Photopolymerization Of Acrylates Research Articles

Unconstrained recovery characterization of shape-memory polymer networks for cardiovascular applications

Shape-memory materials have been proposed in biomedical device design due to their ability to facilitate minimally invasive surgery and recover to a predetermined shape in vivo. Use of the shape-memory effect in polymers is proposed for cardiovascular stent interventions to reduce the catheter size for delivery and offer highly controlled and tailored deployment at body temperature. Shape-memory polymer networks were synthesized via photopolymerization of tert-butyl acrylate and poly(ethylene glycol) dimethacrylate to provide precise control over the thermomechanical response of the system. The free recovery response of the polymer stents at body temperature was studied as a function of glass transition temperature ( T g), crosslink density, geometrical perforation, and deformation temperature, all of which can be independently controlled. Room temperature storage of the stents was shown to be highly dependent on T g and crosslink density. The pressurized response of the stents is also demonstrated to depend on crosslink density. This polymer system exhibits a wide range of shape-memory and thermomechanical responses to adapt and meet specific needs of minimally invasive cardiovascular devices.

Effects of neighboring sulfides and pH on ester hydrolysis in thiol–acrylate photopolymers

Networks synthesized through thiol–acrylate photopolymerization or Michael-type addition step growth reactions contain esters with neighboring sulfide groups. Previous work has demonstrated that these esters are readily hydrolyzable at physiological pH. Here, the influence of the distance between the sulfide and ester, as well as the water concentration, on ester hydrolysis was characterized. These preliminary results indicate that reducing the number of carbons between the sulfide and the ester from 2 to 1 increased the rate of ester hydrolysis from 0.022 ± 0.001 to 0.08 ± 0.015 days −1. Increases in ester hydrolysis rates were also observed as hydrophilicity increased for oligomers prepared from a trithiol, tetrathiol and dithiol monomer (0.012 ± 0.003, 0.032 ± 0.004, and 0.091 ± 0.003 days −1, respectively). Additionally, in bulk-eroding polymeric biomaterials, variations in pH impacted the ester hydrolysis rate. This work confirms that small variations in buffer pH predictably alter the mass loss profile of a thiol–acrylate photopolymer. More specifically, as buffer pH was changed from 7.4 to 8.0, the rate of ester hydrolysis increased from 0.074 ± 0.003 to 0.28 ± 0.005 days −1. The magnitude of this observed change in ester hydrolysis rate was correlated to the increase in hydroxide ion concentration that accompanied this pH change.

On the inhibiting effect of phenolic compounds in the photopolymerization of acrylates under high‐intensity and polychromatic UV/visible lights

AbstractThe photopolymerization of wood coatings under UV and visible light in industrial type conditions has been investigated. The inhibiting effect of the phenolic compounds found in wood extractives, especially quercetin, on the final properties of the coating (hardness, gel content) as well as the polymerization kinetics (rates, final conversion) has been discussed. Model clear‐coating formulations — based on an acrylate oligomer, a reactive diluent and a bis‐acylphosphine oxide as photo‐initiator — have been used. This article focuses on the influence of the nature of the acrylate oligomer (polyester, epoxy, polyurethane), the type of phenolic derivative (POHs) and the irradiation conditions (UV conveyor, Xe lamp). It appears that lead to through the strong inner‐filter effect in the presence of quercetin is responsible for the loss of all the observed properties. In order to mimic what happens at the wood–coating interface, the role of the diffusion of the phenolic derivatives have been also investigated and discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3285–3298, 2007

Gel Permeation Chromatography Characterization of the Chain Length Distributions in Thiol−Acrylate Photopolymer Networks

Crosslinked, degradable networks formed from the photopolymerization of thiol and acrylate monomers are explored as potential biomaterials. The degradation behavior and material properties of these networks are influenced by the molecular weight of the nondegradable thiol-polyacrylate backbone chains that form during photopolymerization. Here, gel permeation chromatography was used to characterize the thiol-polyacrylate backbone chain lengths in degraded thiol-acrylate networks. Increasing thiol functionality from 1 to 4 increased the backbone molecular weight (M̄(w) = 2.3 ± 0.07 × 10(4) Da for monothiol and 3.6 ± 0.1 × 10(4) Da for tetrathiol networks). Decreasing thiol functional group concentration from 30 to 10 mol% also increased the backbone lengths (M̄(w) = 7.3 ± 1.1 × 10(4) Da for the networks containing 10 mol% thiol groups as compared to 3.6 ± 0.1 × 10(4) Da for 30 mol% thiol). Finally, the backbone chain lengths were probed at various stages of degradation and an increase in backbone molecular weight was observed as mass loss progressed from 10 to 70%.

Three component ketocoumarin, amine, maleimide photoinitiator II

Three component photoinitiator systems containing N-substituted maleimide/ketocoumarin/tertiary amine have been used for the visible light photopolymerization of acrylate and thiol-ene monomers. Thin-film calorimetry studies were conducted. The polymerization exotherms of these systems with the blue (470 nm) and cyan (505 nm) LED light sources show that the multicomponent initiator package is an effective system for visible light polymerization of acrylate and thiol-ene monomers. Exotherms of a visible light initiator combination of camphorquinone/amine were recorded for comparison purposes.

Photopolymerization without Light. Polymerization of Acrylates Using Oxalate Esters and Hydrogen Peroxide

We define the photopolymerization of acrylates without light as a process wherein the radical chain polymerization produced by photoinitiators are produced by nonphotochemical means. We use the chemical reactions of the chemiluminescent lightstick to accomplish this. An important potential application is in producing “photopolymers” in areas that are not light accessible as in the inside of a tube or behind a pipe. Polymerizable acrylate mixtures containing dissolved oxalate esters undergo radical chain polymerization when exposed to a flow of nitrogen gas saturated with hydrogen peroxide vapors. We propose aryloxyoxalyl hydroperoxides to be the reactive species.

Acrylate photopolymerization on heterostructured TiO 2 photocatalysts

Heterostructured TiO 2 samples were prepared by precipitation of Al 2O 3, Fe 2O 3 hydrate, AgCl and Ag 2O, respectively, onto the surface of a commercial anatase type pigment. The photopolymerization of an ethoxylated trisacrylate was used as a test reaction to check the photocatalytic activity of the heterostructured TiO 2 samples. The TiO 2 sample coated with Al 2O 3 showed no noticeable photocatalytic activity; the untreated TiO 2 was also not a good photocatalyst; in contrast, the TiO 2 samples which had been coated with Fe 2O 3 or AgCl showed enhanced polymerization rate as well as monomer conversion after 120 s illumination. The results of the photopolymerization experiments are explained on the basis of the thermodynamics of the charge transfer between the photoexcited TiO 2 samples and the acrylate. The photoelectric properties of the TiO 2 samples which were characterized using transient Photo-EMF measurements also play an important role in their photocatalytic activity.

Gradient Structure Polymer Obtained from a Homogeneous Mixture: Synthesis and Mechanical Properties

AbstractSummary: The synthesis of a polymer that exhibits a gradient in mechanical properties, by means of a new method recently developed in our laboratory, is described. The synthesis involves two commercial resins, Laromer® LR 8986 and Laromer® LR 9000. In a first step, an acrylic double bond photopolymerization gradient is created under UV exposure thanks to the decay of UV light intensity through the sample thickness. In a second step, a thermal crosslinking reaction is realized to form a polyurethane network in order to set the obtained gradient. The experimental conditions required to obtain and keep the gradient are investigated by FT‐IR and UV spectroscopies. Thus, an 80% acrylic double bond conversion gradient is obtained in the ultimate 5 mm thick material. Dynamic mechanical analysis reveals an important difference between both sides of the material, the irradiated surface being hard at ambient temperature, meanwhile the underside remains soft.Acrylic double bond conversion after 3 min of irradiation at 30 °C on materials of various thicknesses.magnified imageAcrylic double bond conversion after 3 min of irradiation at 30 °C on materials of various thicknesses.

Oxygen inhibition in thiol–acrylate photopolymerizations

AbstractThe overall effects of oxygen on thiol–acrylate photopolymerizations were characterized. Specially, the choice of thiol monomer chemistry, functionality, and concentration on the extent of oxygen inhibition were considered. As thiol concentration was increased, the degree of oxygen inhibition was greatly reduced because of chain transfer from the peroxy radical to the thiol. When comparing the copolymerization of 1,6‐hexanediol diacrylate with the alkane‐based thiol (1,6‐hexane dithiol) to the copolymerization with the propionate thiol (glycol dimercaptopropionate), it was found that the propionate system was much more reactive and polymerized to a greater extent in the presence of oxygen. In addition, the functionality was considered where the glycol dimercaptopropionate was compared to a tetrafunctional propionate of similar chemistry (pentaerythritol tetrakis(mercaptopropionate)). Given the same thiol concentration, the higher functionality thiol imparted a faster polymerization rate, due to the increased polymer system viscosity, which limited oxygen diffusion and decreased the extent of overall oxygen inhibition. Thus, preliminary insight is provided into how thiol monomer choice affects the extent of oxygen inhibition in thiol–acrylate photopolymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2007–2014, 2006

Role of the Medium on the Reactivity of Cleavable Photoinitiators in Photopolymerization Reactions

The efficiency of 11 cleavable photoinitiators in polymerization reactions was determined in various media, such as oligomer, acrylate, and methacrylate monomers in solution or in poly(methyl methacrylate). It was found that the efficiency of the photoinitiator strongly depends on the polymerized medium. The results are explained and discussed on the basis of the viscosity effect on the rate constants of the processes involved, resulting in good efficiency/reactivity relationships. Quantum yields of initiation were calculated for an acrylate photopolymerization in solution. The efficiency in viscous bulk media is quite well reflected in the dissociation quantum yields of the photoinitiators measured in solution. The role of the other low-viscosity media is also explained. Kinetic treatments were used to examine the influence of the monomer structure on the propagation and termination rate constants of the reaction. These results allowed to shed some light on the influence of the medium on the initiation efficiency and to provide a better knowledge of the key parameters for practical applications.

Holographically formed Bragg reflection gratings recorded in polymer-dispersed Liquid crystal cells using a He-Ne laser

Bragg reflection gratings are holographically recorded in polymer-dispersed liquid crystal materials by using the 632.8-nm wavelength of the He-Ne laser. Mixtures of the commercially available E8 nematic liquid crystal, pentafunctional monomers, and photooxidant dye methylene blue are employed. We demonstrate that Bragg reflection gratings can be formed in this acrylate photopolymer system with reflection efficiencies of 52% with a peak notch at 1165 nm. We also present results for the switching characteristics of these gratings with switching fields on the order of 6MV∕m and rise times of 62μs.

The effect of interpenetrating polymer network formation on polymerization kinetics in an epoxy‐acrylate system

The kinetics of thermally initiated cationic epoxy polymerization and free radical acrylate photopolymerization were studied using photo-differential scanning calorimetry. The reactions of the neat monomers and diluted monomers as well as interpenetrating polymer networks (IPNs) were studied as a function of dilution by the other monomer and temperature. The reaction sequence was also varied to study its effect on the kinetics of formation of the simultaneous IPN's. Both reactions quickly become diffusion controlled. The effects of increasing temperature and dilution on the acrylate polymerization rate profiles are similar, leading to reduced polymerization rate and longer polymerization times. The dilution effect on the epoxy polymerization is similar to that of the acrylate. However, unlike the acrylate reaction the epoxy polymerization rate increases strongly with temperature. The preexistence of one polymer has a significant effect on the polymerization of the second monomer. This effect is larger for the acrylate than for the epoxy polymerization. New kinetic models are needed to capture these complex behaviors.

Highly transparent ZrO2nanoparticle-dispersed acrylate photopolymers for volume holographic recording

We demonstrate and characterize volume holographic recording in ZrO(2) nanoparticle-dispersed acrylate photopolymer films that have very low scattering loss. More than thirty-fold reduction in the scattering coefficient, as compared with those of previously reported TiO(2) nanoparticle-dispersed photopolymers, is achieved. It is shown that the refractive index modulation as high as 5.3x10(-3), together with substantive photopolymerization-shrinkage suppression, is obtained at the nanoparticle concentration of 15 vol.%. Dependences of nanoparticle concentration and grating spacing on the refractive index modulation are also investigated.

Investigations on the Photoinitiator‐free Photopolymerization of Acrylates by Vibrational Spectroscopic Methods

AbstractPhotopolymerization of acrylates without photoinitiators was carried out by irradiation with short‐wavelength UV light from excimer lamps with an emission at 222 or 172 nm. Basic investigations on the reactivity of various acrylates and on the conditions under which they can be UV‐cured were performed by real‐time FTIR‐ATR spectroscopy. Depending on the molar extinction coefficients of a specific acrylate at the wavelength of irradiation, the absorption of the light within the coating leads to a pronounced intensity gradient which significantly influences polymerization rate and conversion. Accordingly, it limits the maximum thickness of the layer that can be cured (ranging from some hundreds of nanometres up to some micrometers). In addition to the basic studies, thin acrylate coatings were also cured on pilot scale. The actual conversion in the layer after UV irradiation was directly monitored by in‐line NIR reflection spectroscopy, and the resulting coatings were characterized by FTIR spectroscopy and hardness measurements.

Construction of micron three-dimensional structures employing multi-photon polymerization

In the current paper, a study is made of the manufacture of three-dimensional structures of micron resolution using two- and three-photon polymerization. A femtosecond laser operating at a wavelength of 1028 nm is employed for the multi-photon polymerization processes. For the component manufacture, two different materials are used. The first material, used in two-photon polymerization, is an acrylate-based photo-polymer that polymerizes by employing green radiation. The second material, used in three-photon polymerization, is an ultraviolet (UV) -photopolymerizable acrylate composite.

Photorheology of Fast UV‐Curing Multifunctional Acrylates

AbstractSummary: The fast photopolymerization of different multifunctional acrylates was analyzed by means of photorheology. The materials studied included a penta/hexaacrylate monomer and two different acrylated hyperbranched polymers. The sensitivity of the commercial rheometer was improved several‐fold, by a combination of an adaptive filter algorithm and improved data treatment, using powerful oversampling acquisition hardware. The novel set‐up was capable of monitoring up to a five orders of magnitude increase in shear modulus within short experiment timescales (about 10 s). The improvement in sensitivity and acquisition rate enabled the induction time, gelation, and vitrification of the multifunctional acrylates to be determined. In addition, the influence of UV intensity on stiffness build‐up within these materials was studied. In the case of the penta/hexaacrylate system, gelation and vitrification were detected as distinct events, in contrast to the second‐generation hyperbranched polyester, for which vitrification could not be identified. These findings are related to the difference in the glass transition temperature of the cured networks.Absolute value of the complex shear modulus as a function of time for different acrylate monomers during UV curing.imageAbsolute value of the complex shear modulus as a function of time for different acrylate monomers during UV curing.

Photopolymerization of Reactive Mesogens

AbstractSummary: The photopolymerization of two reactive mesogens with photopolymerizable acrylate endgroups, the methyl substituted 1,4‐phenylene‐bis{4‐[6‐(acryloyloxy)hexyloxy]benzoate} 1 and acrylic acid 6‐{4‐[6‐(6‐acryloyloxyhexyloxy)naphthalen‐2‐yl]‐phenoxy}hexyl ester 2 has been investigated using Photo‐DSC measurements. Photocrosslinking of 1 in the nematic phase at 100 °C leads to a final conversion of 87% of the acrylate groups. It is possible to perform photopolymerization with very small amounts of photoinitiator. Even with 0.001% (10 ppm) of photoinitiator, 47% of the acrylate groups polymerize within 15 min. The polymerization of the reactive mesogen 2 proceeds faster in the smectic A phase at 100 °C compared to the isotropic phase at 120 °C and leads to a higher conversion of 75%. This can be explained by an increased local concentration of the acrylate groups between the layers of the smectic cores.Photopolymerization of reactive mesogens.magnified imagePhotopolymerization of reactive mesogens.

Synthesis of nanocomposite polymers by UV-radiation curing

Clay-based nanocomposite polymers have been synthesized by photoinitiated crosslinking polymerization of acrylate and epoxy functionalized oligomers. The solvent-free resin containing a small amount (3 wt%) of organophilic clay was cured within seconds upon UV irradiation at ambient temperature. The polymerization reaction was followed by infrared spectroscopy and shown to proceed at a great extent in thick samples (2 mm), due to the higher exotherm and the resulting rise in temperature. The organoclay was shown to have no slowing down effect on the photopolymerization of both acrylate and epoxy resins. The addition of clay nanoparticles was found to reduce the gloss of UV-cured coatings due to an enhanced surface roughness. The viscoelastic and tensile properties of the nanocomposite photopolymer were comparable to those of the neat UV-cured polymer, while their resistance to moisture was significantly increased.

Redox and photoinitiated crosslinking polymerization: II. Neat acrylate resin

Acrylate-functionalized resins, typically utilized as UV-curable coatings, have been thermally cured by using a cerium salt as redox initiator, to achieve an effective hardening of the non-illuminated areas. The acrylate photopolymerization and redox polymerization were followed quantitatively by hardness measurements, infrared spectroscopy and attenuated total reflectance IR spectroscopy. The redox acrylate polymerization, performed at temperatures of 120–140 °C, was shown to be efficient enough to ensure a satisfying hardening of the shadow areas within minutes. The chemical structure of the acrylate-functionalized oligomer was shown to play a key role on the efficiency of the redox polymerization, urethane-acrylates being more reactive than hydroxylated acrylates. Almost similar mechanical properties were obtained whether the coating was UV-cured or thermally cured. This combination of UV and redox polymerizations proved to be also effective to cure thick pigmented specimens.

Comment on ‘Optical poling of oligoether acrylate photopolymers doped by stilbene-benzoatederivative chromophores’

No abstract supplied. See pdf for details.