Relative Reactivity Ratios Research Articles

The effect of network topology on material properties in vinyl-ester/styrene thermoset polymers using molecular dynamics simulations and time–temperature superposition

The time–temperature superposition principle (TTSP) is a promising tool for filling the time-scale gap between molecular dynamics simulation and experiments in polymer systems. Here we propose a molecular dynamics approach to generate vinyl-ester (VE)/styrene (ST) thermoset modulus master curves that are comparable to experiments. Using this approach we generate modulus master curves for VE/ST systems which were generated with various relative reactivity ratios and therefore with vastly different network architectures. The master curves show that, while network architecture is irrelevant for glassy-state moduli measured either at low temperature or high frequencies, it can strongly determine rubbery-state behavior measured at high temperatures or low frequencies. The most important aspects of network architecture are the length of dangling chains and the molecular weight between crosslinks Mc, both of which depend on the relative reactivity of vinyl ester to styrene. We show that the modulus in the transition region between the glassy and rubbery states decreases with increasing Mc at constant monomer composition. Our results provide an explanation for the observation that processing conditions that can affect relative reactivity, such as the processing temperature, can influence Mc and dictate material properties through specific topological features of the cured networks.

Reactivity Ratios Estimation of the Free‐Radical Polymerization of Itaconic Acid and N‐Vinyl‐2‐Pyrrolidone by the Error‐in‐Variables Methodology

AbstractDesigned copolymers require an understanding of the relative reactivity ratios of the monomer pair and a proper regression technique that can extract this data from the experiments. An implementation of the error‐in‐variables method previously describes in the literature is written and made available for use, along with an high‐performance liquid chromatography (HPLC) methodology for acquiring the kinetic data for the regression analysis of the itaconic acid and N‐vinyl‐2‐pyrrolidone (IA/NVP) free‐radical copolymerization system. From the data, it is observed that higher initial mole fractions of IA in the reaction medium change the reaction kinetics, limiting the validity of the Mayo–Lewis model to a narrow range of initial mole fractions of IA. This effect is not observed at molar fractions below 10%, enabling the parameters to be estimated. The performance of the developed algorithm is satisfactory, and within less than 5% error when applied to data found in the literature. The parameters estimated by the algorithm for the IA/NVP system are r1 = 0.3046 and r2 = 0.0170, with IA as compound 1. A rather large deviation is observed for r1 and this is attributed to measurement errors associated with the low IA concentrations and high initial reaction rates.

Separating Electronic from Steric Effects in Ethene/α-Olefin Copolymerization: A Case Study on Octahedral [ONNO] Zr-Catalysts

Four Cl/Me substituted [ONNO] Zr-catalysts have been tested in ethene/α-olefin polymerization. Replacing electron-donating methyl with isosteric but electron-withdrawing chlorine substituents results in a significant increase of comonomer incorporation. Exploration of steric and electronic properties of the ancillary ligand by DFT confirm that relative reactivity ratios are mainly determined by the electrophilicity of the metal center. Furthermore, quantitative DFT modeling of propagation barriers that determine polymerization kinetics reveals that electronic effects observed in these catalysts affect relative barriers for insertion and a capture-like transition state (TS).

Precursor reaction kinetics control compositional grading and size of CdSe1-x S x nanocrystal heterostructures.

We report a method to control the composition and microstructure of CdSe1-x S x nanocrystals by the simultaneous injection of sulfide and selenide precursors into a solution of cadmium oleate and oleic acid at 240 °C. Pairs of substituted thio- and selenoureas were selected from a library of compounds with conversion reaction reactivity exponents (k E) spanning 1.3 × 10-5 s-1 to 2.0 × 10-1 s-1. Depending on the relative reactivity (k Se/k S), core/shell and alloyed architectures were obtained. Growth of a thick outer CdS shell using a syringe pump method provides gram quantities of brightly photoluminescent quantum dots (PLQY = 67 to 90%) in a single reaction vessel. Kinetics simulations predict that relative precursor reactivity ratios of less than 10 result in alloyed compositions, while larger reactivity differences lead to abrupt interfaces. CdSe1-x S x alloys (k Se/k S = 2.4) display two longitudinal optical phonon modes with composition dependent frequencies characteristic of the alloy microstructure. When one precursor is more reactive than the other, its conversion reactivity and mole fraction control the number of nuclei, the final nanocrystal size at full conversion, and the elemental composition. The utility of controlled reactivity for adjusting alloy microstructure is discussed.

Trimethylammonium-Based Polymethacrylate Ionic Liquids with Tunable Hydrophilicity and Charge Distribution as Carriers of Salicylate Anions

Copolymers of [2-(methacryloyloxy)ethyl]trimethylammonium chloride, salicylate or bis(trifluoromethanesulfonate)imide (Cl–, Sal– or Tf2N–), and methyl methacrylate (MMA) were synthesized by atom transfer radical polymerization (ATRP). The effect of different molar fractions of ionic monomer (0.05–1.0) on physicochemical properties was investigated. The relative reactivity ratios of MMA and ionic monomer with the chloride anion (0.88 and 1.13, respectively) were determined by the linearization Jaacks method. The particles formed in water by copolymers with trimethylammonium chloride (≥50 mol %) reached sizes below 10 nm, whereas salicylate-containing copolymers supported strong self-assembly, yielding 200 nm superstructures. The copolymers, after modification by the exchange of Cl– and Sal– with Tf2N–, demonstrated the influence of the anion on solubility, glass transition temperature, and morphology. The anion-modified trimethylammonium copolymers, compared with those directly synthesized from Tf2N-contai...

A microstructural analysis of isoprenol ether-based polycarboxylates and the impact of structural motifs on the dispersing effectiveness

Generally, polycarboxylate superplasticizers (PCEs) are synthesized via aqueous free radical copolymerization. The conditions during copolymerization such as relative reactivity and feeding mode and ratio of monomers can cause different monomer sequences in the final product. In this study, the sequence of monomers in PCE polymers synthesized from acrylic acid and isoprenyloxy polyethylene glycol (IPEG) macromonomer was characterized by 13C nuclear magnetic resonance (NMR) spectroscopy. Three different triads of monomer sequences (EAE, AAE and AAA; E=ether, A=acid monomer) were detected. It was found that IPEG PCEs predominantly contain the structural motifs of AAE and EAE, and less of AAA. Higher additions of acrylic acid do not incorporate into the structure of PCE, but convert to HMW polyacrylate as by-product instead. A PCE with optimal dispersing effectiveness was achieved at high contents of IPEG macromonomer, a molecular weight (Mw) around 40,000Da and narrow molecular weight distribution.

Synthesis of highly water selective copolymer membranes for pervaporative dehydration of acetonitrile

Pervaporative dehydration of highly concentrated (90–99.9%) acetonitrile needs a chemically resistant membrane having high water selectivity. Crosslinking is the usual practice of controlling excessive swelling in solvent and increasing selectivity of a hydrophilic membrane at the cost of flux. A membrane prepared from a copolymer of acrylonitrile and itaconic acid would be chemically resistant due to its acrylonitrile moiety and also hydrophilic due to the presence of bicarboxylic itaconic acid in its structure. Further, crosslinking is not required for preparing this copolymer membrane. Thus, in the present work several hydrophilic membranes were prepared by copolymerizing acrylonitrile (AN) and itaconic acid (IA) at varied molar ratios depending on their relative reactivity ratios. The structure of the copolymer was characterized by FT-IR, XRD and TG-DTA. The membranes prepared with an AN: IA molar ration of 15:1, 12:1 and 10:1 and noted as PANIA1, PANIA2 and PANIA3, respectively showed optimum properties, viz., mechanical stability, flux and selectivity. Thus, for 99wt% acetonitrile in feed at 30°C, these membranes showed a thickness normalized flux of 1.7, 1.8 and 1.9kgμm/m2h and a high water selectivity of 459, 429 and 409, respectively.

Polystyrene with trifluoromethyl units: Monomer reactivity ratios, thermal behavior, flammability, and thermal degradation kinetics

ABSTRACTChemical modification based on incorporation of flame retardants (FR) into the polymer backbone was used in order to reduce polystyrene flammability. 3‐(trifluoromethyl)styrene (StCF3) and 3,5‐bis(trifluoromethyl)styrene (St(CF3)2) were applied as reactive FR. Copolymers were synthesized with different feed ratios and it gave series of copolymers with various amounts of StCF3 and St(CF3)2 (5–50% mol/mol of St). Glass transition temperature (Tg) and thermal stability of obtained (co)polymers were determined from differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. Kinetic parameters such as the thermal decomposition activation energy (E) and frequency factor (A) were estimated by Ozawa and Kissinger models. Pyrolysis combustion flow calorimeter (PCFC) was applied as a tool for assessing the flammability of the synthesized (co)polymers. Relative reactivity ratios were determined by applying the conventional linearization Jaacks method (rSt = 1.34, rStCF3 = 0.54), (rSt = 0.47, rSt(CF3)2 = 0.13). The results suggest that incorporation of fluorinated styrenes into PSt enchance flame retardance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42839.

Distinctive Reactivities at Biotite Edge and Basal Planes in the Presence of Organic Ligands: Implications for Organic-Rich Geologic CO2 Sequestration.

To better understand how scCO2-saturated brine-mineral interactions can affect safe and efficient geologic CO2 sequestration (GCS), we studied the effects of organic ligands (acetate and oxalate) on biotite dissolution and surface morphological changes. The experimental conditions were chosen to be relevant to GCS sites (95 °C and 102 atm CO2). Quantitative analyses of dissolution differences between biotite edge and basal planes were made. Acetate slightly inhibited biotite dissolution and promoted secondary precipitation. The effect of acetate was mainly pH-induced aqueous acetate speciation and the subsequent surface adsorption. Under the experimental conditions, most of acetate exists as acetic acid and adsorbs to biotite surface Si and Al sites, thereby reducing their release. However, oxalate strongly enhanced biotite dissolution and induced faster and more significant surface morphology changes by forming bidentate mononuclear surface complexes. For the first time, we show that oxalate selectively attacks edge surface sites and enhances biotite dissolution. Thus, oxalate increases the relative reactivity ratio of biotite edge surfaces to basal surfaces, while acetate does not impact this relative reactivity. This study provides new information on reactivity differences at biotite edge and basal planes in the presence of organic ligands, which has implications for safe CO2 storage in organic-rich sites.

Vapor-liquid-solid epitaxial growth of Si1−xGex alloy nanowires: Composition dependence on precursor reactivity and morphology control for vertical forests

Growth of high-density group IV alloy nanowire forests is critical for exploiting their unique functionalities in many applications. Here, the compositional dependence on precursor reactivity and optimized conditions for vertical growth are studied for Si1−xGex alloy nanowires grown by the vapor-liquid-solid method. The nanowire composition versus gas partial-pressure ratio for germane-silane and germane-disilane precursor combinations is obtained at 350 °C over a wide composition range (0.05 ≤ x ≤ 0.98) and a generalized model to predict composition for alloy nanowires is developed based on the relative precursor partial pressures and reactivity ratio. In combination with germane, silane provides more precise compositional control at high Ge concentrations (x > 0.7), whereas disilane greatly increases the Si concentration for a given gas ratio and enables more precise alloy compositional control at small Ge concentrations (x < 0.3). Vertically oriented, non-kinking nanowire forest growth on Si (111) substrates is then discussed for silane/germane over a wide range of compositions, with temperature and precursor partial pressure optimized by monitoring the nanowire growth front using in-situ optical reflectance. For high Ge compositions (x ≈ 0.9), a “two-step” growth approach with nucleation at higher temperatures results in nanowires with high-density and uniform vertical orientation. With increasing Si content (x ≈ 0.8), the optimal growth window is shifted to higher temperatures, which minimizes nanowire kinking morphologies. For Si-rich Si1−xGex alloys (x ≈ 0.25), vertical nanowire growth is enhanced by single-step, higher-temperature growth at reduced pressures.

Monomer Sequence Control via Living Anionic Copolymerization: Synthesis of Alternating, Statistical, and Telechelic Copolymers and Sequence Analysis by MALDI ToF Mass Spectrometry

Diphenylethylene (DPE) is a monomer which has attracted significant interest from both academia and industry. DPE can undergo (co)polymerization by living anionic polymerization but is incapable of forming a homopolymer due to steric hindrance. Herein the copolymerization of DPE and 1,1-bis(4-tert-butyldimethylsiloxyphenyl)ethylene (DPE-OSi) with styrene or butadiene is described in order to produce (functional) copolymers with controlled comonomer sequences—either alternating or telechelic. The copolymer sequences are inherently controlled by relative reactivity ratios, which in turn can be tuned by both monomer structure and the polarity of the polymerization solvent. The compositions of the copolymers prepared in this study were analyzed by 1H NMR spectroscopy and MALDI ToF mass spectrometry, the latter offering a unique opportunity to demonstrate perfect alternating sequences and insight into other sequences such as telechelic polymers.

Estimating Monomer Sequence Distributions in Tetrapolyacrylates

Recently Ting et al. [ACS Macro Lett. 2013, 2, 770−774] described the syntheses of acrylic tetrapolymers with controlled molecular weights and tetramonomer compositions. Relative reactivity ratios of all monomer pairs were determined and used in the Walling–Briggs terminal copolymerization model along with Skeist’s equations to address the expected compositional drift in the monomer feed ratios. The anticipated control of monomer incorporation based on this approach was verified experimentally on several tetrapolyacrylates synthesized by RAFT polymerization, which additionally controlled their molecular weights. Their “new and simple paradigm combining both predictive models provides complementary synthetic and predictive tools for designing macromolecular chemical architectures with hierarchical control over spatially dependent structure–property relationships for complex applications” is extended here to the derivation of expected monad compositions, and diad, triad, and tetrad monomer sequence distributions. These were obtained directly from the comonomer reactivity ratios determined experimentally by Ting et al. Our motivation was twofold: (i) The similar chemical structures of the four acrylate monomers they selected (methyl, 2-carboxyethyl, 2-hydroxypropyl, and 2-propylacetyl acrylate) render the experimental determination of sequence distributions in the resulting tetrapolyacrylates problematic. (ii) Because they are spatially dependent structural parameters, the sequence distributions of monomer diads, triads, tetrads, etc., in co-, tri-, tetrapolymers, etc., are generally expected to correlate more closely with their properties than their overall compositions.

Boronated (co)polystyrene: monomer reactivity ratios, thermal behavior and flammability

Chemical modification based on incorporation of flame retardants (FR) into the polymer backbone was used in order to reduce polystyrene flammability. Boronated styrenes such as 4‐vinylphenylboronic acid (StB(OH)2) and 6‐methyl‐2‐(4‐vinylphenyl)‐1,3,6,2‐dioxazaborocane‐4,8‐dione (StBcyclo) were applied as reactive FR. Homo‐ and copolymers of boronated styrenes and styrene (St) were synthesized with different feed ratios using free radical polymerization. It yielded in series of (co)polymers with various amounts of StB(OH)2 and StBcyclo (5–20% mol/mol of St). Copolymer compositions were determined by 1H NMR. The relative reactivity ratios of system St‐StBcyclo were determined by applying the Jaacks method. Glass transition temperature and thermal stability of obtained (co)polymers were determined from DSC and TGA analysis, respectively. The pyrolysis combustion flow calorimeter was applied as a tool for assessing the flammability of the synthesized (co)polymers. Copyright © 2014 John Wiley & Sons, Ltd.

Synthesis and investigation of monomodal hydroxy-functionalized PEG methacrylate based copolymers with high polymerization degrees. Modification by “grafting from”

The synthesis of monomodal copolymers with poly(ethylene glycol) (PEG) side chains from commercial poly(ethylene glycol) methacrylates (PEGMA) by atom transfer radical polymerization (ATRP) is verified. Two hydroxy-functionalized PEGMA macromonomers (520g/mol and 360g/mol) were copolymerized with methyl methacrylate (MMA) using various initial feed (1.5/98.5–50/50mol.%). The copolymers P(MMA-co-PEGMA) with high degree of polymerization, e.g. 100–275 of repeating units in the backbone including 7–56 PEG side chains, were obtained. The relative reactivity ratios of PEGMA and MMA determined by the Jaacks method indicated slightly faster incorporation of macromonomer into polymeric chain than MMA (rMMA=0.79; rPEGMA=1.27). The polymers containing at least 17mol.% of PEGMA units were water-soluble and exhibited clouding point at temperature in a broad range of 39–70°C. The temperature-sensitive effect makes these polymers as a potential carriers in drug delivery systems. In the case of copolymers insoluble in water, a three-step procedure, including esterification to ATRP multifunctional macroinitiators, ATRP of tert-butyl methacrylate (tBMA) by grafting from, deprotection of carboxylic groups by removing tert-butyl groups, was applied to extend PEG grafts and expand the content of hydrophilic fraction (32–94mol.%), what efficiently developed polymer solubility in polar solvents giving possibility for the future biomedical applications.

Halogeno‐modified polystyrene: monomer reactivity ratios, thermal behaviour and flammability

AbstractChemical modification based on incorporation of flame retardants into polymer backbones was used in order to reduce flammability of polystyrene (PSt). The halogeno‐substituted styrenes: 4‐chlorostyrene (ClSt), 4‐bromostyrene (BrSt) and 2,3,4,5,6‐pentafluorostyrene (5FSt) were applied as reactive flame retardants. Homo‐ and copolymers of these halogeno‐substituted styrenes and styrene (St) were synthesized with various feed ratios using free radical bulk polymerization with azobisisobutyronitrile as a initiator. This yielded series of (co)polymers with various amounts of included ClSt, BrSt and 5FSt (5–50 mol% of modified St). Copolymer compositions were determined using 1H NMR spectroscopy. The relative reactivity ratios of the used comonomers were determined by applying conventional linearization methods. The Jaacks (J) method was used for systems including BrSt and ClSt monomers whereas the Fineman–Ross method was additionally used to confirm the values of reactivity ratios of St–5FSt. The reactivity ratios of comonomer pairs obtained from J plots were 0.75 and 0.38 (St–ClSt), 1.65 and 0.46 (St–BrSt), 0.44 and 0.42 (St–5FSt). Glass transition temperature and thermal stability of obtained (co)polymers were determined using differential scanning calorimetry and thermogravimetric analysis (TGA), respectively. The thermal degradation kinetic of PSt, PClSt, PBrSt and P5FSt was studied applying TGA. Kinetic parameters such as thermal decomposition activation energy (E) and frequency factor (A) were estimated using Ozawa and Kissinger models. The resulting activation energies estimated using these two methods were quite close. The values of activation energy (kJ mol−1) increased in the following order: PClSt (E(O) = 216.1) < PSt (E(O) = 219.9) < PBrSt (E(O) = 224.7) < P5FSt (E(O) = 330.9). A pyrolysis combustion flow calorimeter was applied as a tool for assessing the flammability of the synthesized (co)polymers. © 2014 Society of Chemical Industry

Synthesis of polystyrene modified with fluorine atoms: Monomer reactivity ratios and thermal behavior

Homo- and copolymers of 4-fluorostyrene (FSt) and styrene (St) were synthesized with different feed ratios using free radical bulk polymerization with azobisisobutyronitrile (AIBN) as initiator. It yielded series of (co)polymers with various amounts of included FSt, P(St-co-FSt) (5–50 mol%) and PFSt. The effect of the initiator concentration on the molecular weights of the homopolymers, that is, PSt and PFSt was investigated. Copolymer compositions were determined by nuclear magnetic resonance spectroscopy. The relative reactivity ratios of both comonomers were determined by applying the conventional linearization methods of Jaacks (J), Finemann–Ross (F–R), inverted Finemann–Ross (IF–R), and Kelen-Tüdos (K–T). The reactivity ratios values of St and FSt obtained from J plot are 1.06 and 0.84, F–R plot are 1.18 and 1.06, IF–R 1.01 and 0.86, and K–T plot 1.04 and 0.88, respectively. Thermal properties of prepared (co)polymers, that is, glass transition temperature (Tg) and thermal stability, were determined from differential scanning calorimetry and thermogravimetrical measurements. The lack of significant influence of FSt comonomer content on Tg of (co)polymers was observed. Additionally, the thermal degradation kinetics of obtained PSt and PFSt was studied by thermogravimetric analysis. Kinetic parameters such as the thermal decomposition activation energy (E) and frequency factor (A) were estimated by Ozawa model [E(O) and A(O), respectively] and Kissinger model [E(K) and A(K), respectively]. The activation energy and the frequency factor of PFSt (253 kJ/mol) were higher than PSt (236 kJ/mol). The resulting activation energies estimated using the two methods were quite close. POLYM. ENG. SCI., 54:1170–1181, 2014. © 2013 Society of Plastics Engineers

Interfacial shear strength of cured vinyl ester resin-graphite nanoplatelet from molecular dynamics simulations

Interfacial adhesion between a three layer thick graphite nanoplatelet and a vinyl ester (VE) matrix was studied using molecular dynamics simulations. Polymer interphase formation near carbon surfaces influences interfacial bonding and carbon/matrix load transfer. A VE resin was equilibrated near the graphite surfaces and then cured using the Relative Reactivity Volume algorithm to form a crosslinked matrix while enforcing the correct regiochemistry and relative reactivity ratios within the free radical addition cure. The local styrene monomer concentration in both the liquid and cured resin was highest near the graphite sheets, affecting interfacial strength and near-surface crosslink density. The composite's glass transition temperature (466–502 K) was 50–100 K higher than pure VE. The interfacial shear strength was 141 MPa for resin with 87% monomer conversion and 106 MPa for 98% monomer conversion, indicating effective reinforcement/matrix load transfer. This computational methodology provides more chemically realistic predictions of interfacial surface adhesion than has been reported previously.

Thermogravimetric analysis of gasification reactivity of coal chars with steam and CO2 at moderate temperatures

Comparative study on the gasification reactivity of the three types of Chinese coal chars with steam and CO2 at 850–1050 °C was conducted by isothermal thermogravimetric analysis. The effects of coal rank, pore structure, ash behavior, and gasification temperature on the gasification reactivity of coal chars were investigated. It is found that the gasification reactivity difference between different coal chars changes with reaction degree and gasification temperature, and has no immediate connection with coal rank and initial pore structure. Ash behavior plays an important role in the char reactivity, and changes with gasification temperature and reaction degree due to the variation in the compositions and relative amount. The influence of pore structure is more noticeable during a relatively moderate reaction process. The relative reactivity ratio of steam to CO2 gasification generally decreases with the increasing temperature, and is related with the catalytic effect of inherent minerals. The characteristic parameters of the chars were analyzed, finding that the value of half reaction specific rate is approximate to the average specific rate under the same conditions. The nth-order distributed activation energy model is proposed to describe the coal char gasification process, and the results show that the activation energy increases with the increasing carbon conversion.

Novel Hydroxyl-Functionalized Caprolactone Poly(meth)acrylates Decorated with tert-Butyl Groups

A series of new well-defined copolymers containing the hydroxyl-functionalized monomer, caprolactone 2-(methacryloyloxy)ethyl ester (CLMA), and tert-butyl acrylate/methacrylate (tBuA/tBuMA) were synthesized via atom transfer radical polymerization (ATRP). The composition of copolymer strongly depended on the selection of comonomer pair. The relative reactivity ratios of comonomers determined by the Jaacks method indicated significantly higher reactivity of CLMA in methacrylate/acrylate system (rCLMA = 2.53, rtBuA = 0.40), whereas tert-butyl monomer was faster polymerized in case of two methacrylates (rCLMA = 0.61, rtBuMA = 1.63). These results were compared with that obtained for the CLMA/MMA system, which was closer to CLMA/tBuMA, giving rCLMA = 0.83 and rMMA = 1.20. The copolymer composition influenced the glass-transition temperatures (Tgs), which decreased with an increase of CLMA content.

ChemInform Abstract: Armed—Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

AbstractReview: 109 refs.