A kinetic study on MMA bulk radical polymerization

The nonequalities of the reactivity and the micro-environment of propagating radicals has been found in MMA bulk polymerization. This nonequal reactivity results from varying rates of diffusion in different micro-surroundings. The decrease of radical reactivity is caused by the trapping of the segments around the propagating radical.     

Kinetic study of radical polymerization. II. Solid‐state bulk polymerization of sodium methacrylate by differential scanning calorimetry

The solid‐state radical polymerization of sodium methacrylate was investigated. It was initiated by azobisisobutyronitrile, which was used as a radical initiator. Differential scanning calorimetry (DSC) was used to observe the endothermic and exothermic transitions during the polymerization reaction. Structural studies were performed with the DSC thermograms and Fourier transform infrared and ultraviolet–visible spectra, and all of the results confirmed the progress of the reaction. The obtained data revealed that the polymerization reaction proceeded completely with a 100% conversion. ΔH of this reaction was calculated with various amounts of the initiator, and the peak temperatures were determined at different heating rates. The activation energy (19.7 kcal mol^?1) was also obtained by the Kissinger method for this type of solid polymerization reaction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1648–1654, 2003     

Kinetic study of radical polymerization. III. Solution polymerization of acrylamide by 1H‐NMR

Solution and radical polymerization of acrylamide in the presence of potassium persulfate in D₂O was investigated up to high conversion by high‐field ¹H‐NMR spectroscopy. The kinetics of reaction was studied according to the data obtained from the corresponding spectra at various times during the polymerization reaction progress. Processing of the data led us to derive the rate equation of this polymerization reaction and determine the reaction order of each component in the rate equation. The order, with respect to initiator, was consistent with the classical kinetic rate equation (0.45), whereas the order with respect to monomer was greater than unity (1.49). The effect of temperature on the polymerization rate was also investigated and the activation energy of 48.4 kJ mol^?1 was obtained over the temperature range of 60–75°C. Also some mechanistic studies were discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2007–2013, 2004     

A kinetic study on bulk thermal polymerization of styrene

The kinetics of bulk thermal polymerization of styrene over the range of 100–200 °C has been studied based on three stage polymerization model (TSPM) in this paper. TSPM plots showed that the whole polymerization course only exhibits two stages, low conversion stage and gel effect stage, which is consistent with TSPM as the reaction temperature is higher than the glass transition temperature of polystyrene. It was found that the critical conversion, x₁, for the transition from low conversion stage to gel effect stage is independent of the reaction temperature and approximately equal to 0.5. In addition, the apparent reaction rate constants obtained from TSPM plots could be correlated to temperature by Arrhenius equation. Expressions predicting number-average molecular weight were also derived according to TSPM. Using the expressions to treat experimental data available in the literature, it was found that number-average molecular weight is independent of the conversion and relative to the reaction temperature at low conversion stage. However, it varies with the conversions at gel effect stage and the variations are more obvious as the reaction temperature rises.     

Modeling of diffusion‐controlled reactions in free radical solution and bulk polymerization: Model validation by DSC experiments

In this work, a detailed experimental study of diffusion‐controlled reactions in free radical polymerization by using differential scanning calorimetry (DSC) was carried out. The systems studied include the methyl methacrylate bulk polymerization as well as the solution and the bulk polymerization of vinyl acetate at a wide range of experimental conditions including initial initiator concentration, reaction temperature, and type and amount of solvent. The conversion data obtained by DSC was successfully simulated by using a mathematical model based on sound principles such as the free volume theory. The estimated parameters, by fitting predictions of this model to conversion data obtained by DSC were found to be in close agreement with the reported parameters in the literature, thus validating both the experimental and theoretical methods used in this work. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymerization of asymmetric tetrafunctional monomers. I. The study of radical bulk polymerization of acrylic and methacrylic esters of 2-allylphenol

The bulk polymerization of 2-allylphenylacrylic ester and of 2-allylphenylmethacrylic ester at 60–80°C. was studied. It was observed that under these conditions azobisisobutyronitrile, lauroyl peroxide, and benzoyl peroxide have satisfactory activity as initiators. The influence of atmospheric oxygen on AOAF and MOAF polymerization was proved. The peculiarities of AOAF and MOAF polymerization (low molecular weight of the soluble polymers which are formed, the absence of gel effect, relatively low critical conversions) may be explained on the basis of chain transfer reactions by the allylic groups.     

Thermoplastic elastomers via radical polymerization. I

Thermoplastic elastomers were synthesized using a method for preparation of block copolymers introduced by Tobolsky and Rembaum. A hydroxy-terminated polyester or polyether was chain extended with tolylene diisocyanate and capped with cumene hydroperoxide. The high molecular weight peroxycarbamate was used as initiator for polymerization of styrene, methyl methacrylate, or acrylonitrile monomer. Their physical properties were investigated by modulus–temperature curves. The effect of composition on modulus was also examined.     

Free radical polymerization of nitropropyl acrylates and methacrylates. I. Heat of polymerization

The heat of polymerization ΔH_p, of nitropropyl(meth)acrylate monomers has been studied by differential scanning calorimetry (DSC) in dynamic and isothermal modes. DSC showed that ΔH_p of 2‐nitropropyl(meth)acrylate was surprisingly smaller than that of propyl(meth)acrylate but similar to that of 2,2‐dinitropropyl(meth)acrylate. According to molecular structure analysis by a PM3 Hamiltonian in a MOPAC program, the contributing main factor to the lowering of ΔH_p of 2‐nitropropyl (meth)acrylate was found to be the hydrogen bond between the O(?C) and the H atom attached at position C6. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2929–2935, 2001     

原子转移自由基法合成乙丙橡胶接枝物中的热聚合研究

采用原子转移自由基聚合法(ATRP)合成了三元乙丙橡胶与苯乙烯的接枝共聚物(EPDM-g-St),动力学研究表明聚合过程为“活性”聚合。在接枝聚合过程中发现了明显的苯乙烯热聚合现象。对接枝聚合中得到的均聚苯乙烯进行表征的结果表明,苯乙烯在ATRP接枝体系中的热聚合过程在一定程度上受到ATRP机理的控制;升高温度和延长反应时间使得热聚合更为显著。     

A rheokinetic study of bulk free radical polymerization performed with a helical barrel rheometer

The Trommsdorff effect is a non‐linear autoacceleration phenomenon in bulk free radical polymerizations. It is undesired in processes on industrial scale, as is causes hot spots and erratic behavior. In this paper a rheokinetic investigation of the Trommsdorff effect is performed with a helical barrel rheometer. This rheometer can be considered a small‐scale model of large reactors, particularly extruders. The rheokinetic measurements show that the Trommsdorff effect can be reduced when the polymerization is performed at a high rotational velocity of the screw. This confirms a previous study performed with a cone and plate rheometer and is encouraging with a view to designing better‐controlled bulk free radical polymerization processes on industrial scale.     

Magnetic field effects on the free radical solution polymerization of acrylamide

Systematic polymerization experiments quantified magnetic field (MF) influences on the free radical solution polymerization of acrylamide for various polymerization conditions. The type of initiation, the initiator concentration, the monomer concentration, and the viscosity of the aqueous medium were the subject of variation. The initiator efficiency (Φ) increased up to 60% and the initiator exponent of the overall rate expression raised from 0.1 to 0.28 when a weak MF of 0.1 T was applied to photochemical initiation. However, no appropriate effect was observed for thermal initiation. Kinetic analysis proved a reduction of the termination rate coefficient (k_t) up to 40%. Photochemically initiated polymerizations in media of enhanced viscosity revealed the highest increment of the initiator efficiency ratio Φ^MF/Φ and the most pronounced reduction of k_t^MF/k_t. On the contrary, the propagation rate coefficient (k_p) and the monomer exponent were not influenced by MF. Despite considerable increase of the polymerization rate in MF, no reduction of the molar mass was found. Compensation of increased Φ^MF and decreased k_t^MF are suggested as explanation. The singlet-triplet intersystem crossing mechanism for radical pairs served to explain the MF effects.     

The kinetics of two-phase bulk polymerization. I. Monomer and initiator distribution

Rubber-reinforced thermoplastics are produced commercially by dissolving a rubber in the monomer of a glassy polymer and commencing polymerization with a free-radical initiator. Beyond a few per cent conversion, the incompatibility of the two polymers causes a phase separation, with each phase containing one nearly pure polymer. Subsequent polymerization occurs in each phase. The heterogeneous nature of the reaction can influence both the kinetics of the reaction and the amount of grafting in the product. The fact that only monomer which polymerizes in the rubber phase can possibly graft establishes an upper limit to the amount of grafting and hence influences the mechanical properties of the product. It is shown theoretically how unequal partitioning of monomer and initiator between the phases can influence the extent of grafting, and can also explain the kinetic rate reductions which have been observed in such systems. The distributions of monomer and benzoyl peroxide and azobisisobutyronitrile initiators between the phases have been determined experimentally for a styrene–polystyrene–polybutadiene system. They cannot account for the rate reduction observed in such systems.     

Modeling of the bulk free radical polymerization up to high conversion—three stage polymerization model I. Model examination and apparent reaction rate constants

In this paper, a simple and useful model, the three stage polymerization model (TSPM) is proposed on the basis of recent experimental evidence and our preliminary treatment of the experimental kinetic results found in the literature. The model accounts for gel effect and glass effect in bulk free-radical polymerization. Equations for calculating the conversion of the polymerization reaction are derived based on TSPM. Using experimental kinetic data available in the literature, general expressions for apparent reaction rate constants in three stages for methylmethacrylate (MMA) and styrene (St) are obtained. In general, the experimental kinetic data can be treated very well with the TSPM from the low conversion stage to high conversion, except for some experimental data near the transition points. However, the deviation for this data may be reasonably explained by the non-isothermal effects that occur in this regime of experiments. This deviation is smaller for a smaller ampoule reactor used in polymerization experiments because of its better heat transfer ability. In order to establish that there is no glass effect stage when the reaction temperature is greater than the glass transition temperature for a polymerization process, some experimental data for ethylmethacrylate (EMA) bulk polymerization at a reaction temperature higher than its glass transition temperature were checked with TSPM. The plots show that the model is also suitable for EMA bulk polymerization.     

In silico mechanically mediated atom transfer radical polymerization: A detailed kinetic study

Mechanically mediated atom transfer radical polymerization (mechanoATRP) utilizing ultrasound to generate activators and improve the diffusivity of macromolecular chains is introduced as an innovative externally controlled ATRP. Herein, a comprehensive kinetic model with free volume theory based “series” encounter pair model accounting for diffusional limitations on termination, activation, and deactivation is developed for the mechanoATRP of methyl acrylate. Comparative study by using different diffusion models, for example, w_p model and reduced composite k_t model, as well as constant apparent k_j^app model confirms the goodness of the as-developed model. Critically, mechanochemically induced reduction rate coefficient k_r,s as a key kinetic parameter is associated with experimental conditions excluding the sonication effect by a fitting equation for the first time. In silico tracking of polymer dispersity with the help of kinetic model shows a better result compared with that by the classical dispersity equation. By defining an ultrasonic factor γ_j, a qualitative analysis for the effect of ultrasound conditions on the diffusional limitation in mechanoATRP is presented.     

自由基聚合反应动力学常数测定技术

自由基聚合是一类重要的聚合反应,其反应动力学常数的获取对于聚合机理研究、聚合物链结构定制、反应过程调控都有着重要的意义。综述了自由基聚合中最重要的链增长和链终止反应速率常数的测定方法,着重介绍连续脉冲激光引发结合凝胶渗透色谱测定链增长反应速率常数、单脉冲-连续脉冲激光耦合结合近红外光谱与电子顺磁共振波谱测定链终止反应速率常数,涵盖了各方法的检测原理、要求和适用条件,讨论了增长自由基链长对链增长和链终止反应速率常数的影响。此外,对链增长和链终止反应速率常数检测方法的提升和新方法的开发进行了展望。     

Modeling the free radical solution and bulk polymerization of methyl methacrylate

This paper reviews our current understanding of the kinetics and mechanisms of free-radical chain polymerization of methyl methacrylate. A mathematical model previously proposed to describe the bulk polymerization of MMA is here extended to cover solution polymerization. This extended model is validated by comparing its predictions with experimental data over a range of conversions and product molecular weights.     

Thermal decomposition of additive polymerization initiators. I. Azobisisobutyronitrile

We measured the rate of thermal decomposition of azobisisobutyronitrile (AIBN) from the rate of loss of 2,2-diphenylpicrylhydrazyl (DPPH) on reaction of the free radicals formed by thermal decomposition of azobisisobutyronitrile (AIBN) in organic solvents with DPPH. There has been some doubt about the quantitative relation between AIBN and DPPH required to get the rate constant of thermal decomposition of AIBN. In the past, AIBN has been used in excess, and the rate constants measured by using DPPH are smaller than they ought to be. In our experiments we used as little of AIBN relative to DPPH as possible and obtained a value of 3.8 × 10^?4 min.^?1 at 50°C. as the rate constant of the first-order reaction, which was shown satisfactorily by the linearity of the graph. We also obtained 32 kcal./mole as activation energy. We were also able to make clear the meaning of the result when a large quantity of AIBN was used.     

Synthesis and nucleation mechanism of inverse emulsion polymerization of acrylamide by RAFT polymerization: A comparative study

Well-defined poly (acrylamide) is synthesized by RAFT inverse emulsion polymerization using hydrophilic and lipophilic initiators. The kinetic behavior observed for RAFT inverse emulsion polymerization is similar to that for RAFT inverse miniemulsion polymerization. The nucleation mechanism of inverse emulsion polymerization of acrylamide is firstly investigated by RAFT polymerization and verified by GPC and SEM measurements. Droplet nucleation is found to be the primary mechanism in the inverse emulsion polymerization of acrylamide. However, polymerization occurring in the continuous phase is not negligible when lipophilic initiator is used.     

Cure kinetic study of carbon nanofibers/epoxy composites by isothermal DSC

An investigation was carried out into the cure kinetics of carbon nanofibers (CNF)/epoxy composites, composed of tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) resin and 4,4′‐diaminodiphenylsulfone (DDS) as a curing agent. The experimental data for both neat system and CNF/epoxy composites revealed an autocatalytic behavior. Analysis of DSC data indicated that the presence of carbon nanofibers had only a negligible effect on the cure kinetics of the epoxy. Kinetic analysis was performed using the phenomenological model of Kamal and two diffusion factors were introduced to describe the cure reaction in the latter stage. Activation energies and kinetic parameters were determined by fitting experimental data. Comparison between the two diffusion factors was performed, showing that the modified factor was successfully applied to the experimental data over the whole curing temperature range. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 329–335, 2005     

Thermal properties of PMMA/TiO2 nanocomposites prepared by in-situ bulk polymerization

The surface of anatase TiO₂ nanoparticles, obtained by the controlled hydrolysis of titanium tetrachloride, was modified by 6-palmitate ascorbic acid. The surface modified TiO₂ nanoparticles were dispersed in methyl methacrylate and mixed with a appropriate amount of poly(methyl methacrylate) to obtain a syrup. The nanocomposite sheets were made by bulk polymerization of the syrup in a glass sandwich cell using 2,2′-azobisisobutyronitrile as initiator. The molar masses and molar mass distributions of synthesized poly(methyl methacrylate) samples were determined by gel permeation chromatography. The content of unreacted double bonds in synthesized samples was determined by ¹H NMR spectroscopy. The influence of TiO₂ nanoparticles on the thermal stability of the poly(methyl methacrylate) matrix was investigated using thermogravimetric analysis and differential scanning calorimetry. The synthesized samples of poly(methyl methacrylate) have different molar mass and polydispersity depending on the content of the surface modified TiO₂ nanoparticles. The values of glass transition temperature of so prepared nanocomposite samples were lower than for pure poly(methyl methacrylate), while the glass transition temperature of samples preheated in inert atmosphere was very similar to the glass transition temperature of pure poly(methyl methacrylate). The thermal stability of nanocomposite samples in nitrogen and air was different from thermal stability of pure poly(methyl methacrylate). POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers