Low Viscosity Monomer Research Articles

Elastic properties of some selected two-monomer systems as studied by Brillouin spectroscopy

We present results obtained by Brillouin scattering method for four two-component systems comprising of a high viscosity monomer and a low viscosity monomer. The monomers used were crosslinking (divinyl) or linear (monovinyl) ones. The investigated systems were: divinyl/divinyl-bis-GMA/TEGDM; divinyl/monovinyl-bis-GMA/PEGMM; monovinyl/divinyl-bis-MGMA/TEGDM and monovinyl/monovinyl-bis-MGMA/PEGMM; they were formulated at various molar ratios. The measurements have been performed in temperature range 293–353 K. The following physical parameters characterizing the investigated systems were estimated: hypersonic velocity V, attenuation coefficient α and adiabatic compressibility β, all as a function of temperature and monomer molar ratio. The obtained results have been discussed in terms of the influence of the system composition and viscosity on their elastic properties. Speed of changes of the adiabatic compressibility β as derivative have been also discussed in terms of both, the temperature as well as the component of molar ratio.

Role of Bimolecular Homolytic Substitution (SH2) Reactions in Free Radical Photopolymerization Under Air

A set of multivalent atom-containing amines (e.g., tetrakis(dimethylamido)silane, tetrakis(dimethylamido)tin(IV), tetrakis(diethylamido)titanium(IV), tetrakis(dimethylamido)zirconium(IV), and 1,3,5-triaza-7-phosphaadamantane) are proposed as new coinitiators in Type II photoinitiating systems (based, for example, on benzophenone) and additives for Type I photoinitiators (such as phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-1-propanone) for free radical photopolymerization under air. The polymerization rates (Rp’s) were determined under experimental conditions where a strong detrimental oxygen effect is expected, that is, both under low light intensity and in thin low viscosity monomer samples. The remarkable performance achieved under air (up to a 100- and a 5-fold increase in Rp and final conversion (%), respectively) lies on the presence of a bimolecular homolytic substitution (SH2) reaction that allows us to convert peroxyls into new initiating radicals efficiently. The mechanisms are investigated by laser flash photolysis (LFP) and electron spin resonance (ESR) experiments.

Viscosity effects in the photopolymerization of two‐monomer systems

AbstractPhotopolymerization kinetics and viscosity behavior of five different two‐monomer systems forming hydrogen bonds and composed of mixtures of a high viscosity monomer (HVM) and a low viscosity monomer (LVM) at various molar ratios were investigated at six polymerization temperatures. The monomers used were mono‐ or dimethacrylates. Detailed viscosity measurements of the monomer mixtures showed significant negative deviations from the theoretical values (characterized by excess logarithm viscosities) indicating that interactions between the molecules of the same type (in individual monomers) are stronger than those between two molecules of different types (HVM and LVM). The photopolymerization kinetics were analyzed from the point of view of the appearance, viscosity and temperature behavior of the most reactive composition (MRC), the one showing the highest value of the maximum polymerization rate within a range of the HVM: LVM ratios. It was found that MRC appearance is determined mainly by the initial viscosity of the two‐monomer system, whereas the functionality of the monomers (and network formation) is much less important (MRC is observed even in linear systems). The initial viscosity of all the monomer mixtures showing MRC lay in the range of 0.06–2 Pa s, which is narrow compared to the range of viscosities of the monomers (approximately 10−3–103 Pa s). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Full field imprint masks using variable shape beam pattern generators

Imprint lithography has been included on the ITRS lithography roadmap at the 32, 22, and 16nm nodes. Step and flash imprint lithography (S-FIL®) is a unique method that has been designed from the beginning to enable precise overlay for creating multilevel devices. A photocurable low viscosity monomer is dispensed dropwise to meet the pattern density requirements of the device, thus enabling imprint patterning with a uniform residual layer across a field and across entire wafers. Further, S-FIL provides sub-100-nm feature resolution without the significant expense of multielement, high quality projection optics, or advanced illumination sources. However, since the technology is 1X, it is critical to address the infrastructure associated with the fabrication of templates. For device manufacturing, one of the major technical challenges remains the fabrication of full field 1X templates with commercially viable write times. Recent progress in the writing of sub-40-nm patterns using commercial variable shape e-beam tools and nonchemically amplified resists has demonstrated a very promising route to realizing these objectives, and in doing so, has considerably strengthened imprint lithography as a competitive manufacturing technology for the sub-32-nm node. Here the authors report the first imprinting results from sub-40-nm full field patterns, using Samsung’s current flash memory production device design. The fabrication of the template is discussed and the resulting critical dimension control and uniformity are reported. A second experiment has also demonstrated feasibility for resolving several types of features at half pitches of 32nm.

Synthesis and Photopolymerization of 2-(Acryloyloxy)ethyl Pyrrolidine-1-Carboxylate

A low-viscosity monomer, 2-(acryloyloxy)ethyl pyrrolidine-1-carboxylate (AEPC), was synthesized using a non-isocyanate route. The photopolymerization kinetics were monitored by Fourier transform infrared (FT-IR) spectroscopy with a horizontal sample holder. The results indicated that AEPC had a high UV curing rate and final double bond conversion, which could reach 99.5% within 30 s. The T g of 2-(acryloyloxy)ethyl pyrrolidine-1-carboxylate/CN964 (1:4, w/w) and isobornyl acrylate/CN964 (1:4, w/w) was 43 and 57°C, respectively. The cross-link density of 2-(acryloyloxy)ethyl pyrrolidine-1-carboxylate/CN964 (1:4, w/w) was higher than that of isobornyl acrylate/CN964 (1:4, w/w).

Template fabrication for the 32 nm node and beyond

Imprint lithography has been included on the ITRS Lithography Roadmap at the 32 and 22 nm nodes. Step and flash imprint lithography (S-FIL ™) is a unique method that has been designed from the beginning to enable precise overlay for creating multilevel devices. A photocurable low viscosity monomer is dispensed dropwise to meet the pattern density requirements of the device, thus enabling imprint patterning with a uniform residual layer across a field and across entire wafers. Further, S-FIL provides sub-100 nm feature resolution without the significant expense of multi-element, high quality projection optics or advanced illumination sources. However, since the technology is 1X, it is critical to address the infrastructure associated with the fabrication of templates. This paper addresses steps required to achieve resolution at or below 32 nm. Gaussian-beam writers are now installed in mask shops and are being used to fabricate S-FIL templates. Although the throughput of these systems is low, they can nevertheless be applied towards applications such as unit process development and device prototyping. Resolution improvements were achieved by optimizing the ZEP520A resolution and exposure latitude. Key to the fabrication process was the introduction of thinner resist films and data biasing of the critical features. By employing a resist thickness of 70 nm and by negatively biasing features as much as 18 nm, 28 nm half-pitch imprints were obtained. Further processing improvements show promise for achieving 20 nm half-pitch features on a template.

Heteroaromatic Thiols as Co-initiators for Type II Photoinitiating Systems Based on Camphorquinone and Isopropylthioxanthone

The heteroaromatic thiols (imidazole, oxazole, and thiazole derivatives) were investigated in regard to their abilities to function as co-initiators in free-radical photopolymerizations induced by camphorquinone and isopropylthioxanthone. As shown by the kinetic data, these heteroaromatic thiols are efficient co-initiators with activities comparable to aromatic amines. They quenched the triplet states of isopropylthioxanthone and camphorquinone with rate constants determined to be on the order of 109 and 108 M-1 s-1, respectively. The results suggested that rates of polymerization of a low-viscosity monomer (triethylene glycol dimethacrylate) in an inert atmosphere are dependent on the quantum yields of formation of primary thiyl radicals Φ. However, this effect was also moderated by the reactivities of the thiyl radicals that were generated in the photosensitization stage. The observed activities of the initiator/thiol systems also depended on the possibility of initiator photoreduction by the monomer and, in air, on the ability of the co-initiators to reduce oxygen inhibition.

Development of Dental Composite Resin Utilizing Low-shrinking and Low-viscous Monomers

To lower the viscosity of composite resins, experimental composite resins were produced using low-viscosity monomer mixtures of newly developed polyfunctional acrylates, and the mechanical and physical properties of the hardened composites were investigated. Mechanical (i.e., compressive, diametral tensile, and bending) strength of a polymer obtained from one new monomer mixture without fillers was similar to that of a bis-GMA/TEGDMA (2/1 weight ratio) based polymer. As for the hardened composites, the mechanical strength of composites produced using the new monomer mixtures showed a different tendency from that of bis-GMA based composites. Further, even the viscosity of composite pastes with high filler content was markedly lower than that of bis-GMA based composites. In terms of setting shrinkage, the composites consisting of new monomer mixtures exhibited significantly smaller shrinkage than the bis-GMA based composites, and decreased with increase in filler content.

Analysis of photopolymerization behavior of UDMA/TEGDMA resin mixture and its composite by differential scanning calorimetry.

The aim of this study was to investigate the extent of polymerization (Ep) in terms of polymerization rate of UDMA/TEGDMA resin mixtures and its composite resin, by using a differential scanning calorimeter (DSC) technique employing a photopolymerization apparatus. The resin mixtures used in this study consisted of urethane dimethacrylate (UDMA) as a base monomer and triethyleneglycol dimethacrylate (TEGDMA) as a low viscosity monomer. The concentration of TEGDMA in the mixed monomer was varied to 0, 20, 40, 60, 80, and 100 mol %. Additionally, using a base monomer consisting of 60 mol % UDMA and 40 mol % TEGDMA, four kinds of composites with silica filler of 0, 20, 40, 60, and 70 wt %, were prepared in this study. The general reaction profile and Ep values were obtained from the DSC curves. Increasing the concentration of TEGDMA resulted in a decrease in the viscosity of the UDMA/TEGDMA mixture, a delay in the time to maximum polymerization rate, and an increase in the Ep values of the resin mixtures. Furthermore, Ep values decreased with increasing filler content between 0 and 60 wt % but did not decrease further between 60 and 70 wt %.

Solvent effect on TEOS film formation in the sandstone consolidation process

Alkoxysilanes, low-viscosity monomers capable of polymerizing into the porous network of stone by a sol-gel process, are widely used as consolidants in the restoration of stone monuments. However, since consolidation is a non-reversible application capable of causing serious harmful side effects to the original material, stone consolidation is almost always considered a very risky intervention. Alkoxysilanes are insoluble in water, so co-solvented systems are very often used, but even knowing that the solvent is a determinant parameter for sol-gel reactions, there is still a lack of information regarding how it can influence the stone-alkoxysilane affinity. For two different tetraethoxysilane-acidic co-solvented systems we are reporting both the morphological characteristics showed by gels formedin situ and the affinity reached with the stone in the sandstone consolidation process. Aqueous solutions of ethanol and methyl-ethyl-ketone (MEK) were the solvents compared. SEM and 29Si Solid State NMR were used todetermine the alkoxysilane performance on these silicic-based materials. It was found that using MEK solutions resulted in appreciable sandstone-alkoxysilane interaction, forming a more homogeneous film. On the other hand, ethanol does not promote alkoxysilane-sandstone compatibility. A brittle film is obtained when ethanol is used.

Application of mercury porosimetry to the study of xerogels used as stone consolidants

Alkoxysilanes, low-viscosity monomers that polymerize into the porous network of stone by a sol–gel process, are widely used in the restoration of stone buildings. We have used the mercury porosimetry technique to characterize changes in microstructure of three granites following their consolidation with two popular commercial products (Wacker OH and Tegovakon V). The suitability of this technique is questioned because a surprising increase of stone porosity is observed. In order to investigate the feasibility of porosimetry, we analyze the behavior of xerogels prepared from the two commercial products, under mercury pressure. Gels are basically compacted and not intruded by mercury. Thus, the increase of stone porosity after consolidation can actually be associated with gel shrinkage. Mercury porosimetry, therefore, has been found unsuitable for characterizing the microstructure of consolidated rocks. However, it can be employed usefully to evaluate shrinkage of gels under mercury pressure, which permits the behavior of a consolidant during the process of drying in stone to be predicted. It is a key factor because many problems of consolidants are related to their drying process within the stone. Gels under study exhibit a high rigidity and an elastic behavior, as consequence of their microporous structure. Finally, the reduction in the porous volume of gels after the porosimetry test demonstrates that the shrinkage mechanism is based on pore collapse.

Network formation and compositional drift during photo-initiated copolymerization of dimethacrylate monomers

The copolymerization of viscous monomers with a nonviscous diluent comonomer was investigated. Overall, photopolymerization kinetics was compared for equimolar mixtures of triethylene glycol dimethacrylate (TEGDMA), a low viscosity monomer, with either a rigid aromatic dimethacrylate (Bis-GMA) or a flexible aliphatic urethane dimethacrylate (UDMA), as examples of viscous comonomers. Sol fraction analysis from partial cure polymerizations provided individual monomer reactivities as a function of conversion. The resin containing UDMA reached greater maximum polymerization rate and final conversion compared with the resin based on Bis-GMA. The viscous monomers (Bis-GMA or UDMA) were found to be less reactive than the diluent comonomer (TEGDMA) at nearly all stages of the photopolymerization process. The reactivity differential was especially dramatic at the latter stages of the polymerization.

Improvement of Photo Cured Composite Resin Using Low Viscosity Monomer Substituted by Fluorine

Improvement of Photo Cured Composite Resin Using Low Viscosity Monomer Substituted by Fluorine

Free-radical frontal polymerization: self-propagating thermal reaction waves

Frontal polymerization is a mode of converting monomer into polymer via a localized reaction zone that propagates. Such fronts can exist with free-radical polymerization or epoxy curing. The necessary conditions for the existence of the free-radical frontal polymerization regime are considered. The physicochemical properties of monomers are classified in connection with complications arising in the experiments, including low conversion, convection and bubbles. The density gradient in the reaction zone leading to front decay is the most insidious problem. The analysis of forces that can withstand the Taylor instability allowed us to overcome experimental difficulties and develop approaches to polymerize low-viscosity monomers in the frontal mode. The factors affecting front shape, velocity, conversion, and molecular weight are considered.Historically, frontal polymerization has been performed in neat monomer but we have been able to obtain fronts of very reactive monomers in high-boiling-point solvents including water, DMSO and DMF. Periodic frontal polymerization modes have been observed, including single and multi-point spin modes in which ‘hot spots’(local high-temperature regions) migrate around the front as it propagates. We investigated experimentally the occurrence of the different modes as a function of the initial temperature and the intensity of heat losses and made a qualitative comparison to the results of theoretical analyses based on infinitely narrow reaction zone models.The future directions of research with frontal polymerization are considered, especially with regard to applications to materials synthesis.

The concerted use of SEM, TEM, and SCM for examination of resin-dentin interfaces

Restoration of decayed teeth with tooth-colored materials that can be bonded to tooth tissue has been a highly desirable property in restorative dentistry for many years. Advantages of such an adhesive restorative technique over conventional techniques using non-adhesive metal-based restoratives include improved restoration retention with minimal sacrifice of sound tooth tissue for retention purposes, superior adaptation and sealing of the restoration margins in prevention of caries recurrence, improved stress distribution across the tooth-restoration interface throughout the whole tooth, and even reinforcement of weakened tooth structures. The dental adhesive technology is rapidly changing. An efficient resin bond to enamel has already long been achieved. Its bonding mechanism has been fully elucidated and has proven to be a durable and reliable clinical treatment. However, bonding to dentin represents a greater challenge. After the failures of a dentin acid-etch technique in imitation of the enamel phosphoric-acid-etch technique and a bonding procedure based on chemical adhesion, modern dentin adhesives are currently believed to bond to dentin by a micromechanical hybridization process. This process is developed by an initial demineralization of the dentin surface layer with acid etchants exposing a collagen fibril arrangement with interfibrillar microporosities that subsequently become impregnated by low-viscosity monomers. Although the development of such a hybridization process has well been documented in the literature, questions remain with respect to parameters of-primary importance to adhesive efficacy.

Glycolytic recycle of poly(ethylene terephthalate) (PET)

AbstractIn a comparison of PET waste recovery methods, glycolysis to monomer (DHET + low MW oligomers) represents a compromise between regeneration of starting ingredients by methanolysis or hydrolysis and direct remelt extrusion. It is less costly than the former and more versatile than the latter. The resultant easily filtered, low viscosity monomer is repolymerized to a useful molecular weight (MW), used as an ingredient for copolymers and used with additives for controlling luster, color, etc. Glycolytic recycle can be a batch or continuous process, the rate being dependent on temperature, catalyst, state of subdivision of the feedstock and the 2G/T ratio. In addition, the final monomer composition is controlled by the time of reaction and hold‐up time after depolymerization. Low 2G/T ratios permit higher temperatures and faster reactions but result in higher MW oligomers. Side reactions occurring in the depolymerization are minimized by addition of a buffer as sodium acetate and limiting storage time at high temperatures. PET scrap suitable for glycolytic recycle includes production waste, fibers, film, flake, bottles, etc., but ingredients leading to side reactions, copolymers, end caps or color must be minimized for critical products and satisfactory rates of polymerization.