Simultaneous step-growth and chain-growth cationic polymerization of styrenic monomers bearing carbazolyl groups

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Cationic polymerization of two styrene derivatives containing carbazole moiety with different linking topology, 9-(4-vinylphenyl)carbazole (M1) and 3-(4-vinylphenyl)-9-ethylcarbazole (M2), using 1-chloro-1-phenylethane (PhEtCl)/SnCl4 initiating system has been investigated. It was shown that polymerization of M1, which is characterized by higher electron density on the carbon at the 3 position of carbazolyl group than on vinyl group, proceeds predominantly via step-growth (SG) pathway through addition of protonated monomer/oligomers to 3-position of carbazolyl group (electrophilic aromatic substitution). On the contrary, M2, in which 3-position of carbazolyl group is protected via introduction of 4-vinylphenyl group, polymerized predominantly via chain-growth (CG) pathway through addition of carbocation to double bond of monomer. The polymers synthesized via SG mechanism showed different photophysical characteristics in comparison with corresponding monomer, while in case of polymers prepared via CG mechanism the polymer and monomer have the same absorption and fluorescence profiles.

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... However, in all these examples low molecular weight polymers (M n = 1810-5800 g mol −1 ) with high polydispersity (Đ ≤ 8.8) were generated due to the uncontrolled character of the process. Other families of carbazole-containing monomers possessing acrylate [11,12], methacrylate [13][14][15] and styrene [16][17][18] moieties were also synthesized. These monomers were successfully polymerized through conventional radical [12][13][14][15]17], anionic [11,18] and cationic [16] mechanisms affording ill-defined polymers typically with high polydispersity and without control over their molecular weight. ...
... Other families of carbazole-containing monomers possessing acrylate [11,12], methacrylate [13][14][15] and styrene [16][17][18] moieties were also synthesized. These monomers were successfully polymerized through conventional radical [12][13][14][15]17], anionic [11,18] and cationic [16] mechanisms affording ill-defined polymers typically with high polydispersity and without control over their molecular weight. ...
... The main advantage of this approach is the possibility to prepare cross-linkable star-shaped polymers with photoactive end groups, which are promising host materials for solution processable polymeric light emitting devices [33]. However, only monomers bearing electron donating groups could be polymerized using this approach, while the presence of heteroatom (sulfur) negatively influences the thermal properties (T ID ) of the corresponding polymers [16,33]. ...
Atom-transfer radical polymerization of 9-(4-vinylphenyl)carbazole (M1) and 9-(2,3,5,6-tetrafluoro-4-vinylphenyl)carbazole (M2) has been investigated using CuCl/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine as catalyst and ethyl 2-bromoisobutyrate as an initiator. The polymerization of the monomers proceeded in a living fashion affording polymers with controlled molecular weight (Mn = 5000 g mol⁻¹ to 32000 g mol⁻¹) and relatively low polydispersity (Đ = 1.2–1.5). The kinetic investigations showed that M2 polymerized at the faster rate as compared to M1. Block copolymers were successfully prepared starting from the polymerization of more reactive M2 followed by addition of M1. The same initiating system also induced living radical copolymerization of these monomers giving random copolymers. Usage of tetrafunctional initiator pentaerythritol tetrakis(2-bromoisobutyrate) in conjunction with CuCl/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine as catalyst allowed to synthesize star-shaped linear and random copolymers from M1 and M2 with controlled molar mass (up to Mn = 25000 g mol⁻¹) and low polydispersity (Đ < 1.5). The thermal, photophysical and electrochemical properties of the synthesized linear and star-shaped polymers and copolymers were estimated. It was shown that photophysical properties of copolymers can be tuned by changing the copolymer composition.
... In order to tune electrochemical and photophysical properties of poly(N-vinylcarbazole), a great variety of polymers containing carbazole moieties in the side chain were successfully synthesized [5][6][7]. Firstly, poly(meth)acrylates and polystyrenes with pendant carbozolyl group were mainly synthesized through conventional radical mechanism [8][9][10][11][12], although there are several reports where such kind of polymers have been successfully obtained by anionic [13,14] and cationic [15] mechanisms. However, it was difficult to control the molecular weight and architecture of the synthesized polymers that significantly complicated the finding of the correlation between polymer structure and its electronic and photonic properties. ...
... All calculations were performed as described [15]. All optimized structures were checked to be minima, with no imaginary frequencies. ...
... In addition to the chain-growth polymerization with the participation of vinyl groups, a stepgrowth polymerization with the participation of vinyl groups and aromatic moieties apparently takes place. The combination of chain-growth and step-growth polymerizations was recently observed for the polymerization of 9-(4-vinylphenyl)carbazole in the presence of (PhEtCl)/SnCl 4 initiation system [50]. IR spectra of the polymerization products of monomers 7-9 show the decreased intensity of Fig. 4 FT-IR spectra of monomers 7-9 and of their products of polymerization the signals of vinyl groups at 908-907 cm −1 compared to those of the spectra of the monomers (Fig. 4). ...
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Phenanthroimidazole-based monomers with reactive vinyl groups were synthesized, and their thermal, optical, photophysical and electrochemical properties were investigated. The monomers exhibited high thermal stability with 5% weight loss temperatures (Td) ranging from 378 to 409 °C. Thermal degradation of the polymerization products apparently takes place in this temperature range. The solutions of the monomers exhibit emission peaks in the range from 388 to 398 nm. In the solid state, the emission of these molecules shows red shift which is coherent with the similar red shifts of the corresponding absorption spectra. Ionization potential values of the compounds estimated by cyclic voltammetry were found to be close and varied in the range from 5.44 to 5.63 eV. Solid-state ionization potentials estimated by photoelectron emission spectrometry varied in the range from 5.54 to 5.66 eV. Self-polymerization of the synthesized monomers was demonstrated by differential scanning calorimetry. The number average molecular weights of the polymerization products of monomers containing substituents at phenyl rings linked to C-2 and N-1 positions of imidazole ring were found to be 100,100 and 196,000, respectively. The apparent activation energy and pre-exponential factor of self-polymerization were found to be dependent on conversion degree. The values of activation energy for self-polymerization of monomers varied in the range from 78.7 to 136.0 kJ/mol (estimated by Ozawa method) and from 78.3 to 139.0 kJ/mol (estimated by Kissinger method).
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We report the synthesis, characterisation, and spectroscopic investigations of a new solution‐processable N‐styrylcarbazole‐linked tetraphenylethylene (TPE) derivative (TPE‐BCzS), exhibiting green‐orange emission. While the material displayed weak photoluminescence in solution with a low photoluminescence quantum yield (PLQY of 4±0.2%), significant photoluminescence enhancement in neat‐film PLQY (55±8%) was observed. Studies using steady‐state spectroscopy, and femtosecond and nanosecond transient absorption spectroscopy revealed details of the excited‐state dynamics, consisting of the Franck‐Condon (FC) state, non‐radiative conformational relaxation, and formation and decay of the triplet excited‐state generated via intersystem crossing upon ultrafast photoexcitation. Solution processed OLEDs based on TPE‐BCzS displayed maximum external quantum efficiencies of 1.8% and 1.7% for neat and blend films [20wt% in a 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl host], approaching the theoretical efficiency limit for the determined PLQYs of the films. While TPE materials are typically associated with aggregation‐induced emission, we report that the enhanced PLQYs in the solid state are due to restriction of structural relaxations in the solid state—and not to the commonly misunderstood aggregation effect. This article is protected by copyright. All rights reserved.
A new series of monomers consisting of electron-deficient tetrafluorobenzene fragment and electron-donating units such as carbazole, di-tert-butyl carbazole, 9,9-dimethyl acridan and phenothiazine was prepared. Polymers containing well-defined donor-acceptor side chains were obtained via classical free radical polymerization of previously synthesized monomers. Comparative study of photophysical, electrochemical and thermal properties of the synthesized compounds was carried out. It was shown, that emission colour of the compounds from violet to yellow can be effectively adjusted by manipulation of the connected electron-donating fragments. The energy gaps of the compounds can also be fine-tuned by changing the moieties linked to the para-position of pentafluorostyrene moiety. Experimental optical energy gap values varied from 3.57 eV and 3.62 eV for carbazole based monomer and polymer to 2.99 eV and 3.24 for phenothiazine based monomer and polymer. Band gap values of polymers were found to be close to those of the corresponding monomers. The monomers demonstrated violet to yellow fluorescence in the solid state with quantum yields ranging from 1 to 22%. The solid films of polymers demonstrated blue to greenish fluorescence in the region of 456–512 nm with fluorescence quantum yields varying from 1 to 9 %. Monomers exhibited aggregation induced emission enhancement. Pholuminescence quantum yields of their solid samples were found to be higher than those of dilute solutions. Polymers exhibited higher thermal stability, in respect to the corresponding monomers, with 5% weigh loss temperatures reaching 411 °C.
9‐substituted carbazoles were widely used units in materials science, and their oxidative reactions have been utilizing for polymer synthesis and characterizations. Though the oxidative mechanism of carbazoles was recognized very early for a few decades, the structural definition has been remaining difficult because their polymers are generally insoluble with incomplete characterizations and unknown dependence of electrochemical potentials. The oxidative reactions of 9‐substituted carbazoles should be carefully considered under the specific oxidative conditions, otherwise, the structure definitions could be wrong because IR and NMR spectra used previously cannot quantitatively analyze 3,3'‐coupling and 6,6'‐coupling of carbazoles. In this review, we would present our best understanding on C(3)‐C(3') and C(6)‐C(6') oxidative couplings of 9‐substituend carbazoles that what can be benefit from these oxidative reactions from the view of electrochemical synthesis, film engineering, and polymer synthesis and processes.
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Acid induced step-growth polymerizations of bis(p-methoxybenzyl) carbonate (pMBC), bis(m-methoxybenzyl) carbonate (mMBC) and difurfuryl carbonate (DFC) have been performed to produce resin-foams, because controlled release of carbon dioxide takes place during polymerization of those organic carbonates. The monomers are polymerized in bulk using p-toluene sulfonic acid (pTS) as a catalyst. The volume development of the foams is assisted by use of an appropriate surfactant and the crosslinking agent 1,3,5-trioxane as co-components. A portion of carbon dioxide release is a function of the carbenium stability of the reactive intermediate derived from the monomer; DFC > pMBC ≫ mMBC. Resins derived from mMBC can be post-treated to release carbon dioxide after polymerization. The molecular structures of the resulting materials are investigated by solid state ¹³C-NMR spectroscopy and IR spectroscopy. Scanning electron microscopy was used to study foam morphology. The carbon dioxide release was monitored with TG-MS analysis. Finally, the polymer foams have been converted into carbon foams and investigated by means of mercury porosimetry.
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Quasiliving cationic polymerization of styrene was obtained in the system 2-phenyl-2-propano-/AlCl3OBu2/Bu2O in a mixture of 1,2-dichloroethane and n-hexane (55:45 viv) at -15 C. The molecular weights of the polymers (Mn) increased in direct proportion to the monomer conversion. However, the experimental Mns are essentially higher than theoretical ones, indicating that slow initiation relative to propagation takes place. The molecular weight distributions were broad (Mw/Mn2.5), probably due to the slow initiation and slow exchange between reversibly terminated and propagating species.
The simultaneous chain-growth and step-growth polymerization of a monomer is of great interest and importance because it can produce unique macromolecules which are difficult to prepare by other means. However, such a transformation is usually difficult to achieve in one polymerization system because chain-growth polymerization and step-growth polymerization proceed by different reaction mechanisms. Reported here is the simultaneous chain-growth and step-growth polymerization of para- and meta-methoxystyrenes catalyzed by half-sandwich rare-earth alkyl complexes, and the step-growth polymerization proceeds by the C-H polyaddition of anisyl units to vinyl groups. This unprecedented transformation affords a new family of macromolecules containing unique alternating anisole-ethylene sequences. In contrast to para- and meta-methoxystyrenes, ortho-methoxystyrene exclusively undergo syndiospecific, living chain-growth polymerization by continuous C=C bond insertion to give perfect syndiotactic poly(ortho-methoxystyrene) with high molecular weight and narrow polydispersity (rrrr >99 %, Mn up to 280 kg mol(-1) , Mw /Mn <1.10).
The C−H polyaddition of dimethoxyarenes such as 1,4-dimethoxybenzene and 4,4’-dimethoxybiphenyl to unconjugat-ed dienes such as norbornadiene and 1,4-divinylbenzene has been achieved for the first time by using cationic half-sandwich rare earth alkyl catalysts. This protocol afforded novel polymer materials consisting of dimethoxyarene moieties and non-polar hydrocarbon structure motifs (cyclic, linear and aromatic) in perfectly alternating sequences which are otherwise difficult to make. The reaction proceeded via C=C double bond insertion into a C−H bond ortho to each of the two methoxy groups in a step-growth polymerization fashion.
Conference Paper
Polystyrenes with 2-chloro-2-phenylethyl chain end (PSt-Cl) prepared by quasiliving atom transfer radical polymerization (ATRP) are useful intermediates for the synthesis of a variety of well-defined macromolecular architectures. The preparation of star-shaped polystyrenes by quasiliving ATRP of divinylbenzene initiated by PSt-Cl and hyperbranched polystyrene by self-grafting of PSt-Cl mediated with TiCl, is carried out in the course of our studies. Allyl-terminated macromonomers were also prepared by reacting PSt-Cl with allyltrimethylsilane in the presence of TiCl4. This PSt-allyl was copolymerized with propylene by metallocene catalysts yielding novel poly(propylene-g-styrene) (PP-g-PSt) graft copolymers.
Unique, highly branched polyisobutylenes (PIB) were prepared via quasiliving carbocationic copolymerization of isobutylene and styrene (St) monomers. The junction points were formed by Friedel-Crafts self alkylation of PSt segments by the carbocationic chain ends. First, linear PIB was prepared with reactive chain ends. This was reacted with St monomer to form PIB-b-PSt AB, and PSt-b-PIB-b-PSt ABA type triblock copolymers with reactive carbocationic chain ends. The terminal carbonations react with the phenyl group of the polystyrene end-segments of the block copolymers leading to chain coupling, and thus PIB star polymers in the case of AB and hyperbranched PIB from ABA block copolymers. The resulting branched polymers were characterized and the branch formation was confirmed by gel permeation chromatography (GPC) and proton nuclear magnetic resonance spectroscopy (1H NMR).
The cationic polymerization and copolymerization of several vinyl aromatic monomers including 9-vinyl anthracene, vinyl naphthalenes, and 4-vinyl biphenyl have been studied. The experimental reactivities are in agreement with those calculated by quantum chemistry methods. The isomerization of the carbocation of 9-vinyl anthracene has been studied at various polymerization temperatures and it has been shown that its extent depends on this parameter. The 1-vinyl-4-methoxy naphthalene does not copolymerize with styrene; moreover, styrene does not homopolymerize in the presence of this monomer.
Conventional condensation polymerization proceeds in a step-growth polymerization manner, in which the generated polymers possess a broad molecular weight distribution, and control over molecular weight and polymer end groups is difficult. However, the mechanism of condensation polymerization of some monomers has been converted from step-growth to chain-growth by means of activation of the polymer end group, either due to the difference in substituent effects between the monomer and the polymer, or due to successive intramolecular transfer of catalyst to the polymer end. In this article, we review recent developments in chain-growth condensation polymerization (CGCP) in these two areas. The former approach has yielded many architectures containing aromatic polyamides and aromatic polyethers, with unique properties. In the latter case, the mechanism, catalysts, and initiators of Ni- and Pd-catalyzed coupling polymerizations leading to poly(alkylthiophene)s and poly(p-phenylene)s have been extensively investigated. Other well-defined π-conjugated polymers, such as polyfluorenes, n-type polymers, and alternating aryl polymers, have also been synthesized by means of catalyst-transfer condensation polymerization. Many π-conjugated polymer architectures prepared by utilizing catalyst-transfer condensation polymerization are not covered in this article.
A series of brush copolymers bearing N-phenylcarbazole (PK) and 2-biphenyl-5-(4-ethoxyphenyl)-1,3,4-oxadiazole (BEOXD) moieties in various compositions were studied in detail, in particular their electrical memory characteristics, optical and electrical properties, morphological structures, and interfaces. Nanoscale thin films of the brush copolymers in devices were found to exhibit excellent unipolar electrical memory versatility, which can easily be tuned by tailoring the chemical composition and by changing the film thickness. Moreover, the molecular orbitals and band gap can be tuned by changing the chemical composition. The novel memory characteristics of these copolymers originate primarily from the cooperative roles of the ambipolar PK and BEOXD moieties, which have different charge trapping and stabilization properties. The electrical memory behaviors were found to occur via favorable hole injection from the electrode and to be governed by trap-limited space-charge limited conduction combined with ohmic conduction and local filament formation. Overall, the brush copolymers are very suitable active materials for the low-cost mass production of high performance, polarity-free digital memory devices that can be operated with very low power consumption, high ON/OFF current ratios, and high stability.
Transfer and termination constants have been determined for the cationic polymerization of 1- and 2-vinyl naphthalenes and 3-vinyl phenanthrene. They have been compared with the values obtained for styrene under the same experimental conditions. Experimental values are in good agreement with theoretical determinations.
A complete and unambiguous assignment of the proton and carbon-13 spectra of poly(N-vinylcarbazole) using a number of modern gradient two-dimensional nuclear magnetic resonance (NMR) spectra was conducted at 11.74 T magnetic field. The gradients considerably improved the 2D NMR experiments by: (a) suppressing the unwanted magnetization, thus avoiding add/subtract errors in phase-cycling techniques; (b) shortening the measuring time leading to a better signal-to-noise ratio; and (c) yielding pure absorption spectra resulting in a better resolution of signals in crowded spectral regions.
The authors have synthesized a series of new carbazole-containing polyacrylates with a different spacer in the side chains. The relationship between the structure and the electrical properties has been investigated by two kinds of photoinduced discharge measurements. It was found that some of the polymers have greater hole mobility than PVK. This communication describes the synthesis procedure and the result of measurements showing the interesting effect of the spacer length on photoinduced discharge characteristics.
The functional polymer containing carbazole unit, [(poly(9-(4-vinylbenzyl)-9H-carbazole) (PVBK)], was successfully prepared via nitroxide-mediated living free-radical polymerization of 9-(4-vinylbenzyl)-9H-carbazole (VBK). The controlled features of the polymerization were confirmed by the linear increase in the molecular weight with the monomer conversion while keeping the relative narrow molecular weight distribution (Mw/Mn⩽1.51), and successful chain extension with styrene. The resulting polymer absorbed light in the 305–355nm range and exhibited fluorescent emission at 350nm. The fluorescent intensity of the polymer was lower than that of monomer and was affected by the properties of the different solvents, which decreased in the following order: DMF>THF>CHCl3 at the same concentration of carbazole units. The fluorescence intensity of the polymer was apparently influenced by chromophore concentration, and the maximum value was obtained when the carbazole unit concentration was around 8×10−5mol/L. Moreover, it was shown that the strong fluorescence of PVBK can be quenched by methyl acrylate (MA).
The living polymerization of styrene was achieved with the 2,4,4-trimethyl-2-pentyl chloride/TiCl4/MeCl:methylcyclohexane 40:60 v:v/−80°C polymerization system in the presence of di-tert-butylpyridine in concentrations comparable to the concentration of protic impurities. It was determined that the living nature of the polymerization is not due to carbocation stabilization. The polymerization is second order in TiCl4. Side reactions, namely polymerization by direct initiation and intermolecular alkylation, are operational, and a careful selection of experimental conditions is necessary to minimize their effect and obtain apparently living behavior. Polymerization by direct initiation can be minimized by increasing the initiator concentration, and intermolecular alkylation can be reduced by quenching the polymerization system when the conversion reaches close to 100%.
The methacrylic copolymers incorporated with electroactive groups such as thiophene, carbazole, and fluorene moieties on the side chain were synthesized. Our approach consists of incorporating multiple electroactive functional groups onto a polymer backbone that can be used to develop functional materials. All copolymers were characterized, and a systematic structure−property relationship study was established. The structure and morphology of supramolecular self-assembly of copolymers were studied using transmission electron microscopy, wide-angle X-ray diffraction, and atomic force microscopy. Polymers can be patterned using an atomic force microscope, and nanosized lines or dots can be drawn on the polymer films. Polymer nanotubes obtained through self-assembly can be further stabilized by electropolymerization of the side chains.
Five new carbazole-containing polymers have been synthesized. With poly(N-vinylcarbazole) these form two series in which (a) the nitrogen atom of the chromophore is attached to the polymer backbone with an increasingly flexible linking moiety, PNVK, I, -II, -III, and (b) a series in which the backbone is attached to the 9-, 2- and 3-ring positions, I, IV, V. The molecular weights of the polymers have been characterized by membrane osmometry and gel permeation chromatography. These polymers are susceptible to photochemical degradation which causes both scission of the chain backbone and diminution of carbazole chromophore fluorescence. Sensitive viscosity measurements made on samples undergoing this main-chain scission have been used to obtain the intrinsic viscosity-molecular weight K, a values of the resulting fragments. Comparison of the absorption and emission spectra shows that appreciable excimer emission occurs only in the case of poly(N-vinylcarbazole) (PNVK) and poly[2-(9-ethyl)carbazolylmethyl methacrylate] (IV). Excimer emission from the latter is weakest in polar fluid solvents and strongest in a rigid glassy matrix. Luminescence decay measurements in the presence and absence of anthracene quencher suggest that down-chain energy migration is virtually absent in the sterically unhindered polymers I, II, III, and V, and this is confirmed by steady state analysis of collisional quenching. Collisional quenching of monomer excitation from IV indicates that the excitation is effectively immobilized in the region of not more than three neighboring chromophores. These results show that the flexibility of the linking group does not assist the adoption of the parallel overlap interchromophore geometry necessary (to different extents) for both excimer formation and resonance energy migration. However, geometrical constraints imposed by chain linking to the chromophore 2 position (polymer IV) do favor (relative to attachments at the 9- and 3-ring position) the adoption of a ground state interchromophore geometry permitting excimer formation with relatively minor conformational readjustment or monomer excitation energy migration.
A new unsymmetrical AB* inimer, p-(2-bromoisobutyloylmethyl)styrene (BiBMS), was applied to the atom transfer radical polymerization (ATRP) to prepare a family of polymers with the topologies ranging from linear to branched. The catalyst system was Cu/CuBr2 coupled with 2,2′-bipyridine (Bipy) or N,N-bis(2-pyridylmethyl)octylamine (BPMOA) as a ligand in toluene or anisole at different temperatures, which ensured a very low catalyst (CuBr) concentration throughout the polymerization by a slow reduction process. First, BiBMS was polymerized in anisole at 0 °C using Cu/CuBr2/BPMOA as a catalyst system; at this temperature, the initiating activity of the formed A* was frozen and the polymerization was a step-growth polymerization, resulting in the formation of a linear polymer (LP1) whose main chain was linked by ester bonds. Second, BiBMS was polymerized in toluene at 20 °C using Cu/CuBr2/Bipy as a catalyst system. Under this condition, initiation from the B* of BiBMS was slow, followed by a fast radical polymerization of the BiBMS vinyl bonds and a slow deactivation, thereby affording another linear polymer (LP2), the structure of which was the same as that obtained by common free radical polymerization of BiBMS except the end groups. The conversion of BiBMS was controlled to be moderate to suppress the possible initiation from the pendant B* along the polymer main chain. Third, BiBMS was polymerized in anisole at various temperatures using Cu/CuBr2/Bipy as a catalyst system; three branched polymers (BP1, BP2, BP3) with different degree of branching (DB) were obtained, the DB of which could be easily adjusted by changing temperature (BP1, DB = 0.12 at 20 °C; BP2, DB = 0.26 at 40 °C; BP3, DB = 0.37 at 60 °C).
Isotactic poly(2-N-carbazolylethyl acrylate) was synthesized by using ethylmagnesium chloride-benzalacetophenone as catalyst. The polymer showed crystallinity by X-ray diffraction. The temperature and electrical field dependence of hole drift mobility was measured by the time-of-flight method. The room-temperature mobility (1.7 × 10-5 cm2/(V·s) at 2 × 105 V/cm) was considerably higher than that of both atactic polyacrylate and poly(N-vinylcarbazole) and is one of the highest mobility values reported for a photoconductive polymer. The origin of this result is discussed in a model for hopping transport between localized sites.
Living cationic polymerization of N-vinylcarbazole (NVC) was achieved with hydrogen iodide (HI) as an initiator either at -40°C in toluene or at -78°C in methylene chloride containing a catalytic amount of tetra-n-butylammonium iodide as a common ion salt. The number-average molecular weight of the polymers obtained under these conditions was directly proportional to NVC conversion or to the NVC/HI feed ratio and in good agreement with the calculated values assuming that one HI molecule forms one living chain. The polymers exhibited a narrow molecular weight distribution with a M̄w/M̄n ratio from 1.2 to 1.3. The corresponding polymerizations by iodine or a mixture of HI and iodine (HI/I2 initiator) were not living, yielding polymers with a broader molecular weight distribution. The scope of living cationic polymerization is also discussed in terms of the stability of the propagating carbocation and the nucleophilicity of the counteranion.
To establish the optimum conditions for obtaining high molecular weight polyacetals by the self-polyaddition of vinyl ethers with a hydroxyl group, we performed the polymerization of 4-hydroxybutyl vinyl ether (CH2CHOCH2CH2CH2CH2OH) with various acidic catalysts [p-toluene sulfonic acid monohydrate, p-toluene sulfonic anhydride (TSAA), pyridinium p-toluene sulfonate, HCl, and BF3OEt2] in different solvents (tetrahydrofuran and toluene) at 0 °C. All the polymerizations proceeded exclusively via the polyaddition mechanism to give polyacetals of the structure [CH(CH3)OCH2CH2CH2CH2O]n quantitatively. The reaction with TSAA in tetrahydrofuran led to the highest molecular weight polymers (number-average molecular weight = 110,000, weight-average molecular weight/number-average molecular weight = 1.59). 2-Hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, cyclohexane dimethanol monovinyl ether, and tricyclodecane dimethanol monovinyl ether were also employed as monomers, and polyacetals with various main-chain structures were obtained. This structural variety of the main chain changed the glass-transition temperature of the polyacetals from approximately −70 °C to room temperature. These polyacetals were thermally stable but exhibited smooth degradation with a treatment of aqueous acid to give the corresponding diol compounds in quantitative yields. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4053–4064, 2002
A spectroscopic and conductimetric study of the cationic polymerization of 2-vinylfuran (1) and 2-methyl-5-venylfuran (2) showed the existence of an important side reaction originating from a hydride-ion shift from an unsaturated polymer molecule to an active species. The resulting allylic carbocation, in equilibrium with a doubly unsaturated polymer molecule, can react further and the repetition of the mechanism on progressively more conjugated species leads to the formation of a series of highly charge-delocalized carbenium ions absorbing throughout the visible region of the spectrum (and giving high electrical conductivity) and of neutral polyconjugated polymer molecules. Since the hydride-ion abstraction occurs from the tertiary carbon atom of the vinylic chain, vinylidene polymers of monomers such as 2-isopropenylfuran (3) and 2-isopropenyl-5-methylfuran (4) are not susceptible to it. Indeed, their cationic polymerization proceeds without colour formation and conductivity increase.
Friedel-Crafts self-grafting of polystyrene (PSt) under quasiliving carbocationic polymerization was utilized to develop a new rapid one-pot method for the preparation of star-shaped polyisobutylene (PIB). First, the polymerization of isobutylene led to PIB with predetermined molecular weight ((M) over bar (n) = 2 000) and narrow molecular weight distribution ((M) over bar (w)/($) over bar (n) = 1.03). Then addition of relatively small amount of styrene after isobutylene consumption yielded PIB-PSt diblocks. Multiple alkylation of the resulting PSt segments by the polystyryl cations led to hyperbranched PSt cores coupling PIB chains to form a star polymer in short reaction time (within an hour) compared to reported methods. The formation of star polymers by this self-grafting mechanism was proved by gel permeation chromatography equipped with online viscosimeter and (1)H NMR spectroscopy.
Palladium-catalyzed polymer reactions of poly(p-bromostyrene) with carbazole and related heteroarenes containing an N-H bond (phenothiazine, phenoxazine, and iminostilbene) afforded polystyrene derivatives with heteroaromatic groups in the side chains with high conversions and recoveries. Characterization and chemical oxidation properties of the polymers were also examined. Pd-catalyzed N-arylation was applied to the preparation of new polystyrene derivatives containing several functional heteroaromatic substituents in the side chains.
For the application of conjugated polymers in photonics, we synthesized styrene derivatives containing carbazole, 4-(9-carbazolyl)methylstyrene (CMS). The anionic polymerization of CMS was carried out in THF at either −45 or −78°C. It takes around 24 h to get PCMS with 100% yield in THF at −78°C, due to the crystallization of CMS at this temperature. However, the yield exceeded 90% within 10 min. On the other hand, the yield of CMS at −45°C levels up at about 67%, after 30 min. The molecular weight distributions of PCMS obtained at −45°C are broader than those of PCMS synthesized at −78°C. This may be due to the side reactions, such as methylene proton abstraction at the propagating end groups at higher polymerization temperature of −45°C. The glass transition temperature of the polymer measured by DSC was observed in the range of 159–173°C.
The synthesis and properties of carbazole-containing polymers are reviewed with 451 references. After a short discussion of the basic principles of photoconductivity the following classes of organic carbazole-containing polymers are reviewed: polymers with pendant carbazolyl groups, polymers containing electronically isolated carbazole moieties in the main chain, polymers with π-conjugated main chain, and σ-conjugated polymers as well as carbazole-containing molecular glasses. The present and potential applications of these materials, in electrophotographic materials, light-emitting diodes, photorefractive materials and photovoltaic devices are briefly discussed.
Living polymerization has been at the forefront of polymer science and engineering in recent years. The term “living” is used to distinquish polymerizations in which chain breaking processes such as termination and transfer reactions are absent. Living polymerization provides for the control over the molecular weight (MW) and molecular weight distribution (MWD) of the polymer sample. This paper will give a general overview about living carbocationic polymerization, followed by a review of recent developments with emphasis on resonance-stabilized monomers and the use of the living concept for the design and synthesis of new polymeric structures.
All polymerization reactions are categorized into two large different families, chain- and step-growth polymerizations, which are typically incompatible. Here, we report the simultaneous chain- and step-growth polymerization via the metal-catalyzed radical copolymerization of conjugated vinyl monomers and designed monomers possessing unconjugated C horizontal lineC and active C-Cl bonds. Especially, almost ideal linear random copolymers containing both vinyl polymer and polyester units in a single polymer chain were formed by the CuCl/1,1,4,7,10,10-hexamethyltriethylenetetramine- or RuCp*Cl(PPh(3))(2)-catalyzed copolymerization of methyl acrylate (MA) for the chain-growth polymerization and 3-butenyl 2-chloropropionate (1) for the step-growth polymerization. In contrast, other transition metal catalysts, such as CuCl with tris[2-(dimethylamino)ethyl]amine or N,N,N',N'',N''-pentamethyldiethylenetriamine and FeCl(2)/PnBu(3), resulted in branched structures via the concomitant chain-growth copolymerization of 1 with MA. The polymerization mechanism was studied in detail by NMR and MALDI-TOF-MS analyses of the polymerizations as well as the model reactions. Furthermore, a series of copolymers changing from random to multiblock polymer structures were obtained by varying the feed ratios of the two monomers. These copolymers can be easily degraded into lower molecular weight oligomers or polymers via methanolysis of the ester-linkages in the main chain using sodium carbonate.
Polymer latexes are easily prepared on a multimillion ton scale in industry using free radical initiated emulsion and suspension polymerizations in water, a cheap, nonviscous, heat-controlling, and environmentally benign solvent. Until recently, researchers had done little investigation into ionic polymerization because even a small amount of water would easily deactivate the conventional catalysts used in these processes. In the last decade, however, cationic polymerization in aqueous media has emerged as a new and attractive method for controlling the polymerization reactions using mild experimental conditions.
Advances in living polymerization initiators, including the design and synthesis of a variety of new polymers, with a focus on the most recent developments, are reviewed. The fabrication of macromolecular aggregates that display various functions and properties will become increasingly important in the development of polymer synthesis. To accomplish this, it will be necessary to design and synthesize polymers in which the primary structure, including monomer sequences and stereoregularity, is precisely controlled. The importance of the choice of acid catalysts (activator) was shown in cationic polymerization of styrene and its derivatives. It was then known that molecular weight of product polymers became higher when a polar solvent was used. Successful catalytic processes were achieved using metal triflates in the 1990s. Efficient acylation proceeded with a catalytic amount of triflates of Ti, 58 Hf, 59,60 Sc, 61,62 and lanthanides. The development of new polymerization catalyst systems that will serve as the basis for this will be indispensable.
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