Degree Of Monomer Conversion Research Articles

Influence of nanometer scale particulate fillers on some properties of microfilled composite resin

The aim of this study was to evaluate the effect of different weight fractions of nanometer sized particulate filler on properties of microfilled composite resin. Composite resin was prepared by mixing 33wt% of resin matrix to the 67wt% of silane treated microfine silica particulate fillers with various fractions of nanometer sized fillers (0, 10, 15, 20, 30wt%) using a high speed mixing machine. Test specimens made of the composites were tested with a three-point bending test with a speed of 1.0mm/min until fracture. Surface microhardess (Vicker's microhardness) was also determined. The volumetric shrinkage in percent was calculated as a buoyancy change in distilled water by means of the Archimedes principle. The degree of monomer conversion (DC%) of the experimental composites containing different nanofiller fractions was measured using FTIR spectroscopy. Surface roughness (Ra) was determined using a surface profilometer. Nanowear measurements were carried out using a nanoindentation device. The water uptake of specimens was also measured. Parameters were statistically analysed by ANOVA (P<0.05). The group without nanofillers showed the highest flexural strength and modulus, DC% and Ra value. The group with 30% nanofillers had the highest water uptake and volumetric shrinkage. No significant difference was found in Vicker's microhardness and the nanowear of the composites. The plain microfilled composite demonstrated superior properties compared to the composites loaded with nanofillers with the exception of surface roughness.

Evaluation of cytotoxicity and degree of conversion of glass ionomer cements reinforced with resin

The objective of the present study was to evaluate the cytotoxicity and degree of monomer conversion of resin-reinforced glass ionomer cements (RGIC) over different time periods. Four RGICs: Fuji Ortho LC (FOLC), Fuji Ortho Band (FOB), Orthoglass (OGL), and Multicure Glass Ionomer (MCI) were evaluated for cytotoxicity in fibroblastic L929 cells and for their degree of monomer conversion over different time periods. Three control groups were also analysed: positive control (C+), consisting of Tween 80 cell detergent; negative control (C-), consisting of phosphate-buffered saline; and cell control (CC), consisting of cells exposed to any material. To evaluate the cytotoxicity, the dye-uptake technique was used and the degree of conversion was evaluated using infrared spectroscopy. The data obtained were analysed by analysis of variance and the Tukey's test. The results showed cytotoxicity of the RGICs at 1 and 24 hours; the viability values of these materials were statistically different from the C- and CC groups (P < 0.05). After 48 hours, the FOLC group was statistically similar to the CC and C- groups but different from the others. At 1 hour, there was no difference in the degree of conversion between the FOLC and OGL groups (P > 0.05) or between the FOB and MCI (P < 0.05) groups. However, at 48 hours, the FOLC group had greater conversion values than the other groups (P < 0.05). There is a direct relationship between the degree of conversion and RGIC cytotoxicity. Following initial polymerization, cytotoxicity decreases and, consequently, the degree of conversion of the material increases.

Efficiency of different light sources to polymerise composite material

The aim of this in vitro study is to examine the polymerisation efficacy of three different polymerisation units through simulated three different ceramic restorations (5 mm in diameter and 2 mm in height) by determining the degree of monomer conversion of a composite luting material. The curing efficiency was observed with Fourier transform infrared micromultiple internal reflectance spectroscopy after 24 h of polymerisation. The degree of conversion was calculated as a percentage of experimentally polymerised versus maximally polymerised composite. The degree of conversion values varied with the light source (light emitting diode, high intensity halogen and conventional halogen) (p<0·05) and the ceramic system (Cercon, IPS Empress 2 and Cerec) (p<0·05).

Polymerization capacity of orthodontic composites analyzed by Fourier transform infrared spectroscopy

The aim of this in-vitro study was to analyze the polymerization capacity of 5 orthodontic composites by determining the degree of monomer conversion (DC). Fourier transform infrared spectroscopy was used to evaluate the DC of the orthodontic composites immediately after polymerization and after storage in artificial saliva at 37°C ± 1°C for 30 days. The resin-based adhesive composites investigated were Bisco Ortho (Bisco, Schaumburg, Ill), Heliosit Orthodontics (Ivoclar, Schaan, Liechtenstein), Kurasper F (Kuraray, Okayama, Japan), Light Bond (Reliance Orthodontic Products, Itasca, Ill), and Transbond XT (3MUnitek, Monrovia, Calif), cured with Elipar FreeLight 2 (3M ESPE, St Paul, Minn) for the testing of the DC values. Fifty cylindrical specimens were manufactured in molds. The data were analyzed by 2-factor analysis of variance (ANOVA) and Tukey HSD test. According to 2-way ANOVA, the DC was significantly influenced by composite type (P<0.05); after 30 days, there were no differences among the composite types for the DC. The interaction of orthodontic composites and time played a statistically significant role in the DC (P<0.05), but there was no statistically significant influence of time for the DC (P >0.05). The DC was found to change according to composite materials used, and Bisco Ortho showed the most DC performance. The DC of orthodontic composites is a complex process that is affected not only by inorganic filler content of the composite but also the monomer type and many other factors. Sufficient DC values of 5 commercially available orthodontic composites can be achieved with a new-generation light-emitting diode curing light.

Zinc‐based catalyst for the ring‐opening polymerization of cyclic esters

AbstractA zinc‐based catalyst zinc bis[bis(trimethylsilyl)amide] was used for the polymerization of cyclic esters including L‐lactide (L‐LA) and 2‐methyl‐2‐carboxyl‐propylene carbonate (MBC). The polymerization of L‐lactide in THF could be carried out successfully under mild conditions in very short time by using the zinc catalyst and alcohols as the initiators. Kinetic study in solution polymerization prooved the polymerization has high monomer conversion degree close to 100% and the molecular weight of the resulting polyester has linear increase with the increase of [M]0 /[I] (molar ratio of monomer to initiator). Sequential polymerization of L‐LA and MBC in THF also showed high MBC conversion of 94% with a narrow molecualr weight maintained, indicating a living nature of this polymerization. The zinc catalyst system has also been used for the L‐LA bulk polymerization with a high monomer conversion. 13C NMR indicated the polymer possesses high regioregularity and the minor regioirregular component was owing to the D‐LA in the monomer inserted into the polymer mainchain during the transesterifcation. Interaction between monomer and zinc catalyst has been found to be a key factor to sustain a homogenous solution during the initiating procedure. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Influence of microwave heating on the polymerization kinetics and application properties of the PMMA dental materials

AbstractThe effects of heating mode (conventional isothermal heating (CIH) and microwave isothermal heating (MWIH) on the kinetics of polymerization and the properties important for the application (residual monomer, hardness, and water absorption) of three commercial poly(methyl methacrylate) (PMMA) base dental materials were investigated. The degree of monomer conversion was determined by infrared spectrometry. The hardness of the polymerized samples was measured by shore D method, whereas the water absorption was measured gravimetrically. Kinetics models for polymerizations using different heating modes were determined by model fitting method. The rate of the MWIH polymerization was eight times higher compared with the CIH polymerization. The CIH polymerization is found to be the phase–boundary controlled reaction for which the rate of contracting volume is the rate limiting step, whereas MWIH polymerization is found to be the first‐order reaction and the monomer concentration in the polymerization mixture is the rate limiting step. The samples of PMMA base dental materials synthesized by MWIH polymerization exhibit better application properties (hardness and water absorption). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Spectroscopic analysis of poly(methyl methacrylate)/alumina polymer nanocomposites prepared by in situ (bulk) polymerization

Poly(methyl methacrylate) polymer nanocomposites were prepared by in situ bulk free radical polymerization. To ensure high-quality dispersion of the oxide nanoparticles, some composites were prepared from nanoparticles predispersed in propylene glycol methyl ether acetate (PGMEA). The degree to which this additional dispersing medium interacted with the aluminum oxide nanoparticle was studied by attenuated total reflectance (ATR-FTIR), which confirmed secondary bonding and ionic interaction across the particle/dispersing medium interface. Additionally, the effect of the dispersing medium and the nanoparticles on the degree of monomer conversion was determined by Raman spectroscopy. In the presence of oxide nanoparticles alone, the active surface of the nanoparticles traps propagating radicals which significantly reduces monomer conversion. Conversely, the degree of monomer conversion is enhanced in composites containing predispersing nanoparticles, apparently by passivation/functionalization of the oxide surface by the PGMEA.

Multicationic monomethine dyes as sensitizers in two- and three-component photoinitiating systems for multiacrylate monomers

This paper is focused on the description of the synthesis, spectroscopic and electrochemical properties, and the free radical photoinitiation abilities of new multi-cationic monomethine dyes. The new monomethine dyes were employed both as the visible light photoinitiators of acrylate monomer polymerization and as fluorescence probes for monitoring the progress of polymerization. A degree of polymer cure from the measurement of the changes in the probe emission intensity and position shift during the thermally initiated polymerization of monoacrylate was obtained. A distinct increase in the intensity of the dyes fluorescence was observed during polymerization when the degree of monomer conversion was gradually increasing. The second part of this work is the possibility of an application of the dyes synthesized in combination with borate anions, as photoinitiating systems. Novel multi-cationic monomethine dyes paired with n-butyltriphenylborate anions are very efficient visible light photoinitiators of free radical polymerization of acrylate monomers. Their photoinitiating abilities were compared with the photoinitiation ability of Rose Bengal derivative, e.g. typical triplet state photoinitiator. The addition of a second co-initiator to the two-component photoinitiating system (monomethine borate salts) enhances their photoinitiating abilities.

Evaluation of cytotoxicity and degree of conversion of orthodontic adhesives over different time periods

As new orthodontic resin adhesives continue to be marketed, rapid and sensitive tests for examining their toxic effects at the ' cell and tissue level ' are needed because patient safety has been identifi ed as a legal concept. The objective of the present study was to evaluate the cytotoxicity and degree of monomer conversion of orthodontic adhesives over different time periods. Seven adhesives: Transbond® XT, Transbond® Color Change, Quick Cure, EagleBond, Orthobond®, Fill Magic® and Biofix® were evaluated for their cytotoxicity in L929 fibroblastic cells and for their degree of monomer conversion over different time periods. Three control groups were also analysed: Positive control (C+), consisting of Tween 80 cell detergent; Negative control (C-), consisting of PBS; and cell control (CC), consisting of cells exposed to any material. The dye-uptake technique that involves the absorption of a neutral red dye in viable cells was used for the cytotoxicity evaluation and the degree of conversion was evaluated using spectroscopy with infrared. The results showed the cytotoxicity of the adhesives at 24, 48, 72 and 168 hours. At these times, the viability values presented for these materials were statistically different from the groups CC and C- (p 0.05). In the monomer conversions there was a percentage increase of monomer conversion from 24 to 72 hours. A direct correlation could be observed between cytotoxicity and monomer conversions. From this work it can be concluded that all adhesives evaluated are cytotoxic at the times of 24, 48 and 72 hours. Monomers continued conversion even after photopolymerization had stopped.

Enhanced Degree of Monomer Conversion of Orthodontic Adhesives Using a Glass-Fiber Layer under the Bracket

To test the hypothesis that there is no difference in the degree of conversion (DC%) of orthodontic composites during the light-curing process with or without the use of a glass-fiber reinforcement. Two light-curing orthodontic adhesives, Transbond XT (TB) and Beauty Ortho Bond (BO), were used with woven preimpregnated glass fibers. The degree of monomer conversion was determined for both adhesives in three settings (n = 5 per group): in the first group, the adhesive was cured without a bracket (control); in the second group, the bracket was bonded using adhesive without fiber reinforcement; and in the third group, a layer of glass-fiber net was added between the bracket and resin. The adhesive resin was light cured, and the DC% was determined by Fourier transform infrared spectroscopy. A two-way analysis of variance revealed significant differences in the DC% (P < .001) between adhesives and between the fiber-reinforced and nonreinforced groups. When the nonreinforced adhesives were light cured under the brackets, the DC% was significantly lower (TB: 37.0%, SD 3.4; BO: 36.9%, SD 1.9) compared with the control (TB: 54.7%, SD 0.6; BO: 65.9%, SD 0.5). A higher DC% was found when the resin was light cured in the presence of a glass-fiber net (TB: 44.1%, SD 0.3; BO: 55.3%, SD 1.7). The hypothesis is rejected. The degree of monomer conversion of the light-curing adhesive resin under stainless steel bracket can be improved by adding a thin layer of glass-fiber-reinforced composite between the bracket and adhesive resin.

Ultrasound-Induced Cross-Linking and Formation of Macroscopic Covalent Hydrogels in Aqueous Polymer and Monomer Solutions

A new sonochemical method of synthesizing macroscopic permanent hydrogels, that is, water-swellable 3D networks consisting of covalently linked polymer chains, is presented. Subjecting Ar-saturated aqueous solutions of bifunctional monomers, polyethylene glycol diacrylate (PEGDA 700), polyethylene glycol dimethacrylate (PEGDMA 800), and a mixture of PEGDA and vinylpyrrolidone (VP), containing neither initiators nor any other additives to the action of ultrasound leads to the formation of permanent continuous hydrogel filling all of the space previously occupied by monomer solution. For 10% PEGDA solution at an ultrasound frequency of 622 kHz, the reaction time is as short as 30 s. By selecting the appropriate sonication time, frequency of ultrasound, and concentration of substrate, one can control the monomer conversion degree and cross-link density of the resulting gel. Hydrogels can also be obtained by using typical ultrasonic cleaning bath (35 kHz), albeit a higher dose of ultrasound energy (i.e., long...

Effect of various visible light photoinitiators on the polymerization and color of light-activated resins

The purpose of this study was to investigate effects of various visible light photoinitiators on the polymerization efficiency and color of the light-activated resins. Four photoinitiators, including camphorquinone, phenylpropanedione, monoacrylphosphine oxide (TPO), and bisacrylphosphine oxide (Ir819), were used. Each photoinitiator was dissolved in a Bis-GMA and TEGDMA monomer mixture. Materials were polymerized using dental quartz-tungsten halogen lamp (QTH), plasma-ark lamp and blue LED light-curing units, and a custom-made violet LED light unit. The degree of monomer conversion and CIE L*a*b* color values of the resins were measured using a FTIR and spectral transmittance meter. The degree of monomer conversions of TPO- and Ir819-containing resins polymerized with the violet-LED unit were higher than camphorquinone-containing resin polymerized with the QTH light-curing unit. The lowest color values were observed for the TPO-containing resin. Our results indicate that the TPO photoinitiator and the violet-LED light unit may provide a useful and improved photopolymerization system for dental light-activated resins.

Enhanced Degree of Monomer Conversion of Orthodontic Adhesives Using a Glass-Fiber Layer under the Bracket

Enhanced Degree of Monomer Conversion of Orthodontic Adhesives Using a Glass-Fiber Layer under the Bracket

Propagation Rate Coefficient for Radical Polymerization ofN-Vinyl Pyrrolidone in Aqueous Solution Obtained by PLP−SEC

Propagation rate coefficients, kp, of N-vinyl pyrrolidone (NVP) radical polymerization in aqueous solution have been measured via the pulsed-laser polymerization - size exclusion chromatography method (PLP−SEC) over an extended concentration range from 1.8 to 100 wt % NVP at temperatures between 2 and 60 °C. The SEC analyses have been carried out by a modified procedure using dimethyl acetamide as the eluent. An about 20-fold increase of kp is observed in passing from NVP bulk polymerization to reaction in dilute aqueous solution. As with nonionized methacrylic acid (MAA), for which a similarly strong change in kp has recently been reported, the large solvent effect in NVP polymerization is assigned to intermolecular interactions resulting in a significant hindrance of internal rotational motion in the transition state structure for propagation. Some contribution from a minor change in activation energy may however not be ruled out. PLP−SEC studies carried out on aqueous NVP solutions to which either polyNVP or N-ethyl-2-pyrrolidone (NEP), the saturated analogue of NVP, have been added, demonstrate that kp depends on the molecular environment at the reactive site, which is affected by NVP (or NEP) content, but not by the polyNVP content. The lowering of monomer concentration during NVP polymerization to higher degrees of monomer conversion results in an increase of kp. Variation of pH in the range 3 to 10 does not affect kp.

Termination Kinetics of the Free-Radical Polymerization of Nonionized Methacrylic Acid in Aqueous Solution

The termination kinetics of free-radical polymerization of nonionized methacrylic acid (MAA) in aqueous solution has been investigated at two MAA concentrations, 30 and 60 wt %, by single-pulse pulsed-laser initiated polymerization carried out in conjunction with µs time-resolved in-line monitoring of monomer conversion via near-infrared spectroscopy (SP−PLP−NIR). From measured values of kt/kp for 2000 bar, with the conversion-dependent propagation rate coefficient, kp, being inferred from literature data, the chain-length-averaged termination rate coefficient, ⟨kt⟩, is deduced as a function of monomer conversion, x. As with methyl methacrylate polymerization, the ⟨kt⟩ vs x dependence may be modeled under the assumption that, toward higher degrees of monomer conversion, ⟨kt⟩ is successively controlled by segmental diffusion, translational diffusion, and reaction diffusion. For 50 °C, 2000 bar, and initial monomer concentrations in water of 30 and 60 wt %, chemically initiated polymerizations have also been carried out. The resulting ⟨kt⟩ values are in good agreement with the data from SP−PLP−NIR.

Short Glass Fiber-reinforced Composite with a Semi-interpenetrating Polymer Network Matrix for Temporary Crowns and Bridges

The purpose of this study was to investigate the reinforcement effect of short E-glass fiber fillers on some mechanical properties of temporary crown and bridge (TCB) composite resin with a semi-interpenetrating polymer network (semi-IPN). Experimental temporary fiber reinforced (TFC) composite resin was prepared by mixing 15 wt% of short E-glass fibers (3 mm in length) with a 35 wt% of semi-IPN-resin (dual or chemical cure) with 50 wt% of silane treated particulate silica fillers using a high speed mixing device. Temporary crowns (n=6) and test specimens (2 x 2 x 25 mm3) (n=6) were made from the experimental TFC and conventional TCB composite (control, Protemp Garant, 3M-ESPE, St. Paul, MN, USA). A three-point bending test was done according to ISO standard 10477, and a compression loading test was carried out using a steel ball (Ø 3.0 mm) with a speed of 1.0 mm/min until fracture occurred. The degree of monomer conversion (DC%) of both composites was determined by Fourier transfer infrared (FTIR) spectrometry. The analysis of variance (ANOVA) revealed both dual and chemical cure experimental TFC composite resins had statistically significant (p<0.05) higher flexural strengths (117 and 99 MPa, respectively) and compressive load-bearing capacity (730 and 623 N, respectively) compared to the control TCB composite resin (72 MPa, 549 N). The use of short fiber fillers with semi-IPN polymer matrix yielded an improved mechanical performance compared to a conventional TCB composite resin.

Influence of Polymerization Mode on Degree of Conversion and Micropush-out Bond Strength of Resin Core Systems Using Different Adhesive Systems

The aim of this study was to evaluate the influence of different polymerization modes on degree of conversion and micropush-out bond strength of dual-polymerized resin core systems to dentin by using two different adhesive systems. Two resin core systems, Rebilda DC and Build-It FR, were used in combination with total-etch (Adper Scotchbond Multi-Purpose) and self-etch (Clearfil SE Bond) adhesive systems. After treatment of dentin surfaces, resin core systems were applied into the cavities and subjected to different polymerization modes as follows: (1) chemical polymerization; (2) dual polymerization with standard mode of LED (Elipar FreeLight 2 LED); or (3) dual polymerization with exponential mode of LED. The cavities (n=10 per group) were tested in a universal testing machine. Degree of monomer conversion (DC%) was determined by Fourier transform infrared spectroscopy (n=5 cavities per group). ANOVA revealed that resin core (p = 0.002), adhesive system (p < 0.001), and polymerization mode (p < 0.001) had significant effects on bond strength values. The degree of conversion for resin cores decreased significantly (p < 0.001) when only chemical polymerization was employed.

In vitro Mechanical Testing of Glass Fiber-reinforced Composite Used as Dental Implants

The aim of this study was to evaluate the design of fiber-reinforced composite (FRC) on some mechanical properties of a dental implant. FRC implants were fabricated using different polymerization conditions and designs of the glass-fiber structure. Specimens were tested with a cantilever bending test and a torsional test. The degree of monomer conversion (DC%) was measured using a Fourier transform infrared spectroscopy (FTIR). Statistical analysis showed significant differences between groups revealing mean fracture load values from 437 N to 1461 N. The mean torsional force in fracture varied from 0.01 to 1.66 Nm. The DC% varied from 50% to 90%. This study suggests by modifying the polymerization conditions and fiber orientation of FRC implants, the biomechanical properties of an FRC can be tailored to the needs of dental implants.

Effect of nanofiller fractions and temperature on polymerization shrinkage on glass fiber reinforced filling material

Objectives The aim was to evaluate the effect of different nanofiller fractions and temperature on polymerization shrinkage strain and degree of monomer conversion of short glass fibers reinforced semi-interpenetrating polymer network (semi-IPN)-polymer matrix composite resin. Methods Experimental composite resin was prepared by mixing 22.5 wt% of short E-glass fibers (3 mm in length) to the 22.5 wt% of resin matrix with various weight fractions of nanofillers (0, 10, 20, 30, 40, 50 wt%) and then 55 wt% of silane treated silica filler were added gradually using high speed mixing machine. Another study group contained composite resin prepared by mixing 22.5 wt% of resin matrix (without nanofillers) to 77.5 wt% of filler particles (without fiber fillers). As control material, commercial particulate filler composite resin was used. The shrinkage strain of the specimens was measured using the bonded-disk technique at 26 and 37 °C with respect to time. Degree of conversion of the experimental composites containing different nanofiller fractions was measured using FTIR spectroscopy. Results ANOVA revealed that fraction of nanofillers and polymerization temperature had significant effect ( p < 0.05) on the shrinkage strain and degree of conversion of the composite resin. Shrinkage strain correlated with nanofiller fraction and polymerization temperature ( r 2 = 0.96 and 0.95). Significance The use of high nanofiller fraction with short fiber fillers and IPN-polymer matrix yielded improved rate of shrinkage strain.

Mechanism of ɛ-caprolactone polymerization and ɛ-caprolactone/trimethylene carbonate copolymerization carried out with Zr(Acac)4

The paper presents the mechanism of the polymerization of ɛ-caprolactone with the use of Zr(Acac)4. At the first stage of the initiation of the polymerization, a reaction consisting of proton transfer from caprolactone to acetylacetonate ligand and then ligand exchange reaction with release of free acetylacetone (HAcac) occur. Complex 1, arisen as a product of this reaction, is the actual initiator of the observed polymerization. During the conducted polymerization the molar mass increase is directly proportional to monomer conversion degree. On the basis of observed phenomenon, the polymerization of cyclic trimethylene carbonate (TMC) applying ɛ-caprolactone as a co-initiator is possible. Complex 1 arose in the initial phase of this reaction as well, being an equally efficient initiator for TMC polymerization. Using Zr(Acac)4 as an initiator for an ɛ-caprolactone/TMC copolymerization resulted in obtaining a series of copolymers with varied, predicted composition and high molar mass values.