New fluorescent probes for monitoring the polymerization reaction (original) (raw)
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Journal of Polymer Science Part A: Polymer Chemistry, 2004
Fluorescence spectroscopy was used to study the kinetics of polymerization of acrylic adhesive formulations exposed to a 355-nm pulsed emission from an Nd-YAG laser. Nine fluorescent probes were used for monitoring the laser curing, showing different sensitivities. In general, the fluorescence intensity emission increased as crosslinking occurred. In addition, solvatochromic fluorescent probes showed a blueshift in their emission. A relative method was applied for the evaluation of the polymerization rates in three different acrylic systems. Special features of pulsed-laserinduced polymerization were treated in detail, such as the influence of the laser pulse frequency and the incident laser beam intensity. The polymerization rate slowed down as the pulse repetition rate decreased. An inhibition period due to oxygen quenching was observed, and it was highly dependent on the laser repetition rate and the nature of the photoinitiator. The effect of the laser beam intensity on the kinetics of such fast reactions was studied. In general, increasing the laser energy improved the rate of polymerization. The degree of cure improved as the polymerization rate increased as a result of faster crosslinking, rather than relaxation volume kinetics. Moreover, a saturation rate effect occurred that depended on the photoinitiator. The different behaviors of the two photoinitiators in the curing of the same acrylic formulation was explained on the basis of primary radical termination.
STUDY OF LASER ABLATION EFFICIENCY FOR AN ACRYLIC-BASED PHOTOPOLYMERIZING COMPOSITION
Results are presented from study of the effi ciency (ablated mass per unit energy, mechanical recoil momentum per unit energy) of laser ablation for a light-curable polymer. A substantial difference is seen between the thresholds and indicated criteria for laser ablation effi ciency in the liquid and cured phases. The highest energy effi ciency for laser ablation (~22.6%) is achieved when the initially liquid polymer is exposed to radiation with the wavelength optimal for photopolymerization (365 ± 15 nm).
Polymer, 2002
The photoinitiated polymerization of multifunctional (meth)acrylic monomers was simultaneously monitored in real time by fluorescence and differential scanning calorimetry. As the curing proceeds, the fluorescence emission changes due to an increase in the viscosity of the microenvironment. A good correlation between fluorescence intensity and degree of conversion was established by using two different fluorescent probes, each having the same fluorophore, dialkylamino derivatives of 7-nitro-2-oxa-1,3-diazol. One of the probes contains an acrylic moiety which can react with the monomers labelling the formed network. The use of the first moment of fluorescence is presented as a suitable methodology to avoid experimental fluctuations. Furthermore, the influence of the length of the spacer between the acrylic groups in the polymerization reaction kinetics and fluorescence changes has been also discussed in terms of reaction diffusion controlled termination kinetics and free volume fraction. It was concluded that the fluorescence method is a powerful tool to study the kinetics of photopolymerization of multifunctional monomers. q
Fluorescence monitoring of photoinitiated polymerization reactions
Journal of Photochemistry and Photobiology A: Chemistry, 2006
The fluorescence emission of three new fluorescent probes has been studied in environments of different polarity and viscosity. The diazine moieties behave as electron acceptor and a good correlation has been found between their reduction potentials and the dipole moments in the excited state (estimated from solvatochromic plots using Lippert equations). The probes have shown to be sensitive to changes in both microviscosity and micropolarity of the surroundings. They have been used as fluorescent sensors to monitor the photopolymerization reactions of some monoand difunctional methacrylate monomers in bulk. The fluorescence emission band of the probes showed an increase in intensity, as well as an hypsochromic shift, as the degree of conversion increases, throughout the entire polymerization range in the different systems checked.
Experimental study of the acrylamide photopolymer with a pulsed laser
Optics Communications, 2001
We have demonstrated that holograms may be recorded in polyvinyl alcohol/acrylamide photopolymer dry ®lms using pulsed laser exposure with a pulse length of 8 ns. We also studied the eect of the pulse¯uency together with the number of pulses necessary to obtain maximum diraction eciency. The recording was performed using a holographic copying process. The original was a grating of 1000 lines/mm processed using silver halide sensitized gelatin. Diraction eciencies of 55% were obtained with sensitivities similar to those reached with the same material and cw exposure, without the need for pre-processing or ®nal processing of the gratings. Ó
Journal of Polymer Science Part A: Polymer Chemistry, 2002
The photopolymerization of acrylic-based adhesives has been studied by Fourier transform infrared and fluorescence analysis in real time. Real-time infrared spectroscopy reveals the influence of the nature of the photoinitiator on the kinetics of the reaction. Furthermore, the incident light intensity dependence of the polymerization rate shows that primary radical termination is the predominant mechanism during the initial stages of the curing of the acrylic system with bis(2,4,6-trimethylbenzoyl) phenyl phosphine oxide (TMBAPO) as a photoinitiator. The fluorescence intensity of selected probes increases during the ultraviolet curing of the adhesive, sensing microenvironmental viscosity changes. Depending on the nature of the photoinitiator, different fluorescence-conversion curves are observed. For TMBAPO, the fluorescence increases more slowly during the initial stage because of the delay in the gel effect induced by primary radical termination. Mechanical tests have been carried out to determine the shear modulus over the course of the acrylic adhesive ultraviolet curing.
Polymer Engineering & Science, 1996
A fiber optic system has been designed to couple calorimeter and fluorimeter equipment for in situ monitoring of polymerization reactions by both techniques simultaneously. Two acrylic monomers (cyclohexyl methacrylate, CHM, and 2‐ethylhexyl acrylate, EHA) were studied at different temperatures. Pyrene (Py) was employed at a low concentration (≤10−4 mol/L) as a fluorescence probe. The emission spectrum of pyrene shows a broad band peaking at 390 nm, whose intensity grows with polymerization progress. A correlation with conversion degree could be established by collecting fluorescence intensity through the optical fiber at different polymerization times. For the more flexible polymer formed, poly(ethylhexyl acrylate) (PEHA), Py emission sharply increases only when high conversions are reached and continues increasing for a long time after the limiting conversion is attained. For CHM polymerizations, S‐shaped curves are found. Isochronal plots of intensity vs. scaled conversion allow ...
Polymerization kinetics of photocurable acrylic resins
Journal of Polymer Science Part A: Polymer Chemistry, 1998
The polymerization kinetics of photocurable compositions based on an epoxyacrylate oligomer and three analogous diacrylate monomers were investigated. The effects of the oligomer-to-monomer ratio, curing conditions, and monomer structure were considered. The polymerization is characterized by a synergistic effect observed in a wide temperature range and occurring for the polymerization rate both in air and Ar and for final conversions in air. The final conversion in Ar is determined by viscosity of a formulation. The presence of a heteroatom (S or O) in the ester group of the reactive diluent is beneficial for the polymerization course, especially in air atmosphere. The best results were obtained for the sulfur-containing monomer.
Polymer, 2002
A new method has been found for monitoring polymerization reactions in situ and in real time. The first moment of fluorescent emission, knl ¼ P I F ðnÞn= P I F ðnÞ is calculated from fluorescence spectra as a function of polymerization time and can be successfully correlated with the conversion of functional groups, obtained by an independent technique, with a very low level of experimental scatter. The statistical analysis of the method has been performed; some simple computer experiments allowed to study the influence of the most important experimental variables yielding the confidence interval of knl as a function of the noise to signal ratio. This method was applied with stepwise polyaddition (epoxide curing) and polymerization by free radical mechanisms. 5-Dimethylaminonaphthalene-1-sulfonamide derivatives, 4dialkylamino-4 0 -nitrostilbene and pyrene were used as probes and/or labels. Other methods reported in the literature have been applied also. Comparison with them reveals that the first moment method is more reliable for monitoring polyaddition reactions. q