Rheokinetics of free-radical polymerization

The authors elaborate theoretical concepts and obtain mathematical relations describing the increase in viscosity of reactive masses during bulk free-radical polymerization. The results obtained are confirmed experimentally for free-radical polymerization of alkyl methacrylates and styrene.     

Control of free-radical emulsion polymerization of methyl methacrylate by oxygen injection. II. Experimental study

Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate.     

聚氨酯-丙烯酸酯的前端自由基聚合

由甲苯二异氰酸酯（TDI）、聚醚二元醇（N210、220）、丙烯酸-2-羟丙酯（HPA）制得端烯基聚氨酯-丙烯酸酯大分子;然后通过前端自由基聚合;制备了聚氨酯-丙烯酸酯共聚物。研究了引发剂浓度对前端速度和温度分布的影响。FTIR显示前端聚合产物与间歇聚合产物有相似的红外吸收;TGA分析表明;前端聚合产物具有更好的热稳定性。     

Modeling poly(vinyl alcohol)-stabilized vinyl acetate emulsion polymerization. II. Comparison with experiment

The mathematical model presented in Part I, accommodating the emulsion polymerization of vinyl acetate stabilized with poly(vinyl alcohol), predicts experimental conversion and particle size data with reasonable accuracy. Model predictions of measurable variables exhibit sensitivity to variables affecting either primary ungrafted particle nucleation of flocculation kinetics, but are relatively insensitive to variables affecting poly(vinyl alcohol) grafting reactions and the resulting primary grafted particle concentration. Semibatch simulations indicate that independent increases in the vinyl acetate, poly(vinyl alcohol), and initiator levels of all increase the primary grafted particle population. It is unlikely, however, that this population exceeds the ungrafted counterpart under most commercial polymerization conditions. This relative insignificance of grafting during particle nucleation is also noted in literature data simulations where, with appropriate parameter adjustments, the model predictions agree well with the batch, thermal initiation data. © 1993 John Wiley & Sons, Inc.     

The plasma polymerization of vinyl monomers. II. A detailed study of the plasma polymerization of styrene

A study has been made on the plasma polymerization of styrene monomer in a cold, low-power, inductively coupled RF plasma. Styrene monomer yielded an insoluble, crosslinked film which was slightly colored. A kinetic study is reported for styrene. The effects of power level, bleed rate of monomer, pressure, and reactor geometry on the rate of polymer formation are reported. A mechanism is postulated for plasma polymerization. It was found that the initiation step was the rate controlling step and that the reaction followed a cationic polymerization scheme. Both crosslinking and discoloration of the polymers occur at the time of polymerization and are not a result of exposure of the reacted polymer to the plasma. The polymerization was shown to take place in the bulk phase as well as on the reaction wall surfaces.     

Estimation of intrinsic rate coefficients in vinyl chloride suspension polymerization

The pre-exponential factor and the activation energy of the intrinsic rate coefficients for propagation, chain transfer to monomer, chain initiation by a Cl radical and termination in the suspension polymerization of vinyl chloride are estimated by regression of experimental data for the monomer conversion, ranging from 3 to 85%, and for the moments of the molecular mass distribution as a function of batch time over the temperature range of 308-338 K and for initiator (tert-butyl peroxyneodecanoate) concentrations from 0.026 to 3.0 wt%, based on the monomer. Termination by combination is the dominant termination mechanism. Cl radicals, formed in the chain transfer to monomer, contribute to the termination by recombination with macroradicals and, hence, attenuate the gel effect. Physically meaningful and statistically significant estimates for the pre-exponential factors and activation energies, 24.9 kJ mol⁻¹ for propagation and 54.3 kJ mol⁻¹ for chain transfer, allow to describe the experimental data over the full range of investigated conditions.     

Modeling of diffusion-controlled free-radical polymerization reactions

The present paper introduces a new fundamental approach to the modeling of diffusion-controlled free-radical polymerization reactions. Our analysis follows the original work of Chiu, Carratt, and Soong (CCS), according to which the termination and propagation rate constants are expressed in terms of both a purely reaction-limited term and a diffusion-limited one. The contribution of the latter term to the apparent rate constants is described in terms of the polymer and monomer effective diffusion coefficients and an effective reaction radius. It is shown that all parameters appearing in the original CCS model can be calculated from first principles using available data on the physical and transport properties of a particular monomer–polymer binary system. The generalized free volume theory of Vrentas and Duda and the theory of excess chain end mobility are invoked for the calculation of the effective diffusion coefficients and the reaction radius, respectively. The approach followed in this study is general and needs only the specification of one unknown parameter with a clear physical meaning. All other parameters can be readily calculated from available data. The ability of the new model to predict molecular weight developments and monomer conversion in diffusion-controlled reactions is demonstrated by application of the proposed model equations to the bulk polymerization of MMA.     

Qualitative percolation study of free-radical cross-linking polymerization

Summary Simulations of a conceptually simple model for free-radical cross-linking polymerization have been performed in relation to experimental indications for (temporary) microgel particles. Many qualitative features ascribed to microgels show up in the simulation. In particular this model yields qualitative agreement with experiments on the conversion dependence of the number of pendant double bonds.     

Non-classical free-radical polymerization: 3. Diffusion-control in degradative addition

The different kinetic features associated with polymerizations in which retardation arises through degradative transfer and degradative addition processes are considered. Reasons are given for believing that in reactions retarded by degradative transfer neglect of the interaction between ‘inactive’ radicals is justifiable, while with degradative addition this is not so. A kinetic treatment of the latter is developed in which all three termination reactions between propagating and inactive radicals are assumed to be diffusion-controlled with a single rate coefficient and equations are derived which permit from experimental data on rates of polymerization estimation of the definitive kinetic parameters $\text{k}{}_{\mathrm{p}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$, $\text{k}{}_{\mathrm{pm}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$ and $\text{k}{}_{\mathrm{fm}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$ (k_p, k′_t, k_pm, k_fm are the rate coefficients of propagation, termination, reinitiation and degradative additions, respectively). The kinetic equations are satisfactorily consistent with ew experimental data on the polymerization of 1-vinylimidazole in ethanol solution at 70°C, for which there is strong evidence for the occurrence of degradative addition. A modified procedure for processing data for polymerizations with degradative transfer is put forward which is convenient for estimating the kinetic parameters and reveals in a simple manner the importance of re-initiation. It is suggested that this treatment could be generally useful in the early stages of the study of a retarded polymerization.     

氯乙烯聚合车间节能降耗工艺改造

介绍了氯乙烯聚合车间的节能工艺改造措施.利用离心母液水、汽提塔出塔气体、蒸汽冷凝水与去离子水换热,合理利用余热,避免了能源浪费,降低了PVC生产的蒸汽消耗.     

Non-classical free-radical polymerization: 5. The purification and polymerization of 1-vinyl-2-pyrrolidone

The impurities in 1-vinyl-2-pyrrolidone (NVP) have been investigated by g.c./m.s. and ¹³C n.m.r. The inadequacy of normal purification procedures is pointed out, and a simple technique for reducing the impurity-level to undetectable values is described. Sources of non-ideality in free-radical polymerization are classified and it is suggested that a plot of ωj^?0.5 vs. [M] could be particularly valuable in revealing the origins of non-ideal behaviour, including the presence of retarders. (ω, j are the rates of polymerization and initiation, respectively, and M represents monomer). Extensive data on NVP polymerization in ethanol solution at 60°C with azo-bis-isobutyronitrile as initiator have been obtained by dilatometric studies; for this purpose redetermination of the polymer density proved necessary. The data have been analysed as outlined above. The efficacy of the purification procedure in removing ‘active’ impurities has thus been demonstrated and it is concluded that, as already suggested by others, the polymerization under the prevailing conditions is subject to a medium effect operating principally on the propagation process. This is discussed briefly.     

Studies in radiation-induced polymerization of vinyl monomers at high dose rates. II. Methyl methacrylate

The radiation-induced polymerization of methyl methacrylate was investigated with radiation sources of cobalt 60 and accelerated electrons at dose rates up to 3 Mrads/sec. Extrapolation of previous rates of polymerization at dose rates of 0.01–200 rads/sec coincided with the present results, the rates being approximately proportional to the square root of the dose rate throughout the entire set of dose rates measured. The molecular weights seemed to be independent of dose rate at the highest dose rates investigated. A combination of high polymer with a much higher molecular weight than expected was formed, together with a substantial portion of low molecular weight polymer. The reason for this behavior is not clear at this time. The G(M·) calculated from the molecular weights and fraction of polymer and resin was 6.0, which approaches that reported in previous investigations at low dose rates. There was no significant effect of air on the polymerization kinetics of methyl methacrylate at above 1 Mrad/sec. Nitrogen also did not influence the measured rates. Conversions to polymer were not substantially reduced by the presence of inhibitor at above 1.26 × 10⁵ rads/sec. Water did not influence the rates of polymerization, except at the highest temperature (50°C) investigated. A large posteffect was observed in sealed degassed ampoules after 25% conversion to polymer. Only 3.4% additional polymer was formed in 24 hr after irradiation in the presence of air. The activation energy for the electron beam polymerization of methyl methacrylate was about 7.0 kcal/mole. This value, considering the complications in technique such as beam heating, did not differ from literature data enough to suggest any mechanistic difference in the polymerization at high dose rates.     

The manganic hydroxide–hydrazine system as an initiator of vinyl polymerization. II. The emulsion polymerization of methyl methacrylate

The reaction between hydrazine hydrate and manganic hydroxide has been studied as an initiator for the emulsion polymerization of methyl methacrylate. The system has proved to be effective, and polymerization occurs at favorable rates over a wide temperature range extending from below 10°C to over 50°C. The pH range, however, is rather limited, the most effective value being 9. The main features of the initiator's behavior are similar to those found previously in the corresponding solution polymerization and are explained on the basis of a surface reaction between the hydrazine and the insoluble hydroxide. A complicating feature is the reaction between hydrazine and monomer, which exerts an inhibiting influence.     

Termination kinetics of free-radical polymerization in ionic liquids

Termination rate coefficients, k_t, for free-radical polymerization of 15 vol.-% methyl methacrylate (MMA) dissolved in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide and in 1-butyl-3-methylimidazolium tetrafluoroborate were measured at 10 °C via the single pulse − pulsed laser polymerization − electron paramagnetic resonance (SP-PLP-EPR) technique. Whereas absolute k_t in ionic liquid solution is by about one order of magnitude below the associated bulk MMA value, the chain-length dependence of k_t is very similar in both liquid environments.     

Continuous emulsion polymerization of vinyl acetate. Part: II Parameter estimation and simulation studies

Conversion data obtained over a wide range of operation of a continuous latex reactor for vinyl acetate polymerization were used to estimate the unknown kinetic parameters of a transient CSTR reactor model. Conversion-time histories were adequately fitted by models of two levels of sophistication: a comprehensive model which solves for the age distribution function of polymer particles, and a simplified model that neglects the effect of particle size distribution for the case of continuous particle nucleation. These models were then used for simulation and control studies in an attempt to devise a practical control strategy⁽¹¹⁾. The existence of sustained oscillations was investigated by examining the behavior of the state variables in the phase-plane.     

Graft polymerization of some vinyl monomers onto acrylic rubber. II. Mechanical properties of graft polymers

Some mechanical properties of styrene and acrylonitrile copolymers grafted onto acrylic rubber are investigated. The impact strength of graft polymers depended upon the nature and the concentration of the catalyst, the composition and the intrinsic viscosity of the rubber, and the acrylonitrile content in the rigid matrix. The most desirable result was obtained when benzoyl peroxide as the catalyst, n-butyl acrylate–acrylonitrile copolymer of 7–10% acrylonitrile content, and about 0–5% acrylonitrile in the rigid matrix were used. Dynamic mechanical tests show the increase in efficiency of rubber modification by the grafted chains. The better weathering resistance of these graft polymers, as compared with commercial ABS plastics, was confirmed.     

Radiochemical studies of free-radical vinyl polymerizations: 7. Polymerization of methyl acrylate

Termination of poly(methyl acrylate) radicals in benzene solution has been studied by polymerization of the monomer using [¹⁴C] azoisobutyronitrile as initiator. When polymerizations were initiated thermally at 60° and 45°C values for the number of initiator fragments per polymer molecule, n, were substantially less than 2 but were dependent upon the rate of initiation, R_j. As R_j was increased n increased, indicating that chain transfer reactions were important. By correcting n for chain transfer it was shown that the polymer radicals most probably terminated by combination. The results at 25°C were more conclusive. With higher rates of photochemical initiation chain transfer reactions became unimportant, values of n were close to 2 and polymer radicals terminated almost exclusively by combination.     

Studies of the polymerization of methacrylic acid via free-radical retrograde precipitation polymerization process

In this paper, we present some new results of our work in a novel polymerization process (called the free-radical retrograde precipitation polymerization, or FRRPP, process) that occurs at temperatures above the lower critical solution temperature. Our polymerization experiments basically involve the methacrylic acid–poly(methacrylic acid)–water system. Experimental results indicate a gradual increase in conversion with time after what seemingly is the onset of phase separation. In an equivalent solution polymerization system, conversion of methacrylic acid reaches almost 100% at a much shorter time than in the FRRPP system. Molecular weights of poly(methacrylic acid) at different times for the FRRPP system are not dramatically different from those obtained in the solution system. However, the FRRPP system yields a relatively narrow molecular weight distribution at a wide range of conversion compared to that obtained in the equivalent solution system. The unique characteristics of the FRRPP process is shown in the asymptotic time behavior of the free-radical concentration compared to the decay behavior in other polymerization systems. © 1996 John Wiley & Sons, Inc.