An experimental and theoretical study of the carbazole to carbazole intramolecular energy transfer in N‐vinylcarbazole/vinyl tert‐butyl‐benzoate copolymers of different molar compositions

Fluorescence depolarization and quenching measurements of N‐vinyl carbazole/vinyl tert‐butyl‐benzoate copolymers in dilute solution of several fluid solvents and in a rigid poly(methyl methacrylate) matrix were performed to study the effect of copolymer composition on the intramolecular energy transfer (IET) between carbazole groups (Cz) along the polymer chain. IET efficiency, as the amount of Cz? Cz intramolecular excimer formation, monotonically increases with Cz content up to a number average sequence length of carbazole of ca 12 (Cz molar content ≥ 90%). After this value, IET efficiency remains almost constant. Molecular dynamics simulations on isotactic and syndiotactic copolymer fragments of several monomer compositions were used for obtaining different parameters related to the efficiency for the IET process between Cz units along the polymer chain. Copyright © 2011 Society of Chemical Industry     

Photophysical studies of copolymers of N‐vinylcarbazole

The absorption, fluorescence excitation and emission spectroscopy, and time‐dependent spectrofluorimetry have been used to study the photophysics of copolymers of N‐vinylcarbazole with different monomers like vinyl acetate, methyl acrylate, methyl methacrylate, butyl acrylate, and butyl methacrylate in dichloromethane. In all the copolymers and at different N‐vinylcarbazole content, the absorption spectra reflect only the monomer carbazole units. The two kinds of excited monomer species of N‐vinylcarbazole are present in S₁ state. Short‐lived (～3 ns) excited monomer decays forming low energy excimer obtained by the complete overlap of the excited carbazole monomer. The long‐lived excited monomer (～8 ns) decays to ground state without formation of any excimer. The high energy excimer is relatively short‐lived and is formed by the partial overlap of the carbazole units. The presence of bulky group in the copolymer chain hinders the formation of excimers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 372–380, 2006     

N,N-dicyclohexylcarbodiimide assisted synthesis and characterization of poly(vinyl alcohol-co-vinyl levulinate)

Poly(vinyl alcohol-co-vinyl levulinate) was synthesized by N,N-dicyclohexylcarbodiimide assisted esterification of poly(vinyl alcohol) with free levulinic acid using 4-pyrrolidino pyridine as a catalyst in N,N-dimethyl acetamide/lithium chloride solvent system in order to optimize the reaction condition. The vinyl levulinate content in the copolymer was attained up to 0.95. The ¹³C NMR dyad compositional analysis indicated the block character of the copolymer was 0.92, suggesting almost random poly(vinyl alcohol-co-vinyl levulinate) was formed. Glass transition temperature dependence on vinyl levulinate content of the copolymers fitted better into Gordon-Taylor equation as compared with Fox equation and the glass transition temperature of poly(vinyl levulinate) was given as 2.3 °C by the least regression method.     

Synthesis and characterization of a novel bipolar Alq<Subscript>3</Subscript>-based copolymer containing carbazole and phenothiazine groups

A novel bipolar copolymer combining hole-transporting units, electron-transporting units and light-emitting units (Alq₃) had been synthesized via free radical copolymerization of N-vinylcarbazole and Alq₃ monomer containing phenothiazine group. The chemical structure and composition of the copolymer were characterized by ¹H NMR, ¹³C NMR, FT-IR spectroscopy, and elemental analysis as well as gel permeation chromatography (GPC). The number-average molecular weight (M _n) and polydispersity of these copolymers with different Alq₃ contents were around 20000 and 1.4, respectively. The DSC and TGA measurements indicated that the copolymer has excellent thermal stability and high glass transition temperatures (T _g). The optical properties of the copolymer in solution and solid state were investigated by UV-vis and photoluminescence (PL) spectra. Additionally, the effects of Alq₃ content, concentration, excitation wavelength and solvent on PL spectra were studied and the results indicated that there exists efficient energy transfer in the process of photoluminescence. The introduction of carbazole and phenothiazine, as hole-transporting groups and energy transfer stages, provides an effective way to improve carries transporting property and energy transfer efficiency, consequently improving luminescence properties of Alq₃-based copolymer.     

Radical copolymerization of N-vinylcarbazole and p-bromostyrene: determination of monomer reactivity ratios by SEC-multidetection

N-Vinylcarbazole (A)/p-bromostyrene (B) copolymers were prepared by radical copolymerization. Size exclusion chromatography (SEC) equipped with a refractometer and UV-vis spectrophotometer was found to be a very convenient technique to follow copolymerizations and to determine monomer conversions, copolymer composition, average molecular weights, polydispersity indexes versus time. The monomer reactivity ratios r_A (N-vinylcarbazole) and r_B (p-bromostyrene) were determined by using the Finemann-Ross (FR), the inverted Finemann-Ross (IFR), the Kelen-Tüdos (KT), and the fitting curve graphical methods. The four methods were in good agreement and led to very different values for r_A (0.55) and r_B (12.3) which induces a preference for the incorporation of B in the copolymer structure. Eventually, with these results the influence of initial feed on the microstructure of the copolymer has been predicted.     

Novel carbazole phenoxy-based methacrylates to produce high-refractive index polymers

A novel, high-refractive index homopolymer was produced by incorporating carbazole and phenol into the methacrylate monomer structure. The reaction of phenol with 9-(2,3-epoxypropyl)-carbazole, followed by the reaction of the carbazole phenoxy-based intermediate with methacryloyl chloride or methacrylic anhydride, and recrystallization from methanol, produced a good yield of highly pure carbazole phenoxy functionalized methacrylate monomer. Subsequent free radical polymerization or UV photopolymerization of the functionalized methacrylate monomer, in addition to copolymerizations with methyl methacrylate, provided for high-refractive index materials well suited for lightweight optical applications. Unlike N-vinyl carbazole, the novel carbazole phenoxy-based methacrylate readily copolymerized with methyl methacrylate. Statistical copolymers of carbazole based methacrylates with methyl methacrylate were produced by free radical solution polymerization in DMAC or by photopolymerization in DMF. The carbazole phenoxy-based methacrylate monomer was characterized for molecular weight using gel permeation chromatography (GPC), for melting point and glass transition temperature using differential scanning calorimetry (DSC), for decomposition using thermal gravimetric analysis (TGA), and for chemical composition by one- and two-dimensional ¹H nuclear magnetic resonance (NMR) spectroscopy and by elemental analysis. The AIBN initiated carbazole phenoxy-based methacrylate polymerization was followed using in situ FTIR, which showed the reaction to be complete within 40 min in DMAC at 90 °C. Refractive indices of the carbazole based methacrylate homopolymers and copolymers ranged from 1.52 to 1.63. PhotoDSC was used to determine the heat of polymerization (ΔH_p) for the carbazole phenoxy-based methacrylate (ΔH_p=−39.4 kJ/mol). The carbazole phenoxy-based methacrylate homopolymer had a surprisingly high onset of decomposition temperature (T_onset=316 °C). ¹³C NMR spectroscopy experiments and molecular modeling were used to explore the configuration of the polymerized carbazole phenoxy-based methacrylate. The lack of head-to-head linkages due to steric considerations reasonably explains the high thermal stability observed for the carbazole phenoxy-based methacrylate polymer.     

Conductivities of poly(N-vinyl carbazoles) containing cation-radicals

Partial oxidation of poly(N-vinyl carbazole) (PNVC) to produce crosslinked PNVC containing dimeric carbazylium cation radicals is shown to produce material with significant semiconductivity (σ) up to ～10^?5ohm^?1cm^?1 at 293K. The synthesis of these materials (including partly ring-chlorinated analogues) is described and their semiconductivities and activation energies for conductance (E_a) examined as a function of cation-radical content. It is demonstrated that the extent of reaction essentially determines the semiconduction of these materials, provided homogeneous conditions are maintained. The starting molecular weight of the PNVC, and whether or not it is partly chlorinated, have minimal effect on σ.     

Synthesis,fluorescence emission spectra and chiroptical properties of copolymers of N-vinylcarbazole and optically active fumarates

Optically active (?)menthylethylfumarate (2) and (?)dimenthylfumarate (3) have been synthesised and free radically copolymerized with N-vinylcarbazole (1). Copolymers of (1) and (2) exhibit a strong tendency to alternation in agreement with earlier conclusions from studies of copolymerization of (1) with diethylfumarate. Surprisingly the much more hindered, but symmetrical fumarate, (3) yields copolymers which always have carbazole monomer contents in excess of the 1:1 alternating ratio. Chiroptical measurements indicate significant induced optical activity in the carbazole chromophores of all the copolymers obtained but, in accord with the predominance of alternating structures, there is no real evidence for any sequence-determined maximum in induced circular dichroism. Fluorescence emission spectra of all copolymer samples exhibit significant asymmetric broadening on the long wavelength (low energy) side of the normal carbazole monomeric emission. This broadening is exhibited even by poly (1-co-2) samples for which the monomer compositions strongly indicate alternating sequences and must, therefore, represent interaction between carbazole segments. Accordingly, and in contrast to widely held assumptions, it is concluded that excimer-like emission may be exhibited by alternating copolymers of N-vinylcarbazole. Further evidence for electronic interactions between non-nearest neighbour carbazole units is provided by u.v. absorption and ¹H-n.m.r. spectra of appropriate copolymers.     

Synthesis and photolytic properties of 1,5-di-N,N′-dialkylaminoanthraquinones containing acryloyl groups

Several l,5-di-N,N′-dialkyaminoanthraquinones containing acryloyl groups were synthesized and characterized by Fourier transform infrared (FTIR) and ¹H NMR spectroscopy. The photophysical and photoinduction properties of these anthraquinone derivatives were examined in solution, in combination with free radical producing agents such as hexa-aryl-bis-imidazoles (HABI). When UV–vis absorption and fluorescence spectroscopy were employed to investigate the photophysical process, results showed that the photobleaching rate of N-alkylaminoanthraquinones containing an acrylate group and HABI was much faster than the acrylate group-free N-alkylaminoanthraquinone/HABI combination. N-alkylaminoanthraquinone induced polymerization of 2-phenoxyethyl acrylate (POEA)/N-vinyl carbazole (NVC)/cellulose acetate butyrate (CAB) mixtures was studied using real-time infrared spectroscopy (RTIR). It was found that the rate of polymerization was faster if the acryloyl groups were connected to the N,N′-dialkylaminoanthraquinone structure and that 1,5-di-N,N′-dialkylaminoanthraquinone containing acryloyl groups was more sensitive to visible light system.     

Optically active vinyl polymers containing fluorescent groups: 5. Fluorescence properties of poly(9-vinyl carbazole) and optically active polymers containing carbazole units

The optically active homopolymers polyl, polyll, and polylll and copolymers of 9-vinyl carbazole with (?)menthyl vinyl ether all exhibit fluorescence related to that of cationically and free radically prepared poly(9-vinyl carbazole). The fluorescence is interpreted for all polymers as arising from three components: monomeric carbazole emission, high energy excimer emission (termed dimer emission for convenience), and a more usual excimer emission arising from conformationally eclipsed carbazole units. Correlations of fluorescence and fluorescence quenching by maleic anhydride, with chiroptical properties and copolymer compositions, suggest that excimer formation is a consequence of rotational freedom within or between isotactic carbazole sequences in the polymer backbones. The isotactic copolymers of (?)menthyl vinyl ether and 9-vinyl carbazole exhibit a relatively strong excimer fluorescence even though mean sequence lengths of carbazole units are comparatively short.     

Influence of electrochemically prepared poly(pyrrole-co-N-methyl pyrrole) and poly(pyrrole)/poly(N-methyl pyrrole) composites on corrosion behavior of copper in acidic medium

Poly(pyrrole-co-N-methyl pyrrole) copolymer and poly(pyrrole)/poly(N-methyl pyrrole) bilayer composites were electrochemically synthesized on copper by cyclic voltammetry from aqueous solution of 0.3 M oxalic acid and 0.1 M monomer. Synthesis of copolymers were performed with different monomer feed ratios (pyrrole:N-methyl pyrrole, 8:2, 6:4, 5:5, 4:6 and 2:8) and in order to determine the copolymer, which has the best corrosion performance, anodic polarization was applied to copolymer coated samples. It was found that the performance of coatings was strongly dependent to the monomer feed ratio and the copolymer synthesized with 8:2 concentration ratio showed the most protective property compared to others. Bilayer of poly(pyrrole)/poly(N-methyl pyrrole) was also synthesized to compare the anticorrosive properties. Polymer films were characterized by ATR-FTIR spectroscopy and SEM techniques. Corrosion behavior of polymer composites was investigated in 0.1 M H₂SO₄ solution by anodic polarization and electrochemical impedance spectroscopy. Different approaches such as phase angle at high frequency and areas under Bode plots were used to evaluate corrosion performances of the coatings. Copolymer and bilayer coatings were found to have higher protection effect than single polypyrrole coatings. Moreover, bilayer coating exhibited better protection efficiency than copolymer coating against corrosion of copper when the obtained results were compared.     

Radical copolymerization of sulphur dioxide and styrene: 4. Intramolecular excimer formation in poly(styrene sulphone)s

Intramolecular excimer formation in poly(styrene sulphone)s with various compositions has been investigated based on the characteristic monomer sequence distributions which were determined experimentally. The fluorescence spectra of the poly(styrene sulphone)s show two emission bands at 285 nm and 330 nm as for polystyrene, corresponding to the monomer and the excimer bands, respectively. The ratio of the excimer to the monomer emission intensities (I_e/I_m) is linearly correlated with the mole fraction of styrene. This observation is a consequence of the characteristic sequence distributions in poly(styrene sulphone)s. containing a very small fraction of SMS units (S = SO₂; M = styrene). The efficiency of excimer formation in poly(styrene sulphone)s with regular styrene sequences, e.g. dyad sequence only, was calculated from the sequence distribution and empirical I_e/I_m. It is concluded that the excimer formation in poly(styrene sulphone)s is very efficient. Energy migration along the copolymer chain was also demonstrated by measuring the degree of polarization as a function of copolymer composition. The efficient excimer formation and the depolarization in poly(styrene sulphone)s suggest that the SO₂ unit in poly(styrene sulphone)s does not act as a barrier or trap to energy migration unlike the methyl methacrylate unit.     

Adsorption of N,N′-dimethylthiourea at a mercury/aqueous solution of NaClO4 interface; dependence on the supporting electrolyte concentration

Adsorption of N,N′-dimethylthiourea (DMTU) on mercury electrode from 0.1, 1 and 5 M NaClO₄ was studied as the function of electrode charge density and adsorbate bulk concentration. In the study, the experimental data obtained from the measurements of differential capacity of double layer were used, the measurements of zero charge potential and surface tension at the zero charge potential. In each system studied the values of the relative surface excess increase with an increase of the concentration of N,N′-dimethylthiourea and NaClO₄. The adsorption parameters were obtained from the Frumkin, virial and modified Flory-Huggins isotherms. It was found that the values of free adsorption energy, interactions constants and integral capacity depends on the supporting electrolyte concentration. The strength of the surface bond formed between N,N′-dimethylthiourea and the electrode surface and the influence of water present on the electrode surface in the obtained results of calculations were discussed.     

Dispersion polymerization in supercritical carbon dioxide using comb-like fluorinated polymer surfactants having different backbone structures

Comb-like fluorinated polymers with different backbone structures, poly(heptadecafluorodecyl acrylate) (PA-R_f), poly[oxy[(2-perfluorooctylethylene)thiomethyl]ethylene] (PEO-R_f), and poly[p-[[(perfluorooctylethylene)thio]methyl]styrene] (PS-R_f), were used as surfactants in dispersion polymerization to examine the effect of backbone structure on the formation of polymer particles. Dispersion polymerization of monomers with different polarities using these comb-like fluorinated polymer surfactants in CO₂ showed that PEO-R_f containing a polar oxyethylene backbone was an effective surfactant for the dispersion polymerization of a polar monomer, such as N-vinyl-2-pyrrolidone, whereas PA-R_f was effective for less polar monomers, such as methyl methacrylate and N-vinyl caprolactam.     

Atom transfer radical polymerizations of styrene and butadiene as well as their copolymerization initiated by benzyl chloride / 1-octanol-substituted MoCl<Subscript>5</Subscript> / PPh<Subscript>3</Subscript>

A novel initiator system, benzyl chloride / 1-octanol-substituted MoCl₅ / triphenyl phosphine (PPh₃), was applied to the atom transfer radical polymerizations (ATRP) of both butadiene and styrene as well as their copolymerization. Characterization revealed a linear increase in the number average molecular weight with monomer conversion and rather wide molecular weight distributions of the polymerization products. Increasing the polymerization temperature promoted the reaction rate and narrowed the polydispersity index of polystyrene proportionally. The polymerization rule for butadiene catalyzed by the above Mo-based system catalyst is similar to that of styrene. The microstructure of the butadiene was investigated by IR and ¹H NMR. IR, ¹³C NMR and DSC measurements showed that the butadiene and styrene copolymer was a random copolymer. The chlorine atom at the ω end group of the polymer and the change in the valence state of molybdenum, as explored by UV-Vis spectroscopy, revealed that the polymerization proceeded in a manner closest to the mechanism of ATRP.     

High vinyl high styrene solution SBR

Objective: the objective of this study is to prepare high vinyl copolymers containing various levels of styrene and butadiene, and also to prepare random butadiene in high styrene content styrene-butadiene copolymers (SBR) while controlling the styrene block length. These materials could be used in race tread applications. Summary: This reports presents the synthesis and characterization of random, high vinyl copolymers containing styrene and butadiene (SBR's). The styrene content of these SBR's ranged from 10 to 80%. These SBR's were synthesized via anionic polymerization initiated by a catalyst system with a ratio of 1/0.4/5 of n-butyllithium (n-BuLi) to sodium dodecylbenzene sulfonate (SDBS) to N,N,N′,N′-tetramethylethylenediamine (TMEDA). Kinetic data as well as NMR and ozonolysis techniques confirm that random SBR copolymers are being produced for low styrene content polymers. The glass transition temperature (T_g), increased dramatically as the styrene content was increased. The amount of vinyl based upon the polymer's total composition within the copolymer was found to decrease linearly as you increase the amount of styrene in the polymer. TGA results show that high styrene content polymers degrade at lower temperatures. The RPA confirms that as the styrene content increases, the elastic modulus decreases. As the frequency increased, the tan delta decreased for each polymer. Tan delta does not appear to be a function of styrene content. TEM results helped to describe polymer microstructure.     

Synthesis and characterization of a novel graft copolymer with poly(n-octylallene-co-styrene) backbone and poly(?-caprolactone) side chain

A novel graft copolymer consisting of poly(n-octylallene-co-styrene) (PALST) as backbone and poly(?-caprolactone) (PCL) as side chains was synthesized with the combination of coordination copolymerization of n-octylallene and styrene and the ring-opening polymerization (ROP) of ?-caprolactone. Poly(n-octylallene-co-styrene) (PALST) backbone was prepared from the copolymerization of n-octylallene and styrene with high yield by using the coordination catalyst system composed of bis[N,N-(3,5-di-tert-butylsalicylidene)anilinato]titanium(IV) dichloride (Ti(Salen)₂Cl₂) and tri-isobutyl aluminum(Al(i-Bu)₃). The molar ratio of each segment in the copolymer, and the molecular weight of the copolymer as well as the microstructure of the copolymer could be adjusted by varying the feeding ratio of both styrene and n-octylallene. The hydroxyl functionalized copolymer PALST-OH was prepared by the reaction of mercaptoethanol with the pendant double bond of PALST in the presence of radical initiator azobisisbutyronitrile (AIBN). The target graft copolymer [poly(n-octylallene-co-styrene)-g-polycaprolactone] (PALST-g-PCL) was synthesized through a grafting-from strategy via the ring-opening polymerization using PALST-OH as macroinitiator and Sn(Oct)₂ as catalyst. Structures of resulting copolymer were characterized by means of gel permeation chromatography (GPC) with multi-angle laser light scattering (MALLS), ¹³C NMR, ¹H NMR, DSC, polarized optical microscope (POM) and contact angle measurements.     

Controlled/living free-radical copolymerization of allyl glycidyl ether with methyl acrylate under Co γ-ray irradiation

An investigation on the copolymerization of allyl glycidyl ether (AGE), an epoxy-functional monomer, with methyl acrylate (MA) was performed in the presence of benzyl 1H-imidazole-1-carbodithioate (BICDT) under ⁶⁰Co γ-ray irradiation. The polymerizations revealed good characteristics of RAFT process. The content of AGE incorporation into the copolymer increased with higher monomer conversion and higher molar fraction of the AGE in the monomer feed. However, the polymerization could slow down when the fraction of AGE increased in the monomer feed, which might be attributed to the low activity of AGE. Taking advantage of RAFT process, functional block copolymer poly(AGE/MA)-block-poly(styrene) was prepared in the presence of poly(styrene) macroRAFT agent, and the copolymer was characterized by ¹H NMR spectra and GPC.     

Poly[(styrene-co-p-methylstyrene)-b-isobutylene-b-(styrene-co-p-methylstyrene)] triblock copolymers. 1. Synthesis and characterization

The synthesis of poly(isobutylene) (PIB)-based triblock copolymers having copolymer end blocks containing styrene and p-methylstyrene (pMSt) repeat units was investigated in an attempt to minimize chain-coupling reactions that occur at the 4-position on styrene repeat units during end block polymerization. Model end block copolymerizations using varying feed ratios of styrene and pMSt were conducted, and it was determined by ¹H NMR analysis that the addition of pMSt to the living chain end was favored slightly at low conversion. However, DSC revealed a single T_g that increased with increasing pMSt content verifying the absence of blockiness in the microstructure. Poly[(styrene-co-pMSt)-b-isobutylene-b-(styrene-co-pMSt)] triblock copolymers were synthesized using varying feed ratios of styrene and pMSt. The rate of end block propagation increased with increasing pMSt in the feed, and the end block copolymerizations initiated by PIB displayed longer reaction times and more curvature in their first order plots than did the model end block copolymerizations initiated by TMPCl. This effect was attributed to lower ionization equilibrium constant and higher degree of termination caused by the more non-polar local reaction medium provided by the PIB center blocks in block copolymerization. GPC analysis of the final BCPs revealed a decrease in a high molecular weight peak representing the chain-coupled product as the concentration of pMSt in the feed was increased.     

P2VP-b-PS-b-PI三嵌段共聚物的RAFT合成及表征

以S-十二烷基-S’-(α,α’-二甲基-α’’-乙酸)-三硫代碳酸酯(DDMAT)为链转移剂,通过可逆加成-断裂链转移自由基聚合(RAFT)方法制备了窄分布的聚2-乙烯基吡啶。再以该聚合物为大分子链转移剂,引发苯乙烯的RAFT聚合,得到聚2-乙烯基吡啶-b-聚苯乙烯(P2VP-b-PS)的两嵌段共聚物。以P2VP-b-PS为RAFT试剂,合成聚2-乙烯基吡啶-b-聚苯乙烯-b-聚异戊二烯(P2VP-b-PS-b-PI)的三嵌段共聚物。运用1H NMR、IR和凝胶渗透色谱(GPC)等技术对产物的结构和分子量及分子量分布进行表征,采用原子力显微镜(AFM)观察三嵌段共聚物薄膜的微相分离结构。结果表明,所得三嵌段共聚物P2VP72-b-PS136-b-PI300分子量分布较窄(PDI=1.69),合成过程具有活性/可控聚合特征,聚合物薄膜经溶剂退火处理后出现了明显的微观相分离结构。