The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Christopher N. Bowman - One of the best experts on this subject based on the ideXlab platform.
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Deconvoluting the impact of intermolecular and intramolecular interactions on the Polymerization Kinetics of ultrarapid mono(meth)acrylates
Macromolecules, 2007Co-Authors: Harini Kilambi, Jeffrey W. Stansbury, Christopher N. BowmanAbstract:Polymerization studies in the presence of extensive amounts of solvent are used here to deconvolute the effects of intermolecular interactions such as bulk medium polarity, π−π stacking, and hydrogen bonding and characterize the contribution of intramolecular conformational effects to monomer reactivity. For that purpose the solution Polymerization Kinetics of various monomers in the presence of 95 wt % 1, 4-dioxane were measured and compared to bulk Polymerization Kinetics. The studies revealed that traditional aliphatic acrylates like hexyl acrylate exhibit approximately 2−3-fold reduction upon dilution. Monomers characterized by only hydrogen-bonding features such as hydroxyethyl acrylate exhibit an 8−12-fold reduction upon dilution. Monomers possessing only aromatic ring stacking interactions such as phenyl acrylate exhibit approximately a 5−10-fold reduction upon dilution under similar conditions. Even at a concentration of 5 wt % monomer in 1,4-dioxane, there were approximately 2−5-fold differences ...
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The effect of functionalized nanoparticles on thiol–ene Polymerization Kinetics
Polymer, 2006Co-Authors: Tai Yeon Lee, Christopher N. BowmanAbstract:Abstract Functionalized silica nanoparticles with thiol or acrylate groups were synthesized, and the effect of the functionalized particles on the thiol–ene photoPolymerization Kinetics was investigated by real-time FTIR spectroscopy. To explain the effect of the nanoparticles on thiol–ene Polymerization Kinetics, the thiol–ene Polymerization at the interface of the particle and the bulk monomer was studied in conjunction with the effects of light intensity and viscosity changes caused by the nanoparticles. These results are compared with corresponding nanofilled acrylate systems. Nanoparticles were not found to significantly affect the Polymerization of acrylate-based nanocomposites regardless of the functional group type attached to the particle surface while significant changes in Polymerization Kinetics were observed with thiol–ene based nanocomposites. The thiol–ene Polymerization rate decreases with increasing particle content for small amounts of particle loadings due to a stoichiometric imbalance of thiol and ene groups at the particle surface. However, the Polymerization rates increase with larger particle loadings because of Polymerization viscosity enhancements. Thiol–ene based nanocomposites exhibit higher final conversions than acrylate systems, reduce the oxygen inhibition relative to acrylate Polymerizations, and still react rapidly to form highly crosslinked, hard, high glass transition temperature materials.
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The effect of primary cyclization on free radical Polymerization Kinetics: experimental characterization
Polymer, 2003Co-Authors: Jeannine E. Elliott, Jun Nie, Christopher N. BowmanAbstract:Abstract Free radical Polymerization Kinetics are influenced by many factors including solvent concentration during Polymerization, monomer structure, and comonomer composition. This study isolates the effects of the balance between primary cyclization and crosslinking on the Polymerization Kinetics. Isomeric crosslinking agents, 1,2-cyclohexanediol dimethacrylate (1,2-CHDDMA), 1,3-cyclohexanediol dimethacrylate (1,3-CHDDMA), and 1,4-cyclohexanediol dimethacrylate (1,4-CHDDMA), were utilized for the study because they have differing cyclization rates due to the conformation of the two methacrylate groups in the monomer, but they are otherwise similar. In coPolymerizations of 1, 2, 5, and 10% crosslinking agents with 2-methoxyethyl methacrylate (MEMA), the 1,4-CHDDMA samples were always found to have an earlier onset of autoacceleration than 1,2-CHHDMA samples. 1,3-CHDDMA copolymerized with MEMA had a Polymerization rate between the 1,2-CHDDMA and 1,4-CHDDMA, as expected. Mechanical property data showed that copolymer samples made with the 1,4-CHDDMA crosslinking agent exhibited a lower M c and higher T g than the analogous 1,2-CHDDMA copolymers. It is concluded that reduced mobility from greater crosslinking than cyclization causes the earlier onset of autoacceleration in the 1,4-CHDDMA copolymers.
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Effect of Primary Cyclization on Free Radical Polymerization Kinetics: Modeling Approach
Macromolecules, 2002Co-Authors: Jeannine E. Elliott, Christopher N. BowmanAbstract:A modified kinetic model is developed which captures how the cross-linked network structure and its evolution in loosely cross-linked polymers affects the Polymerization Kinetics. In our previous work, diffusion-controlled Kinetics has been modeled through the change in free volume of the system as monomer converts to polymer.1,2 Here, the additional effect of the resistance caused by the need to diffuse through the cross-linked network is incorporated into a model of the Polymerization Kinetics. With this model, the effects of cross-linking and cyclization observed in experimental systems are predicted. The model quantitatively predicts experimental results for varying concentrations of 1,4-cyclohexanediol dimethacrylate and 1,2-cyclohexanediol dimethacrylate copolymerized with methoxy ethyl methacrylate.
Timothy J White - One of the best experts on this subject based on the ideXlab platform.
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Polymerization Kinetics and monomer functionality effects in thiol ene polymer dispersed liquid crystals
Macromolecules, 2007Co-Authors: Timothy J White, Vincent P Tondiglia, Lalgudi V Natarajan, And Timothy J Bunning, Allan C GuymonAbstract:Polymer dispersed liquid crystals (PDLCs) are a class of electrooptic materials most often formed by polymer-induced phase separation, a one-step fabrication technique often based on photoPolymerization of the commercial thiol−ene mixture NOA65. To allow further understanding regarding PDLC formation, this work systematically examines processing variables that influence thiol−ene-based PDLC morphology and subsequent performance, namely Polymerization Kinetics, polymer gel point, and liquid crystal (LC) phase separation. PDLC formulations containing a wide range of thiol and ene monomers were examined as a function of monomer (thiol and ene) functionality, thiol−ene stoichiometry, and ene monomer composition. Simultaneous examination of polymer evolution and LC phase separation by real-time infrared (RTIR) spectroscopy shows that both Polymerization Kinetics and the gel point of thiol−ene PDLC formulations are influential on the extent of LC phase separation. Increasing monomer functionality (both thiol an...
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Polymerization Kinetics and Monomer Functionality Effects in Thiol−Ene Polymer Dispersed Liquid Crystals
Macromolecules, 2007Co-Authors: Timothy J White, Lalgudi V Natarajan, Vincent P Tondiglia, And Timothy J Bunning, C. Allan GuymonAbstract:Polymer dispersed liquid crystals (PDLCs) are a class of electrooptic materials most often formed by polymer-induced phase separation, a one-step fabrication technique often based on photoPolymerization of the commercial thiol−ene mixture NOA65. To allow further understanding regarding PDLC formation, this work systematically examines processing variables that influence thiol−ene-based PDLC morphology and subsequent performance, namely Polymerization Kinetics, polymer gel point, and liquid crystal (LC) phase separation. PDLC formulations containing a wide range of thiol and ene monomers were examined as a function of monomer (thiol and ene) functionality, thiol−ene stoichiometry, and ene monomer composition. Simultaneous examination of polymer evolution and LC phase separation by real-time infrared (RTIR) spectroscopy shows that both Polymerization Kinetics and the gel point of thiol−ene PDLC formulations are influential on the extent of LC phase separation. Increasing monomer functionality (both thiol an...
Dimitris S. Achilias - One of the best experts on this subject based on the ideXlab platform.
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Polymerization Kinetics of n-Butyl Methacrylate in the Presence of Graphene Oxide Prepared by Two Different Oxidation Methods with or without Functionalization
Industrial & Engineering Chemistry Research, 2018Co-Authors: Ioannis S. Tsagkalias, Symela Papadopoulou, George D. Verros, Dimitris S. AchiliasAbstract:Nanocomposite materials based on poly(butyl methacrylate) and either graphene oxide (GO) or functionalized graphene oxide (F-GO) were produced using the in situ bulk radical Polymerization technique. It was found that the Hummers method results in a higher degree of oxidation, compared to the Staudenmaier, whereas F-GO was produced using a silane-modifying agent. Polymerization Kinetics were studied both experimentally and theoretically, and it was found that the presence of hydroxyl groups in the surface of GO results in scavenging the primary initiator radicals, thus reducing the initiator efficiency and the reaction rate, whereas the number-average molecular weight of the polymer formed was increased. The presence of F-GO affected the Polymerization Kinetics in a different way resulting in partially grafted structures. The theoretical study included the addition of a phenomenological transfer to the polymer side-reaction to account for the Polymerization occurring at the F-GO surface.
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Polymerization Kinetics of Poly(2-Hydroxyethyl Methacrylate) Hydrogels and Nanocomposite Materials
2017Co-Authors: Dimitris S. Achilias, Panoraia I. SiafakaAbstract:Hydrogels based on poly(2-hydroxyethyl methacrylate) (PHEMA) are a very important class of biomaterials with several applications mainly in tissue engineering and contacts lenses. Although the Polymerization Kinetics of HEMA have been investigated in the literature, the development of a model, accounting for both the chemical reaction mechanism and diffusion-controlled phenomena and valid over the whole conversion range, has not appeared so far. Moreover, research on the synthesis of nanocomposite materials based on a polymer matrix has grown rapidly recently because of the improved mechanical, thermal and physical properties provided by the polymer. In this framework, the objective of this research is two-fold: to provide a kinetic model for the Polymerization of HEMA with accurate estimations of the kinetic and diffusional parameters employed and to investigate the effect of adding various types and amounts of nano-additives to the Polymerization rate. In the first part, experimental data are provided from Differential Scanning Calorimetry (DSC) measurements on the variation of the reaction rate with time at several Polymerization temperatures. These data are used to accurately evaluate the kinetic rate constants and diffusion-controlled parameters. In the second part, nanocomposites of PHEMA are formed, and the in situ bulk radical Polymerization Kinetics is investigated with DSC. It was found that the inclusion of nano-montmorillonite results in a slight enhancement of the Polymerization rate, while the inverse holds when adding nano-silica. These results are interpreted in terms of noncovalent interactions, such as hydrogen bonding between the monomer and polymer or the nano-additive. X-Ray Diffraction (XRD) and Fourier Transform Infra-Red (FTIR) measurements were carried out to verify the results.
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Investigation of the radical Polymerization Kinetics using DSC and mechanistic or isoconversional methods
Journal of Thermal Analysis and Calorimetry, 2014Co-Authors: Dimitris S. AchiliasAbstract:In this research, an effort was undertaken to investigate radical Polymerization Kinetics using experimental data from DSC measurements and mechanistic or isoconversional models. Polymerization of a polar monomer, namely 2-hydroxyethyl methacrylate in the presence of benzoyl peroxide initiator was studied. The variation of the effective activation energy with conversion was directly interpreted in terms of the physical phenomena taking place during the reaction in a microscale. Both isothermal and non-isothermal DSC data were employed and the effect of diffusion-controlled phenomena on the reaction Kinetics at different conversion regimes was assessed. Finally, the effect of the presence of nanofiller on Polymerization Kinetics and the activation energy values were estimated and correlated to physical phenomena taking place during Polymerization.
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Polymerization Kinetics and Thermal Degradation of Poly(2‐hydroxyethyl methacylate) / Organo‐Modified Montmorillonite Nanocomposites Prepared by In Situ Bulk Polymerization
Macromolecular Symposia, 2013Co-Authors: Panoraia I. Siafaka, Dimitris S. AchiliasAbstract:Summary Poly(2-hydroxyethyl methacrylate) based nanocomposites with nano-clay were prepared using the in situ bulk radical Polymerization technique. XRD analysis revealed mainly intercalated and partially exfoliated structures. Polymerization Kinetics was investigated with DSC and found that the presence of small amount of nanofiller could slightly affect Polymerization rate and monomer conversion. Thermal stability of the nanocomposites is enhanced according to the presence of nanoclay.
Timothy E. Long - One of the best experts on this subject based on the ideXlab platform.
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Stable free radical Polymerization Kinetics of alkyl acrylate monomers using in situ FTIR spectroscopy: Influence of hydroxyl-containing monomers and additives
Macromolecular Chemistry and Physics, 2004Co-Authors: Jeremy R. Lizotte, Timothy E. LongAbstract:Summary: The homoPolymerization and coPolymerization of various alkyl acrylate monomers was studied under stable free radical Polymerization (SFRP) conditions using in situ FTIR spectroscopy to monitor Polymerization Kinetics. The IR absorbance corresponding to the CH deformation of the monomer (968 cm−1) was measured to determine monomer conversion in real-time fashion. The monomer disappearance profiles were subsequently converted to pseudo-first order kinetic plots. Altering the alkyl ester chain length and configuration did not reveal a significant trend in the resulting Polymerization Kinetics. However, addition of 2-hydroxyethyl acrylate (HEA) to a Polymerization of n-butyl acrylate (nBA) substantially accelerated the rate of total monomer conversion, increasing the observed rate constant almost two times. 1H NMR spectroscopy also showed that the resulting HEA/nBA copolymers were enriched with the HEA monomer. Moreover, a similar but enhanced effect was also observed upon the addition of small amounts of dodecanol to an n-butyl acrylate homoPolymerization resulting in more than a doubling of the observed rate constant. Resonance forms associated with the DEPN nitroxide and stabilization resulting from hydrogen bonding.
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Determination of solution Polymerization Kinetics by near-infrared spectroscopy. 1. Living anionic Polymerization processes
Macromolecules, 1993Co-Authors: Timothy E. Long, H. Y. Liu, Brian Andrew Schell, David M. Teegarden, D. S. UerzAbstract:Near-infrared (NIR) spectroscopy (1.0-2.5 μm or 10000-4000 cm -1 ) was successfully utilized to monitor monomer conversion during conventional, anionic solution Polymerization. The conversion of the vinyl protons in the monomer to methylene protons in the polymer was easily monitored under conventional (10-20% solids) solution Polymerization conditions. Despite the presence of the NIR probe, the «living» nature of the Polymerizations was maintained in all cases. Both styrene and isoprene Polymerization Kinetics were investigated in nonpolar and polar solvents, and relative rate constants were compared to values previously reported in the literature
C. Allan Guymon - One of the best experts on this subject based on the ideXlab platform.
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Polymerization Kinetics and Monomer Functionality Effects in Thiol−Ene Polymer Dispersed Liquid Crystals
Macromolecules, 2007Co-Authors: Timothy J White, Lalgudi V Natarajan, Vincent P Tondiglia, And Timothy J Bunning, C. Allan GuymonAbstract:Polymer dispersed liquid crystals (PDLCs) are a class of electrooptic materials most often formed by polymer-induced phase separation, a one-step fabrication technique often based on photoPolymerization of the commercial thiol−ene mixture NOA65. To allow further understanding regarding PDLC formation, this work systematically examines processing variables that influence thiol−ene-based PDLC morphology and subsequent performance, namely Polymerization Kinetics, polymer gel point, and liquid crystal (LC) phase separation. PDLC formulations containing a wide range of thiol and ene monomers were examined as a function of monomer (thiol and ene) functionality, thiol−ene stoichiometry, and ene monomer composition. Simultaneous examination of polymer evolution and LC phase separation by real-time infrared (RTIR) spectroscopy shows that both Polymerization Kinetics and the gel point of thiol−ene PDLC formulations are influential on the extent of LC phase separation. Increasing monomer functionality (both thiol an...