Monomer continued ratio, water

The copolymer composition may drift during the course of an emulsion copolymerization because of differences in monomer reactivity ratios or water solubilities. Various techniques have been developed to produce a uniform copolymer composition. The feed composition may be continuously or periodically enriched in a particular monomer, to compensate for its lower reactivity. A much more common procedure involves pumping the monomers into the reactor at such a rate that the extent of conversion is always very high [>about 90%]. This way, the polymer composition is always that of the last increment of the monomer feed. 

In these studies, polymeric nanocapsules with encapsulated dsDNA (790 base pairs) were produced via anionic polymerization of n-butylcyanoacrylate (BCA) carried out at the interface of homogeneously distributed aqueous droplets in inverse miniemulsion which are in a second step then redispersed in an aqueous continuous phase. The obtained capsules were characterized in terms of size, size distribution, morphology, polymer molecular weight, and encapsulation efficiency of DNA. The effects of surfactant type and concentration, viscosity of the continuous phase, monomer amount, and water-to-oil ratio were investigated and results are discussed in this paper. 

Epichlorohydrin Elastomers without AGE. Polymerization on a commercial scale is done as either a solution or slurry process at 40—130°C in an aromatic, ahphatic, or ether solvent. Typical solvents are toluene, benzene, heptane, and diethyl ether. Trialkylaluniinum-water and triaLkylaluminum—water—acetylacetone catalysts are employed. A cationic, coordination mechanism is proposed for chain propagation. The product is isolated by steam coagulation. Polymerization is done as a continuous process in which the solvent, catalyst, and monomer are fed to a back-mixed reactor. Pinal product composition of ECH—EO is determined by careful control of the unreacted, or background, monomer in the reactor. In the manufacture of copolymers, the relative reactivity ratios must be considered. The reactivity ratio of EO to ECH has been estimated to be approximately 7 (35—37). 

Soapless seeded emulsion copolymerization has been proposed as an alternative method for the preparation of uniform copolymer microspheres in the submicron-size range [115-117]. In this process, a small part of the total monomer-comonomer mixture is added into the water phase to start the copolymerization with a lower monomer phase-water ratio relative to the conventional direct process to prevent the coagulation and monodispersity defects. The functional comonomer concentration in the monomer-comonomer mixture is also kept below 10% (by mole). The water phase including the initiator is kept at the polymerization temperature during and after the addition of initial monomer mixture. The nucleation takes place by the precipitation of copolymer macromolecules, and initially formed copolymer nuclei collide and form larger particles. After particle formation with the initial lower organic phase-water ratio, an oligomer initiated in the continuous phase is... 

Thomas and Webb (129), using an emulsion polymerization model, calculated k2 from Rp and the number of particles. Their value at room temperature was 2 x 104 1 m-1l-1, in good agreement, perhaps fortuitously, with Dainton and Eaton (49). This treatment assumes that the monomer water ratio at the particle is the same as in the continuous phase. If allowance were made for adsorption of monomer this value of k2 would fall to approach more closely the level observed in DMF. 

Figure 6. Example data acquisition for the continuous emulsion polymerization of MM A showing conversion and surface tension oscillations (Run 15, Recipe 8 T = 40°C initiator (ammonium persulfate) =0.01 gmol/L H20 emulsifier (SLS) = 0.02 gmol/L H20 wt. ratio monomer/water = 0.43)...

The process usually starts with the polymerization of a small proportion of the reagents at a very low monomer to water ratio (the seed stage), followed by the feeding of the remaining monomer (which may take several hours) and of other materials (if needed) once the conversion in the reactor has reached 70% or more. The in-reactor conversion will then depend upon the rate of polymerization compared to the rate of feed. If the reaction is continued under the so-called monomer-starved conditions, the in-reactor conversion is kept at a high 80-90%, which reduces the polymerization rate. To compensate, temperature is raised however, then the initiator depletes faster and more has to be added during the reaction. 

Abstract This review describes how the unique nanostructures of water-in-oU (W/0), oil-in-water (0/W) and bicontinuous microemulsions have been used for the syntheses of some organic and inorganic nanomaterials. Polymer nanoparticles of diameter approximately 10-50 nm can easily be obtained, not only from the polymerization of monomers in all three types of microemulsions, but also from aWinsor l-like system. A Winsor 1-like system with a semi-continuous process can be used to produce microlatexes with high weight ratios of polymer to surfactant (up to 25). On the other hand, to form inorganic nanoparticles, it is best to carry out the appropriate chemical reactions in W/0- and bicontinuous microemulsions. 

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