Atom transfer radical polymerization and copolymerization of vinyl acetate catalyzed by copper halide/terpyridine

Copper‐mediated atom transfer radical polymerization (ATRP) is versatile for living polymerizations of a wide range of monomers, but ATRP of vinyl acetate (VAc) remains challenging due to the low homolytic cleavage activity of the carbon‐halide bond of the dormant poly(vinyl acetate) (PVAc) chains and the high reactivity of growing PVAc radicals. Therefore, all the reported highly active copper‐based catalysts are inactive in ATRP of VAc. Herein, we report the first copper‐catalyst mediated ATRP of VAc using CuBr/2,2′:6′,2″‐terpyridine (tPy) or CuCl/tPy as catalysts. The polymerization was a first order reaction with respect to the monomer concentration. The molecular weights of the resulting PVAc linearly increased with the VAc conversion. The living character was further proven by self‐chain extension of PVAc. Using polystyrene (PS) as a macroinitiator, a well‐defined diblock copolymer PS‐b‐PVAc was prepared. Hydrolysis of the PS‐b‐PVAc produced a PS‐b‐poly(vinyl alcohol) amphiphilic diblock copolymer. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Neural network-based hybrid models developed for free radical polymerization of styrene

In the present work, the free radical polymerization of styrene is modeled by considering the phenomenology of the process (a simplified model, which does not include the diffusional effects, gel, and glass effects) in combination with an empirical model represented by an artificial neural network. Differential evolution (DE) algorithm, belonging to the class of evolutionary algorithms, is applied for developing the neural models in optimal forms. For improving the results—predicted conversion and molecular weights as function of time, temperature, and initiator concentration—different combinations between phenomenological model and neural network are tested; also, individual and stacked neural networks have been developed for the polymerization process. This methodology based on hybrid models, including neural networks aggregated in stacks, provides accurate results.     

Kinetic modeling of simultaneous polycondensation and free radical polymerization for polyurethane/poly(methyl methacrylate) interpenetrating polymer network

A comprehensive kinetic Monte Carlo algorithm has been developed to investigate the formation process of a polyurethane/poly(methyl methacrylate) (PU/PMMA) interpenetrating polymer network (IPN), in which a component independent strategy is proposed to perform the simulation of simultaneous polycondensation and free radical polymerization. An empiric diffusion model based on the mass fraction of polymer is used to quantify the effect of diffusional limitations on MMA polymerization. Results show that the presence of acrylic monomers has little impact on the formation rate of PU, but the presence of the PU network can accelerate the polymerization of MMA. In addition, the effects of component mass ratio, acrylic cross-linker concentration, and [NCO]/[OH] ratio on the IPN formation kinetics are investigated based on the kinetic model. It is believed that the as-developed modeling strategy can be extended to other IPN systems and provide a better understanding of the interactions between chemically independent networks.     

Synthesis of new phase transfer‐catalyzed free radical polymerization of ethyl methacrylate: A kinetic study

In this study, a new phase transfer catalyst has been synthesized and characterized, which is used for the study of kinetics and mechanism of the free radical polymerization of ethyl methacrylate. The reactions were carried out using peroxodisulfate as initiator in inert and unstirred condition at 60°C ± 1°C. The order with respect to monomer, initiator, and catalyst were found to be 1, 0.7, and 0.5, respectively. The rate of polymerization is independent of ionic strength and pH. Based on the results obtained, a mechanism has been proposed for the polymerization reactions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and thermal property of hybrid nanocomposites by free radical copolymerization of styrene with octavinyl polyhedral oligomeric silsesquioxane

The poly(styrene‐co‐octavinyl‐polyhedral oligomeric silsesquioxane) (PS–POSS) organic–inorganic hybrid nanocomposites containing various percent of POSS were prepared via one‐step free radical polymerization and characterized by FTIR, high‐resolution ¹H NMR, ²⁹Si NMR, GPC, DSC, and TGA technologies. The POSS contents in these nanocomposites were determined using FTIR calibration curve. The result shows that the POSS contents in nanocomposites can be tailored by varying the POSS feed ratios. On the basis of the POSS contents in the nanocomposites and the ¹H NMR spectra, the number of reacted vinyl groups of each octavinyl‐POSS macromonomer were calculated to be 6–8. DSC and TGA measurements indicate that the incorporation of POSS into PS homopolymer can apparently improve the thermal properties of the polymeric materials. The dramatic T_g and T_dec increases are mainly due to the formation of star and low cross‐linking structure of the nanocomposites, where POSS cores behave as the joint points and hinder the motion and degradation of the polymeric chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Probing the reaction kinetics of vinyl acetate free radical polymerization via living free radical polymerization (MADIX)

Living free radical polymerization technology (macromolecular design via the interchange of xanthates (MADIX)) was applied to give accesses to chain length and conversion dependent termination rate coefficients of vinyl acetate (VAc) at 80 °C using the MADIX agent 2-ethoxythiocarbonylsulfanyl-propionic acid methyl ester (EPAME). The kinetic data were verified and probed by simulations using the PREDICI^® modelling package. The reversible addition-fragmentation transfer (RAFT) chain length dependent termination (CLD-T) methodology can be applied using a monomer reaction order of unity, since VAc displays significantly lower monomer reaction orders than those observed in acrylate systems (ω(VAc, 80 °C)=1.17±0.05). The observed monomer reaction order for VAc is assigned to chain length dependent termination and a low presence of transfer reactions. The α value for the chain length regime of log(i)=1.25−3.25 (in the often employed expression ) reads 0.09±0.05 at low monomer to polymer conversion (10%) and increases significantly towards larger conversions (α=0.55±0.05 at 80%). Concomitantly with a lesser amount of midchain radicals, the chain length dependence of k_t is significantly less pronounced in the VAc system than in the corresponding acrylate systems under identical reaction conditions. The RAFT(MADIX)-CLD-T technique also allows for mapping of k_t as a function of conversion at constant chain lengths. Similar to observations made earlier with methyl acrylate, the decrease of k_t with conversion is more pronounced at increased chain lengths, with a strong decrease in k_t exceeding two logarithmic units from 10 to 80% conversion at chain lengths exceeding 1800.     

Application of the Monte Carlo simulation method to the investigation of peculiar free‐radical copolymerization reactions: Systems with both reactivity ratios greater than unity (rA > 1 and rB > 1)

With a Monte Carlo simulationmethod, copolymer properties have been thoroughly studied, and the influence of the reactivity ratios and feed composition has been taken into consideration. Instantaneous alterations of the copolymer composition and copolymer heterogeneity, which is also called a randomness parameter, have been examined with data obtained from the simulation at each stage of the copolymerization reaction. The results prove the azeotropic behavior of copolymerization reactions in which both reactivity ratios are greater than unity, although some special reactivity ratio combinations ignore the azeotropic behavior. The copolymer composition reaches an azeotrope point at the end of the copolymerization reaction when the copolymerization is an azeotropic reaction. In addition, the randomness parameter takes its maximum value at the azeotrope point when reactivity ratio r_A is equal to reactivity ratio r_B. Finally, increasing the reactivity ratios causes no change in the trend of copolymer composition/feed composition curves when r_A is equal to r_B. However, the curves produced with larger r_A and r_B values show more fluctuations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

伴有水解缩合反应的种子乳液聚合动力学(I)模型

伴有水解缩合反应的自由基种子乳液聚合反应是制备有机-无机杂化乳胶粒的一种新方法，水解缩合反应和自由基聚合这两种反应在乳液体系中的动力学耦合过程决定了聚合产物的微结构和应用性质。通过单体的分配系数建立了单体在乳液体系中各相的分配模型，进而建立了考虑单体分配的自由基种子乳液共聚合的动力学模型。针对功能基团在乳液各相中水解缩合反应的特点，结合自由基种子乳液共聚合的动力学模型，建立了伴有水解缩合反应的自由基种子乳液聚合动力学模型。该模型反映了反应过程中的物质传递规律、非均相反应特点、自由基共聚合和水解缩合反应间的耦合关系。     

A new general approach to determine more accurate comonomer reactivity ratios in controlled/living radical copolymerization systems

In controlled/living radical copolymerization (atom transfer radical copolymerization in this study) and in any other living chain‐growth copolymerization, the possible preferential addition of one of the comonomers onto the (macro)initiator‐derived (macro)radical can affect the copolymer composition, especially at low conversion; this results in inaccurate comonomer reactivity ratio estimation by the classic approach. A new general approach is introduced in this article, which allowed us to exclude the influence of the possible preferential addition of one of the comonomers onto the (macro)initiator‐derived (macro)radical on the copolymer composition at any conversion. According to this approach, copolymer chain grown during time t (t ≠ 0) is considered to be, in fact, the macroinitiator terminated with one of the comonomers under study, which will further grow during the time interval Δt′ = t′ ? t [where any reaction time t′ is considered to be grater than reaction time t, i.e. t′ > t] from a comonomer mixture with composition of f(t) [where f(t) is the molar ratio of comonomer i to comonomer j in the comonomer mixture] at time t. In such a situation, it is possible to obtain individual comonomer conversions [x_i(Δt′) and x_j(Δt′)], the overall comonomer conversion [x_ov(Δt′)], and the cumulative average copolymer composition for the copolymer formed during Δt′, from which more accurate comonomer reactivity ratios can be calculated by the various low‐ or high‐conversion methods, depending on the overall comonomer conversion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Free‐radical copolymerization and kinetic treatment of methyl methacrylate with N‐P‐tolylmaleimide

The free‐radical copolymerization of methyl methacrylate (MMA) with N‐P‐tolylmalemide (NPTMI) at 77°C in cyclohexanone solution initiated by AIBN was studied. The copolymer composition was calculated from the nitrogen content estimated by the Mico–Kijedldahl's method and by elemental analysis. The reactivity ratios have been calculated by Fineman and Ross method. The monomer reactivity ratios were r_NPTMI = 1.24, r_MMA = 2.1. The glass transition temperature (T_g) of the copolymers were determined by torsion braid analysis (TBA). The thermal stability was determined by thermogravimetric analysis (TGA). T₅₀, temperature at which the weight loss reaches 50%, was abstained. The results showed that the M _n and M _w increased, whereas the NPTMI feed content increased. The T_g and T₅₀ increased dramatically. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 867–870, 2004     

Polymerization of acrylonitrile using potassium peroxydisulfate as an initiator in the presence of a multisite phase‐transfer catalyst: A kinetic study

In this article, the kinetics and mechanism of the free‐radical polymerization of acrylonitrile (AN) using potassium peroxydisulfate (PDS) as a water‐soluble initiator in the presence of synthesized 1,4‐bis(triethyl methyl ammonium) benzene dichloride (DC‐X) as a phase‐transfer catalyst (PTC) were studied. The polymerization reactions were carried out under inert and unstirred conditions at a constant temperature of 60 ± 1°C in cyclohexane/water biphasic media. The rate of polymerization (R_p) increased with an increase in the concentrations of AN, PTC, and PDS. The order with respect to the monomer, initiator, and PTC was found to be 1.0, 0.5, and 0.5, respectively. R_p was independent of the ionic strength and pH of the medium. However, an increase in the polarity of the solvent slightly increased the R_p value. On the basis of the obtained results, a mechanism is proposed for the polymerization reaction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Bulk free radical polymerizations of methyl methacrylateunder non-isothermal conditions and with intermediate additionof initiator: Experiments and modeling

Experimental data on the monomer conversion, x_m, and the weight average molecular weight, M_w, have been generated under several isothermal and non-isothermal conditions for the polymerization of methyl methacrylate in a rheometer-reactor assembly. The non-isothermal results, in particular, can be used to provide more stringent tests of kinetic models than isothermal data alone. A simple empirical model has been used to describe this system that accounts for the gel (Trommsdorff) and glass effects. The model involves only x_m and the temperature, and is quite general. The model parameters are tuned using only three sets of isothermal data. Good agreement is found between the experimental results and model predictions for a whole variety of experimental conditions, including non-isothermal operation and with intermediate addition of initiator. Because of its generality, this model is quite suitable for use for on-line optimizing control as well as for describing industrial reactors.     

Thermal characterization of poly(vinyl chloride) samples prepared by living radical polymerization: Comparison with poly(vinyl chloride) prepared by free radical polymerization

Poly(vinyl chloride) (PVC) samples were synthesized by a living radical polymerization (LRP) method and compared with commercial PVC prepared by the conventional free radical polymerization (FRP). The differences were assessed, for the first time, in terms of viscosimetry parameters and thermal analysis. The LRP method used to prepare the PVC‐LRP samples is the only one available to obtain this polymer free of structural defects, being of commercial interest in a view of preparing a new generation of PVC‐based polymer with outstanding performance. The polymerization temperature selected (35°C) to prepare the LRP samples is currently used in the industry to prepare PVC‐FRP grades with moderate to high molecular weight. Since the thermal stability is a direct consequence of the polymer structure, this study is of vital importance to understand the potential of new PVC‐LRP. The thermoanalytical measurements demonstrate an enhanced thermal stability of PVC‐LRP when compared with its FRP counterpart. The PVC‐LRP sample with very low molecular weight reveals a higher thermal stability than the most stable PVC‐FRP sample. It is the first report dealing with thermal analysis of PVC prepared by LRP. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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

Free‐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 r_VAc = 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     

Atom transfer radical homo‐ and copolymerization of styrene and methyl acrylate initiated with trichloromethyl‐ terminated poly(vinyl acetate) macroinitiator: A kinetic study

Atom transfer radical bulk copolymerization of styrene (St) and methyl acrylate (MA) initiated with trichloromethyl‐terminated poly(vinyl acetate) macroinitiator was performed in the presence of CuCl/PMDETA as a catalyst system at 90°C. Linear dependence of ln[M]₀/[M] versus time data along with narrow polydispersity of molecular weight distribution revealed that all the homo‐ and copolymerization reactions proceed according to the controlled/living characteristic. To obtain more reliable monomer reactivity ratios, the cumulative average copolymer composition at moderate to high conversion was determined by ¹H‐NMR spectroscopy. Reactivity ratios of St and MA were calculated by the extended Kelen‐Tudos (KT) and Mao‐Huglin (MH) methods to be r_St = 1.018 ± 0.060, r_MA = 0.177 ± 0.025 and r_St = 1.016 ± 0.053, r_MA = 0.179 ± 0.023, respectively, which are in a good agreement with those reported for the conventional free‐radical copolymerization of St and MA. Good agreement between the theoretical and experimental composition drifts in the comonomer mixture and copolymer as a function of the overall monomer conversion were observed, indicating that the reactivity ratios calculated by copolymer composition at the moderate to high conversion are accurate. Instantaneous copolymer composition curve and number‐average sequence length of comonomers in the copolymer indicated that the copolymerization system tends to produce a random copolymer. However, MA‐centered triad distribution results indicate that the spontaneous gradient copolymers can also be obtained when the mole fraction of MA in the initial comonomer mixture is high enough. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009