Photo-differential Calorimetry Research Articles

Real-time monitoring of vegetable oils photo-oxidation kinetics using differential photocalorimetry

This study introduced differential photocalorimetry (DPC) as a method for real-time monitoring of the photo-oxidation kinetics of vegetable oils. DPC measures the heat flow generated during the oxidation of oils upon light exposure. Experiments conducted with stripped linseed oil (SLSO), an oil depleted from its natural antioxidants, showed no induction time (τ). Conversely, spiking SLSO with increasing concentrations of trans-ferulic acid resulted in an induction time (τ) proportional to the antioxidant concentration (R2 = 0.99). A comparative study among different vegetable oils revealed that rice bran oil exhibited the highest resistant to photo-oxidation, followed by corn, soybean, and sunflower oils. The results are discussed in terms of sample oxidizability and antioxidant efficiency (A.E.), and validated through high-performance liquid chromatography with diode array detection (HPLC-DAD). Furthermore, the measured heat flow enabled the determination of the rates of inhibited (Rinh) and uninhibited (Runi) periods, as well as the rate constant of propagation (kp) and inhibition (kinh) reactions.

Curing Kinetic Analysis of Acrylate Photopolymer for Additive Manufacturing by Photo-DSC.

In this research, the curing degree of an acrylate-based monomer using direct UV-assisted writing technology was characterized by differential photo calorimetry (Photo-DSC) to investigate the curing behavior. Triggered by the UV light, the duo function group monomer 1,6-Hexamethylene diacrylate (HDDA), photoinitiator 1173 and photoinhibitor exhibit a fast curing process. The exothermal photopolymerization reaction was performed in the isothermal mode in order to evaluate the different thermal effects that occurred during the photopolymerization process. The influences of both UV light intensity and exposure time were studied with single-factor analysis. The results obtained by photo-DSC also allow us to perform the kinetic study of the polymerization process: The results show that, for the reaction, the higher the UV intensity, the higher the curing degree together with faster curing speed. At the same time, the effect of the heat released during the exothermic reaction is negligible for the polymerization process. When increasing the exposure time, limited improvement of curing degree was shown, and the distribution is between 65–75%. The reaction enthalpy and related curing degree work as a function of time. The Avrami theory of phase change was introduced to describe the experimental data. The functions of a curing degree with light intensity and exposure time were achieved, respectively.

A facile antibacterial coating based on UV-curable acrylated imidazoliums

Using ultraviolet (UV)-curable 3-(2-(methacryloyloxy)ethyl)-1-alkyl imidazoliums with different alkyl substituents as the bactericidal monomers and trimethylolpropane triacrylate as the crosslinker, highly efficient antibacterial coatings were designed and facilely prepared by a one-step UV-curing method. The differential photocalorimetry experiment showed these monomers polymerized within 120 s under UV irradiation, indicating a very good curable property. The excellent antibacterial activity of these coatings, which reached up to 99.8% ratio against Escherichia Coli, was demonstrated by a shake flask test method.

Investigation of photoinduced polymerization of doxycycline-imprinted hydrogels: effect of template on initiator reactivity, conversion, and reaction rate

Photopolymerization kinetics of doxycycline hyclate (DOX)-imprinted hydrogels were monitored by real-time Fourier transform infrared spectroscopy and differential photocalorimetry. 2-Hydroxyethyl methacrylate-based hydrogels were synthesized by using ethylene glycol dimethacrylate as a cross-linker, acrylic acid (AA) as a functional monomer, and 2,2-dimethyl-2-hydroxy acetophenone as a photoinitiator. For imprinting DOX in hydrogels, the molar ratio of template to functional monomer (DOX:AA) was chosen as 1:8 and 1:16. The polymerization was achieved at two different initiator concentrations. The conversion and reaction rate were calculated as a function of the molar ratio of template, and the results were compared to those of nonimprinted ones. In order to reveal the effect of DOX on the photoinduced radical polymerization, thermal polymerization was also performed for imprinted and nonimprinted hydrogels by using 2,2$' $-azobis(2,4-dimethyl-pentanenitrile) as a thermal initiator. All results showed that there is a significant effect of DOX concentration on the conversion and reaction rate of the photopolymerization reaction. The conversion and reaction rate decreased during photopolymerization when the template concentration increased in the monomer mixture.

Morphogenesis of Photo-Polymerized Dimethacrylate Networks, Kinetics of Curing and Viscoelastic Parameters

The paper refers to the process of dimethacrylate networks morphogenesis. These stiff and highly cross-linked networks have been extensively used as a polymeric matrix of dental composites for decades. In the study, common co-monomer mixtures used in dental resin formulations were employed. This includes rigid aromatic base monomers, bisphenol A glycerolate dimethacrylate (Bis-GMA) and its ethoxylated alternative (Bis-EMA). Flexible aliphatic monomer, triethylene glycol dimethacrylate (TEGDMA), was used as the viscosity reducer. Kinetics of the polymerization process was studied regarding the structural differences and varying molar ratio of the co-monomers. Kinetic data provided the base for understanding the supra-molecular structure evolution. Consequently, an attempt to quantify the relationship between the resulting network morphology and complex viscoelastic moduli was made. Curing kinetics was studied using differential photo-calorimetry (DPC). Complex modulus was measured using dynamic-mechanical analysis (DMA). Thermal degradation kinetic data (TGA) were used in order to confirm the estimated morphology of cured networks. Reactivity of the monomer is derived from its molecular structure. The potential for non-covalent physical interactions along with monomer backbone rigidity significantly decrease polymerization rate and resulting double bond conversion. The diffusion-controlled kinetics dominates over the chemically controlled kinetics throughout most of the polymerization process. Dilution by the low viscous and flexible monomer shifts the diffusion-controlled kinetics to the later stages of the polymerization. However, the flexibility of the monomer backbone promotes the origination of structural heterogeneities, characterized by micro-gel domains formation. This is associated particularly with the anomalous pendant double bond reactivity and ineffective cross-linking.

Study on curing behaviors of epoxy acrylates by UV with and without aromatic component

Two kinds of epoxy acrylates, aromatic BAGEDA (bisphenol A diglycidyl ether diacrylate) and aliphatic BDGEDA (1,4-butanediol diglycidyl ether diacrylate), were prepared from BADGE (bisphenol A diglycidyl ether) and BDDGE (1,4-butanediol diglycidyl ether) respectively by reacting with acrylic acid. Synthesis and change in functional groups were confirmed by FTIR spectra. In the studies of UV curing behaviors by Photo-DSC (differential photocalorimetry), rate constants and conversions under isothermal conditions (T cure =30-80 °C) were determined by exothermic heat flows. Thus, maximum reaction rates of BAGEDA and BDGEDA were 4.06×10-2 s-1 and 5.01×10-2 s-1 respectively. UV curing behaviors were confirmed to follow Kamal equation model. Activation energies were 23.5 kJ/mol (E a1) and 12.0 kJ/mol (E a2) for BAGEDA, and 25.0 kJ/mol (E a1) and 11.3 kJ/mol (E a2) for BDGEDA. In the UV curing reaction of BAGEDA, the maximum reaction rate constants and conversions were increased by increasing reaction temperatures (T cure ), while in that of BDGEDA those were increased until 60 °C followed by a gradual decrease above 60 °C. These phenomena were understood by Gillham’s time-temperature-transformation (TTT) diagram in which curing behavior was determined by the glass transition temperature (T g ) of cured material at each reaction temperature.

Photopolymerization kinetics of 2-phenylethyl (meth)acrylates studied by photo DSC

The present work deals with the photopolymerization of 2-phenylethyl (meth)acrylates and estimation of their kinetic parameters. Formulations were made by independently homogenizing the monomers with photoinitiators of two different classes. Two different compositions of photoinitiators were used to study the effect of concentration of photoinitiator on cure kinetics. These compositions obtained were tested for photo curing performance using differential photocalorimetry (DPC) or photo DSC under polychromatic radiation. The heat flow against time was recorded for all formulations under isothermal conditions and the rates of polymerization as well as the percentage conversions were estimated. It was observed that due to a longer timescale for reaction diffusion, the methacrylate formulations showed a higher conversion than acrylate formulations. Other parameters such as induction time, maximum rate and conversion attained as well as the time to attain peak maximum were noted. The photopolymerization and kinetic estimations of the formulations including evaluation of kinetic models are discussed.

Synthesis, Characterization and Performance Study of Borosilazane as UV-Curable Borazine-Type Single Source Precursors for SiBNC Ceramic

A novel borosilazane monomer terminated with Si-Cl groups: B,B',B"-tris[(trichlorosilyl)methyl] borazine (TSMB) was synthesized through one-step route by reacting boron trichloride (BCl3), chloromethyl trichlorosilane (CH2ClSiCl3) with hexamethyldisilazane (HMDZ) as the starting materials. From functionalizing TSMB by 2-hydroxethyl acrylate and 2-hydroxyethyl vinyl ether, two UV-curable single source precursors a-TSMB and e-TSMB were obtained, respectively. Then ceramic materials C1 and C2 can be prepared with a-TSMB and e-TSMB through UV-curing and cracking under 1400 °C for 2 h. The chemical composition, structure, photo-curing performance and ceramic yield of the TSMB, a-TSMB and e-TSMB were investigated using infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), differential photocalorimetry (DPC), real time infrared spectroscopy (RT-IR) and thermo gravimetric analyzer (TGA). The content and high temperature performance of the ceramic C1 and C2 were studied by element analysis, X-ray photoelectron spectroscopy analysis (XPS) and X-ray diffraction (XRD). Results show that both the two ceramic precursors molecules, a-TSMB and e-TSMB, contain the B-N six-member 1036 化 学 学 报 Vol. 70, 2012 ring structure, and are terminated with acrylate or vinyl ether functional groups, which matches well with the theoretical design. The photo polymerization of the a-TSMB and e-TSMB can finish 82% and 67% in 25 s, the final conversion of the double bond can reach 90.0% and 74.0%, and the corresponding ceramic yield at 1300 °C is 57.9% and 48.5%, respectively. There are five elements, Si, B, C, N, and O in the C1 and C2 ceramic materials, and the contents of B are 4.4% and 4.9%, respectively, which can achieve the requirement for the high temperature ceramic material on the B element. Both the ceramic materials C1 and C2 can preserve amorphous states at 1400 °C and have excellent high-temperature resistance properties.

Enhanced cationic photocuring of epoxides with styrene oxide as a reactive diluent

Styrene oxide [StO] has been investigated as a reactive diluent for cationic photocurable formulations to provide key requirements such as low viscosity and negligible odor, in addition to high photoreactivity. The formulations were composed of commercial cyclic ethers including epoxides and oxetanes in StO using diaryliodonium salt as a photoinitiator, and they gave enhanced photocuring by analyzing with differential photocalorimetry. In particular, the cationic formulations composed of StO, bisphenol A diglycidyl ether, (3-glycidoxypropyl)trimethoxysilane and others rendered improved mechanical and thermal properties when their photocured coatings were examined. The gel content and pencil hardness values of photocured films were determined to evaluate the formulations. For the mechanistic explanation of the enhanced photoreactivity, the polymer-bound benzyl cations formed by a chain process in the polymer chains comprising StO moieties were postulated to serve as additional sites for the initiation of cationic photopolymerization of StO and cyclic ether monomers.

Photo-polymerization of photocurable resins containing polyhedral oligomeric silsesquioxane methacrylate

Photocurable resins, bisphenol A propoxylate glycerolate diacrylate (BPA-PGDA, containing two hydroxyl) and bisphenol A propoxylate diacrylate (BPA-PDA), with fixed photoinitiator (Irgacure 907) concentration and various contents of methacrylisobutyl polyhedral oligomeric silsesquioxane (MI-POSS) were prepared and characterized by FTIR spectroscopy, scanning electron microscope and differential photocalorimetry. The MI-POSS molecules form crystals or aggregated particles in the cured resin matrix. The BPA-PGDA series photocurable resins show higher viscosity and lower photo-polymerization reactivity than the BPA-PDA series resins. The photo-polymerization rate and conversion of BPA-PGDA series are improved with increasing MI-POSS content. On the contrary, the photo-polymerization behavior of BPA-PDA series photocurable resins remains nearly unchanged by the addition of MI-POSS. Hydrogen-bonding interaction between the hydroxyl of BPA-PGDA and the siloxane of MI-POSS tends to attract and concentrate these acrylate double bonds around MI-POSS particles and thus enhances the photo-polymerization rate and conversion.

Diallyl Tartrate as a Multifunctional Monomer for Bio-polymer Synthesis

This paper introduces the use of a diallyl dicarboxylate compound, diallyl tartrate, as a monomer in the synthesis of a biodegradable polymer. Although the allyl functional group is generally known for not being able to polymerize to high conversions, it was found in this study that by using photoinitiation instead of thermal initiation, a highly cross-linked polymer could be obtained from the polymerization of diallyl tartrate in a relatively short time. The details of the polymerization reaction were investigated in detail using differential photocalorimetry (DPC). The final thermoset obtained was shown to be completely amorphous and rigid, with a glass transition temperature of approx. 90°C and a storage modulus of approx. 1 GPa at room temperature, via thermal analysis. It was also found to biodegrade in vitro via hydrolysis of its ester groups at a moderate rate, taking nearly 12 weeks to lose 50% of its mass. Both the photo-polymerized material and its water-soluble degradation products were further shown to be non-cytotoxic to fibroblast cells over at least 24 h of exposure. These results aim to initiate the use of this class of monomers in the synthesis of new polymers with tailored properties for biomaterial applications.

Fast cure kinetics of a UV-curable resin for UV nano-imprint lithography: Phenomenological model determination based on differential photocalorimetry results

The fast cure kinetics of an ultraviolet (UV) light-curable resin for UV nano-imprint lithography (UV-NIL) was measured using a differential photocalorimeter (DPC). A simple phenomenological model was formulated to describe the curing behaviors of the UV-curable resin, i.e., the initial fast reaction rate at a small degree of cure and the autocatalytic reaction rate at a larger degree of cure. Kinetic model parameters were best fitted to the measured cure rate by using an error minimization technique. The practical applicability of the phenomenological model developed herein was demonstrated by a good agreement between the measured and modeled curing behaviors of the UV-curable resin. The effect of cure conditions on the estimated kinetic model parameters was also investigated.

Self-initiated photopolymerization of hyperbranched acrylates

Abstract Self-initiated photopolymerization of hyperbranched acrylates (HBAs) has been investigated. The photopolymerization progress was monitored by differential photo-calorimetry (DPC). It was shown that HBAs were able to self-initiate photopolymerization rapidly under the irradiation of medium-pressure mercury lamp. This behavior was explained by the longer wavelength absorption (∼286 nm) of HBAs, which results from the overlapping of π-conjugated orbitals of acrylate groups. Autoacceleration effect was observed. The autocatalytic model was used to analyze the photopolymerization kinetics and found to well match the experimental data. It was found that acceleration stage ended at low conversion ( α R m α f was lower than 40% in most cases. This was attributed to the poorer ability of HBAs to generate primary radicals and thus the insufficiency of free radicals in polymerization. Factors in favor of generating primary radicals extended the autoacceleration stage to higher conversion and gave higher final conversion. The values of activation energy were calculated to be in the range of 5.7–7.5 kJ mol −1 , analogous to those for the free radical photopolymerization of acrylate monomers in the presence of photoinitiator.

SYNTHESIS AND CHARACTERIZATION OF UV CURABLE POLYVINYLSILAZANE

Polyvinylsilazane (PVSZ) is a well known ceramic precursor for the fabrication of high performance ceramic structures which are involved in harsh environments.The shaping process for ceramic structures usually involves thermal or photo curing techniques with the aids of polydimethylsiloxan (PDMS) molds to transform liquid preceramic polymer into well-shaped solid structures.Thermal curing of PVSZ needs more than 60～120 min at about 100℃,and photo curing needs about 20 min at room temperature.Both these two curing methods are very hard to get fine microstructures because of the absorption or adhesion between the surface of preceramic polymer and PDMS molds.In order to develop a preceramic photoresist based on PVSZ for the fabrication of non-oxide SiCN ceramic microstructures by a mold-free fast photocuring shaping process,UV sensitive acrylate functional groups were successfully grafted onto the backbone of PVSZ by its reaction with ethyl-4-bromocrotonate(EBC) via a high efficiency allyl bromide electrophilic substitution process.In a typical reaction,3 g of EBC was added drop-wisely into 4 g of PVSZ dissolved 20 mL of toluene.The mixture was heated in an oil bath at 90℃ for 72 h with continuously magnetic bar stirring.Finally,the white HBr precipitate was removed by high speed centrifugal treatment and a filtration process; the solvent and unreacted precursor was subsequently removed by vacuum pump.All of the processes were carried out in an inert gas atmosphere to avoid exposure to moisture,utilizing standard Schlenk techniques.The as-modified polymer was characterized by 1H nuclear magnetic resonance (1H-NMR) and 2D-1H-1H-NMR (COSY) spectroscopy,and its UV sensitivity was investigated by differential photocalorimetry (DPC) and Fourier transform infrared (FT-IR) spectroscopy.The samples for photosensitive checking were prepared by an addition of 5 wt% of photoinitiator IRGACURE369.The results of 1H-NMR pointed out that the hydrogens on the NH groups of PVSZ at δ=0.65 were obviously consumed after chemical modification,and there was a new peak at δ=2.23 on the 1H-NMR spectra of m-PVSZ which was assigned to the hydrogen of (CH_2—N).The results of 2D-1H-1H-NMR gave out further evidence of the newly appeared chemical bond (CH_2—N).The peak at δ=2.23 (CH_2—N) was correlated to the peak at δ=7.01 (—CHCH—),which had confirmed that there was a group like (N—CH_2—CHCH—) on m-PVSZ.The new chemical bond of (CH_2—N) strongly supported the chemical modification of grafting UV sensitive acrylate functional groups onto the backbone of PVSZ.The results of DPC pointed out that 90% UV curing of m-PVSZ could be finished within 60 s with a peak heatflow of 1.18 w/g; however,it would take about 20 min for PVSZ for curing at the same conditions as m-PVSZ.The results of TGA pointed out that the chemical modification had some negative effects on its ceramic yield,the final ceramic yield of m-PVSZ at 1000℃ was 55.34%,and that was 63.13% for PVSZ.All the above results showed that m-PVSZ is a promising candidate of negative photoresist for the fabrication of micro ceramic structures by photolithography.The dramatically increased UV curing speed would be good for the fabrication of fine ceramic microstructures,which is still under progress in our group.

Synthesis of telechelic methacrylic siloxanes with cycloaliphatic substituents groups for UV-curable applications

Methacrylic functionalized siloxanes were prepared in a two-step process. In the first step, a series of telechelic glycidyl epoxy siloxanes were prepared, substituted with either methyl, cyclopentyl, or cyclohexyl groups. In the second step, the telechelic glycidyl epoxy groups were reacted with methacrylic acid. The reaction was monitored via acid value, and when the acid value was ⩽10, the reaction was terminated. Characterization of the methacrylic telechelic siloxane polymers were performed using 1H NMR, 13C NMR and FT-IR. The methacrylated siloxanes were formulated with a free radical photo-initiator, UV-cured, and the rate of polymerization was monitored via photo-differential calorimetry. After curing, viscoelastic properties, and oxygen-permeability were evaluated. In addition, X-ray was used to evaluate the structure of the cured films. The rate of polymerization was dependent on substituent and increased with increasing substituent size. The oxygen permeability was dependent on crosslink density, and increased with increasing substituent size. The increase in permeability, and thus free volume was supported by X-ray studies which showed an increase in d-spacing with increasing alkyl size.

Acrylation of polyvinylsilazane with allyl bromide for an UV photosensitive inorganic polymer

A novel inorganic polymer resin with high photosensitivity was prepared by grafting acrylate functional groups onto the backbone of polyvinylsilazane through a reaction with methyl-2-(bromo-methyl)acrylate via the highly efficient electrophilic substitution of allyl bromide. The as-modified polymer was characterized by 1H NMR and 2D- 1H– 1H NMR (COSY) methods to determine the reaction mechanism. Differential photocalorimetry, FT-IR spectroscopy and TGA were used to examine its properties. The modified polyvinylsilazane is a promising inorganic polymer photoresist with a high UV sensitivity and a 55% ceramic yield, which is useful for fabricating non-oxide ceramic microstructures using mold free photocuring shaping processes.

Dendritic carbosilane‐based macrophotoinitiator: synthesis, characterization, and photoinitiating behavior

AbstractA novel radical dendritic macrophotoinitiator, bearing alkyl pheone moieties linked to the surface of the dendrimer, was synthesized via alcoholysis of carbosilane dendrimer and the small‐molecule photoinitiator 2‐hydroxy‐2‐methyl‐1‐(4‐tert‐butyl)phenylpropane‐1‐one. The structure of the dendritic carbosilane‐based macrophotoinitiator (MPI) was characterized using Fourier transform infrared spectroscopy, 1H NMR, 13C NMR, 29Si NMR, elemental analysis, size exclusion chromatography/multi‐angle laser light scattering, UV‐visible spectroscopy, and differential photocalorimetry (DPC). UV‐visible analysis indicates that the absorption band of photosensitive moieties shifts towards high wavelength by introducing the carbosilane dendrimer core. The DPC results demonstrate that the initiating efficiency of MPI is effective when using epoxy acrylate (EA) as a model resin. Furthermore, thermogravimetric analysis of cured EA resin indicates that the thermal stability can be improved markedly by the incorporation of MPI in the curing formulation. Copyright © 2007 Society of Chemical Industry

Kinetic study of negative dry-film photoresists

Thanks to the differential photocalorimetry technique DPC, characteristics of negative photoresists (Riston® PM 215 and Riston® MM 140, 1 mil or 25.4 μm thickness) to be developed in nonorganic aqueous medium) used in microlithography are highlighted. The photoreactivity (being evaluated by DPC) of the matrix polymer involved in these Riston® is critical for ensuring good lithographic performance. The influence of temperature and irradiation intensity on kinetic parameters such as the enthalpy of reaction ΔH, the time of induction (It), the conversion rate to the maximum peak (RPM), the coefficient rate of the reaction (k), the conversion rate α, and the polymerization rate Rp were studied. All the results highlights not only the strong differences between the two Riston® studied, but also the great reactivity of Riston® PM 215 compared to Riston® MM 140.

Synthesis and study of novel polyol‐bound photosensitizers for cationic UV‐curable systems

AbstractNovel cationic intramolecular hydrogen abstraction photosensitizers (IHA‐PSs) based on a proposed intramolecular hydrogen abstraction photosensitization (IHAP) mechanism were synthesized and found to have a pronounced photosensitization effect in cycloaliphatic epoxide based cationic UV‐curable systems using sulfonium salt photoinitiators. A series of polyol‐based photosensitizers were synthesized with naphthalene attached. One photosensitizer, P‐Na, was found to have a more pronounced photosensitization effect in three different formulation systems, as revealed by real‐time Fourier transform infrared and differential photocalorimetry experiments. Such a phenomenon can be explained by a proposed facile IHAP mechanism, which is possible only with the unique molecular structure of P‐Na. The effect of P‐Na was further confirmed by comparison with two non‐polyol‐type photosensitizers. A designed IHA‐PS molecule was synthesized with the proposed principles ofthe IHAP mechanism, and it achieved a photosensitization effect similar to that of P‐Na with a much lower molecular weight and fewer hydroxyl groups per molecule. This further validated the proposed IHAP mechanism. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4435–4449, 2006

Photoinitiating behavior of macrophotoinitiator containing aminoalkylphenone group

Photoinitiating behaviors of oligo(α-aminoketones) (OAK) macrophotoinitiator containing aminoalkylphenone group on free-radical photopolymerization had been investigated by differential photo-calorimetry (DPC). The macrophotoinitiator showed comparative performance with those commercial photoinitiators with lower molecular mass. The effect of photoinitiator concentrations and UV intensity on the polymerization rate was investigated, and the value of exponential factor was found to be 0.5 at the beginning of polymerization, suggesting that the photopolymerization initiated by OAK followed biradical termination mechanism. Photosensitizer isopropyl thioxanthone (ITX) and oxygen severely restricted the polymerization in these systems. Photoinitiators with lower molecular mass showed higher reactivity than those with higher molecular mass.