitrile solutions on an indium tin oxide (ITO) electrode. The influences of concentration of titanium dioxide (TiO2) on the electrochemical properties of these composite materials were also investigated. The results of scanning electron microscopy (SEM) confirm the presence of TiO2 in the composite, which consequently modifies the morphology of the film significantly. Topographical analysis has shown that TiO2 nanoparticles (NPs) affect the morphology of thin films (roughness). The analysis of the voltammograms of PVK and of (PVK+PANI) before and after the addition of TiO2 at different concentrations shows a redox couple which was not observed in the absence of TiO2. The impedance spectroscopy study shows that the resistance of the PVK and (PVK+PANI) films decreases with increasing of TiO2 concentration, and this in turn contributes to a good conductivity of the film. The optical characterization of the composites has been carried out by UV-Vis absorption and photoluminescence (PL) spectroscopy and it was noted that the samples (PVK+10−2 TiO2) exhibited high transmittance (83%) in the visible region and a low gap value (2.69 eV) which confirms that this material can be used in a photovoltaic cell. This is explained by the introduction of the donor levels in the band gap of PVK by the TiO2, due to an effective doping.

Stereospecific Living Cationic Polymerization of N-Vinylcarbazole through the Design of ZnCl2-Derived Counteranions.

Highly stereospecific living polymerization of N-vinylcarbazole (NVC) successfully proceeded via a cationic mechanism as a result of the elaborate design of counteranions using an initiating system consisting of CF3SO3H, nBu4NX (X = Cl, Br, I), and a Lewis acid catalyst. The use of ZnCl2 and an appropriate amount of nBu4NCl quantitatively generated highly isotactic polymers (mm = 94%) with narrow molecular weight distributions (Mw/Mn ∼ 1.3) and molecular weights proportional to monomer conversion. In this system, a ZnCl42- species, which was formed as a counteranion of the propagating carbocation, most likely contributed to the stereoregulation of the polymers because the mm value drastically varied depending on the polymerization conditions, such as the Lewis acid catalyst and amount of added salt. Isotactic poly(N-vinylcarbazole) (PVK) showed different properties than atactic PVK based on fluorescence and differential scanning calorimetry (DSC) analysis.

Electron transport and photoelectrical behavior of poly(N-vinylcarbazole)/Poly(3,4-ethylenedioxythiophene) composite honeycomb-patterned films

New type of poly(N-vinylcarbazole) (PVK) polymer nanocomposites were prepared by a solid-state polymerization of N-vinylcarbazole in the presence of different concentration (wt%) of poly(3,4-ethylenedioxythiophene) (PEDOT). The prepared PVK/PEDOT nanocomposites were characterized by using Fourier transform infrared (FTIR) and UV-vis spectra. The transmission electron microscopy (TEM) and X-diffraction studies were performed to understand the surface morphology and nature of the polymer composites. The characterization and morphological studies suggest that there is a conjugation between PVK and PEDOT. Furthermore, the honeycomb-patterned films were obtained by dissolving the PVK/PEDOT nanocomposites into the chloroform solvent under humid conditions. The temperature-dependent DC electrical conductivity and room temperature photo-electrical conductivity of the honeycomb-patterned films were measured. Results showed that the incorporation of PEDOT in PVK polymer has greatly improved the electrical conductivity and photo-electrical behavior of the PVK/PEDOT nanocomposites.

Asymmetric polymerization of N-vinylcarbazole with optically active anionic initiators

The anionic polymerization of N-vinylcarbazole (NVC) by using optically active anionic initiators such as the lithium salts of (S)-1-(9H-fluoren-2-yl)-4-isopropyl-4,5-dihydrooxazole ((S)-1-FIDH) and (S)-2-(9H-fluoren-2-yl)-4- isopropyl-4,5-dihydrooxazole ((S)-2-FIDH) and complexes of (-)-Sparteine with n-butylithium (n-BuLi-(-)-Sp) or fluorenyl lithium (FILi-(-)-Sp) was achieved. The yield and specific rotation of poly(N-vinylcarbazole)s (poly(NVC)s) were considerably affected by the molar ratio of (S)-FIDH to NVC. The highest yield and specific rotation were obtained with Li- (S)-1-FIDH as an initiator, with a molar ratio of monomer and initiator [M]/[I] = 10/1. The effects of the chiral initiators, type of solvent and the polymerization temperature were investigated. The obtained optical activity of polymers was attributed to asymmetric induction of the chiral initiators.

Synthesis and Properties of Poly(N-vinylcarbazole) Covalently Functionalized Zinc Oxide Nanocomposites

Poly(N-vinylcarbazole) covalently grafted zinc oxide nanoparticles (ZnO-g-PNVC) were synthesized with a simple route using surface initiated reversible addition-fragmentation chain transfer (RAFT) polymerization. Initially, the surface of ZnO nanoparticles was modified by the condensation reaction of 3-chloropropyltrimethoxysilane, and it was subsequently reacted with potassium xanthogenate to produce ZnO nanoparticles having RAFT functionality (ZnO-RAFT). The controlled radical polymerization of N-vinylcarbazole in the presence of ZnO-RAFT afforded ZnO-g-PNVC composites. FT-IR, EDX, XRD, and SEM analyses demonstrated the grafting of PNVC onto ZnO nanoparticles. Thermal stability of ZnO-g-PNVC composites was revealed by TGA analysis. UV-Vis absorption and photoluminescence results suggested ZnO-g-PNVC composites as a potential material in optical application.

Synthesis and Characterization of Poly(<I>N</I>-vinylcarbazole)/Graphene Nanocomposites

The present work describes the dual role of graphene as an initiator and filler for polymerization of N-vinylcarbazole and formation of poly(N-vinylcarbazole)/graphene (PVK/Gr) nanocomposites. Fourier transformation infrared (FTIR) and X-ray diffraction (XRD) studies confirmed the formation of PVK as well its graphene nanocomposites. Scanning electron micrograph (SEM) and transmission electron microscopy (TEM) revealed the graphene platelets are dispersed in the matrix of spherical PVK. X-ray photoelectron spectroscopy (XPS) also revealed formation of PVK and presence of interaction between PVK and graphene. Thermograivmetric analysis (TGA) have shown that the thermal stability of PVK/graphene (0.5 wt%) is maximum improved by -76 degrees C compared to neat PVK, when 20 wt% weight loss is taken as a point of comparison. Ultraviolet (UV) and photoluminescence (PL) studies established the charge transfer from polymer chains to the graphene platelets. Dielectric measurements have shown the maximum improvement (87%) in dielectric constant (ε) with 1 wt% graphene loading. The variation of ac conductivity (σ) with frequency (ψ) confirmed the insulating behavior of PVK/graphene nanocomposites possessing high dielectric constant.

Electrolytic Formation of Poly (N-vinylcarbazole)

Electrochemical polymerization of N-vinylcarbazole was carried out in a solution of tetramethyl ammonium chloride in dichloroethane at a constant current. The polymer yields increase with increasing concentration of monomer, impressed current level andelectrolysis time. The inhibition of polymer formation by a free radical scavenger, 2-2-diphenyl-1-picrylhydrazyl supports a free radical mechanism. The free radical species are generated in situ during the electrolysis of polymerizing mixture. Cyclic voltammograms demonstrate the polyvinylcarbazole formed electrochemically in a solution of (C4H5)4NSbC16 or (C4H9)4NClO4 in DCE undergoes oxidation-reduction states. The polymerization of NVCZ resulted in the formation of cross linked conductive polymers on the anode. The conductivity was found to be about 10−6 scm−1.

Cyclic poly(vinylcarbazole) via ring-expansion polymerization-RAFT (REP-RAFT)

In this paper, we demonstrate the formation of cyclic poly(vinylcarbazole) via a ring-expansion polymerization reversible addition-fragmentation chain transfer (REP-RAFT). A cyclic dixanthate RAFT chain transfer agent (CTA) was synthesized and employed for controlled free radical polymerization of N-vinylcarbazole (NVK). The molecular weight in relation to polymerization time suggested the formation of a polymer with well-controlled molecular weight and ring size. The obtained macromolecules were characterized by nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS) and dynamic light scattering (DLS). Atomic force microscopy (AFM) was also employed to directly observe the cyclic polymers with different ring sizes.

Ultrasound-assisted synthesis of hybrid nanostructures using RAFT polymerization from the surface of quantum dots

Poly(N-vinylcarbazole) (PVK) grafted ZnS quantum dots (QDs) (ZnS-g-PVK) involving covalent bonds between the inorganic and organic segments were synthesized by a facile ultrasonic irradiation technique. The hydroxyl group-coated ZnS QDs were first prepared using zinc chloride and sodium sulfide in the presence of 2-mercaptoethanol. The ZnS QDs were then coupled with the reversible addition-fragmentation chain transfer agent 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DTMPA) by condensation reaction. Subsequently, the surface initiated graft polymerization of N-vinylcarbazole from the DTMPA functionalized ZnS QDs surface was accomplished upon exposure to ultrasonic irradiation to deliver covalently attached PVK with ZnS QDs. The chemical structure of the nanocomposites was investigated by FT-IR and XPS analyses. Molecular weight and polydispersity index of the cleaved PVK from the nanocomposites were determined by GPC. The physical structure and thermal properties of the nanocomposites were studied by XRD and TGA. TEM images suggested that ZnS QDs were uniformly distributed in PVK matrices. The nanocomposites showed good optical properties as studied by photoluminescence spectroscopy.

Homogeneously Dispersed Silver Nanoparticles on the Honeycomb-Patterned Poly(N-vinylcarbazole)-cellulose triacetate Composite Thin Films by the Photoreduction of Silver Nitrate

The photocontrolled reduction of silver nitrate to silver (Ag) nanoparticles on honeycomb-patterned poly(N-vinylcarbazole) (PVK)-cellulose triacetate (CTA) composite thin films was studied. The composites were prepared via the oxidative polymerization of N-vinylcarbazole with ferric chloride using different CTA concentrations. A honeycomb-patterned film was fabricated by casting the composite solution under humid conditions. Ag particles with a homogeneous distribution were produced by the composite film in a moderate CTA concentration, whereas aggregated Ag was obtained from the pure PVK film.

Characterization and electrical behavior of biodegradable poly(N-vinylcarbazole)/poly(3-hydroxybutyric acid) composite films

Poly(N-vinylcarbazole) (PVK) composites containing poly(3-hydroxybutyric acid) (PHB) were synthesized via in situ deposition. The oxidative polymerization of N-vinylcarbazole was carried out by dissolving different weight percentages (10, 20, 30, 40, and 50 wt%) of PHB using ferric chloride as an oxidant. The as-synthesized composites were characterized by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface morphology of the resulting composites was studied by transmission electron microscopy, and the biodegradability of the composites was tested by the Sturm method. The temperature-dependent DC conductivity of the synthesized composite films was measured, and the activation energy responsible for the conductivity was examined. The incorporation of PHB in the synthesis of PVK composites significantly increased the conductivity and biodegradability of the resulting products. Thus, the newly synthesized composites have potential applications in the biological, medical, and engineering fields.

The reactivity of N-vinylcarbazole in RAFT polymerization: trithiocarbonates deliver optimal control for the synthesis of homopolymers and block copolymers

The use of various RAFT agents (ZC(S)SR) including dithiobenzoates (Z = Ph), trithiocarbonates (Z = SR′), xanthates (Z = OR′), and conventional and switchable N-aryldithiocarbamates (Z = NR′Ar) in RAFT polymerization of N-vinylcarbazole (NVC) has been explored with a view to establishing which is most effective. Consistent with earlier work, we find that xanthates and N-aryldithiocarbamates give adequate control (dispersities (Đ) < 1.3) while dithiobenzoates give marked retardation. However, contrary to popular belief, we find that the polymerization of NVC is best controlled with trithiocarbonate RAFT agents, which provide both good molecular weight control, very narrow dispersities (Đ < 1.1), and high end-group fidelity. The results demonstrate that NVC has intermediate reactivity, i.e. between that of the traditional more activated (MAMs; styrene, acrylates) and less activated monomers (LAMs; vinyl acetate, N-vinylpyrrolidone). A further key to good control is the selection of RAFT agent R substituent to be both a good leaving group and a good initiating radical. The cyanomethyl group meets these criteria whereas phenylethyl is a poor initiating radical for NVC polymerization. A further demonstration of the intermediate reactivity of NVC and the derived propagating radical was the successful preparation of both poly(n-butyl acrylate)-block-poly(N-vinylcarbazole) and poly(N-vinylcarbazole)-block-poly(n-butyl acrylate) with a trithiocarbonate RAFT agent (the sequence of block synthesis is not important). Two-dimensional, liquid chromatography near critical conditions-gel permeation chromatography (LCCC-GPC) has been applied to demonstrate block purity. The corresponding styrene-based blocks can also be successfully synthesized, however, the reinitiation of NVC polymerization by the polystyryl radical proved to be a constraint on the purity of polystyrene-block-poly(N-vinylcarbazole).

Water-soluble poly(N-vinyl-1,2,4-triazole) star and amphiphilic star block copolymers by RAFT polymerization

Water-soluble star polymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinyl-1,2,4-triazole (NVTri), which is a non-conjugated N-vinyl monomer having an aromatic heterocycle. Four-arm poly(NVTri)s having low polydispersities and controlled molecular weights were obtained using a xanthate-type tetrafunctional chain transfer agent (CTA). Amphiphilic star block copolymers having inner water-soluble segments connected to the core were synthesized by RAFT polymerization of N-vinylcarbazole (NVC) using poly(NVTri) star as a macro-CTA. In contrast, RAFT polymerization of NVTri using poly(NVC) star afforded star block copolymers with block arms consisting of inner optoelectronic poly(NVC) segment and outer hydrophilic poly(NVTri) segment. Assembled structures of these amphiphilic star block copolymers formed in selective solvents and characteristic optoelectronic properties were evaluated by dynamic light scattering (DLS), UV–vis, and fluorescence spectroscopic methods.

Preparation and evaluation of microstructure, dielectric and conductivity (ac/dc) characteristics of a polyaniline/poly N-vinyl carbazole/Fe3O4 nanocomposite

A poly N-vinyl carbazole- Fe3O4 hybrid composite was prepared by solid state polymerization of N-vinyl carbazole (NVC) monomer in presence of Fe3O4 powder. This hybrid composite was dispersed in aqueous medium containing a known amount of potassium perdisulfate (KPS) as oxidant under constant sonication. A known amount of aniline (ANI) was injected in the system which started changing color and ultimately a black mass of (PANI-PNVC-Fe3O4) separated out. The composite was characterized by FTIR, FESEM and HRTEM analyses. XRD analyses using Williamson-Hall plot revealed average particle size of the PANI-PNVC-Fe3O4 composite to be around 34 nm. HRTEM analyses confirmed the particle size to be in the range 25–40 nm. The dielectric constants of PNVC–Fe3O4 system was low at 0.1–25 kHz whereas the PANI encapsulated PNVC–Fe3O4 nanocomposites showed significantly higher values of dielectric constant (>5500) at 0.1 kHz implying that the interfaces between grain and grain boundary of the composite play a dominant role for enhancing dielectric properties of the system. The ac conductivity was found to be independent of frequency in the range 102–103 Hz for all the nanocomposites implying contribution of free charges and rise thereafter appreciably in the frequency range of 1–25 kHz due to trapped charges in the grain boundary.

Synthesis of Star Poly(N-vinylcarbazole) by Microwave-Assisted Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT)

Controlled radical polymerization of N-vinylcarbazole (NVK) via microwave-assisted reversible addition-fragmentation chain transfer (RAFT) polymerization is described. As chain transfer agent, 1,3,5-benzyl tri (diethyldithiocarbamate), was used. The chain transfer agent, containing a 1.3.5-trisubstituted benzene ring as core and three dithiocarbamate functionalities attached through an intermediate for fragmenting covalent bonds, led to poly(N-vinylcarbazole) (PVK) with star architecture. Polymerizations were carried out in 1,4-dioxane as solvent, at 70 °C, and studied for different polymerization times and monomer/CTA/initiator ratios. The SEC molecular weight curves exhibit a trimodal distribution, assigned to the linear and star-star coupling polymers, accompanying the real star polymer (as main product).

Characterization and electrochemical behaviors of honeycomb-patterned poly(N-vinylcarbazole)/polystyrene composite films

Poly(N-vinylcarbazole)/polystyrene composites were prepared through simple radical polymerization of N-vinylcarbazole in the presence of polystyrene. Honeycomb-patterned composite thin films were fabricated by casting the composite solutions under humid conditions. The scanning electron microscopy (SEM) images of the resulting honeycomb pattern on the composites show a higher regular structure compared to those of films prepared from the poly(N-vinylcarbazole) homopolymer. The pressure-area isotherms and photoelectrochemical behaviors of the patterned films were also observed. The photoconductivity of the patterned thin films increased with increasing poly(N-vinylcarbazole) concentration. This enhancement is attributed to the effects of the honeycomb structures and the charge transfer across the donor/acceptor hybrid interface in the composite films.

Novel Complex Polymers with Carbazole Functionality by Controlled Radical Polymerization

This review summarizes recent advances in the design and synthesis of novel complex polymers with carbazole moieties using controlled radical polymerization techniques. We focus on the polymeric architectures of block copolymers, star polymers, including star block copolymers and miktoarm star copolymers, comb-shaped copolymers, and hybrids. Controlled radical polymerization ofN-vinylcarbazole (NVC) and styrene and (meth)acrylate derivatives having carbazole moieties is well advanced, leading to the well-controlled synthesis of complex macromolecules. Characteristic optoelectronic properties, assembled structures, and three-dimensional architectures are briefly introduced.