N-vinyl carbazole copolymers

The synthesis of N-vinyl carbazole (VCbz) copolymers, some of which contain electron-accepting groups, is described. The new copolymers are: copoly[N-vinyl carbazole-di(2-N-carbazylethyl)-fumarate](II); copoly(N-vinyl carbazole-vinyl-2,4-dinitrobenzene-sulfonate)(IV); copoly(N-vinyl carbazole-vinyl-2,4-dinitrobenzene-sulfenate)(V); copoly(n-butyl acrylate-t-butyl peracrylate)(VII); copoly(n-butyl acrylate-t-butyl acrylate-graft-N-vinyl carbazole)(VIII).     

N-乙烯基咔唑标记甲基丙烯酸-苊烯共聚物的荧光特性

合成了苊烯(ACE)含量依次为4.3、7.5、15.1及20.8 mol％的N 乙烯基咔唑(NVCz)标记甲基丙烯酸(MAA) 苊烯共聚物(PMAA ACE/NVCz）和ACE含量仅为0.5 mol％的ACE MAA共聚物（PMAA ACE）,研究了各共聚物在稀水溶液中的荧光行为和pH、表面活性剂等对共聚物荧光特性的影响.实验发现:在酸性介质中共聚物的压缩线团构象使激发态缔合物荧光相对增强,ACE到NVCz能量转移效率增加;碱性介质中共聚物构象相对松散,ACE到NVCz能量转移效率降低,因此荧光光谱中NVCz特征几乎消失.阴离子表面活性剂十二烷基磺酸钠(SDS),阳离子表面活性剂十六烷基三甲基溴化铵(AHTB)以及中性表面活性剂吐温80的引入使共聚物在酸性介质中的单体荧光特征增强,ACE到NVCz的能量转移效率下降;在碱性介质中引入AHTB部分中和了共聚物链上的负电荷,使共聚物构象重新卷曲,ACE到NVCz的能量转移效率提高,荧光光谱中NVCz特征重新出现,ACE单体荧光特征相应减少;在碱性介质中引入SDS以及吐温80对共聚物荧光光谱影响不大.     

Configurations conducive to the formation of intramolecular excimers in poly(N‐vinyl carbazole) and its copolymers

The ratios of the intensity of excimer and monomer emissions, denoted I_E/I_M, in poly(N‐vinyl carbazole) and copolymers of N‐vinyl carbazole and methyl methacrylate were measured with steady‐state fluorescence. Measurements were performed in dilute solutions of several fluid solvents at 25 °C and in a solid matrix of poly(methyl methacrylate) at room temperature. The values of I_E/I_M depended on the nature of the solvent, the emission wavelength, and the copolymer composition. Molecular dynamics simulations were performed for diastereoisomers of 2,4‐di(N‐carbazolyl)pentane and for isotactic and syndiotactic trichromophoric copolymer fragments to assist in the identification of the thermally accessible conformations capable of forming intramolecular excimers and the configurational relationship of the carbazole units in these complexes. Nearest neighbor carbazole groups made the dominant contribution to the excimers. Excimers were more likely in isotactic sequences than in syndiotactic sequences, as was also the case for the low‐energy excimer arising from the complete overlap of two carbazole units. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1272–1281, 2001     

Singlet energy migration and excimer formation in polymers of 2-tert-butyl-6-vinylnaphthalene

The homopolymer of 2-tert-butyl-6-vinylnaphthalene (BVN) and its copolymers with styrene were prepared to examine the effects of the bulky tert-butyl groups on singlet energy migration and excimer formation among the naphthalene chromophores. The intensity of naphthalene excimer emission relative to that of monomer emission was found to depend linearly on the concentration of the potential excimer forming site, i.e., the BVN dyad fraction of the polymer. The rate of fluorescence quenching by biacetyl, on the other hand, increased only slightly with the increase in the BVN content. These results are consistent with the slow energy hopping model and suggest that the neighboring naphthalene chromophores are virtually isolated from one another owing to the unfavorable interactions of the tert-butyl groups.     

Photophysical properties of poly-2-phenyl-5-(p-vinyl)-phenyloxazole

2-Phenyl-5-(p-vinyl)phenyloxazole (POS) has been synthesized. Copolymers of POS with styrene and the homopolymer poly–POS have been prepared. The polymers have been characterized through measurements of fluorescence decay times (using synchrotron radiation for excitation) and examination of excimer formation in the homopolymer. Fluorescence decay times of 0.6(±0.4) nsec and 9 (±0.2) nsec have been recorded at 298°K in toluene solution for monomer and excimer, respectively. Poly-POS exhibits excimer formation characterized by an activation energy of 5.9(±0.5) kJ/mole and a binding energy of 17.0(±1.0) kJ/mole.     

Characterization of N-vinyl carbazole/vinyl 4-tert-butyl-benzoate copolymers of several molar compositions: SEC, DSC and intramolecular excimers in dilute solutions

Several N-vinylcarbazole/vinyl p-tert-butyl-benzoate copolymers of different molar monomer compositions and their respective homopolymers have been synthesized by free-radical polymerization. Their solution properties were characterized by size-exclusion chromatography (SEC) coupled with a differential refractive index (RI) and multiangle light scattering (MALS). Differential scanning calorimetry (DSC) was also used to investigate the glass transition temperatures, T_g. In addition, steady-state fluorescence emission spectra in a dilute solution of several fluid and non-fluid solvents were obtained to study the influence of monomer composition on the intramolecular carbazole excimer formation. The amount of excimers strongly depends on the solvent nature and copolymer composition. Molecular Dynamics (MD) simulations on iso- and syndiotactic homopolymer and copolymer fragments were used to obtain the probability of the conformations that satisfy excimer requirements. The analysis of the MD trajectories allows us to evaluate the amount and types of intramolecular excimers for the different systems.     

Nonlinear depression of the lower critical solution temperatures in aqueous solutions of thermo-sensitive random copolymers

We develop a theoretical model of cooperative hydration to clarify the molecular origin of the observed nonlinear depression of the lower critical solution temperature (LCST) in the aqueous solutions of thermosensitive random copolymers and find the monomer composition at which LCST shows a minimum. Phase diagrams of poly(N-isopropylacrylamide-co-N,N-diethylacrylamide) copolymer solutions are theoretically derived on the basis of the theory of cooperative hydration by introducing the microscopic structure parameter η which characterizes the distribution of the monomer sequences along the chains. We compared them with the experimental data of LCST of random copolymers with various monomer compositions and also of the diblock copolymers with equimolar monomer composition. The transition temperature shifts to lower than those of homopolymer counterparts when the monomer sequence of the chains has an alternative tendency. On the contrary, for the blocky polymers such as diblock copolymers, the transition temperature remains almost the same as those of the homopolymers. Thus, the nonlinear effect in phase separation appears when the average block length of the copolymers is shorter than the average sequence length of the cooperative hydration. The degree of hydration is calculated as a function of the temperature and polymer concentration for varied distribution of the copolymer compositions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1112–1123     

Photophysical properties of N-acylated linear polyethylenimine and dehydroalanine main-chain polymers containing carbazole or pyrene groups in side chains

A comparison of the UV absorption spectra of a carbazole-substituted N-acylated linear polyethylenimine (PEI) ( 5, 6 ) with its monomer ( 1, 2 ) and dimer ( 3, 4 ) model compounds shows the presence of local conformational order of the carbazole groups in 3, 5 , and 6 since these compounds exhibit hypochromism. The UV absorption spectra of carbazole-substituted N-acrylated dehydroalanine main-chain polymer (PDA) ( 12, 13 ) and monomer ( 10, 11 ) model compounds indicate that the extent of local conformational order of the carbazole groups is reduced in 12 and 13 compared to that in 5 and 6 . The UV absorption spectra of a pyrene-substituted PEI ( 9 ) and PDA ( 15 ) and those of their monomer model compounds ( 7, 14 ) indicate that the extent of local conformational order of the pyrene groups is greater in 9 than in 15 and furthermore the pyrene-substituted polymers ( 9, 15 ) show more local conformational order than analogous carbazole-substituted polymers ( 5, 12 ). The emission spectra of 5 and 12 show carbazole monomer emission, while those of 9 and 15 are dominated by pyrene excimer emission. The formation of excimer emission is more efficient in 9 than in 15 . Fluorescence lifetime measurements indicate interactions of excited carbazole groups in 5 and 13 but not in 12 . The quenching of carbazole fluorescence by dimethyl terephthalate is more efficient in 5 than that in 12 , indicating more efficient transfer of electronic energy in 5 . These measurements show that the PEI main-chain polymers are conducive to interactions of the pendant groups.     

Electrochemical impedance spectroscopy and in situ UV‐vis spectroelectrochemistry studies of Poly(N‐vinyl carbazole)/ Polydimethylsiloxane composite electrodes

Poly(N‐vinyl carbazole)/polydimethylsiloxane (PNVCz/PDMS) composite electrodes were prepared by electrochemical polymerization of NVCz monomer onto PDMS‐coated platinum (Pt) and glassy carbon (GC) electrode surfaces to investigate the influence of the insulating constituent, PDMS and process temperature on the capacitive performance of the coated layers. The electrochemical properties of the bilayer coatings were studied by electrochemical impedance spectroscopy and UV‐vis spectroelectrochemistry measurements. The low‐frequencies capacitance values of composite electrodes indicated that the capacitive behaviors of the composites decreased with increasing PDMS content (from 5.0 to 10.0; in wt/v%) in coating solutions at 25 °C, and with decreasing coating temperatures (from 25 °C to ? 15 °C) of PDMS and PNVCz and, more resist PDMS/PNVCz layers formed. Copyright © 2011 John Wiley & Sons, Ltd.     

Spectroscopic evidences for grafting of N-vinyl carbazole on cellulose-acetate film

N-vinyl carbazole (VCZ) was grafted on cellulose acetate film using simultaneous cobalt-60-γ ray irradiation grafting technique. Absorption, excitation, and emission spectral studies on the grafted film were carried out to ascertain the grafting of VCZ on the polymer matrix. Laser-flash photolysis studies with the solution of grafted film indicate the opening of the double bond of VCZ, which leads to the grafting. On the basis of the observed results, the mechanism of grafting in the system was proposed. © 1994 John Wiley & Sons, Inc.     

Energy migration in poly(N‐vinyl carbazole) and its copolymers with methyl methacrylate: Fluorescence polarization,quenching, and molecular dynamics

Fluorescence polarization and quenching measurements were used to examine intramolecular energy migration for poly(N‐vinyl carbazole) and copolymers of N‐vinyl carbazole with methyl methacrylate. Quenching measurements of the carbazole fluorescence by CCl₄ were performed in dilute solution in toluene, and fluorescence anisotropy, r, was measured for the chains dispersed in a solid matrix of poly(methyl methacrylate) (PMMA). The results suggested that the chains with a high carbazole content, that is, a high content of excimer trapping sites, do not show the highest values of the singlet energy‐migration rate. Isotropies, r^?1, of the samples in vitrified PMMA corroborated such conclusions. Molecular dynamics simulations on isotactic and syndiotactic trichromophoric copolymer fragments were used to obtain parameters related to the energy‐transfer process as a function of the methyl methacrylate content. The parameters from the simulations supported the interpretation of the experiments. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1615–1626, 2003     

Excimer kinetics in poly(n-vinyl carbazole)

The kinetics of excimer formation and decay in dilute dichloromethane solutions of poly(N-vinyl carbazole) have been investigated using time-resolved fluorescence spectroscopy. Further evidence for dual excimer formation in this polymer is presented; interconversion of the excimeric states appears to be a significant process at room temperature.     

Copolymerization of N-vinylcaprolactam with N-vinyl(benz)imidazoles and the properties of aqueous solutions of the copolymers

The free-radical solution copolymerization of N-vinylcaprolactam with 1-vinylimidazole, 1-vinyl-2-methylimidazole, 1-vinyl-2-methyl-3-propylimidazolium iodide, or 1-vinyl-2-methylbenzimidazole was investigated and the monomer reactivity ratios in the copolymerization were calculated. It was shown that 1-vinylimidazole exhibits a relatively higher activity in the copolymerization as compared to the monomers that bear substituents on the ring. It was established that, except for the copolymers of 1-vinyl-2-methylbenzimidazole, water-soluble products could be obtained. Aqueous solutions of N-vinylcaprolactam copolymers with N-vinyl(methyl)imidazoles were found to have a higher phase separation temperature relative to poly(N-vinylcaprolactam) solutions. The thermal stability of the aqueous solutions increases with a rise in the amount of hydrophilic 1-vinyl-and 1-vinyl-2-methylimidazole units in macromolecular chains and in the presence of NaCNS or KBr. The effect of salts on the thermal stability of aqueous copolymer solutions has the same character as in the case of the N-vinylcaprolactam homopolymer.     

The variation of the ratio of excimer/monomer emission and its relation to energy migration

A model is proposed to account for the changes in the intensity of excimer to monomer fluorescence emission with varying molecular weight and copolymer composition. The theory is applied to published data for polystyrene homopolymers and copolymers, and satisfactorily accounts for the excimer;'monomer fluorescence ratio without involving the concept of energy migration.     

Fluorescence and energy transfer in polyvinyl carbazole

A model is proposed to explain the kinetics of fluorescence and energy transfer in thin films of polyvinyl carbazole based on the migration of monomer excitons with activator molecules, dimers, and excimer forming sites competing as traps for the exciton energy.     

Critical micelle concentrations of block and gradient copolymers in homopolymer: Effects of sequence distribution,composition, and molecular weight

The critical micelle concentrations (CMCs) of styrene–methyl methacrylate (S-MMA) block and gradient copolymers present in a homopolymer poly(methyl methacrylate) (PMMA) matrix were determined using an intrinsic fluorescence technique based on the ratio of excimer to monomer fluorescence from styrene repeat units. The homopolymer molecular weight (MW) and copolymer MW, composition, and sequence distribution were varied to determine their effects on the CMC, and comparisons were made to theory. Although the effects of these parameters on micelle formation have been the focus of significant theoretical study, few experimental studies have addressed these issues. The MW of the S block (forming the micelle core) has a strong effect on the CMC. For example, an order of magnitude reduction in the CMC (from ∼ 1 to ∼ 0.1 wt %) is observed when the S block MW is increased from 51 to 147 kg/mol while maintaining the MMA block and PMMA MWs at 48–55 kg/mol. Increasing the PMMA matrix MW also has a strong an effect on the CMC, with the CMC for a nearly symmetric S-MMA block copolymer with each block MW equal to 48–51 kg/mol decreasing by a factor of 5 and by several orders of magnitude when the matrix MW is increased from 55 to 106 kg/mol and 255 kg/mol, respectively. In contrast, similar changes in the MMA block MW have little effect on the CMC. Finally, when present in a 55 kg/mol PMMA matrix, a 55 kg/mol S-MMA gradient copolymer with a styrene mole fraction of 0.51 exhibits a factor of 6 larger CMC than a block copolymer of similar MW and composition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2672–2682, 2008     

Amphiphilic copolymers with increased affinity for substrates

The copolymers of methyl quaternized 2-dimethylaminoethyl acrylate and styrene, 2-vinyl naphthalene, acrylic acid iso-octyl ester, or acrylic acid n-butyl ester have been prepared. Studies were made of the binding of a “binding probe,” methyl orange, by the copolymers in aqueous solution. The first binding constants and the thermodynamic parameters in the course of the binding were evaluated. Furthermore, the intensity of fluorescence of a hydrophobic fluorescent probe, 2-p-toluidinylnaphthalene-6-sulfonate, in the presence of these polymers was investigated. In addition, the fluorescence spectra of monomer and excimer emissions of the polymers with aromatic residues were measured. The excimer/monomer fluorescence intensity ratio was studied in the presence of various additives such as methyl orange, urea, methanol, and NaCl to gain an insight into the nature of microdomains in the polymer. The nature and phenomena of dye binding and hydrophobic fluorescent probe binding with the polymers are discussed. © 1993 John Wiley & Sons, Inc.     

Temperature dependence of the fluorescence quantum yields of diphenylsiloxane‐based copolymers in dilute solutions

The monomer and excimer fluorescence quantum yields of well‐defined poly(dimethylsiloxane‐co‐diphenylsiloxane)s with different diphenylsiloxane (Ph₂SiO) contents have been determined, along with those of 1,1,3,3‐tetraphenyl‐1,3‐dimethyldisiloxane and 1,1,3,3,5,5‐hexaphenyltrisiloxane‐1,5‐diol used as model compounds, in a dilute organic solvent at different temperatures. The measured fluorescence quantum yields of the copolymers are correlated with the fraction of the ? (CH₃)₂SiO? (Ph₂SiO)_n? (CH₃)₂SiO? structures. The monomer fluorescence yield for copolymers with low Ph₂SiO contents is dominated mainly by the isolated ? (CH₃)₂SiO? (Ph₂SiO)? (CH₃)₂SiO? unit, and the apparent mean binding energy of the excimer does not increase significantly with increasing Ph₂SiO content. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 854–861, 2002     

Synthesis and photophysics properties of novel bipolar copolymers containing quinoline aluminum moieties and carbazole segments

A novel polymerizable 8-hydroxyquinoline aluminum (Alq₃) complex monomer and its copolymers (Alq₃/N-vinylcarbazole (NVK)) with different mole fractions of Alq₃ in feed were designed and synthesized. The structure of the Alq₃-complex monomer was characterized by ¹H NMR, FT-IR and elemental analysis, and the bipolar copolymers with various desired Alq₃ loading were characterized by ¹H NMR, FT-IR, elemental analysis, and gel permeation chromatography (GPC). The results indicate that these copolymers have moderate molecular weight as well as good solubility in common organic solvent. Thermal properties measurement and analysis show that these copolymers possess excellent thermal stability and high glass transition temperature (T_g). The photophysics properties of the copolymers were studied by UV–vis and fluorescence spectra. Nearly monochromatic yellow–green emission from Alq₃ was observed in high concentration solution and solid state, showing effective energy transfer characteristic. The results demonstrate that introduction of carbazole as hole-transporting and energy transfer group is a potential method to improve the luminescent performance of the Alq₃-based polymers.