Emulsion polymerization of methyl methacrylate

Four polymerization examples are presented here to illustrate both available sensitivity, experimental difficulties, and hopefully some interesting aspects of the polymerization processes. The first two examples are the semi-continuous emulsion polymerization of methyl methacrylate (MMA) and styrene, respectively. The third example is a batch charged copolymerization of butyl acrylate (BA) with MMA. The fourth example is a semi-continuous solution polymerization of an acrylic system. In this last example aliquots were taken manually and analyzed at 29.7°C under static conditions. No further polymerization occurred after the samples were cooled to this temperature. 

The available data from emulsion polymerization systems have been obtained almost exclusively through manual, off-line analysis of monomer conversion, emulsifier concentration, particle size, molecular weight, etc. For batch systems this results in a large expenditure of time in order to sample with sufficient frequency to accurately observe the system kinetics. In continuous systems a large number of samples are required to observe interesting system dynamics such as multiple steady states or limit cycles. In addition, feedback control of any process variable other than temperature or pressure is impossible without specialized on-line sensors. This note describes the initial stages of development of two such sensors, (one for the monitoring of reactor conversion and the other for the continuous measurement of surface tension), and their implementation as part of a computer data acquisition system for the emulsion polymerization of methyl methacrylate. 

Figure 7- Isothermal multiplicity for the emulsion polymerization of methyl methacrylate in a CSTR (20h). S = 0.03...

Figure 8. CSTR emulsion polymerization of methyl methacrylate. Residence time = 1+7 min., temperature = 1+0 °C (20l). S = 0.02 moles/ -water I =0.01 moles/ -water.

Synthesis. A series of latexes was prepared by semicontinuous emulsion polymerization of methyl methacrylate. A dialkyl ester of sodium sulfosuccinic acid surfactant yielded the narrow particle size distribution required. An ammonium persulfate/sodium metabisulfate/ferrous sulfate initiator system was used. The initiator was fed over the polymerization time, allowing better control of the polymerization rate. For the smaller size latexes (200 to 450 nm), a seed latex was prepared in situ by polymerizing 10% of the monomer in the presence of the ammonium persulfate. Particle size was adjusted by varying the level of surfactant during the heel reaction. As the exotherm of this reaction subsided, the monomer and the sodium metabisulfate/ferrous sulfate feeds were started and continued over approximately one hour. The... 

Monteiro et al. have used a RATF Transurf in the ab initio emulsion polymerization of methyl methacrylate at 70° C. The Transurf was synthesized by esterifying a methyl methacrylate dimer with 1,10 decandiol followed by sulfonation. The authors found that only a small amount of Transurf was incorporated and suggested that, in order to increase the Transurf incorporation, the ratio of monomer to Transurf should be kept as low as possible, as achieved, e.g. in starved-feed conditions [12]. 

Monteiro, M.J., Brussels, R. and Wilkinson, T.S. (2001) Emulsion polymerization of methyl methacrylate in the presence of novel addition-fragmentation chain-transfer reactive surfactant (transurf). /. Polym. Sci., A 39,2813-20. 

Figures 4, 5, 6. Comparison between experimental and theoretical conversion histories in emulsion polymerization of methyl methacrylate, styrene, and vinyl acetate. (—), model with gel-effect (—), model without gel-effect.

Normal behavior is observed in the emulsion polymerization of methyl methacrylate at low conversions and generally when the polymer particle sizes are small. The rate of polymerization is observed to accelerate, however, at high conversion levels when the polymer particles are large. Explain briefly. 

In the emulsion-polymerization of methyl methacrylate by carbonyl initiators, intramicellar processes have been found to reduce the conversion rate. On the other hand, the application of weak magnetic fields has been found to increase the conversion of emulsion-polymerized vinyl monomers using triplet ketone sensitizers. Here external magnetic fields will decrease the efficiency of triplet-to-singlet radical-pair intersystem crossing within the micelles and thus increase the function of radical pairs that escape without terminating the polymer chains. 

In the photopolymerization of methacrylamide by benzoin methyl ether, chain-transfer to monomer has been found to be important, and benzalde-hyde is reported to be an inefficient photoinitiator of methyl methacrylate polymerization unless benzophenone and triethylamine are present. Acetophenone has been found to sensitize the cycloaddition of maleic anhydride to 7-oxabicyclo[2.2.1]heptan-5-one-2,3-dicarboxylic anhydride, , a-hydroxy-acetophenone derivatives have been found to be non-yellowing initiators, and h.p.l.c. has been used to determine residual carbonyl photoinitiators in u.v.-cured resins. In the emulsion-polymerization of methyl methacrylate using an aromatic ketone and a continuous or intermittent laser, the former conditions were found to be similar to those under continuous u.v. irradiation. The dependence of the polymerization rate and average chain-length on the absorbance of the initiator used in the photoinitiated polymerization of vinyl monomers has been studied. Interestingly, irrespective of all conditions, maximum conversion is observed when initiator absorbance is 2.51. "... 

Acres and Dalton (1963a) also studied the emulsion polymerization of methyl methacrylate initiated by Co y radiation using a recording dilatometer. Only the conversion-time curves were measured with constant dose rate, varying monomer concentration, and with constant monomer concentration at different dose rates. Except at the lowest monomer concentration a clear gel effect was observed, with linear rates up to that point. The linenr rates increased with increasing monomer concentration up to about 0.4 mol/liter and then leveled oif. The dependence of the rate, before the gel effect, on the dose rate was 0.4 and, unlike their findings with styrene, not dependent on the monomer concentration. Their results were consistent with those of Hummel ei al. that methyl methacrylate follows, with y radiation, the generally accepted Smith-Ewart Case 2 kinetics except for the marked gd effect. 

These values for styrene at 50° C. are to be compared with those determined in solution or bulk, which are in the range (0.5 to 3) X 10 liters mole sec. . In methyl methacrylate polymerizations, k( is particularly strongly aflFected by conversion. The gel effect in bulk polymerization of this monomer has been determined by Robertson (53) and Benough and Melville (3). Robertson showed the decrease of kt to start at conversions as low as 5% in certain systems. In emulsion polymerization of methyl methacrylate, the low value of kf causes the gel effect to occur from very early in the reaction on, as demonstrated by Zimmt (71). The dependence of k on viscosity of the medium has been determined by Benson and North (9), who found that for methyl methacrylate, k( decreases by a factor of about 100 when the viscosity is increased from a very low value to about 200 centipoises. 

Kato S, Noguchi J, Nomura M. Kinetics of emulsion polymerization of methyl methacrylate using poly(methyl methacrylate-co-methacrylic acid) as polymeric emulsifier. Polym Mat Sci Eng 1999 80 552—553. 

Under correctly chosen conditions (mainly an appropriate emulsifier), the radiation-chemical yield of emulsion polymerization attains very high values. For instance, if sodium lauryl sulphate is used for the radiation-induced emulsion polymerization of methyl methacrylate, we have Gp = 105, and for that of butyl acrylate, Gp = 106 molecules/100 eV. 

Emulsion polymerization of methyl methacrylate under the action of pulsed microwave irradiation was studied by Zhu et al. [11], The reactions were conducted in a self-designed single-mode microwave reaction apparatus with a frequency of 1250 MHz and a pulse width of 1.5 or 3.5 ps. The output peak pulse power, duty cycles, and mean output power were continuously adjustable within the ranges 20-350 kW, 0.1-0.2%, and 2-350 W, respectively. Temperature during microwave experiments was maintained by immersing the reaction flask in a thermostatted jacket with a thermostatic medium with little microwave absorption (for example tetrachloroethylene). In a typical experiment, 8.0 mL methyl methacrylate, 20 mL deionized water, and 0.2 g sodium dodecylsulfonate were transferred to a 100-mL reaction flask which was placed in the microwave cavity. When the temperature reached a preset temperature, 10 mL of an aqueous solution of the initiator (potassium persulfate) was added and the flask was exposed to microwave irradiation. 

Process models are also important components of reactor control schemes. Kiparissides et al. [17] and Penlidis et al. [16] have used reactor models for control simulation studies. Particle number and size characteristics are the most difficult latex properties to control. Particle nucleation can be very rapid and a strong function of the concentration of free emulsifier, electrolytes and various possible reagent impurities. Hence the control of particle number and the related particle surface areas can be a difficult problem. Even with on-line light scattering, chromatographic [18], surface tension and/or conversion measurements [19], control of nucleation in a CSTR system can be difficult. The use of a pre-made seed or an upstream tubular reactor can be utilized to avoid nucleation in the CSTR and thereby imjHOve particle number control as well as increase the number of particles formed [20-22]. Figures 8.6 and 8.7 illustrate open-loop CTSR systems for the emulsion polymerization of methyl methacrylate with and... 

Muller and coworkers prepared disc-like polymer Janus particles from assembled films of the triblock copolymer SBM and, after hydrolysis of the ester groups into methacrylic acid units, used these as Pickering stabilizer in the soap-free emulsion polymerization of styrene and butyl acrylate [111]. Armes and coworkers described the synthesis of PMMA/siUca nanocomposite particles in aqueous alcoholic media using silica nanoparticles as stabilizer [112], extending this method to operate in water with a glycerol-modified silica sol [113, 114]. Sacanna showed that methacryloxypropyltrimethoxysilane [115] in the presence of nanosized silica led to spontaneous emulsification in water, which upon a two-step polymerization procedure afforded armored particles with an outer shell of PMMA [116]. Bon and coworkers demonstrated the preparation of armored hybrid polymer latex particles via emulsion polymerization of methyl methacrylate and ethyl methacrylate stabilized by unmodified silica nanoparticles (Ludox TM O) [117]. Performance of an additional conventional seeded emulsion polymerization step provided a straightforward route to more complex multilayered nanocomposite polymer colloids (see Fig. 14). 

Yu C-L, Kang J-S, Zhang F-A (2009) The effect of nano-Si02 coUoid on soap-free emulsion polymerization of methyl methacrylate and hydroxyethyl methacrylate. J Macromol Sci A Pure Appl Chem 46(9) 870-875... 

Thomson, B., Wang, Z., Paine, A., Lajoie, G., and Rudin, A., A Mass Spectrometry Investigation of the Water-Soluble Oligomers Remaining after the Emulsion Polymerization of Methyl Methacrylate, J. Polum. Set. Part A Polym. Chem., 33, 2297, 1995. 

Figures. Conversion (digital densitometer) and surface tension (bubble tensiometer) monitoring during batch emulsion polymerization of methyl methacrylate.

Suddaby, K.G., Haddleton, D.M., Hastings, (.)., Richards, S.N., and O Donnell, ).P. (1996) Catalytic chain transfer for molecular weight control in the emulsion polymerization of methyl methacrylate and methyl methacrylate-styrene. Macromolecules,... 

C.F. Lee, W.Y. Chiu, Soap-free emulsion polymerization of methyl methacrylate in the presence of CaSO, Polym. Int. 1993, 30, 475-481. 

Combination of turbidity and conductivity, surface tension, Fourier-transformed infrared spectroscopy Nucleation during emulsion poljmierization of styrene, vinyl acetate, and methyl methacrylate continuous emulsion polymerization of methyl methacrylate, phase transition of polystyrene oligomers with Fourier-transformed infrared spectroscopy 93... 

Other Mechanistic Aspects.—Stannett et al have reported on the kinetics of the emulsion polymerization of styrene initiated by irradiation with cobalt-60 y-rays. The conclusion is reached that Smith-Ewart Case 2 kinetics are obeyed if the reaction system is such that compliance with Smith-Ewart Case 2 would be expected were initiation effected by the thermal decomposition of potassium persulphate. The efficiency of utilization of the radicals produced by radiolysis of the aqueous phase appears to be in the range 0.3—0.5. Chatterjee, Banerjee, and Konar have investigated the molecular weight of polystyrene produced by emulsion polymerization at low monomer concentration, and compared their observations with the predictions of the theories of Harkins, Smith-Ewart, and Gardon. These workers have also investigated the dependence of rate of polymerization upon monomer concentration in the emulsion polymerization of styrene. Arai, Arai, and Saito" have studied the persulphate-initiated surfacant-free emulsion polymerization of methyl methacrylate, and have proposed a model for the reaction. 

A theoretical treatment of soapless emulsion polymerization of methyl methacrylate in water has shown that the number of particles is determined during the initial stages, and has clarified the relationships between this method, normal emulsion polymerization, and bulk polymerization. Differences between the heterogeneous polymerization of acrylonitrile and vinyl chloride have been discussed, following the development of an elaborate model for the former case in which propagation proceeds in the liquid and, eventually, also in the solid phase. ... 

Interest continues to be shown in the use of surfactant HLB values for predicting behaviour in emulsion polymerization tems. Askarov and Trubitsyna have studied the kinetics of the emulsion polymerization of methyl methacrylate in the presence of polymeric surfactants. They find that both the rates of polymerization and the molecular weights of the products are Iowa than those obtained using conventional surfactants. They interpret these observations in terms of less efficient particle nucleation when polymeric surfactant is used. 

Generally there are three sources of surface stabilizing groups, the emulsifier, ionic comonomer and the initiator. The importance of the last should not be overlooked. For example Fitch and Tsai found that in the emulsion polymerization of methyl methacrylate (MMA) the particle number was proportional to surfactant... 

Cutting GR, Tabner BJ. Radical termination and radical concentrations during the batch emulsion polymerization of methyl methacrylate studied by electron spin resonance spectroscopy. Macromolecules 1993 26 951-955. 

FIGURE 17.5 Steady-state oscillations during the emulsion polymerization of methyl methacrylate in a single CSTR. (a) Single CSTR (b) tubular reactor followed by a single CSTR. Reprinted (adapted) with permission from Nomura M, Harada M. On the optimal reactor type and operations for continuous emulsion polymerization. In Bassett DR, Hamielec AE, editors. Emulsion Polymers and Emulsion Polymeriz0ion. Washington, DC p 121-144. 1981 American Chemical Society. 

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