Rate coefficient for radical desorption in emulsion polymerization

Investigators have proposed the rate coefficient for radical desorption from polymer particles to explain the kinetic deviation of the emulsion polymerization of water-soluble monomers such as vinyl acetate and vinyl chloride from the classical Smith and Ewart theory.⁶ In this article, the rate coefficient for radical desorption is theoretically derived by a different approach, and its applicability to vinyl acetate and vinyl chloride emulsion polymerization is examined in detail using experimental data available in the literature. The theory developed here predicts the average number of radicals per polymer particle in the emulsion polymerization of vinyl acetate and vinyl chloride.     

A kinetic study of the emulsion polymerization of vinyl acetate

The emulsion polymerization of vinyl acetate was studied at 50°C. It was found that the rate of polymerization was proportional to the 0.5 power of the initiator concentration and the 0.25 power of the number of particles. The number of particles was proportional to the power 0.5 ± 0.05 of the emulsifier concentration, but independent of the initiator concentration. The limiting viscosity number of the polymers produced was independent of the initiator concentration and number of polymer particles. It is suggested that the mechanism of vinyl acetate emulsion polymerization is similar to that of vinyl chloride. The linearity of the conversion-versus-time curve is explained as being due partly to a decrease in the desorption rate of radicals from the polymer particles and partly to a decrease in the termination rate constant.     

丙烯酸改性聚醋酸乙烯酯乳液聚合的研究

通过丙烯酸与聚乙二醇共聚合成了具有反应活性的丙烯酸聚氧乙烯酯（简称大单体）,将大单体作为表面活性剂对醋酸乙烯酯乳液聚合的动力学进行了研究;同时在性能上与普通的乳液聚合体系进行了比较。实验结果表明聚合速率随亲水链长度、乳化剂浓度、引发剂浓度、温度的增大而增大,pH值的减小而加快,乳液性能也有了很大的改善．     

Reaction kinetics of vinyl acetate emulsion polymerization

Transport of free radicals out of latex particles into the aqueous phase plays an important role in the emulsion polymerization of vinyl acetate. This so-called “desorption” process involves chain transfer to monomer which generates a mobile and rather stable monomer-unit free radical followed by the diffusion of this free radical out of the latex particle. A kinetic model is developed based on the reaction mechanisms of such an emulsion system. The experimental data available in the literature are used to test the model under various polymerization conditions. Reasonable agreement between the model predictions and experimental data is observed.     

Seeded emulsion polymerization of vinyl acetate: order of reaction with respect to initiator

The emulsion polymerization of vinyl acetate has been studied using carefully prepared seed lattices. Experiments were carried out in which temperature, particle size and the monomer-polymer ratio could be varied independently. In all cases the polymerization rate was proportional to the initiator concentration raised to the 0.7 power. No new particles were formed. The importance of polymerization in the aqueous phase and changes in the propagation rate coefficient are discussed.     

Radiation-induced emulsion polymerization of vinyl acetate and styrene

Studies have been made of the γ-induced emulsion polymerization of styrene and comparisons made with chemically initiated emulsion polymerization. The polymerization proceeded smoothly to high conversions at 0 and 60°C, the reaction showing a high G (monomer) value. Complete conversions were obtained with total doses of less than 0.05 Mrad. In accordance with the behavior expected of systems having a constant rate of initiation, the molecular weight was found to decrease with decreasing temperature. The molecular weight and particle size distributions were narrower than those obtained in chemically initiated emulsion polymerizations at the same temperature. The radiation-induced emulsion polymerization of vinyl acetate proceeded smoothly at temperatures in the range 0–50°C to give polymers of much higher molecular weight than these obtained from chemically initiated polymerizations at the same temperature. Complete conversion was attained after a dose of 0.02 Mrad for latices approaching 50% solids. The elimination of ionic endgroups in the poly(vinyl acetate) radicals tends to drive the polymerization from the aqueous phase, resulting in faster rates and higher molecular weights than are obtained from chemically initiated systems. Rates of polymerization were found to be independent of temperature and the molecular weight of the polymer to be independent of dose rate. Latices of poly(vinyl acetate) of high solids content were evaluated for latex and film properties and found to have improvements over commercially available samples in both areas, especially in clarity of film and scrub resistance. A number of acrylate and maleate esters were copolymerized with vinyl acetate in a radiation-initiated emulsion system. High molecular weight copolymers were produced after low dose.     

氧化还原引发乳液聚合单体水溶性与动力学之间的关系

本文研究了以过硫酸钾／焦亚硫酸钠为氧化还原引发体系，在苯乙烯、醋酸乙烯酯为具体单体的乳液聚合中，单体水溶性与动力学之间的关系。通过实验考察了聚合温度、搅拌速率、电解质浓度对聚合反应转化率～时间关系的影响，并讨论了单体水溶性、自由基水相反应和聚合速率等之间的内在联系。同时得出该氧化还原引发下苯乙烯和醋酸乙烯酯体系的表观活化能分别为４７．０６ｋｊ／ｍｏｌ和约７０ｋＪ／ｍｏｌ。     

以PAM,CMC和EC代替PVA作醋酸乙烯酯乳液聚合保护胶体的研究

本文尝试用聚丙烯酰胺、羧甲基纤维素及乙基纤维素代替聚乙烯醇作醋酸乙烯乳液聚合的保护胶体。实验结果显示,聚丙烯酰胺、乙基纤维素可以作为醋酸乙烯乳液聚合的保护胶体。本文对所得乳液的物化性质尚未进行详细研究。     

Kinetics of vinyl chloride and vinyl acetate emulsion polymerization

The kinetics of vinyl chloride and vinyl acetate emulsion polymerization are reexamined. The validity of Ugelstad's model for systems with high desorption rate is confirmed by simulating conversion histories for both systems at different initiator concentrations and particle numbers. On the basis of the model, it is shown that at ordinary initiation rates, termination reactions are unimportant with respect to molecular weight development in both systems, and as a consequence, molecular weight development is independent of number and size distribution of polymer particles and of initiator and emulsifier level. Based on this conclusion, it is shown that in accordance with experimental facts, the molecular weight distribution obtained in vinyl chloride emulsion polymerization is the most probable distribution, and it is concluded that the number of long-chain branch points per repetition unit is less than 2 × 10^?4 at high conversions. In vinyl acetate emulsion polymerization, an almost logarithmic normal distribution is obtained. The distribution is strongly broadened by branching reactions with the number of long-chain branch points increasing rapidly with monomer conversion. The increase of M_n with increasing conversion is due to terminal double-bond polymerization, while the increase in M_w is due mainly to transfer to polymer.     

The effect of radical desorption on the particle size distribution in vinyl acetate emulsion polymerization

The effect of free radical desorption is studied by using a mathematical model of particle size distribution in continuous emulsion polymerization. By comparing the theoretical prediction with experimental data, the value of D_o for the vinyl acetate (VAc) system is best chosen as 0.19 × 10^?7 cm²/h. The effect of radical desorption as well as mean residence time on the absolute particle size distribution, total concentration of polymer particles, conversion, and average number of radicals per polymer particle are analyzed by the model proposed.     

Thermodynamic studies related to emulsion polymerization

Liquid–liquid and vapor–liquid phase equilibria for the binary, ternary, and quaternary systems of vinyl acetate, surfactant, water, and poly(vinyl acetate) (PVAc) were obtained using liquid–liquid equilibria, inverse gas chromatography, and the headspace methods. The Flory–Huggins interaction parameters for the different species in the emulsion polymerization of PVAc latices are reported. These parameters could not be used to predict the phase equilibria because of their strong dependence on concentration. The UNIFAC‐vdW‐FV model was applied to predict the vapor–liquid equilibria in the binary and ternary systems containing vinyl acetate, 4‐nonylphenol polyethoxilate surfactant, and PVAc. The predicted results compare favorably with the experimental data for all systems. Diffusion coefficients were also measured for the solvents in the PVAc. Analysis confirmed that the diffusion in the latex particles was so fast compared to the reaction that the assumption of uniform monomer composition through the particles was valid. On the other hand, the results indicate that the complex thermodynamic interactions will lead to changes with time in the monomer concentration in the reacting polymer phase. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A calorimetric investigation of suspension and emulsion polymerization of vinyl chloride

An isothermal calorimeter for studying radical polymerization in heterogeneous systems is presented. The calorimeter was used for investigation of suspension and emulsion polymerization of vinyl chloride at 50°C. The results from the suspension polymerization experiments showed that the termination rate constant in the PVC phase was diffusion controlled and very sensitive to the vinyl chloride activity. During suspension polymerization the pressure started to drop at a much lower conversion than in emulsion polymerization. Mass balance calculations showed that this was due to entrapment of a large amount of liquid vinyl chloride in the fine capillary system of the suspension particles. The results from emulsion polymerization experiments in which the particle number spanned the range from 0.094.10¹⁸ to 1.7.10¹⁸ dm^?3, were analyzed according to the kinetic model developed by Ugelstad et al. Using the concentration-dependent termination rate constant obtained from the suspension experiments and assuming proportionality between the radical adsorption and desorption rate constants, this model gave a very good fit of the experimental rate over the entire interval II and most of interval III. The results strongly indicated that termination in the aqueous phase was of measurable importance during interval II and became the dominating termination in interval III.     

On the graft polymerization of styrene and acrylonitrile onto polybutadiene in the presence of vinyl acetate. I. Preparation of graft polymers

In order to modify the graft polymers of styrene and acrylonitrile onto polybutadiene (ABS polymers), the preparation of the graft products of styrene, acrylonitrile, and vinyl acetate onto polybutadiene rubber by emulsion polymerization was described and theoretically studied up to a high degree of conversion. Depending on the residual monomer content of the products, the polymer composition obtained in the experiment was compared with the theoretical one for the substitution of certain quantities of styrene, acrylonitrile, or styrene and acrylonitrile by vinyl acetate in the mass ratio of 3 : 1. Deviations were discussed. The specific viscosity of the polymers of styrene, acrylonitrile, and vinyl acetate separated from the elastomer phase, considerably decreases during the substitution of acrylonitrile by increased vinyl acetate quantities.     

提高聚醋酸乙烯酯乳液性能的实验研究

目的:提高聚醋酸乙烯酯乳液的稳定性和耐水性.方法:采用醋酸乙烯酯为聚合单体、聚乙烯醇为胶体保护剂及乳化剂壬基酚聚氧乙烯醚的聚合反应,制备聚醋酸乙烯酯乳液.再利用单组实验法研究聚乙烯醇、乳化剂、引发剂、加料方式及反应温度等对制备稳定性和耐水性好的聚醋酸乙烯酯乳液的影响规律.结果:制备粘接强度、稳定性和耐水性良好的聚醋酸乙...     

有机硅改性醋丙乳液的制备与表征

采用半连续种子乳液聚合技术,以丙烯酸丁酯、醋酸乙烯酯和有机硅单体合成了有机硅改性醋丙乳液,并研究了有机硅含量、复合乳化剂配比、种子单体含量等对乳液聚合稳定性及乳液性能的影响。制备出的乳液稳定性良好,随着种子乳液单体含量的增加,乳胶粒粒径变小。     

The radiation-induced emulsion copolymerization of vinyl chloride with vinyl acetate in an engineering flow system

A flow reactor system was used to study the radiation-induced emulsion copolymerization of vinyl chloride with vinyl acetate. The emulsion was recirculated from a stirred vessel through transfer lines to a tubular reactor located within a high-intensity Co-60 source. The effects of physical chemical variables such as soap concentration, phase ratio, reaction temperature and residence time distribution on the molecular weight properties were investigated. The rate of copolymerization was found to be proportional to the 0.17 power of the soap concentration. Variation of the monomer-water ratio produced no significant change in rate. The rate increased with an increase in temperature over the range 5–50°C, while the average molecular weights of the copolymer increased with decreasing polymerization temperature. The molecular weight distribution in this engineering system was found to be essentially similar to those produced in a batch system.     

Synthesis of high-molecular weight poly(vinyl alcohol) by low-temperature emulsifier-free emulsion polymerization of vinyl acetate and saponification

High-molecular weight (HMW) poly(vinyl alcohol) (PVA) was prepared via an emulsifier-free emulsion polymerization of vinyl acetate (VAc) using a redox initiation system in low temperatures, and the subsequent saponification with potassium hydroxide in methanol. The effect of the polymerization conditions on the conversion, molecular weight, and branching degree was investigated. PVA with maximum viscosity-average degree of polymerization (DP) of 8270 could be prepared by saponification of poly(vinyl acetate) (PVAc), with DP of 10,660 obtained at temperature of 10°C, monomer concentration of 30%, potassium persulfate molar ratio to monomer of 1/2000, agitation speed of 160 rpm. The conversion was above 90%. From the emulsifier-free emulsion polymerization of VAc in low temperature, PVAc with HMW and high linearity was effectively prepared, which might be useful for the preparation of high-strength and high-modulus PVA fiber. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

聚醋酸乙烯酯乳液的改性研究

本文以醋酸乙烯酯为主要单体,壳聚糖作为改性剂,采用半连续乳液聚合方法制备改性聚醋酸乙烯酯乳液,探讨了引发剂用量和壳聚糖用量对改性乳液性能的影响。结果表明：引发剂用量为0．6％,壳聚糖用量为1．25％（占单体总量）是最佳用量,此条件下合成的改性乳液胶粘剂的耐水性、抗冻性均有所提高,具有较高的粘接能力。红外结果表明,壳聚糖与醋酸乙烯酯发生了共聚反应。     

聚醋酸乙烯酯/纳米SiO_2复合乳液的制备与性能

采用原位乳液聚合法制备了聚醋酸乙烯酯／纳米二氧化硅复合乳液。考察了纳米二氧化硅在聚醋 酸乙烯酯乳液内及乳胶膜中的分散性:纳米二氧化硅用量对复合乳液性能的影响。结果表明:与普通乳液相 比,复合乳液的干态粘接强度和耐水性明显提高。     

Photo‐induced emulsion polymerization of vinyl acetate in the presence of poly(oxyethylene) nonyl phenyl ether,a nonionic emulsifier (II)

Synthesis of high molecular weight poly(vinyl acetate) having less branched structure via photo‐induced emulsion polymerization of vinyl acetate in the presence of poly(oxyethylene)₂₀ nonyl phenyl ether, a nonionic emulsifier, was attempted at 0°C or even below 0°C in the presence of methanol. It was found that 100% conversion is always achieved in all runs and poly(vinyl acetate) having the number‐average degree of polymerization of 9000 with less branched structure (degree of branch < 0.5) can be obtained from this photo‐induced emulsion polymerization system. Mechanisms of the polymerization were also discussed on the basis of the kinetic results. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2153–2158, 2002