Comonomer Mixture Research Articles

Tris(trimethylsilyl)silane as a co-initiator for dental adhesive: Photo-polymerization kinetics and dynamic mechanical property

ObjectivesThe purpose of this study was to evaluate the polymerization behavior of a model dentin adhesive with tris(trimethylsilyl)silane (TTMSS) as a co-initiator, and to investigate the polymerization kinetics and mechanical properties of copolymers in dry and wet conditions. MethodsA co-monomer mixture based on HEMA/BisGMA (45/55, w/w) was used as a model dentin adhesive. The photoinitiator system included camphorquinone (CQ) as the photosensitizer and the co-initiator was ethyl-4-(dimethylamino) benzoate (EDMAB) or TTMSS. Iodonium salt, diphenyliodonium hexafluorophosphate (DPIHP) serving as a catalyst, was selectively added into the adhesive formulations. The control and the experimental formulations were characterized with regard to the degree of conversion (DC) and dynamic mechanical properties under dry and wet conditions. ResultsIn two-component photoinitiator system (CQ/TTMSS), with an increase of TTMSS concentration, the polymerization rate and DC of CC double bond increased, and showed a dependence on the irradiation time and curing light intensity. The copolymers that contained the three-component photoinitiator system (CQ/TTMSS/DPIHP) showed similar dynamic mechanical properties, under both dry and wet conditions, to the EDMAB-containing system. SignificanceThe DC of formulations using TTMSS as co-initiator showed a strong dependence on irradiation time. With the addition of TTMSS, the maximum polymerization rate can be adjusted and the network structure became more homogenous. The results indicated that the TTMSS could be used as a substitute for amine-type co-initiator in visible-light induced free radical polymerization of methacrylate-based dentin adhesives.

Effect of proanthocyanidin incorporation into dental adhesive on durability of resin–dentin bond

BackgroundProanthocyanidin has shown to have beneficial effects on dentin bonding via its collagen cross-linking and protease inhibitory effects. ObjectiveThis study evaluated the effect of incorporation of 1–3% PA into a dental adhesive on durability of resin–dentin bond. Materials and methodsThe experimental adhesive was first formulated by combining 50wt% comonomer mixtures with 50wt% ethanol. PA was then added to the ethanol-solvated adhesive to yield three groups of adhesives at concentrations of 1.0wt%, 2.0wt% and 3.0wt%. The PA-free adhesive served as control. Flat dentin surfaces from forty extracted third molars were etched with 32% phosphoric acid and the specimens were randomly assigned to one of the four adhesive groups. Two layers of experimental adhesives were applied to etched dentin and light-cured for 20s after solvent evaporation. Composite build-ups were performed using Filtek Z250 (3M ESPE). The bonded teeth were divided into three subgroups for different methods of storage: (1) 24h indirect water exposure (IE), (2) 6 M IE and (3) 6 M direct water exposure (DE). After the designated period of water storage, the bonded teeth were sectioned into 0.9mm×0.9mm beams for bond strength testing. Bond strength data were evaluated by two-way ANOVA and Tukey׳s tests (α=0.05). Interfacial nanoleakage was examined using a field-emission scanning electron microscopy. Two-way ANOVA and Tukey׳s tests were used to examine the effects of PA concentration and water exposure on bond strength and percentage of nanoleakage (α=0.05). ResultsTwo-way ANOVA showed that the factors, water exposure and PA concentration had a significant effect on bond strength (p<0.001). Interaction between the two factors was also significant (p<0.001). Bond strength of all four adhesives decreased with PA concentrations and ageing. Type of water exposure had no effect on the bond strength of PA-incorporated adhesive; while direct water exposure significantly reduced the bond strength of PA-free adhesive. Conversely, the factors, water exposure and PA concentration showed a significant effect on nanoleakage percentage (p<0.001). Interaction between the two factors was not significant (p>0.05). ConclusionIncorporation of proanthocyanidin into a dental adhesive did not prevent resin–dentin bond degradation over time.

Compositional design and optimization of dentin adhesive with neutralization capability

ObjectivesThe objective of this work was to investigate the polymerization behavior, neutralization capability, and mechanical properties of dentin adhesive formulations with the addition of the tertiary amine co-monomer, 2-N-morpholinoethyl methacrylate (MEMA). MethodsA co-monomer mixture based on HEMA/BisGMA (45/55, w/w) was used as a control adhesive. Compared with the control formulation, the MEMA-containing adhesive formulations were characterized comprehensively with regard to water miscibility of liquid resin, water sorption and solubility of cured polymer, real-time photopolymerization kinetics, dynamic mechanical analysis (DMA), and modulated differential scanning calorimetry (MDSC). The neutralization capacity was characterized by monitoring the pH shift of 1mM lactic acid (LA) solution, in which the adhesive polymers were soaked. ResultsWith increasing MEMA concentrations, experimental copolymers showed higher water sorption, lower glass transition temperature and lower crosslinking density compared to the control. The pH values of LA solution gradually increased from 3.5 to about 6.0–6.5 after 90 days. With the increase in crosslinking density of the copolymers, the neutralization rate was depressed. The optimal MEMA concentration was between 20 and 40wt%. ConclusionsAs compared to the control, the results indicated that the MEMA-functionalized copolymer showed neutralization capability. The crosslinking density of the copolymer networks influenced the neutralization rate.

Minimally invasive characterization of covalent monolayer sheets using tip-enhanced Raman spectroscopy.

Synthetic covalent monolayer sheets and their subclass, two-dimensional polymers are of particular interest in materials science because of their special dimensionality which renders them very different from any bulk matter. However, structural analysis of such entities is rather challenging, and there is a clear need for additional analytical methods. The present study shows how tip-enhanced Raman spectroscopy (TERS) can be performed on monomer monolayers and the covalent sheets prepared from them by [4 + 4]-cycloaddition to explore rather complex structural and mechanistic issues. TERS is a surface analytical method that combines the high lateral resolution of scanning probe microscopy (SPM) with a greatly enhanced Raman scattering intensity. The high spatial resolution (<60 nm) and the significantly improved sensitivity (contrast factor of >4000) compared to confocal Raman microscopy provides new insights into the formation of this new and exciting material, namely significant consumption of the reactive units (anthracenes) and exclusion of the alternative [4 + 2]-cycloaddition. Moreover, due to the high lateral resolution, it was possible to find a first spectroscopic hint for step growth as the dominant mechanism in the formation of these novel monolayer sheets. In addition, TERS was used to get first insights into the phase behavior of a comonomer mixture.

Plasma Copolymerization of Fluorinated and Acrylate Monomers: Kinetics and Chemical Structure Study

The plasma homo‐ and co‐polymerization of a fluorinated monomer and an acrylate one are studied in pulsed mode. The proportion of each monomer in the mixture, input power, on and off‐times are varied. Their effects are examined on the growth kinetics and on the chemical structure of the obtained layers. The chemical structure of the films is characterized using Fourier Transform Infra‐Red and X‐ray photoelectron spectroscopies. The results show the formation of a polymer blend or a block copolymer rather than a new material. The variation of power and on‐time affects the acrylate unit structure more than it does the fluorinated monomer, both in the homopolymers and in the copolymer. The deposition kinetics of the copolymer seems to be governed by the fluorinated monomer that plays a catalytic role in the comonomer mixture.

A comprehensive study on kinetics of free-radical solution copolymerization of vinyl acetate and dibutyl maleate in chloroform

Free radical solution copolymerization of vinyl acetate (VAc) and dibutyl maleate (DBM) initiated by AIBN was performed in the presence of chloroform as both solvent and chain transfer agent at various temperatures, comonomer mixture composition and initiator concentrations. Structures of the copolymers were characterized by FT-IR and 1H-NMR techniques. Effect of the above-mentioned variables on the copolymerization rate was investigated via data obtained from 1H-NMR spectra. Value of the “lumped” kinetic parameter, i.e. kp.kt −0.5, was calculated for various initial mole fractions of the comonomers. Reactivity ratios of the VAc and DBM were calculated for the first time from medium/high conversion data to be 0.1102, 0.0421, respectively, by extended KT method and 0.1135 and 0.0562, respectively, by MH method. A good fitting between the theoretical and experimental drifts in the comonomer mixture and copolymer compositions with conversion was observed, indicating accuracy of the reactivity ratios calculated for the present pair comonomers.

Partitioning of monobutyl itaconate and β‐carboxyethyl acrylate between organic and water phases

ABSTRACTUnsaturated carboxylic acids are usually used as functional monomers at low concentrations in emulsion polymerization to improve the colloidal stability and the mechanical properties of the films prepared from the corresponding latexes. These acids are distributed between the aqueous and organic phases to different extents due to their various water solubilities. The partitioning behavior of two new vinyl acids, monobutyl itaconate (MBI) and β‐carboxyethyl acrylate (β‐CEA), between n‐butyl methacrylate (BMA) and the water phases was studied in this work. In addition, the partitioning of commonly used acrylic acid (AA) and methacrylic acid (MAA) was also determined as a benchmark. It was found that the partition coefficients (D) of MBI and β‐CEA depended to a large extent on the acid concentration in the total comonomer mixture; the same trends were observed for AA and MAA. With the variation in monomer to water ratio (M/W), the D value of lipophilic acid MBI changed significantly, while for hydrophilic acid β‐CEA, the D value changed very little. Furthermore, the values of the partition coefficient of MBI and β‐CEA were very strong functions of pH, decreasing rapidly as the pH is increased. On the other hand, temperature has little effect on the partition coefficients for vinyl acids under typical emulsion polymerization reaction conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40868.

Toughening Effect of Ethylene Propylene DieneTerpolymer-Graft-Styrene-Acrylonitrile Copolymer (EPDM-g-SAN) on SAN Resin

The reaction product EPDM-g-SAN, synthesized by suspension graft copolymerization of styrene (St) and acrylonitrile (AN) in the presence of ethylene-propylene-diene terpolymer (EPDM), was blended with a commercial styrene-acrylonitrile copolymer (SAN resin) to prepare AES blends with high impact strength. The effects of AN mass percentage in the St-AN comonomer mixture (f AN), EPDM mass percentage in the feed of EPDM and St-AN (f EPDM) and reaction time on monomer conversion ratio (CR), grafting ratio (GR), and AES notched Izod impact strength were characterized. The notched Izod impact strength of AES containing 15 wt% EPDM reached its maximum with f AN of 40 wt% and f EPDM of 45 wt%; this was attributed to the polarity of the SAN copolymer obtained being appropriate with that of the SAN resin matrix. The dependences of GR and the notched Izod impact strength of AES containing 25 wt% EPDM on the reaction time were in rough agreement. The effect of EPDM content on the AES notched Izod impact strength indicated that the brittle-ductile transition of AES occurred for an EPDM content from 12.5 to 15 wt%. TEM and SEM analysis showed that the phase structure of AES exhibited a “salami” like structure, and the toughening mechanism of AES was shear yielding of the SAN resin matrix, which endowed AES with excellent toughness.

A comprehensive study on the kinetics of aqueous free-radical homo- and copolymerization of acrylamide and diallyldimethylammonium chloride by online 1H-NMR spectroscopy

Free-radical homo- and copolymerization of acrylamide (AAm) and diallyldimethylammonium chloride (DADMAC) initiated with potassium persulfate (KPS) were performed in the presence of 0.1 M NaCl solution in D2O at 50 °C. Online 1H-NMR kinetic experiments were used to study polymerization kinetics via determination of the individual and overall conversion of the comonomers and compositions of the comonomer mixture and produced copolymer as a function of the reaction time. Reactivity ratios of the AAm and DADMAC were calculated by Mao-Huglin (MH) and extended Kelen-Tudos (KT) methods to be 7.0855 ± 1.3963, 0.1216 ± 0.0301 and 6.9458 ± 2.0113, 0.1201 ± 0.0437 respectively. “Lumped” kinetic parameter (k p k − 0.5 ) was estimated from experimental data. Results showed that k p k − 0.5 value increases by increasing mole fraction of the AAm in the initial reaction mixture. Drift in the comonomer mixture and copolymer compositions with reaction progress was evaluated experimentally and theoretically. Theoretical values were calculated from Meyer-Lowry equation by using reactivity ratios obtained from MH method. A good fitting between the experimental and theoretical values was observed, indicating accuracy of the reactivity ratios estimated in the present work. It was found from following changes in the copolymer composition with the comonomer conversion that produced copolymer has a statistical structure.

Effect of organomodified clay on the reaction kinetics, properties and thermal degradation of nanocomposites based on poly(styrene-co -ethyl methacrylate)

In this research, synthesis of novel nanocomposites based on a poly(styrene-co-ethyl methacrylate) copolymer matrix was investigated with different types and amounts of organomodified montmorillonite (MMT) clays. The in situ polymerization technique was selected with dispersion of the MMT nanoparticles into the comonomer mixture and subsequent bulk radical polymerization. Reaction kinetics was measured gravimetrically and it was found that the existence of rigid phenyl rings in the organomodifier may result in a hindered reaction rate especially at high clay loadings. Structural characteristics of the nanocomposites formed were verified with XRD and Fourier transform infrared analysis and mainly intercalated/partially exfoliated structures were verified; their glass transition temperature was measured with DSC, and their molecular weight distribution and average molecular weights were measured with gel permeation chromatography. The latter was also used to measure the variation of the copolymer average molecular weight with conversion. Slightly higher average molecular weight and Tg values for the copolymer in the nanocomposites were measured, compared with neat copolymer. The thermal stability of the nanocomposites was measured with TGA and found to be significantly improved. One-step degradation revealed the existence of macromolecular chains without defective structures. Finally, pyrolysis of the nanocomposite copolymers resulted in the production of both comonomers in high amounts, followed by some dimers or trimers. © 2013 Society of Chemical Industry

Calculation of reactivity ratios of methacrylic acid-ethyl acrylate copolymer by on-line quantitative 1H NMR spectroscopy

The solution copolymerization of methacrylic acid (MAA) and ethyl acrylate (EA) was studied by online proton nuclear magnetic resonance spectroscopy (1H NMR) using 2,2′–azobisisobutyronitrile as an initiator in deuterated dimethyl sulfoxide at 60 °C. The chemical compositions of the copolymer and the comonomer concentrations were determined from the conversion of comonomers to copolymer by quantitative in situ NMR monitoring to estimate the reactivity ratios of the comonomers at low conversion. This is a new and easy methodology to analyze radical copolymerization. In this research, it is shown that monomer reactivity ratios can be calculated by data collected only from one initial comonomer mixture composition via online monitoring progress of the copolymerization reaction. The reactivity ratios of MAA and EA are equal to 2.360 and 0.414, respectively. This approach is used to compute the monomer reactivity ratios in a nonlinear integrated form of the copolymerization equation which is described by Mayo and Lewis terminal model. The fairly good agreement between the results and the literature data reported for the emulsion system represent the accuracy of the reactivity ratios calculated by this new approach. The calculated reactivity ratios for emulsion copolymerization are rMAA = 2.040 and rEA = 0.470, and the previous literature data are rMAA = 2.580 and rEA = 0.157.

Synthesis of a Photocurable Ladder-like Poly(phenyl-co-mercaptopropyl)silsesquioxane as Gate Dielectric Material

A new photocurable ladder-like poly(phenyl-co-mercaptopropyl)silsesquioxane (LPPMPSQ) was synthesized in one pot via base catalyzed hydrolysis-polycondensation of a comonomer mixture of phenyltrimethoxysilane and 3-mercaptopropyltrimethoxysilane. Obtained LPPMPSQ was characterized by 1H NMR, FT-IR, 29Si NMR, TGA, and the electrical (k = 3.6) and mechanical properties (surface modulus = 4.9 GPa) found to be suitable for application as a photocurable gate dielectric material.

Synthesis and characterization of novel nanocomposite materials based on poly(styrene-co-butyl methacrylate) copolymers and organomodified clay

In this research, synthesis of nanocomposites based on poly(styrene-co-butyl methacrylate) copolymer matrix was investigated with different types and amounts of organomodified MMT clays under the trade names Cloisite 15A and 10A. The in situ polymerization technique was selected with dispersion of the MMT nanoparticles into the corresponding co-monomer mixture and subsequent bulk radical polymerization. Reaction kinetics was measured gravimetrically and the structural characteristics of the nanocomposites formed were verified with XRD and FTIR analysis. Their glass transition temperature was measured with DSC, while their molecular weight distribution and average molecular weights with GPC. Thermal degradation characteristics of the nano-hybrids formed were measured with TGA. The copolymer composition was verified with 1H NMR spectroscopy. It was found that, since diffusion-controlled phenomena did not affected much the polymerization kinetics, also the presence of the nano-filler did not influence much the variation of conversion with time. In addition, the average molecular weights and the glass transition temperature of the polymer in the nanocomposites was not changed significantly compared to the neat polymer. However, the thermal stability of the nanocomposites formed was significantly improved with the presence of the nano-filler.

Effect of proanthocyanidins and photo-initiators on photo-polymerization of a dental adhesive

ObjectivesTo evaluate the effects of proanthocyanidins (PA) and photoinitiator type on the degree of conversion (DC) and polymerization rate (PR) of a model dental adhesive. MethodsThree types of photo-initiation systems were introduced into the Bis-GMA/HEMA co-monomer mixture, resulting in four resin formulations including CQ/A (0.5wt% CQ and EDMAB), CQ/A/I-1 (0.5wt% CQ, EDMAB and DPIHP), CQ/A/I-2 (1.0wt% CQ, EDMAB and DPIHP), and TPO (2.1wt% TPO). For each resin formulation, adhesives containing 0%, 2.5%, 5% and 10% of PA with respect to the weight of resin were produced after mixing the resin with various amount of PA/ethanol solution. When light-cured, the RP and DC of each adhesive was determined using ATR-FTIR spectroscopy. ResultsAcross and within the initiator groups, the DC followed the general trend of CQ/A<CQ/A/I-1<CQ/A/I-2<TPO and 0-PA>2.5-PA>5-PA>10-PA, respectively. The change of PR with respect to photo-initiation systems and PA content was in a similar but less pronounced pattern. ConclusionPA hampered the polymerization of all adhesives regardless of photoinitiators used. The initiator formulations CQ/A/I-2 and TPO are better fit for PA-containing adhesives, both leading to >65% DC in the presence of 5% PA. Clinical significanceThe inclusion of PA in dental adhesives has been limited by its interference with the light-curing of adhesive resins. This study found photo-initiation formulations that could maintain a satisfactory degree of monomer conversion while a significant amount of PA is incorporated.

Gamma radiation-induced grafting of acrylamide and dimethyl diallyl ammonium chloride onto starch

Corn starch graft copolymers were prepared from acrylamide/dimethyl diallyl ammonium chloride binary monomers (AM/DMDAAC) by a simultaneous radiation grafting method, and were characterized by FTIR and 1H NMR techniques, weight measurement and titration method. The copolymers with high grafting ratio and high grafting efficiency of binary monomers were achieved at absorbed doses of 2kGy and 3kGy using a 6:9.8:4.2 (w/w/w) ratio of starch/AM/DMDAAC, but their cationic degrees were low. Grafting ratio, grafting efficiency and cationic degree of the copolymers increased with increasing AM content in comonomer mixtures and then decreased at 3kGy using a 6:14 ratio of starch:total comonomers, but their cationic degrees generally decreased with increasing AM content. The grafting ratio, the grafting efficiency and the cationic degree of the copolymers increased, but the grafting efficiency of DMDAAC decreased with varying starch/(AM+DMDAAC) ratio from 6:3 to 6:18 at 3kGy by using a fixed 7:3 ratio of AM:DMDAAC.

Water sorption of CH3- and CF3-Bis-GMA based resins with additives

ObjectivesTo evaluate the effect of additives on the water sorption characteristics of Bis-GMA based copolymers and composites containing TEGDMA, CH3Bis-GMA or CF3Bis-GMA. Material and methodsFifteen experimental copolymers and corresponding composites were prepared combining Bis-GMA and TEGDMA, CH3Bis-GMA or CF3Bis-GMA, with aldehyde or diketone (24 and 32 mol%) totaling 30 groups. For composites, barium aluminosilicate glass and pyrogenic silica was added to comonomer mixtures. Photopolymerization was effected by 0.2 wt% each of camphorquinone and N,N-dimethyl-p-toluidine. Specimen densities in dry and water saturated conditions were obtained by Archimedes' method. Water sorption and desorption were evaluated in a desorption-sorption-desorption cycle. Water uptake (%WU), water desorption (%WD), equilibrium solubility (ES; µg/mm3), swelling (f) and volume increase (%V) were calculated using appropriate equations. ResultsAll resins with additives had increased %WU and ES. TEGDMA-containing systems presented higher %WU, %WD, ES, f and %V values, followed by resins based on CH3Bis-GMA and CF3Bis-GMA. ConclusionsAldehyde and diketone led to increases in the water sorption characteristics of experimental resins.

Controlled synthesis of copolymers of vinyl acetate and n-butyl acrylate mediated by trithiocarbonates as reversible addition-fragmentation chain-transfer agents

The formation of copolymers of vinyl acetate and n-butyl acrylate via polymerization mediated by di-tert-butyl trithiocarbonate and dibenzyl trithiocarbonate as reversible addition-fragmentation chain-transfer agents is studied. Copolymerization mediated by low-molecular-mass reversible addition-fragmentation chain-transfer agents and by the copolymers formed in their presence proceeds via the pseudoliving mechanism. As a result, the controlled synthesis of narrowly dispersed copolymers of various compositions and desired molecular masses may be implemented. Variation in the compositions of the copolymers with conversion is investigated, and the reactivity ratios of the comonomers are found to differ significantly (rVA = 0.01 and rBA = 5.38). Our experimental data make it possible to infer that gradient copolymers are formed in the systems of interest in a wide range of comonomer mixture compositions.

Ion exchange kinetics of some heavy metals from aqueous solutions onto poly (acrylic acid-acrylonitrile) potassium titanate

Heavy metals released by a number of industrial processes are major pollutants. Ground, industrial and even treated wastewaters, heavy metals can be extremely toxic as they damage nerves, liver, kidney and bones. So, our work was concerned to prepare composite inorganic-organic absorbers which represent a group of inorganic ion exchangers modified using binding organic materials. Polyacrylonitrile (PAN) has been used as a universal binding polymer for a number of inorganic ion exchangers. Acrylic acid-acrylonitrile (AA-AN) comonomer mixture was prepared at the optimum copolymerization process and potassium titanate was synthesized by adding 200 ml of 2.2 M TiCl4, and 800 ml of 2.8 M KOH were prepared and mixed with constant stirring to the 1000 ml of AA-AN. These composites have been tested for separation of various contaminants from aqueous solutions. Their high selectivity and sorption efficiency are advantageous for treatment of various industrial waste waters. The kinetic of lead (Pb2+), cadmium (Cd2+) and zinc (Zn2+) ions on the prepared material were studied by applying the Nernest-plank equation. The rate of exchange is controlled by particle diffusion mechanism. The physical thermodynamic parameters such as activation energy and entropy of activation have been evaluated. The selectivity order towards the ions was found: Pb (II) > Cd (II) > Zn (II). Key words: Adsorption, polyacrylic acid-acrylonitrile, heavy metals, potassium titanate, equilibrium.

Effect of proanthocyanidin incorporation into dental adhesive resin on resin–dentine bond strength

ObjectivesThis study evaluated the effect of proanthocyanidin (PA) incorporation into experimental dental adhesives on resin–dentine bond strength. MethodsFour experimental hydrophilic adhesives containing different PA concentrations were prepared by combining 50wt% resin comonomer mixtures with 50wt% ethanol. Proanthocyanidin was added to the ethanol-solvated resin to yield three adhesives with PA concentrations of 1.0, 2.0 and 3.0wt%, respectively. A PA-free adhesive served as the control. Flat dentine surfaces from 40 extracted third molars were etched with 32% phosphoric acid. The specimens were randomly assigned to one of the four adhesive groups. Two layers of one of the four experimental adhesives were applied to the etched dentine and light-cured for 20s. Composite build-ups were performed using Filtek Z250 (3M ESPE). After storage in distilled water at 37°C for 24h, twenty-four bonded teeth were sectioned into 0.9mm×0.9mm beams and stressed to failure under tension for bond strength testing. Bond strength data were evaluated by one-way ANOVA and Tukey's test (α=0.05). Interfacial nanoleakage was examined in the remaining teeth using a field-emission scanning electron microscope and analysed using the Chi-square test (α=0.05). ResultsNo significant difference in bond strength was found amongst PA-free, 1% and 2% PA adhesives. However, incorporation of 3% PA into the adhesive significantly lowered bond strength as demonstrated by a greater number of adhesive failures and more extensive nanoleakage along the bonded interface. ConclusionIncorporation of 2% proanthocyanidin into dental adhesives has no adverse effect on dentine bond strength. Clinical significanceThe addition of proanthocyanidin to an experimental adhesive has no adverse effect on the immediate resin–dentine bond strength when the concentration of proanthocyanidin in the adhesive is less than or equal to 2%.

Free‐radical homo‐ and copolymerization of vinyl acetate and n‐butyl acrylate: Kinetic studies by online 1H NMR kinetic experiments

AbstractFree‐radical homo‐ and copolymerization of vinyl acetate (VAc) and n‐butyl acrylate (BA) in benzene‐d6 were performed by using benzoyl peroxide as an initiator at 70°C. Polymerization kinetic was followed by online 1H NMR kinetic experiments. Significant drift in the comonomer mixture composition with reaction progress was observed. Reactivity ratios of VAc and BA were calculated by terminal unit model (TUM) as well as by simplified penultimate unit model (PUM) with rVAc = 0. It was found that copolymer composition can be described well by the TUM. “Lumped” kinetic parameter ( $ k_p .k_t^{ - 0.5} $) was estimated from experimental data. A good fitting between the theoretical and experimental drifts in the comonomer mixture and copolymer compositions with reaction progress was observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011