Polymerization kinetics of photocurable acrylic resins (original) (raw)
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Kinetics characterization of a novel photopolymerizable siloxane-modified acrylic resin
Thermochimica Acta, 2010
An experimental study was carried out for the development and characterization of innovative photopolymerizable siloxane-modified acrylic formulations for possible use as protective coatings. The kinetics of the radical photopolymerization mechanism induced by UV and visible radiations in presence of suitable photoinitiators was studied by a calorimetric analysis by varying the testing conditions (temperature, light power emission, atmosphere). The reactivity, expressed in terms of both heat developed and rate of reaction, was generally found to decrease when the photopolymerization was carried out in air, due the inhibiting action of the oxygen towards the free-radical polymerization. The addition of both a silane coupling agent or a high molecular weight polysiloxane monomer to the acrylic resin was found to reduce the heat of reaction. Experimental data were fitted to a kinetic model to quantify the effects of light intensity and temperature on reaction rates and extent of reaction. A good agreement between the experimental data and the theoretical model was generally found.
Copolymerization and dark polymerization studies for photopolymerization of novel acrylic monomers
Polymer, 2007
The copolymerization behavior and the dark polymerization kinetics of highly reactive novel acrylic monomers were compared to traditional acrylate monomers. Copolymerization of thiol functionalities with novel acrylic monomers was characterized, and it was observed that the inclusion of secondary functionalities such as carbamates, carbonates, and cyclic carbonates, in acrylic monomers significantly alters the relative reactivity of the novel acrylates with thiols. While traditional aliphatic acrylates exhibited propagation to chain transfer ratios ranging between 0.8 (± 0.1)-1.5(± 0.2), the novel acrylates characterized by secondary functionalities exhibited much higher propagation to chain transfer ratios ranging from 2.8(± 0.2)-4(± 0.2). In the dark polymerization studies, the kinetics of the novel acrylates were evaluated following cessation of the UV light. The novel acrylates exhibited extensive polymerization in the dark compared to most traditional acrylates and diacrylates. For instance, cyclic carbonate acrylate was observed to attain 35 % additional conversion in the dark when the UV light was extinguished at 35 % conversion, whereas traditional acrylates such as hexyl acrylate attained only 3 % additional conversion when the UV light was extinguished at 35 %, and a diacrylate such as HDDA attained 15 % additional conversion when the UV light was extinguished at 40 % conversion. Also, through choice of appropriate monomers, the dark polymerization studies were performed such that the polymerization rate was approximately the same at the point the light was extinguished for all these monomers. The copolymerization and dark polymerization studies support the hypothesis that the nature of the propagating species in the novel acrylates is altered as compared to traditional acrylic monomers and polymerizations.
Macromolecules, 2003
A systematic study on the effect of molecular structure on the photoinitiated polymerization of acrylates was undertaken. Initially, the research was focused on the effect of hydrogen bonding, and it was found that preorganization via hydrogen bonding enhances the maximum rate of polymerization (R p). This hydrogen bonding facilitated preorganization also affected the tacticity of the resultant polymer. Next, the effect of polarity as represented by the calculated dipole moment (µcalc) of a given monomer was investigated. A direct linear correlation between Rp and the calculated Boltzmann-averaged dipole moment (µcalc) was observed. The Rp-µcalc correlation holds for pure monomers, mixtures of monomers, and even mixtures of monomers with inert solvents. This correlation enables the rational design of monomers with a required reactivity. In addition, these studies suggest that the propagation step of polymerization is influenced by hydrogen bonding while the dipole moment influences the termination rate constant. These two mechanistic explanations can be regarded as complementary factors that influence the speed of acrylate polymerization.
Polymer, 1996
The influence of temperature on the photopolymerization kinetics of three analogous monomers, 2.2'thiobisethanol diacrylate, 2,2'-oxybisethanol diacrylate and 1.5-pentanediol diacrylate, has been studied by isothermal differential scanning calorimetry in the temperature range of 30-100°C in air and in Ar atmosphere. The presence of the heteroatom markedly enhances the final conversion and maximum polymerization rate in air over the whole temperature range. This effect is much more pronounced for the sulfur-containing monomer. The final conversions of the monomers increase with temperature up to 100°C in air but in Ar they pass through a maximum at about 70°C in the case of monomers that do not contain sulfur. The sulfide group prevents the drop of cure extent in Ar at higher temperatures. The obtained results (kinetic parameters, activation energy) are discussed mainly in terms of hydrogen abstraction reaction.
Materials Chemistry and Physics, 2011
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.
Journal of Applied Polymer Science, 2008
The photopolymerization kinetics and viscosity behavior of 11 2,2-bis[4-(2-hydroxymethacryloxypropoxy)phenyl]propane/triethylene glycol dimethacrylate mixtures were investigated. The viscosity was studied at six temperatures (20-70 C), and the activation energies for the viscosity were determined. The excess logarithm viscosities were calculated and found to be negative over the whole composition and temperature ranges; they were fitted to the Redlish-Kister polynomial equation. The kinetic analysis of the photopolymerization was carried out at three polymerization temperatures (20, 40, and 60 C). The results proved the existence of the most reactive composition (reaching the highest value of the maximum polymer-ization rate), but the ratio of the monomers in this composition, close to equimolar, showed a tendency to change with the polymerization temperature. The viscosities of the most reactive compositions lay in the range of about 0.1-1.2 Pa s, which was narrow in comparison with the range of viscosities of all the compositions used in the kinetic studies (from 3 Â 10 À3 to 1.5 Â 10 3 Pa s). The activation energies for the polymerization rates were calculated and correlated with the viscosity changes.
Photopolymerization of acrylate suspensions
Journal of Photochemistry and Photobiology A: Chemistry, 2012
Polymerization time parameters, induction time t 0 and t 50 obtained from Boltzmann sigmoidal fitting, were determined from photorheology experiments performed on diacrylate and glycol dimethacrylate suspensions with silicon dioxide, with varying photoactives concentration and in the presence of diluents. The experiments were performed at the intensity ∼23 mW/cm 2 . t 0 and t 50 are linearly proportional to reciprocal photoinitiator concentration 1/c P , dye concentration c D and inhibitor concentration c INH as predicted by modified inhibitor exhaustion model. Further, the effect of a reactive and an inert diluent is shown.
Polymer, 1996
The polymerization of three analogous monomersP2.2'-thiobisethanol dimethacrylate. 2.2'-oxybisethanol dimethacrylate and 1,5-pentanediol dimethacrylate-has been studied in the temperature range 3OG95"C by isothermal d.s.c. The temperature and heteroatom effects on the polymerization course were considered from the point of view of the occurrence and relative importance of hydrogen abstraction reaction which is manifested by chain transfer and chain peroxidation processes. Generally the advantageous effect of the sulfide group is revealed in reduction of oxygen inhibition and suppression of the drop of final conversion with increasing temperature above 70°C in the absence of oxygen. However, the influence of the sulfide group on the polymerization of dimethacrylates is not so great as on diacrylates due to various factors of both a physical and chemical nature. (Keywords: dimethacrylates; sulfide group; temperature effect on photopolymerization)
Journal of Photochemistry and Photobiology A-chemistry, 1995
The influence of the type of photoinitiator, type of polymerizable reactive diluent and added amine synergist on the yellowing which occurs during the curing of clear films is examined. Type I photoinitiators based on acetophenone give rise to ~he least yellowing. The presence of amines, such as N-methyldiethanolamine, increases yellowing to a noticeable extent. Amino groups present in the initiator or the reactive diluent lead to marked yellowing. The chemistry responsible for the yellowing is explored.