Monitoring of swelling of interpenetrating polymer network of polyethylene/poly(styrene-co-butylmethacrylate) (PE/P(S-co-BMA)) in toluene and cyclohexane using fluorescence spectroscopy

A real-time monitoring of excimer emission fluorescence probe di(1-pyrenemethyl)ether (DiPyM) was used for study swelling interpenetrating polymer network (IPN) consisting of polyethylene/poly(styrene-co-butylmethacrylate) (PE/P(S-co-BMA)) and containing different network density. DiPyM was introduced into IPN during polymerisation or was penetrated into blocks from toluene solution. The effect of solvent quality for swelling of IPN and density of IPN network was also studied. From steady-state measurements of monomer and excimer emission ratio (I_e/I_m), no difference was found between rate of swelling IPN with 0.5, 1 and 3 mol% of cross-linker. The rate of IPN swelling seems to be rather high. Some differences was found at real-time monitoring of excimer emission (λ_em=495 nm) of DiPyM measured during desorption of DiPyM from swelled IPN blocks. At higher content of cross-linker, a slower rate of DiPyM desorption from IPN matrix was observed.     

Decay Lifetimes of Para-Substituted Polystyrene in Solid Films and in Dichloromethane

The fluorescence decay times of polystyrene, poly(4-bromostyrene), poly(4-chlorostyrene), poly(4-methylstyrene), poly(α-methylstyrene), poly(4-methoxystyrene), and poly(4-tert butylstyrene) were measured in solid films and in dichloromethane solution. A detailed analysis of the emission profile performed by nanosecond time resolved fluorescence spectroscopy confirmed the presence of monomer fluorescence as well as excimer fluorescence in both media. Monomer fluorescence decay times gave shorter times compared with that of excimer decay times in dichloromethane solution. Fluorescence from substituted polystyrene was mainly excimer fluorescence with shift of maximum emission to longer wavelength. The ratio of monomer to excimer contributions was found to be dependent on the emission wavelength, but was not affected by polymer concentration. Both monomer and excimer fluorescence lifetimes as well as excimer intensity increase with increasing emission wavelength. An accompanying decrease in monomer contribution is also observed is solution in comparison with that in solid films.     

The effect of solid content on latex coalescence and film formation: Steady-state energy transfer study with fluorescence labeled polymers

The steady-state fluorescence technique was used to examine the healing and interdiffusion of polymer molecules as a function of solid content during annealing of latex films above the glass transition (T_g). Films were prepared from a mixture of naphthalene (N)- and pyrene (P)-labeled poly(methy methacrylate) (PMMA) latex particles. Above T_g, interdiffusion of polymer chains was observed by detecting the steady-state energy transfer from excited naphthalene to pyrene molecules. Various latex films with different latex content were used to measure the critical occupation percent for the reliable steady-state fluorescence measurements. Diffusion activation energies in these latex films were measured and found to be around 30 kcal/mol, which was attributed to the backbone motion of PMMA chains. © 1996 John Wiley & Sons, Inc.     

Self-association of hyperbranched poly(sulfone-amine) in water: studies with pyrene-fluorescence probe and fluorescence label

Both pyrene-fluorescence probe and fluorescence label techniques are used to investigate the association behaviors of hyperbranched poly(sulfone-amine) (HPSA) in aqueous solution. In the presence of HPSA, excimer emission peak evidently appeared, while no excimer peak was observed in the emission spectra in the absence of HPSA. The excitation spectrum monitored at excimer emission red shifts by about 38-40 nm compared to that monitored at monomer emission, which shows that the excimer is formed by preassociated pyrene chromophores. In the same concentration of pyrene, monomer emission of pyrene decreases but excimer emission increases with increasing the concentration of HPSA; the ratio of excimer-to-monomer emission intensity (I_E/I_M) gradually increases, reaches a critical point at 5-7 g/l, and sharply increases with the concentration. Pyrene-labeled hyperbranched poly(sulfone-amine) (Py-HPSA) was synthesized from 4-(1-Pyrene)butyroyl chloride and HPSA. The monomer emission and excimer emission of Py-HPSA show the concentration-quenching effect, while I_E/I_M increases monotonously, approaches a critical point, and then suddenly increases with increasing the concentration of Py-HPSA. Influences of acidity and solvents on the fluorescence emission were studied. In high concentrations of hyperbranched polymer, pH and DMSO significantly influence the emission of pyrene, and excimer peak disappears at 72% of DMSO fraction.     

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.     

Morphological studies of elongated PMMA by excimer formation

The technique of excimer fluorescence has been employed to study the orientational structure of poly (methyl methacrylate) (PMMA). The PMMA films used contain a small amount of naphthalene‐labeled PMMA, and were uniaxially stretched to various elongation at 80°C. The results show that the fluorescence intensity ratio of excimer to monomer, I_E/I_M , increases with the elongation ratio. The increase of excimer forming sites in the system after drawing is attributed to the orientation of both the chain segments and side groups along the drawing direction. The orientation leads to highly dense packing of the PMMA molecules. The conclusion drawn from excimer fluorescence is in agreement with those from other techniques. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1869–1872, 2000     

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     

In situ fluorescence experiments for real-time monitoring of annealed high-T latex film dissolution

A new technique, based on steady-state fluorescence measurements, is introduced for studying dissolution of polymer films. These films are formed from naphthalene and pyrene labeled poly(methyl methacrylate) (PMMA) latex particles, sterically stabilized by polyisobutylene. Diffusion of solvent (chloroform) into the annealed latex film was followed by desorption of polymer chains. Annealing was performed above T_g at various temperatures for 30-min time intervals. Desorption of pyrene labeled PMMA chains was monitored in real time by the pyrene fluorescence intensity change. Desorption coefficients were found to be between 1 and 4 × 10⁻¹⁰ cm²/s and two different dissolution mechanisms were detected. © 1996 John Wiley & Sons, Inc.     

Transient decay studies of photophysical processes in aromatic polymers: 2. Investigation of intramolecular excimer formation in copolymers of 1-vinyl naphthalene and methyl acrylate

Transient decay studies of the copolymer system 1-vinyl naphthalene/methyl acrylate using pulsed laser excitation have shown that monomer and excimer decay rates are not described by dual exponential functions. Triple exponential decays are attributed to the existence of emission from two kinetically distinct monomer sites in addition to that of the excimer. Variation of intramolecular chromophore concentration in the copolymers allows adoption of a versatile series of extrapolation procedures to derive individual rate constants in the photophysical reaction scheme governing intramolecular excimer formation. Use of this procedure yields a rate parameter governing excimer formation in which the dependence upon local chromophore concentration within the polymer coil is removed to a degree not possible in studies of homopolymers alone.     

Microenvironments in poly(1,4-butylene terephthalate) solids revealed by fluorescence spectroscopy

The relationship between the fluorescence behavior and crystallinity of poly(1,4-butylene terephthalate) (PBT) films, prepared by a spin-casting method, was investigated. Throughout the fluorescence measurements of PBT thin films having different crystallinities, the main-chain phenylene fluorescence near 320 nm and that near 365 nm were assigned to monomer fluorescence mainly from crystalline regions and excimer fluorescence from amorphous regions, respectively. It was found that the ratio of the fluorescence intensity at 320 nm to that at 365 nm can be an effective indicator of PBT crystallinity. The present work should provide a quick and nondestructive method for determining the crystallinity of PBT factory products.     

Fluorescence from poly(N-vinylcarbazole) in uniaxially stretched polymer films

Steady-state and time-resolved fluorescence properties of poly(N-vinylcarbazole) (PVCz) dispersed in a polystyrene (PS) cast film were studied under tensile loadings at room temperature. The excited monomer emission of PVCz located around 350 nm decreased with increasing applied tensile strain from 0 to 0.8%. The strain enhanced the emission which was ascribed to the partial-overlap excimer of PVCz in a 360–430 nm region. The emission due to the full-overlap excimer of PVCz between 430 and 500 nm was unchanged by the action of the tensile loadings. The ratio of fluorescence intensities at 375 nm and 345 nm I₃₇₅/I₃₄₅ was proportional to the applied strain. The time-resolved fluorescence study indicated that the lifetimes of the excited monomer and of the partial-overlap excimer were not affected by the strain. The obtained results mean that the strain applied to the PS matrix increases the partial-overlap conformation of two adjacent carbazolyl chromophores in a PVCz chain and suggest that PVCz is a useful probe for detecting residual strains in polymer matrices. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1569–1573, 1997     

Fluorescence from soluble polythiophenes in uniaxially stretched polymers

Fluorescence behavior of poly(3-alkylthiophenes) (P3ATs) in poly(methyl methacrylate) (PMMA) films was studied under tensile loadings. The elastic deformation of the matrix induced by small strains up to 0.2% had a greater influence on time-resolved fluorescence rather than the steady-state one from P3ATs. The decay time of fluorescence decreased linearly as the applied stress was increased, and reached a minimum. We maintained that the attractive phenomenon for the time-resolved fluorescence under the tensile loadings was associated with distortion or deformation of the π-conjugated structure in P3AT chains having large molecular weight. When the applied strain exceeded the elastic limit of the matrix, the time-resolved or steady-state fluorescence behavior was unchanged. However, large elongation over 10% led to the red-shift of the steady-state fluorescence maximum and an increase in the decay time. These fluorescence properties, indicating the growth of the π-conjugation, were mainly governed by strain. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 259–266, 1998     

Chiroptical and fluorescence properties of copolymers of (−)menthyl acrylate and (−) menthyl methacrylate with 1-vinylnaphthalene

Copolymerization of (?)menthyl acrylate(MtA) and (?)menthyl methacrylate(MtMA) with 1-vinylnaphthalene(1VN) were carried out in bulk at 65°C using 2,2′-azoisobutyronitrile(AIBN) as initiator. Reactivity ratios and distribution parameters were calculated for both systems.Alternating copolymers were prepared by donor-acceptor complex polymerization with Et₃Al₂Cl₃. The polymers were characterized by viscosity, n.m.r., i.r. and u.v. measurements. Chiroptical and fluorescence properties of the naphthalene chromophore in these copolymers are related to composition and sequence length. Possible mechanisms of optical activity induction in the naphthalene chromophore are discussed.     

Measuring Tg in ultra‐thin polymer films with an excimer fluorescence technique

An excimer fluorescence technique has been applied to the measurement of T_g of ultra‐thin polystyrene films. This technique utilizes an excimer‐forming molecule with fluorescent emission in two wavelength bands. The intensity ratio of these bands is a sensitive measure of local viscosity. This technique has been applied to five polystyrene films in the thickness range of 25 nm to 200 nm supported on quartz substrates. The observed T_g for the five ultra‐thin polymer films was similar to the bulk T_g with no observed dependence upon thickness. Additionally, the T_g determined for each film did not show any dependence upon thermal history.     

Fluorescence study of the dynamics of a star-shaped poly(?-caprolactone)s in THF: A comparison with a star-shaped poly(l-lactide)s

Molecular dynamics of 2-, 4- and 6-arm star-shaped poly(?-caprolactone)s (PCLs) functionalized with pyrene at all chain ends followed by excimer formation were investigated in THF as a solvent. Dilute solutions (10⁻⁸ to 10⁻⁶ mol L⁻¹) of these polymers revealed excimer emission due to the intramolecular cyclization, proceeding via chain end interaction. Time-resolved fluorescence measurements of star-shaped PCLs showed complex decay profiles of monomer and excimer fluorescence. An intensity rise component of decay profiles monitored in excimer region (500 nm) was observed for star-shaped polymers due to dynamic formation of excimers. Dipyrene-PCL (2-arm) also showed partial formation of static pyrene excimers as followed from measurement of excitation spectra at ambient temperature in THF. Excimer intensity of di- and four pyrene-telechelic PCLs was found to be comparable with that of di- and four pyrene-telechelic polylactide (PLA) polyesters having similar molar masses. 6-Arm PCL showed depressed excimer formation with regard to 6-arm PLA under the otherwise identical conditions contrary to the conclusion expected from the higher flexibility of the PCL chain. Eventually, molecular dynamic simulations showed that possible explanation can be related to different conformations of 6-arm PLA versus PCL stars.     

Cd2+-sensiting bichromophore: Excimer emission from an EDTA-methylnaphthalene derivative

Chelating EDTA-based bichromophores, 1,4-bis(methylenecarboxy)-1,4-bis(N-1-naphthylmethylacetamide)-1,4- diazabutane (1) and its 2-napthyl isomer (2), were synthesized, and their fluorescence emission and complexation with Cd²⁺ and Zn²⁺ were studied. The fluorescence spectrum of 2 exhibited an emission band due to intramolecular excimer at about 400 nm in addition to a band from a monomeric (or isolated) chromophore at 335 nm. Complexation with Cd²⁺ sensitively intensified the excimer band and weakened the monomer band, as a result of formation of a [CdL₂]²⁻ type complex. In contrast, Zn²⁺ formed [ZnL]⁰, leading to depression of the excimer emission and enhancement of the monomer emission. The extent of the changes in emission intensities in the Cd²⁺ complex was larger than that of the Zn²⁺ complex contrary to the common metal-ion effect on fluorescence. Such a characteristic emission property was not observed for isomer 1. Ligand 2 has the high Cd-sensing capability that originates from monomer–excimer interconversion.     

Phosphorescence and fluorescence of poly(vinyl alcohol) films

Luminescence properties of poly(vinyl alcohol) (PVA) films were investigated at room and low (103 K) temperatures. It was estimated that the PVA films can be regarded as luminescentless matrices when excited by radiation of wavelengths greater than 420 nm (λ_exc ≥ 420 nm).     

Picosecond excimer fluorescence spectroscopy: applications to local motions of polymers and polymerization monitoring

The local motions of α,ω-bis-(1-pyrene)alkanes and pyrene-labelled poly(methyl methacrylate) polymers in solution were characterized by picosecond excimer fluorescence spectroscopy. The experimental results showed that 1,3-bis-(1-pyrene)propane and 1,10-bis-(1-pyrene)decane have similar local motions that bring two pyrene groups together to form excimers. Further, poly(1-pyrenylmethyl methacrylate) and a copolymer of methyl methacrylate and 1-pyrenylmethyl methacrylate in solution were found to have similar local motions that lead to excimer formation. In addition, the viscosity change during the polymerization of methyl methacrylate was monitored by measuring with picosecond fluorimetry the fluorescence lifetime of a trace amount of 1,3-bis-(1-pyrene)propane dissolved in methyl methacrylate.     

Potential of Pyridine Amphiphiles as Staphylococcal Nuclease Inhibitor

The present study explores the potential of pyridine‐based synthetic amphiphiles C1 and C2 having 4‐carbon and 12‐carbon hydrophobic tails, respectively, as staphylococcal nuclease inhibitors. UV–visible titration with calf‐thymus DNA (CT‐DNA) revealed a hypochromic shift in the absorbance bands of C1 and C2, whereas fluorescence titration indicated a reduction in the emission intensity of the monomer bands of the amphiphiles. Interaction of deoxyribonuclease I (DNase 1) and micrococcal nuclease (MNase) with C1 or C2 led to a decrease in the emission intensity of tryptophan at λ=345 nm along with an increase in the monomer emission intensity of C1 and C2 at λ=375 nm for DNase I and excimer emission intensity at λ=470 nm for both DNase I and MNase. Scatchard's analysis indicated superior interaction of C2 with DNase I. Circular dichroism spectroscopy revealed major changes in the secondary structures of both DNase I and MNase upon interaction with the amphiphiles. A solution‐based nuclease assay in conjunction with gel electrophoresis indicated amphiphile‐mediated protection against nuclease‐directed DNA cleavage. Interestingly, C2 could render inhibition of nuclease present in the culture supernatant of Staphylococcus aureus MTCC 96, which highlights the therapeutic prospect of the amphiphile against S. aureus.     

Time-resolved fluorescence of excimer-forming polymers in solution

The kinetics of excited dimer (excimer) formation in small molecules, and in excimer-forming polymers, is discussed. The use of time-resolved fluorescence to study molecular order, and heterogeneity, segmental motion and energy migration in synthetic polymers in solution is described with respect to p-phenylene diacrylic acid, a cross-linkable commercial polymer, and copolymers of methyl methacrylate and 1-vinyl naphthalene, respectively.