Unreacted Monomer Research Articles

Estimating the Mass of Chemicals Associated with Ocean Plastic Pollution to Inform Mitigation Efforts.

Plastic pollution in the marine environment is well documented. What remains less recognized and understood are the chemicals associated with it. Plastics enter the ocean with unreacted monomers, oligomers, and additives, which can leach over time. Moreover, plastics sorb organic and inorganic chemicals from surrounding seawater, for example, polychlorinated biphenyls (PCBs) and metals. Thus, interception and cleanup of plastics reduces the amount of chemical contaminants entering or reentering the oceans and removes those already present. Here, we estimate 1) the mass of selected chemical additives entering the global oceans with common plastic debris items, and 2) the mass of sorbed chemicals (using PCBs as a case study) associated with microplastics in selected locations. We estimate the mass of additives that entered the oceans in 2015 as constituents of 7 common plastic debris items (bottles, bottle caps, expanded polystyrene (EPS) containers, cutlery, grocery bags, food wrappers, and straws or stirrers). We calculate that approximately 190 tonnes (t) of 20 chemical additives entered the oceans with these items in 2015. We also estimate the mass of PCBs associated with microplastics in 2 coastal (Hong Kong and Hawaii) and 2 open ocean (North Pacific and South Atlantic gyres) locations, as comparative case studies. We find that the mass of chemicals is related to the mass of plastics in a location, with greater mass of PCBs closer to the source (i.e., land), where there is more plastic per unit area compared to the open ocean. We estimate approximately 85 000 times more PCBs associated with plastics in an average 4.5-km stretch of beach in Hong Kong than from the same size transect in the North Pacific gyre. In conclusion, continuing efforts for plastic interception and cleanup on shorelines effectively reduces the amount of plastic-related chemicals entering and/or reentering the marine environment. Integr Environ Assess Manag 2019;15:596-606. © 2019 SETAC.

Downstream Monomer Capture and Polymerization during Vapor Phase Fabrication of Porous Membranes

Porous membranes can be formed by the polymerization of solid monomer by a vapor-phase initiator followed by sublimation of the unreacted monomer. This versatile bottom-up process can be used to deposit porous polymer membranes on a variety of substrates including planar, curved, and structured surfaces. In this paper, we incorporate additional thermoelectric coolers (TECs) into the reactor in order to study downstream monomer capture and polymerization. Better uniformity across the TECs is achieved by capturing the unreacted monomer from the preceding surface instead of capturing the monomer onto multiple surfaces at once. We show that the surface temperature of the downstream TEC affects the membrane morphology and the kinetics of polymerization. Lower capture temperatures lead to better surface coverage while higher temperatures promote the polymerization rate. The morphological differences are further confirmed by coating the membranes with a fluoropolymer to study variations in hydrophobicity. Our ab...

New synthetic route for polyricinoleic acid with Tin (II) 2-ethylhexanoate

Polyricinoleic acid (PRA) is a biodegradable polymer of ricinoleic acid, a hydroxy fatty acid present in castor oil. Depending upon the chain length, this homopolymer finds varied applications in oleochemical and allied industries. In the current research, we have first demonstrated synthesis route for PRA using Tin (II) 2-ethylhexanoate as a catalyst. The multiple operational variables such as the effect of the reaction time, temperature, catalyst loading, water condensation and recuperation of polymer were studied systemically. Under the optimized conditions, PRA with a molecular weight of ∼4kD was synthesized at 150 °C within 14 hrs. Using solvent extraction, the unreacted monomer and catalyst were recycled back to the next round of polymerization. The final PRA product was characterized as a single molecule with superior functional properties and suggesting to its use as an environmentally friendly biopolymer.

Investigating the in vitro metabolism of the dental resin monomers BisGMA, BisPMA, TCD-DI-HEA and UDMA using human liver microsomes and quadrupole time of flight mass spectrometry

Dental resin systems have been in use for several decades. (Meth)acrylic monomers are an important part of the matrix system and are either based on BPA while others lack the BPA core. The degree of conversion during restoration is in general between 50–70 % allowing leaching from unreacted monomers to the oral cavity where they can be taken up through the pulp or gastrointestinal tract after ingestion with subsequent hepatic metabolism. This study identified the in vitro Phase I and Phase II metabolism of the dental resin monomers BisGMA, UDMA, BisPMA and TCD-DI-HEA, using human liver microsomes (HLM) and human liver cytosols. During Phase I incubation with HLM, the (meth)acrylic acid in the monomers was rapidly removed followed by oxidative and hydroxylation pathways. For BisPMA an O-dealkylation pathway occurred resulting in the formation of BPA. The carbamates present in TCD-DI-HEA and UDMA were resistant to biotransformation reactions. Phase II biotransformation products were only observed for BisPMA and included conjugation reactions with sulphate and glucuronic acid. In total 4, 3, 12 and 3 biotransformation products were identified in this study for BisGMA, UDMA, BisPMA and TCD-DI-HEA respectively. Possible human health effects of these biotransformation products remain unclear due to limited data availability.

The repair bond strength to resin matrix in cured resin composites after water aging

The repair microshear bond strengths (µSBSs) to resin matrices in 4 different cured-composites after water storage (0, 60 s, 1 week, 1 month) were evaluated. Three different adhesive application methods to the cured-composites were performed; (1) none, (2) onestep self-etch adhesive application, and (3) one-step self-etch adhesive application with a silane coupling agent. Degree of conversion (DC) of the composite discs was determined using ATR/FT-IR with a time-based spectrum analysis. Initially, the amount of un-reacted resin monomers in the repaired cured-composite contributed to the bonding performance of newly-filled uncured-composite to resin matrix of the cured-composite. Adhesive application could not improve their repair µSBS. After 1-month of water-storage, the repair µSBS was dependent on material, which either reduced or did not and was not influenced by their amount of un-reacted resin monomers. When repairing aged composite resin, the appropriate adhesive application procedures were different among resin composites.

Architectural Control of Isosorbide-Based Polyethers via Ring-Opening Polymerization.

Isosorbide is a rigid, sugar-derived building block that has shown promise in high-performance materials, albeit with a lack of available controlled polymerization methods. To this end, we provide mechanistic insights into the cationic and quasi-zwitterionic ring-opening polymerization (ROP) of an annulated isosorbide derivative (1,4:2,5:3,6-trianhydro-d-mannitol, 5). Ring-opening selectivity of this tricyclic ether was achieved, and the polymerization is selectively directed toward different macromolecular architectures, allowing for formation of either linear or cyclic polymers. Notably, straightforward recycling of unreacted monomer can be accomplished via sublimation. This work provides the first platform for tailored polymer architectures from isosorbide via ROP.

ENZYMATICALLY SYNTHESIZED pH-RESPONSIVE IPN FOR IN-SITU RELEASE OF PANTOPRAZOLE SODIUM

Objective: This study involves the synthesis of Gum tragacanth (gt) based interpenetrating polymer network (ipn) and its utilization for sustained release of anti-ulcerative drug i.e. pantoprazole sodium.
 Methods: IPN was synthesized from Gum tragacanth, polyacrylic acid (gt-cl-paa) hydrogel. gt-cl-paa was kept in distilled water. Further, acryamide (aam) and methylmethacrylate (mma) was added and then kept for overnight. Later on, lipase and glutaraldehyde were added. Homopolymers and the unreacted monomers were removed using acetone. Synthesized IPN was dried at 50 °C for further study.
 Synthesized ipn was swelled in water and the drug was added to it. The drug was entrapped in the pores of the synthesized ipn and then drug release behavior was studied using uv-vis spectrophotometer.
 Results: Gt, paa and mma based crosslinked IPN were synthesized using lipase-glutaraldehyde as initiator-crosslinker system. The synthesized IPN was pH sensitive and possessed the desired swelling capacity required for the controlled and systematic liberation of pantoprazole sodium at 37 °C. The kinetic of drug release was studied and found that lateral diffusion (DL) of drug was higher as compared to the initial diffusion (DI). The prepared IPN can be used as prospective carrier for prolonged drug delivery.
 Conclusion: A novel pH sensitive and colon targeted IPN was synthesized. It acts as an effective device for the controlled release of drug pantoprazole sodium.

Toxicity and photosensitizing assessment of gelatin methacryloyl-based hydrogels photoinitiated with lithium phenyl-2,4,6-trimethylbenzoylphosphinate in human primary renal proximal tubule epithelial cells

Gelatin methacryloyl (GelMA) and lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) photoinitiator are commonly used in combination to produce a photosensitive polymer but there are concerns that must be addressed: the presence of unreacted monomer is well known to be cytotoxic, and lithium salts are known to cause acute kidney injury. In this study, acellular 10% GelMA hydrogels cross-linked with different LAP concentrations and cross-linking illumination times were evaluated for their cytotoxicity, photosensitizing potential, and elastic moduli. Alamar Blue and CyQuant Direct Cell viability assays were performed on human primary renal proximal tubule epithelial cells (hRPTECs) exposed to extracts of each formulation. UV exposure during cross-linking was not found to affect extract cytotoxicity in either assay. LAP concentration did not affect extract cytotoxicity as determined by the Alamar Blue assay but reduced hRPTEC viability in the CyQuant Direct cell assay. Photocatalytic activity of formulation extracts toward NADH oxidation was used as a screening method for photosensitizing potential; longer UV exposure durations yielded extracts with less photocatalytic activity. Finally, elastic moduli determined using nanoindentation was found to plateau to approximately 20-25 kPa after exposure to 342 mJ/cm2 at 2.87 mW of UV-A exposure regardless of LAP concentration. LAP at concentrations commonly used in bioprinting (<0.5% w/w) was not found to be cytotoxic although the differences in cytotoxicity evaluation determined from the two viability assays imply cell membrane damage and should be investigated further. Complete cross-linking of all formulations decreased photocatalytic activity while maintaining predictable final elastic moduli.

Direct Monitoring of Microgel Formation during Precipitation Polymerization of N-Isopropylacrylamide Using in Situ SANS.

Poly(N-isopropylacrylamide) microgels have found various uses in fundamental polymer and colloid science as well as in different applications. They are conveniently prepared by precipitation polymerization. In this reaction, radical polymerization and colloidal stabilization interact with each other to produce well-defined thermosensitive particles of narrow size distribution. However, the underlying mechanism of precipitation polymerization has not been fully understood. In particular, the crucial early stages of microgel formation have been poorly investigated so far. In this contribution, we have used small-angle neutron scattering in conjunction with a stopped-flow device to monitor the particle growth during precipitation polymerization in situ. The average particle volume growth is found to follow pseudo-first order kinetics, indicating that the polymerization rate is determined by the availability of the unreacted monomer, as the initiator concentration does not change considerably during the reaction. This is confirmed by calorimetric investigation of the polymerization process. Peroxide initiator-induced self-crosslinking of N-isopropylacrylamide and the use of the bifunctional crosslinker N,N′-methylenebisacrylamide are shown to decrease the particle number density in the batch. The results of the in situ small-angle neutron scattering measurements indicate that the particles form at an early stage in the reaction and their number density remains approximately the same thereafter. The overall reaction rate is found to be sensitive to monomer and initiator concentration in accordance with a radical solution polymerization mechanism, supporting the results from our earlier studies.

Vicker’s-Hardness Evaluation of Light Cured Resin Impregnated Fiber Glass Reinforced Complete Denture

Background: Hardness could found to be sensitive to the residual monomer content in the polymerized resins; the hardness is an effective method to evaluate the polymerization depth of resin materials. In addition, hardness had used to predict the wear resistance of dental materials. Materials and Methods: Acrylic resin specimens had divided into two groups according to the type of material tested (group I: conventional heat cured acrylic resin, group II: resin impregnated fiberglass reinforced complete denture base). Vicker`s micro hardness tester was used to measure Vicker`s hardness number (VH) of the acrylic specimens in which diamond indenter was applied under 25 g load for 10 seconds time evaluated by 20 x objective lens. Results: The VH values of resin impregnated fiberglass reinforced acrylic resin showed statistically insignificant lower values (as P < 0.05) than conventional heat cured acrylic resin. Conclusion: Unreacted monomer would act as a plasticizer and weaken the matrix. Heat cured PMMA could perform better in this aspect that the residual monomer content was less when compared to PMMA reinforced through other mechanisms. Key words: Hardness, Fiber, Reinforce, Denture.

Confinement driven crystallization of ABA crystalline-soft-crystalline block copolymers synthesized via RAFT mediated miniemulsion polymerization

Waterborne ABA block copolymers of stearyl acrylate (SA) and 2-ethylhexyl acrylate (2EHA) containing crystalline A block and soft middle B block, were synthesized via two-step reversible addition fragmentation chain transfer (RAFT) polymerization, using S,S-dibenzyl trithiocarbonate (DBTTC) bifunctional RAFT agent. First, miniemulsion polymerization was used for the synthesis of the crystalline domains. Then in the second step 2EHA was fed to the system as a pre-emulsion and soft domains were formed. For the sake of simplicity sequential monomer addition was performed without any removal of the unreacted monomer in the first step. Thermal properties of the obtained block copolymers were investigated by means of DSC, which revealed reduced crystallinity by the formation of the block copolymers compared to the crystallinity of the polySA initial block. Morphological properties were studied by means of microscopic techniques after film formation at different conditions. Lamellar phase separation induced by confined crystallization in the particles was shown in the films dried at room temperature. Particle coalescence and higher ordering of the lamellar structure was obtained upon film annealing above the melting temperature of the crystalline domains and the structure obtained was comparable with the one of films casted from THF solution, indicating that equilibrium morphology was already obtained by annealing. Mechanical properties studied using DMTA revealed two transition temperatures and reduced storage modulus as the length of the middle block and casting temperature of the film was increased.

Effect of nitrile butadiene rubber/Al2O3/YSZ fillers for PMMA denture base on the thermal and mechanical properties

This study is to investigate the effect of nitrile butadiene rubber (NBR as impact modifier) together with Al2O3/YSZ (toughening) as filler loading in PMMA denture base on the thermal and mechanical properties. PMMA matrix without fillers was mixed between PMMA powder and 0.5 mass% of BPO, and it is used as the control group. The liquid components consist of 90% of methyl methacrylate (MMA) and 10% as the cross-linking agent of ethylene glycol dimethacrylate. The denture base composites were fabricated by incorporating PMMA powder and BPO and fixed at 7.5 mass% NBR particles and filler loading (1, 3, 5, 7 and 10 mass%) of Al2O3/YSZ mixture filler by (1:1 ratio) as the powder components. The ceramic fillers were treated with silane (γ-MPS) and the powder/liquid ratio (P/L) according to dental laboratory practice. The TGA data obtained show that the PMMA composites have better thermal stability compared to unreinforced PMMA, while DSC curves show slightly similar Tg values. DSC results also indicated the presence of unreacted monomer content for both reinforced and unreinforced PMMA composites. The fracture toughness, Vickers hardness and flexural modulus values were statistically increased compared to the unreinforced PMMA matrix (P < 0.05).

Evolution of Morphology of POEGMA-b-PBzMA Nano-Objects Formed by PISA.

The evolution of particle morphology occurring during polymerization-induced self-assembly (PISA) of a block copolymer poly(oligo(ethylene glycol) methacrylate)-b-poly(benzyl methacrylate) (POEGMA-b-PBzMA) is studied. A well-controlled reversible addition-fragmentation chain transfer (RAFT) polymerization yields nano-objects with various morphologies: spheres, aggregates, worm-like structures, and vesicles. A comparison of the morphology of the nano-objects formed from two different chain-length stabilizers established that the unreacted monomer played an important role during the morphology transitions, which is contrary to previous observations. In addition, morphology evolution to higher-order structures could be attained simply by extending the reaction time, after reaching full monomer conversion.

Penyerapan Air Dan Kelarutan Bahan Semen Ionomer Kaca Sebagai Penutup Pit Dan Fisur Gigi

BACKGROUND: Pit and fissure sealants are materials that are often used for preventive maintenance, especially on occlusal surfaces of teeth that are susceptible to caries. All restoration materials that come into contact with water will experience 2 mechanisms, namely the absorption of water, which causes matrix swelling and increased mass and water solubility, namely the release of components from unreacted monomers and causing reduced mass. OBJECTIVE: Measure the value of water absorption and solubility of glass ionomer cement as a cover of the pit and fissure of the tooth. METHODS: 18 specimens of glass ionomer cement sealant material manipulated according to the manufacturer's instructions consisted of six specimens measuring 15 mm in diameter and 1 mm in thickness made for each immersion time. The specimen was put into a desiccator at 37°C for 22 hours and then put into another desiccator with a temperature of 23°C for 2 hours. The specimen was weighed with a precision scale of 0.1 mg. Measurements are carried out repeatedly until a constant mass is obtained (M1). Next, the specimen was put into 40 ml of aquabides and stored in a desiccator at 37°C for 1 day, 2 days and 7 days. At the end of each immersion time, the specimen was removed from aquabides, dried with suction paper and vibrated in the air for 15 seconds. Specimens are weighed to get M2. The specimens were reconditioned to the desiccator at 37°C for 22 hours and then put into another desiccator with a temperature of 23°C for 2 hours and this procedure was repeated one day later, then the mass was weighed repeatedly until a constant mass was obtained (M3). RESEARCH RESULTS: The Kruskal-Wallis statistical test shows that there is no significant difference in the average water absorption value and solubility of materials for immersion for 1 day, 2 days and 7 days. CONCLUSIONS AND RECOMMENDATIONS: The absorption rate of glass ionomer cement as a cover of dental pit &amp; fissure decreased until the second day and increased until the seventh day, with an average absorption of water for 1 day immersion of 42.68mg/mm³, 2 days 40, 53mg/mm³ and 7 days 42.99mg/mm³. Solubility value in water of glass ionomer cement as a cover of dental pit &amp; fissure decreased until the second day then increased until the seventh day, with an average solubility of material for immersion for 1 day at 41.46mg/mm³, 2 days 39.39mg/mm³ and 7 days 41,91mg/mm³. It was said that there was no significant difference in the value of water absorption and solubility of materials during the immersion period of 1, 2 and 7 days. It is recommended that in the application of glass ionomer cement as a cover of dental pits and fissures, please note in the provision of varnish or protector to reduce the occurrence of water absorption and solubility of the material. In addition, the pit and fissure of the tooth that has been covered should be controlled 3 months later to find out if the cover is still intact or has been damaged or loose. It is also recommended that there is further research to determine the value of water absorption and solubility of ingredients if soaked in artificial saliva for more than 7 days.

Preparation and characterization of a nitrogen-doped mesoporous carbon aerogel and its polymer precursor

Nitrogen-containing carbon aerogel was prepared from resorcinol–melamine–formaldehyde (R–M–F) polymer gel precursor. The polymer gel was supercritically dried with CO2, and the carbonization of the resulting polymer aerogel under nitrogen atmosphere at 900 °C yielded the carbon aerogel. The polymer and carbon aerogels were characterized with TG/DTA–MS, low-temperature nitrogen adsorption/desorption (− 196 °C), FTIR, Raman, powder XRD and SEM–EDX techniques. The thermal decomposition of the polymer aerogel had two major steps. The first step was at 150 °C, where the unreacted monomers and the residual solvent were released, and the second one at 300 °C, where the species belonging to the polymer network decomposition could be detected. The pyrolytic conversion of the polymer aerogel was successful, as 0.89 at.% nitrogen was retained in the carbon matrix. The nitrogen-doped carbon aerogel was amorphous and possessed a hierarchical porous structure. It had a significant specific surface area (890 m2 g−1) and pore volume (4.7 cm3 g−1). TG/DTA–MS measurement revealed that during storage in ambient conditions surface functional groups formed, which were released upon annealing.

Physical-chemical properties of dental composites and adhesives containing silane-modified SBA-15.

The aim of this study was to synthesize and characterize mesoporous materials SBA-15 and SBA-15 modified with 3-(methacryloxy)-propyl-trimethoxysilane (MPS) to be used as inorganic filler in restorative dental composites and adhesives, and evaluate the main physical-chemical properties of the resulting material. The SBA-15 and SBA-15/MPS were characterized by FTIR, BET and X-Ray and combined with TEGDMA, bis-GMA and commercial spherical silica to produce dental composites. Afterwards, the mesoporous materials were combined with TEGDMA, bis-GMA and HEMA to make adhesives. To compare the results, composites and adhesives containing only commercial spherical silica were investigated. Some physical-chemical properties such as degree of conversion (DC), flexural strength (FS) and modulus (FM), water sorption and solubility (Wsp and Wsl), specific area (BET), and the leachable components were evaluated. The SBA-15/MPS can be used to prepare dental restorative materials, with some foreseeable advantages compared with pure SBA-15 dental materials and with improved properties compared with commercial spherical silica dental materials. An important improvement was that the dental materials based on modified SBA-15 presented a reduction of approximately 60% in leaching of unreacted monomers extracted by solvent compared to the control group.

Comparison of residual styrene monomer determination of pharmaceutical materials packed with polystyrene using gas chromatography and ultraviolet/visible spectrophotometer

Background: Plastics such as plastic wrapping are an integral part of today’s society. Plastics are made by polymerization of styrene monomers. If the polymerization reaction is not perfect, then there will be unreacted monomer residues. Although styrene is still considered harmless, if there is a metabolic process will form styrene oxide that can cause effects that are carcinogenic. Aims and Objectives: This study aims to determine the residue of pharmaceutical styrene materials packed with polystyrene using gas chromatography (GC) and ultraviolet (UV)/visible spectrophotometers which are usually available in chemical analysis laboratories. Materials and Methods: Orientation of analysis method was performed using latex polystyrene sample. Styrene monomer analysis was performed using a GC and UV/visible spectrophotometer. Then a comparative study was conducted on both methods. Once this method was accepted, it was applied to a polystyrene-containing sample obtained from the market. Styrene was isolated from the sample; then, both methods were tested and compared. Results: Using polystyrene latex sample and varying column temperature, for GC, the optimum condition was obtained at column temperature 110°C, detector temperature 200°C, and temperature of injector 200°C. Using the packing column, we got a repeatability of 96.67%, PRECISION test of 2.81%, 96.49% recovery test, and a detection limit of 0.25 ppm. For the quantitative test of latex polystyrene samples, the average residual content obtained was 0.276%. When using GC with a capillary column, used column DB-17 at 110°C, detector, and injector temperature at 200°C, the average content of styrene residue was 0.278%. When using the spectrophotometer UV/visible, λ maximum at 280.5 nm, the reliability, assay, recovery test, and detection limits were 94.83%, 4.36%, 93.72% and 0.30 ppm, respectively. The residual styrene results obtained with this instrument was an average of 0.271%. Using variance analysis with the fixed model for all three methods (GC with the capillary column, GC with packing column, and spectrophotometer UV/visible) obtained H0 hypothesis was rejected so that it was continued with Duncan test with the result of all three methods could be used for analysis of styrene residue. The result of average analysis for beverage sample with Spectrophotometer UV/visible method was 0.0220%, packed column GC was 0.0221% packing, and capillary column GC of 0.0.223%. For medication samples in each instruments were found 0.0239%, 0.0241%, and 0.0242%, whereas for food samples obtained 0.0236%, 0.0238%, and 0.0239%. Conclusions: A GC method with either a packing column or a capillary column and a spectrophotometer UV/visible could be used to analyze the residual styrene monomer of a polystyrene-grade pharmaceutical sample. The best analysis could use GC with a capillary column. It is recommended to use differential scanning calorimetry and thermogravimetric analysis, if available, as well as infrared spectrophotometer to obtain a cheaper and better method.

Studies on the properties of RO membranes for salt and boron removal: Influence of thermal treatment methods and rinsing treatments

The physicochemical properties and performance of thin film composite (TFC) membranes depend on its synthesis conditions. In this study, TFC membranes were fabricated using interfacial polymerization (IP) method and the effects of heat treatment methods and post-IP rinsing (prior to heat curing step) on the membrane performances were investigated. Keeping the substrate in minimal heat exposure could prevent substrate pore annealing that potentially reduces the membrane water permeability. Evidently, the membranes with only polyamide (PA) layer being heat-treated exhibited >250% enhancement in pure water flux (PWF) compared to the membranes where both PA and substrate layer were heat-treated. Also, the membranes rinsed with pure n-hexane tended to display higher PWF without significantly decreasing solute rejection, possibly due to the reduced membrane cross-linking following the removal of unreacted monomers and excess solvent from the membrane surface. The membrane performance became practically the same after post-IP rinsing, regardless of the solvent used in the IP reaction, suggesting that the disparity in the membrane performance is mainly caused by the difference in solvent evaporation rate during heat treatment. The variations in solvent surface tension and viscosity during the IP reaction meanwhile did not play a key role affecting PA layer chemistry and performance.

Stochastic simulation of the UV curing process in nanoimprint lithography: Pattern size and shape effects in sub-50 nm lithography

The authors have performed stochastic simulations of the ultraviolet (UV) curing process of the resist in nanoimprint lithography. Chain formation between an activated monomer and a randomly selected monomer within the critical reaction radius occurred until there was no unreacted monomer within the reaction radius. A deactivation mechanism was introduced to prevent the chain reaction at the resist surface by setting a smaller maximum reaction radius at the resist surface than in the middle of the resist. By introducing the deactivation effect, the conversion ratio of the UV-cured resist decreased with decreasing resist pattern size and depended on the pattern shape. Resist pattern shrinkage after UV curing was also simulated by relaxing the structures with the molecular mechanics method.

Evaluation of relationship among filler amount, degree of conversion, and cytotoxicity: Approaching performance enhancement novel design for dental Bis-GMA/UDMA/TEGDMA composite

ABSTRACTDental composites of A2 color using Bis-GMA, urethane dimethacrylate and triethyleneglycol dimethycrylate resins (70/20/10), and silica filler (70 wt%, 75 wt%, and 80 wt%), a hybrid of nano- and microsilica particles, are made and subjected to the following tests: Fourier transform infrared spectroscopy (FTIR), particle size analyzer, scanning electron microscope (SEM), and also cytotoxicity. FTIR results show that an increase in filler amount yields to a decrease in degree of conversion. Therefore, there should be a compromise between degree of conversion and the filler amount. SEM images manifest the uniformity of silica particles. It is shown from the cytotoxicity tests that as the unreacted monomers increased, the biocompatibility of the composites decreased.