Agitation effect on the rate of soapless emulsion polymerization of methyl methacrylate in water

In order to identify the factors causing an agitation effect on the rate of soapless emulsion polymerization, the polymerization of methyl methacrylate was carried out in water. Experimental results indicated the significance of monomer transfer from monomer droplets to water. A kinetic model was proposed which would take into account this monomer transfer. This model enabled the effect of monomer transfer on the rate of soapless emulsion polymerization to be evaluated for the present system and the experimental results to be interpreted qualitatively.     

Kinetics of emulsion polymerization of methyl methacrylate

The kinetics of the emulsion polymerization of methyl methacrylate at 50°C have been studied in seeded systems using both chemical initiation and γ-radiolysis initiation. Both steady-state rates and (for γ-radiolysis) the relaxation from the steady state were observed. The average number of free radicals per particle was quite high (e.g., ～0.7 for 10^?3 mol dm^?3 S₂O²₈ initiator). The data are quantitatively interpreted using a generalized Smith–Ewart–Harkins model, allowing for free radical entry, exit, biomolecular termination within the latex particles, and aqueous phase hetero-termination and re-entry. From this treatment, there results (i) the dependence of the termination rate coefficient (k_t) on the weight fraction of polymer (w_p), (ii) lower bounds for the dependence of the entry rate coefficient on initiator concentration, and (iii) the conclusion that most exited free radicals undergo subsequent re-entry into particles rather than hetero-termination. The results for k_t(w_p) are consistent with diffusion control at temperatures below the glass transition point. Comparisons are presented of the behavior of methyl methacrylate, butyl methacrylate, and styrene in emulsion polymerization systems.     

The effect of sodium methacrylate on the soapless emulsion copolymerization of methyl methacrylate and n-butyl acrylate

The soapless emulsion polymerization of methyl methacrylate (MMA) and n-butyl acrylate (BA) containing various concentrations of sodium methacrylate (NaMA) or methacrylic acid (MMA) is studied. The hydrosoluble yields in final latexes are not larger than 1.3–5%, depending on the concentration of NaMA used. Below 25% conversion, the change of conversion with reaction time follows the square rule and the particle size is proportional to the 2/3 power of time. Above 25% conversion, serious gel effect occurs, and the conversion follows the seventh power on time and the growth of particle diameter obeys the 2.5 power on time. The multiple glass transition (T_g) occur below 20% conversion, where monomer droplets exist. NaMA added induces more T_gs. The effect of molecular weight of the copolymers obtained on T_g (even the molecular weight distributions were shown to be shouldertype bimodal) is estimated to be insignificant. Thus, the heterogeneity of copolymer compositions for multiple T_gs is ascribed to be caused from neither the molecular weight heterogeneity nor the shifts in compositions due to the difference of the monomer reactivity ratios. Referring to the results mentioned, we assume the sublayer surrounding the particle, rich with SO₄^? and COO^? groups, and the concentration gradients of monomers in particles to illustrate particle morphology. In addition, the relatively hydrophilic sublayer is proposed to be closely relative with the occurrence of the composition heterogeneity in particles.     

Ultrasonically initiated emulsion polymerization of methyl methacrylate

The ultrasonically initiated emulsion polymerization of methyl methacrylate (MMA) was investigated. Experimental results show that sodium dodecyl sulfonate (SDS) surfactant plays a very important role in obtaining a high polymer yield, because in the absence of SDS, monomer conversion is near zero. Thus, the surfactant serves as an initiator and as interfacial modifier in this system (MMA/H₂O), and the monomer conversion increases significantly with increasing SDS concentration. An increase in the reactor temperature also leads to an increase in the monomer conversion. An appropriate increase in the N₂ purging rate also leads to higher conversion. The conversion of MMA decreases with increasing monomer concentration because of the higher viscosity of the system. With the experimental results, optimized reaction conditions were obtained. Accordingly, a high monomer conversion of about 67% and a high molecular weight of several millions can be obtained in a period of about 30 min. Furthermore, transmission electron micrographs show that the latex particles prepared are nanosized, indicating a promising technique for preparing nanoscale latex particles with a small amount of surfactant. In conclusion, a promising technique for ultrasonically initiated emulsion polymerization has been successfully performed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3356–3364, 2001     

Polymer particle formation in soapless emulsion polymerization

Polymer particle formation in soapless emulsion polymerization for monomers that are soluble in diluent is studied theoretically and experimentally. A kinetic model is proposed assuming that polymer particles are formed by homogeneous nucleation of both growing radicals and dead polymer molecules above the critical size in solution. Based on this model, the dependence of the number of polymer particles on the concentration of initiator and monomer in solution is discussed for the polymerization system of methyl methacrylate–potassium persulfate–water. Experimental results of the number of polymer particles in this system can reasonably be interpreted by this model.     

Semibatch emulsion polymerization of methyl methacrylate using different polyurethane particles

Aqueous acrylic‐polyurethane (AC–PU) hybrid emulsions were prepared by semibatch emulsion polymerization of methyl methacrylate (MMA) in the presence of four polyurethane (PU) dispersions. The PU dispersions were synthesized with isophorone diisocyanate (IPDI), 1000 and 2000 molecular weight (MW) poly(neopentyl) adipate, 1000 MW polytetramethyleneetherglycol, butanediol (BD), and dimethylol propionic acid (DMPA). MMA was added in the monomer emulsion feed. We studied the effect of the use of different PU seed particles on the rate of polymerization, the particle size and distribution, the number of particles, and the average number of radicals per particle. The PU rigidity was controlled by varying the polyol chemical structure, the polyol MW (M_n), and by adding BD. The monomer feed rate was varied to study its influence on the process. It was observed that the PU particles that had been prepared with a higher MW polyol swelled better with MMA before the monomer‐starved conditions occurred. There seemed to be no significant discrepancies between the series with different PU seeds in the monomer‐starved conditions. The overall conversion depended on the monomer addition rate, and the polymerization rate acquired a constant value that was comparable to the value of the monomer addition rate. The instantaneous conversion increased slightly. The average particle size increased, and the total particle number in the reactor was constant and similar to the number of PU particles in the initial charge. The average number of radicals per particle increased. The differences between the system with a constant particle number and average number of radicals per particle and the system with a fixed radical concentration are discussed. The semibatch emulsion polymerization of MMA in the presence of PU particles studied was better compared to the system with a fixed radical concentration. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 844–858, 2005     

Poly(methyl methacrylate) hollow particles by water-in-oil-in-water emulsion polymerization

Poly(methyl methacrylate) particles having hollow structures were produced by water-in-oil-in-water (W/O/W) emulsion polymerization where sorbitan monooleate (Span80) was used as a primary surfactant and sodium laurylsulfate and Glucopen (APG, polypeptide derivative) were used as secondary surfactants. Urethane acrylate having a molecular structure with a hard segment in the molecular backbone, a long soft segment in the middle, and vinyl groups at both ends was employed as a reactive viscosity enhancer. At low concentration of urethane acrylate, only a few particles contained a void in the polymer phase. However, as the concentration of urethane acrylate increased, the number of the particles containing the void increased. This was because urethane acrylate increased the viscosity of the monomer mixture and helped to form the stable W/O/W emulsion droplets, which possibly restricted droplet coalescence during emulsion polymerization. Moreover, at high concentration of urethane acrylate (above 7 wt%), multi-hollow-structured particles were obtained. It is believed that the increase in the lyophilicity of the monomer mixture caused by urethane acrylate led to stronger interfacial activity of the primary surfactant (Span80) and finally resulted in many internal aqueous droplets. Received: 31 July 1998 Accepted: 13 October 1998     

Effect of shear rate on the rate of radical polymerization of methyl methacrylate

The effect of shear rate on the radical polymerization of methyl methacrylate at 50°, in bulk as well as in solution, has been studied. The rate of polymerization increases by as much as 15% at high shear rates. This increase is explained in terms of changes in the initiator efficiency with shear rate.     

Uniform encapsulation of fine inorganic powder with soapless emulsion polymerization

The encapsulation of inorganic powder of submicron sizes was attempted with soapless emulsion polymerization of methyl methacrylate in water in the presence of the powder. The powders used were barium sulfate and calcium carbonate. The polymerizations were initiated by potassium persulfate and by sodium bisulfite-oxygen redox reaction. The encapsulation state of the powder with the polymer formed varied considerably with the initiators used. With potassium persulfate initiator the powder surface was partially or totally covered by polymer particles, while with redox initiator under air atmosphere the powder surface was well encapsulated with a film-like polymer layer. From the differences in the encapsulation states, an encapsulation mechanism is suggested for each initiator system. Based upon this mechanism, a new encapsulation process capable of covering uniformly fine powders with a film polymer is proposed. An important factor in the new process is the addition of an extremely small quantity of a surfactant into the reaction system prior to the polymerization.     

The soapless emulsion polymerization for the encapsulation of aluminosiloxane sol with PMMA

In the methyl methacrylate (MMA)-K₂S₂O₈-H₂O system we investigated the effect of initiator concentration, monomer amount, and quantity of aluminosiloxane sol on the rate of soapless emulsion polymerization. The kinetic characteristic suggests that the particles grow in accordance with the encapsulation mechanism. FT-IR confirmed that PMMA had been covalently combined with the aluminosiloxane sol. The morphology analysis by TEM confirmed that the composite particles have core-shell structure.     

Soapless emulsion polymerization of methyl methacrylate in water in the presence of calcium sulfite

A kinetic study performed on the polymerization of the MMA-K₂S₂O₈-CaSO₃-H₂O system shows that two different shapes of the time-conversion curve were obtained according to the presence or absence of calcium sulfite powder in the reaction mixture. In the absence of the powder, the polymerization behavior is similar to that of the MMA-K₂S₂O₈-H₂O system reported earlier. An attempt was made to apply the kinetic model of the rate of polymerization and the self-nucleation model of polymer particle formation in soapless emulsion polymerization to the present system. One is able to express the experimental time-conversion curves reasonably well. The other can account for the number of polymer particles formed in polymerizations initiated with potassium persulfate alone or calcium sulfite alone but not that in polymerization initiated by both. In the latter case the rate of radical generation and the ionic strength were appreciably enhanced compared with the former. These enhancements might affect the mechanism of polymer particle formation; certain nucleations, such as an aggregative nucleation, might occur simultaneously in addition to the self-nucleation. In the presence of the solid phase the time-conversion curves were similar to that of emulsion polymerization rather than soapless emulsion polymerization, and the molecular weight of polymer formed was smaller than in the absence of the solid phase. It was shown experimentally that the rate of polymerization was remarkably enhanced by an increase in the solid content, whereas the molecular weight of polymer was only slightly affected. As a result, it is considered that calcium sulfite solid provides an important polymerization locus and probably also plays a significant role in radical generation.     

Soapless emulsion polymerization of methyl methacrylate in water in the presence of barium sulfate

To investigate the kinetics of soapless emulsion polymerization in the presence of a solid phase, polymerization experiments were carried out for the methyl methacrylate? K₂S₂O₈? H₂O system using barium sulfate powder, which is assumed to be chemically inert. Reaction conditions were varied with respect to the ranges of initiator concentration, monomer concentration, agitation speed, and quantity of powder. Experimental results showed that the polymerization rate is greatly affected by the addition of powder. It is concluded that the physical circumstances of the polymerization are changed considerably with the addition of the powder. A conceptual model for the mechanism of the polymerization was proposed to explain the effects of the experimental variables.     

Reversible addition–fragmentation chain transfer polymerization of methyl methacrylate in emulsion

Theoretical simulations showed that for controlled/living radical polymerization in an emulsion system, some of the earliest born particles could be superswollen to a size close to 1 μm. We hypothesized that the superswelling of these particles would lead to colloidal instability. Under the guidance of the simulation results, reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization of methyl methacrylate (MMA) was carried out. Experimental results showed that increasing the initiation rate, surfactant level, and targeted molecular weight could improve the colloidal stability of the RAFT polymerization of MMA in an emulsion. The experimental results were in full accord with the theoretical predictions. The poor control of the molecular weight and polydispersity index was found to have a close relationship with the colloidal instability. For the first time, we demonstrated that RAFT polymerization could successfully be implemented with little coagulum, good control of the molecular weight, and a low polydispersity index with the same process used for traditional emulsion polymerization but with higher surfactant levels and initiation rates. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:2837–2847, 2006     

Thermal properties of poly(methyl methacrylate) prepared by emulsifier-free emulsion polymerization

Emulsifier-free emulsion polymerization of methyl methacrylate in the presence of potassium persulfate initiator, taken in several different concentrations, at various pH values was studied with the aim to obtain colloidal crystals. The thermal properties of poly(methyl methacrylate) prepared by emulsifier-free emulsion polymerization, as the starting material for fabrication of photonic crystals, were examined in relation to the synthesis conditions.     

The morphology of composite polymer particles produced by multistage soapless seeded emulsion polymerization

 Composite polymer particles which contain poly(methyl methacrylate) (PMMA) and polystyrene (PS) components (PMMA/PS composite particle) were synthesized by the method of multistage soapless seeded emulsion polymerization. In this study, the process of multistage soapless seeded emulsion polymerization included two-stage polymerization, three-stage polymerization or four-stage polymerization. The morphologies of the PMMA/PS composite particles were studied. The kinetic factor was the main force to control the morphology of the linear PMMA–PS composite particles which were synthesized by the method of two-stage reaction. Both the kinetic factor and the thermodynamic factor decide the morphology of the linear composite particles which were synthesized by the method of either three-stage or four-stage reaction. However, the thermodynamic factor cannot influence the morphology of the PMMA/PS composite particles with a cross-linked structure which were synthesized by the method of three-stage reaction. The cross-linked composite polymer particles had the morphology of a multilayer structure, which showed that the polymer layers accumulated in their order of production. Received: 9 January 2001 Accepted: 14 June 2001     

A mass spectrometric investigation of the water-soluble oligomers remaining after the emulsion polymerization of methyl methacrylate

A “surfactant-free” emulsion polymerization of methyl methacrylate was conducted at 80°C with ammonium persulfate initiator. The water-soluble MMA-based oligomers re-maining were isolated and analyzed both as-produced and after hydrolysis. NMR analysis revealed that the mole ratio of MMA repeat units to sulfate end groups in the former is 6.5. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and gel permeation chromatography both showed that the mean number of MMA repeat units comprising the extracted material is 8–9. The hydrolysis procedure rids the oligomers of their terminal groups and converts some of the methyl ester groups to acid, greatly sim-plifying the mass spectrum. This appears to be the first direct measurement of “surfactants” produced in situ from monomer and persulfate initiator. © 1995 John Wiley & Sons, Inc.     

Study on CaCO3/PMMA nanocomposite microspheres by soapless emulsion polymerization

A soapless emulsion polymerization method was applied to synthesize CaCO₃/PMMA spherical composite with different loading of CaCO₃. CaCO₃ nanoparticles were pretreated with oleic acid after the carbonation process of Ca(OH)₂ slurry by CO₂, in order to improve the compatibility between the CaCO₃ particles and MMA monomer in emulsion system. The results of photon correlation spectroscopy (PCS) showed the particles size of composites were bigger than the pure PMMA. And the size increased with the increase of the content of CaCO₃ nanoparticles. TEM images showed that the morphology of the composite microspheres was uniform and CaCO₃ nanoparticles can be well encapsulated in the polymeric microsphere, and were located at the edge of the spheres. The results of DTG and TG indicated that the CaCO₃ nanoparticles could improve the thermal stability of PMMA. Moreover, capsulation of CaCO₃ by PMMA can increase the acid-resistant of CaCO₃ nanofillers.     

Ferric oxide-catalyzed polymerization of methyl methacrylate

The polymerization of methyl methacrylate was carried out in water at various concentrations of sodium bisulfite, ferric oxide, and methyl methacrylate at 30, 40, and 50°C. The effect of ferric oxide on the rate of polymerization was studied at 50°C. Rates of polymerization increased in the presence of ferric oxide. For example, the rate of polymerization increased from 3.4 × 10^?5 mole/l.-sec to 11.8 × 10^?5 mole/l.-sec when the ferric oxide concentration was varied from 0 to 15 g/l. water. The molecular weight of the polymer decreased from an average of 1.4 × 10⁶ in the absence of ferric oxide to 2.8 × 10⁵ when the ferric oxide was present. The variation of molecular weight of the polymers with temperature and conversion was studied. At a fixed conversion of 80%, the average molecular weight decreased from 3.4 × 10⁵ at 30°C to 2.2 × 10⁵ at 50°C. The average molecular weight was also found to increase with increasing monomer and initiator concentrations. It increased from 8.1 × 10⁴ to 5.3 × 10⁵ and from 3.4 × 10⁵ to 8.9 × 10⁵ as the initiator and monomer concentrations increased from 0.01 to 0.05 mole/l. and from 0.235 to 0.705 mole/l., respectively. The apparent energy of activation for the polymerization was found to be 15.6 and 9.7 kcal/mole in absence and in presence of ferric oxide, respectively.