Experimental studies and mathematical modeling of the curing reaction of bioinspired copolymers

Polymer curing is a complex process that significantly delineate the final properties of the synthetized material. In this work, the photo-induced crosslinking reaction of synthetic “bio-inspired” copolymers based on thymine and ionic groups was studied by gel permeation chromatography and UV absorption spectroscopy. A mathematical model for the curing process based on statistical techniques and coupled to the kinetics of crosslinking was developed. The model allows to predict both, the evolution of the crosslinking degree as a function of curing time and the gel times as a function of the molecular structure of the copolymer and the curing conditions. The theoretical values showed a very good agreement with the UV–Vis and GPC spectroscopy experimental results for all the copolymers studied. A better knowledge of the curing kinetics of thymine-based biopolymers will enable to develop materials with pre-specified properties and to improve their applications.     

Kinetic study of epoxy curing in the glass fiber/epoxy interface using dansyl fluorescence

The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.     

The effect of light intensity,film thickness,and monomer composition in styrene-based bioinspired polymers

Abstract

The effect of irradiation light intensity, film thickness, and polymer composition upon photo-irradiation of water-soluble polymers containing thymine was studied by ultraviolet (UV)-vis spectroscopy. Coatings of aqueous solution of the polymer on PET substrates were exposed to UV light at 254 nm through a standard mask. The effect of irradiation dose is similar to the typical behavior of photo-resists: the degree of crosslink increases over the time until it reaches saturation. The polymer composition effect shows an expected trend on the curing process, the more vinylbenzylthymine (VBT) content in the copolymer the higher the degree of crosslinking, a situation that agrees with the fact the VBT is the monomer playing the main role in the photo-reaction. It was observed that the effect of film thickness was as expected, the thicker the film the slower the immobilization of the polymer on the substrate. It was demonstrated that by varying these parameters one could control the crosslinking rate of the polymer.     

Preparation by controlled radical polymerization and self‐assembly via base‐recognition of synthetic polymers bearing complementary nucleobases

The radical polymerization of three monomers bearing nucleobases 1‐(4‐vinylbenzyl)thymine (VBT), 1‐(4‐vinylbenzyl)uracil (VBU) and 9‐(4‐vinylbenzyl)adenine (VBA) was investigated. The corresponding homopolymers could be prepared in high yields via conventional radical polymerization. However, the resulting polymers were found to be only soluble in a few polar solvents. On the other hand, copolymers of dodecyl methacrylate (DMA) with either VBT or VBA could be prepared via both free radical polymerization and atom transfer radical polymerization and could be dissolved in a large variety of organic solvents. Moreover, the formed complementary copolymers P(VBT‐co‐DMA) and P(VBA‐co‐DMA) were found to self‐assemble in dilute solutions in dioxane or chloroform via base recognition, as evidenced by a significant hypochromicity effect in UV spectroscopy. Nevertheless, at higher concentrations in chloroform, both dynamic light scattering and optical microscopy indicate that P(VBT‐co‐DMA), P(VBA‐co‐DMA), or P(VBT‐co‐DMA)/P(VBA‐co‐DMA) mixtures spontaneously self‐assemble into micron size spherical aggregates. ¹H NMR and FTIR studies confirmed that the self‐assembly process is driven in all cases via H‐bond formation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4805–4818, 2005     

Electrochemical copolymerization of 9,10-dihydrophenanthrene and 3-methylthiophene and characterization of their copolymer with tunable fluorescence properties

Electrochemical copolymerization of 9,10-dihydrophenanthrene and 3-methylthiophene was successfully achieved in boron trifluoride diethyl etherate by direct anodic oxidation of the monomer mixtures. The structure and properties of the copolymers were investigated with ultraviolet–visible, Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance, fluorescence spectra, and thermal analysis. The novel copolymers had the advantages of both poly(9,10-dihydrophenanthrene) and poly(3-methylthiophene), such as good electrochemical behavior, good mechanical properties, and high electrical conductivity. Fluorescence spectroscopy studies revealed that the copolymers had good fluorescence properties, and the emitting properties of the copolymer could be parameters by changing the feed ratio of the monomer mixtures during the electrochemical polymerization.     

Photosensitization of bioinspired thymine-containing polymers

Here, we report a sensitization study on a family of water-soluble photopolymers based on thymine. The goal of this study was to determine whether the presence of sensitizer molecules would promote photocrosslinking/immobilization of the polymers using low-energy irradiation (520 nm) as compared to the UV irradiation (approximately 280 nm) necessary for the standard photoinduced process to take place. With the aid of Eosin Y Spirit Soluble (EY) as a sensitizer, water-soluble polystyrene copolymers of vinylbenzylthymine-vinylbenzyltriethylammonium chloride (VBT-VBA) were immobilized after exposure to visible irradiation. By exciting the sensitizer molecule in the presence of VBT copolymers at a wavelength where absorption by the latter does not occur, the triplet state of the sensitizer is generated in high yields, and consequently, polymer photocross-linking takes place. UV-vis spectroscopy has been used to study the effect of irradiation dose, copolymer composition, and sensitizer concentration on the photoreactivity of VBT polymers. These studies demonstrate the feasibility of using Eosin Y as a sensitizer to achieve the thymine photodimer formation, resulting in immobilization of VBT-VBA-EY films on PET substrate. This provides complementary information on photoinduced immobilization of VBT-VBA films that are crucial for developing new classes of environmentally benign materials and new energy-saving methods.     

Achieving second order advantage with multi-way partial least squares and residual bi-linearization with total synchronous fluorescence data of monohydroxy–polycyclic aromatic hydrocarbons in urine samples

An attractive approach to handle matrix interference in samples of unknown composition is to generate second- or higher-order data formats and process them with appropriate chemometric algorithms. Several strategies exist to generate high-order data in fluorescence spectroscopy, including wavelength time matrices, excitation–emission matrices and time-resolved excitation–emission matrices. This article tackles a different aspect of generating high-order fluorescence data as it focuses on total synchronous fluorescence spectroscopy. This approach refers to recording synchronous fluorescence spectra at various wavelength offsets. Analogous to the concept of an excitation–emission data format, total synchronous data arrays fit into the category of second-order data. The main difference between them is the non-bilinear behavior of synchronous fluorescence data. Synchronous spectral profiles change with the wavelength offset used for sample excitation. The work presented here reports the first application of total synchronous fluorescence spectroscopy to the analysis of monohydroxy-polycyclic aromatic hydrocarbons in urine samples of unknown composition. Matrix interference is appropriately handled by processing the data either with unfolded-partial least squares and multi-way partial least squares, both followed by residual bi-linearization.     

Microwave‐assisted synthesis of copolymers of luminol with anisidine: Effect on spectral,thermal and fluorescence characteristics

With the aim to investigate variation in the spectral, morphological, and fluorescence characteristics of a chemiluminescent moiety upon copolymerization with an aniline derivative, the present preliminary work reports for the first time the microwave‐assisted copolymerization of luminol and o‐anisidine in acidic and basic media. Characterization of the resulting copolymers was performed by Fourier transform infrared spectroscopy, UV‐visible studies, fluorescence studies, X‐ray diffraction, and transmission electron microscopy measurements. Polymerization of luminol and its copolymers was noticed to be different in acidic and basic media, which was confirmed by IR analysis while UV‐visible as well as fluorescence studies revealed a major decrease in the intensity of the peaks associated with polyluminol that reflected the quenching nature of o‐anisidine. Peak broadening at higher loading of o‐anisidine comonomer confirmed intense interaction of the 2 monomers via hydrogen bonding. To predict the possible use of luminol copolymers as biosensors, bovine serum albumin was chosen as a model protein for performing the adsorption studies. Results revealed that the copolymers reflected immense potential to be used as a protein biosensor.     

Singlet energy migration along an alternating block copolymer of oligothiophene and oligosilylene in solution

The singlet excited-state properties of the block copolymers of oligothiophene and oligosilylene in solution were investigated with several fast spectroscopic methods. Time-resolved fluorescence measurements at room temperature and in a glassy matrix revealed that the singlet excited states of the block copolymers are deactivated accompanying structural changes of the polymer. It became clear from the transient absorption spectroscopy that the absorption peak of the singlet excited state shifted to the longer wavelength side compared to that of the corresponding oligothiophenes because of the sigma-pi conjugation of the oligothiophene and oligosilylene. The intersystem crossing process generating the triplet excited state was also revealed by the transient absorption spectroscopy. Energy migration along the polymer chain was revealed by the fluorescence anisotropy measurements. The time constant for the energy migration became faster as the size of the oligothiophene in the polymer repeating unit became shorter. From comparison with the F?rster theory, the energy migration process was attributed to an incoherent hopping mechanism.     

New three-arm amphiphilic and biodegradable block copolymers composed of poly(epsilon-caprolactone) and poly(N-vinyl-2-pyrrolidone). Synthesis, characterization and self-assembly in aqueous solution

The synthesis, characterization and the self-assembly process of a novel biodegradable block copolymer containing a poly(epsilon-caprolactone), PCL, central block and three poly(N-vinyl-2-pyrrolidone), PVP, arms are reported. Three samples with different amounts of PVP were investigated. The copolymers were characterized by FTIR spectroscopy, (1)H NMR and viscosity measurements. The composition and the molecular weights of the block copolymers were established using size exclusion chromatography SEC and (1)H NMR. Micelle formation by these copolymers was monitored by using the vibrational fine structure of pyrene monomer fluorescence and the critical aggregation concentrations, cac, of the copolymers in aqueous solution were determined using sigmoid Boltzmann-type fitting of the fluorescence data. Dynamic light scattering measurements showed a bimodal size distribution for the copolymers in solution, indicating that the micellization is an intermolecular process. Partitioning coefficients of pyrene between copolymer micelles and water were also determined and increase in magnitude with increasing epsilon-caprolactone content of the copolymer.     

Photochemistry and chemometrics—An overview

Photochemistry has made significant contributions to our understanding of many important natural processes as well as the scientific discoveries of the man-made world. The measurements from such studies are often complex and may require advanced data interpretation with the use of multivariate or chemometrics methods. In general, such methods have been applied successfully for data display, classification, multivariate curve resolution and prediction in analytical chemistry, environmental chemistry, engineering, medical research and industry. However, in photochemistry, by comparison, applications of such multivariate approaches were found to be less frequent although a variety of methods have been used, especially with spectroscopic photochemical applications. The methods include Principal Component Analysis (PCA; data display), Partial Least Squares (PLS; prediction), Artificial Neural Networks (ANN; prediction) and several models for multivariate curve resolution related to Parallel Factor Analysis (PARAFAC; decomposition of complex responses). Applications of such methods are discussed in this overview and typical examples include photodegradation of herbicides, prediction of antibiotics in human fluids (fluorescence spectroscopy), non-destructive in- and on-line monitoring (near infrared spectroscopy) and fast-time resolution of spectroscopic signals from photochemical reactions. It is also quite clear from the literature that the scope of spectroscopic photochemistry was enhanced by the application of chemometrics.To highlight and encourage further applications of chemometrics in photochemistry, several additional chemometrics approaches are discussed using data collected by the authors. The use of a PCA biplot is illustrated with an analysis of a matrix containing data on the performance of photocatalysts developed for water splitting and hydrogen production. In addition, the applications of the Multi-Criteria Decision Making (MCDM) ranking methods and Fuzzy Clustering are demonstrated with an analysis of water quality data matrix. Other examples of topics include the application of simultaneous kinetic spectroscopic methods for prediction of pesticides, and the use of response fingerprinting approach for classification of medicinal preparations. In general, the overview endeavours to emphasise the advantages of chemometrics’ interpretation of multivariate photochemical data, and an Appendix of references and summaries of common and less usual chemometrics methods noted in this work, is provided.     

Chemometric processing of second-order liquid chromatographic data with UV–vis and fluorescence detection. A comparison of multivariate curve resolution and parallel factor analysis 2

Second-order liquid chromatographic data with multivariate spectral (UV–vis or fluorescence) detection usually show changes in elution time profiles from sample to sample, causing a loss of trilinearity in the data. In order to analyze them with an appropriate model, the latter should permit a given component to have different time profiles in different samples. Two popular models in this regard are multivariate curve resolution-alternating least-squares (MCR-ALS) and parallel factor analysis 2 (PARAFAC2). The conditions to be fulfilled for successful application of the latter model are discussed on the basis of simple chromatographic concepts. An exhaustive analysis of the multivariate calibration models is carried out, employing both simulated and experimental chromatographic data sets. The latter involve the quantitation of benzimidazolic and carbamate pesticides in fruit and juice samples using liquid chromatography with diode array detection, and of polycyclic aromatic hydrocarbons in water samples, in both cases in the presence of potential interferents using liquid chromatography with fluorescence spectral detection, thereby achieving the second-order advantage. The overall results seem to favor MCR-ALS over PARAFAC2, especially in the presence of potential interferents.     

Synthesis of methacrylic copolymers with nona‐1‐butoxy trititanosiloxane as side groups and its application as a thermosetting resin

Methacrylic copolymers with a hydroxyl group on one end of the main chain and nona‐1‐butoxytrititanosiloxane as side groups (called methacrylic hybrid copolymers) were synthesized for use as baked‐finish‐type coating resins. The chemical structures of the side groups in the methacrylic hybrid copolymers were confirmed with the ash weight of the copolymers after combustion, the elemental ratio analysis of Si and Ti in the ash determined by inductively coupled plasma emission spectrometry, and the characteristic absorption band determined by Fourier transform infrared spectrophotometry. The methacrylic hybrid copolymers were cured at temperatures less than 150 °C in the absence of a curing accelerator. The cured copolymers exhibited a high thermal stability. The curing temperature of the copolymers was determined by the change in the absorption peak strength (peak area) of the 1655 cm⁻¹ band in the IR difference spectrum. The thermal stability of the copolymers was evaluated as the thermal‐degradation temperature measured by thermogravimetric analysis. The methacrylic hybrid copolymers were then be used as effective curing resins. The mixture, consisting of thermoplastic methacrylic terpolymer with hydroxyl and carboxyl groups and the methacrylic hybrid copolymers, were cured at less than 150 °C in the absence of a curing accelerator and exhibited a higher thermal‐degradation temperature than the copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1090–1098, 2001     

A multivariate chemometric approach to fluorescence spectroscopy

A multivariate approach to the solution of problems often encountered in the spectrofluorometry of natural samples, utilising information from whole spectra is presented. (a) Piecewise direct standardisation is implemented and employed to transfer emission spectra measured with two different xenon lamps of different ages as if the spectra were measured with the same lamp. (b) It has been shown using a multivariate analysis approach that it is possible to use the raw data points instead of the smoothed data based on an algorithm included in the instrument software by the manufacturer. (c) It is documented that Raman scattering does not hamper the performance of multivariate calibration; on the contrary, in an experiment with sugar samples the concentration prediction errors become about five times lower by including the whole emission spectrum in the analysis instead of using a univariate calibration based on an emission wavelength that only reflects the analyte of interest. (d) An algorithm for variable selection is implemented and employed in the selection of optimal excitation wavelengths. Among 13 emission spectra recorded for a sugar sample at different excitation wavelengths, four of these are chosen that describe 98.51% of the total variance in the original data. (e) Finally the combination of fluorescence spectroscopy and multivariate calibration with conventional chemical data according to the near-infrared black box model is presented. The refined sugar quality parameter, the ash content and the fluorescence emission spectra are correlated by a partial least-squares regression model. Five experiments employing different monochromator slit widths and sugar concentrations are performed, and the best correlation obtained by full cross-validation of the 15 sugar samples is R = 0.98.     

可生物降解聚酯P(DHCA-co-LA)的合成与表征

由3,4-二羟基肉桂酸(DHCA)与D,L-乳酸(LA)经熔融缩聚法得到了新型可生物降解聚酯P(DHCA-co-LA),采用傅立叶变换红外(FTIR),核磁共振(1H-NMR)和凝胶渗透色谱(GPC)对该共聚物的组成与相对分子量进行表征,结果表明其结构明确.改变DHCA与LA单体的配比,得到的P(DHCA-co-LA)的分子量和分子量分布在同一数量级.通过差示扫描量热仪(DSC)、紫外(UV)和荧光光谱研究了共聚物的热性能、紫外与荧光性能,结果表明,P(DHCA-co-LA)有明显的玻璃化转变温度(Tg),随LA的投料比从0增加至50 mol%时,其Tg从132.26℃下降至99.12℃;当LA的投料比为20 mol%时,所得到的聚酯型共聚物溶液呈现最强的荧光强度;在紫外光照下,共聚物可进行环加成反应,但交联度总体较低;紫外光照65 min后,在荧光显微镜下观察到交联颗粒形态稳定、有较强的荧光.X-射线衍射(XRD)测定结果显示,由结晶性DHCA和LA共聚形成的P(DHCA-co-LA)为无定形聚合物,有利于生物降解.共聚物在土壤中的降解实验表明,其降解速度随体系中LA含量的增加而减缓.     

The use of Fourier Transform Raman spectroscopy in the forensic identification of illicit drugs and explosives

For routine identification of forensic samples many techniques are employed. These include ultraviolet spectrophotometry, combined gas chromatography—mass spectroscopy together with high performance liquid chromatography, infrared spectroscopy and X-ray powder diffraction.Conventional Raman spectroscopy is not routinely used by forensic laboratories for the identification of drugs and explosives because of high background scatter and time consuming sample alignment.One way of overcoming these problems is to use the newly developed technique of Fourier Transform Raman spectroscopy. Here negligible sample alignment is required, and there is reduced sample fluorescence.FTR spectra were recorded of pure and contaminated illicit drug samples, together with some explosive materials. Identification of an unknown explosive (Semtex) was also conducted. FTR provides a simple and satisfactory method of identifying certain drugs and explosives. The technique is non-destructive, utilizing small samples with no sample preparation being required.     

Monitoring the vulcanization of elastomers: Comparison of curemeter and ultrasonic online control

The vulcanization of elastomeric materials has a high impact on the properties of the final product. Therefore, it is important to monitor and control this crosslinking process. A common technique to attain the necessary curing time is the use of a curemeter in accordance with ISO 6502 in order to determine the time for full cure of a sample with a standardized geometry. Based on this result and a lot of practical experience, the required curing time for a given product geometry is estimated. Within the scope of this work, a new analysis technique will be compared with the standard procedure. The ultrasonic online control employs ultrasound waves to measure the changes in material properties caused by vulcanization. For this study, a natural rubber compound with a conventional curing system was investigated by both techniques. It was found that the results of the ultrasonic technique show good agreement with the results of the curemeter.     

Analysis of Complex Molecular Systems: The Impact of Multivariate Analysis for Resolving the Interactions of Small Molecules with Biopolymers – a Review

This review is focused on the impact of chemometrics for resolving data sets collected from investigations of the interactions of small molecules with biopolymers. These samples have been analyzed with various instrumental techniques, such as fluorescence, ultraviolet–visible spectroscopy, and voltammetry. The impact of two powerful and demonstrably useful multivariate methods for resolution of complex data—multivariate curve resolution–alternating least squares (MCR–ALS) and parallel factor analysis (PARAFAC)—is highlighted through analysis of applications involving the interactions of small molecules with the biopolymers, serum albumin, and deoxyribonucleic acid. The outcomes illustrated that significant information extracted by the chemometric methods was unattainable by simple, univariate data analysis. In addition, although the techniques used to collect data were confined to ultraviolet–visible spectroscopy, fluorescence spectroscopy, circular dichroism, and voltammetry, data profiles produced by other techniques may also be processed. Topics considered including binding sites and modes, cooperative and competitive small molecule binding, kinetics, and thermodynamics of ligand binding, and the folding and unfolding of biopolymers. Applications of the MCR–ALS and PARAFAC methods reviewed were primarily published between 2008 and 2013.     

Characterization in the Toughening Process of CTBN Modified Epoxy Resins Induced by Electron Beam Radiation

Epoxy resins are widely utilized as high performance thermosetting resins for many industrial applications but characterized by a relatively low toughness. Electron beam (EB) curing of polymer resins has a number of advantages over conventional thermal curing, such as shorter curing time, low energy consumption, low cure temperature, dimensional stability, reduced manufacturing cost. In the present work liquid carboxyl-terminated butadiene acrylonitrile (CTBN) copolymers containing 8% acrylonitrile is added at different contents to improve the toughness of diglycidyl ether of bisphenol A (DGEBA) epoxy resins using triarylsulfonium hexafluoroanimonate as a photointiator. The EB irradiation was conducted 5 kGy to 250 kGy in nitrogen. The physics properties of CTBN modified epoxy resins were examined by determine gel content, DMA (dynamic mechanical analysis), UTM (Instron model 4443), SEM (scanning electron microscopy).     

Resolution of ultrafast pyrene excimer emission rise times in zeolites X and Y

Pyrene has been a favorite photophysical probe molecule for zeolite research because of its ability to exhibit both monomer and excimer emission upon excitation. This study combines the use of ultrafast time-resolved fluorescence spectroscopy with steady-state fluorescence spectroscopy to study the excimer emission of pyrene incorporated within zeolites LiY, NaY, KY and NaX. The effects of sealing technique and coincorporated solvents are also explored. Pyrene excimer emission is resolvable with the use of an ultrafast streak camera under all conditions examined in this study with a rise-time range of 6.8 to 16.0 picoseconds. For each zeolite sample the addition of cosolvents decreases the rise time, with a greater decrease for polar solvents than for a nonpolar solvent. The presence of a detectable rise time for excimer emission indicates that pyrene excimer formation is a dynamic process when pyrene is embedded within the cavities of zeolite host materials.