Polymerizing acrylic dispersions rapid

Relationship of Morphology to Mechanical Properties of Rapidly Polymerizing Acrylic Dispersions... 

The mechanical properties of rapidly polymerizing acrylic dispersions, in simulated bioconditions, were directly related to microstructural characteristics. The volume fraction of matrix, the crosslinker volume in the matrix, the particle size distribution of the dispersed phase, and polymeric additives in the matrix or dispersed phase were important microstructural factors. The mechanical properties were most sensitive to volume fraction of crosslinker. Ten percent (vol) of ethylene dimethacrylate produced a significant improvement in flexural strength and impact resistance. Qualitative dynamic impact studies provided some insight into the fracture mechanics of the system. A time scale for the elastic, plastic, and failure phenomena in Izod impact specimens was qualitatively established. The time scale and rate sensitivity of the phenomena were correlated with the fracture surface topography and fracture geometry in impact and flexural samples. 

Stable aqueous emulsions of poly(2-ethylhexyl acrylate) (PEHA) were also produced by RESAS from CO2 (68). In this case, a polymer suspension in CO2 was expanded instead of a dissolved solute. A C02-philic surfactant, Monasil PCA (PDMS-g-pyrrolidonecarboxylic acid), was utilized in dispersion polymerization to form a stable polymer suspension at 65°C and 345 bar. A hydrophilic surfactant, (e.g., SAM 185, Pluronic L61, or Pluronic L62), that is soluble in CO2 and CO2/2-EHA monomer mixtures as well as water was added to CO2 to stabilize the suspension after it had been rapidly expanded through a capillary into aqueous solution. The resulting aqueous emulsion with up to 15.6 wt % polymer content was stable for weeks with an average particle size of 2 to 3 pm. Another approach is to introduce the hydrophilic surfactant in the aqueous phase in addition to the surfactant in the CO2 phase. This approach is more general, since many hydrophilic surfactants are not soluble in CO2. During expansion of the suspension into an aqueous solution, the hydrophilic surfactant—for example, triblock Pluronic copolymers—dilfuses to the particle surface to provide stabilization. The resulting aqueous latexes were stable for 100 days for a polymer content reaching 12.7 wt %. 

The PMMA produced by samarocene GTP is mono-disperse and predominantly syndiotactic (up to >96% rr at lower temperatures) and the polymerizations are very rapid, although extremely sensitive to water and air. Acrylates are also polymerized by these catalysts in a well-defined manner, as are lactonesZ A number of well-defined (meth)acrylic block copolymers and special-architecture macromolecules have been prepared with these catalysts. 

In contrast to these oil-in-water emulsions, it is possible that the emulsion polymerization can also be carried out with inverse emulsions. Inverse (water-in-oil) emulsion polymerization in which an aqueous solution of a water miscible hydrophilic monomer such as acrylamide, acrylic add, or methacrylic acid is dispersed in a continuous hydrophobic oil phase with the aid of a water-in-oil emulsifier such as sorbitan mono-oleate or -stearate. The emulsifier is ordinarily above the CMC. Polymerization can be initiated with either oil-soluble or water-soluble initiators. If an oil-soluble initiator is used, the system is an almost exact mirror-image of a conventional emulsion polymerization system. The final latex is a colloidal dispersion of submicroscopic, water-swollen particles in oil. This type of emulsion pol3unerization enables the preparation of high molecular weights water-soluble polymers at rapid reaction rates. It is also possible that the water-swollen polymer particles produced by this emulsion pol)nnerization transfer to aqueous phase rapidly by inversion of the latex. 

Reversible atom transfer free radical polymerization of n-butyl acrylate was conducted in miniemulsion systems using the water-soluble initiator 2,2 -azobis(2-amidinopropane) dihydrochloride (V-50) and the hydrophobic ligand 4,4 -di(5-nonyl)-4,4 -bipyridine to form a complex with the copper ions [67, 80]. The resultant Cu(II) complex has a relatively large solubility in the continuous aqueous phase, but this should not impair its capability of controlling the free radical polymerization. This is because the rapid transport of the Cu(II) complex between the dispersed organic phase and the continuous aqueous phase assures an adequate concentration of the free radical deactivator. As a consequence, the controlled free radical polymerization within the homogenized monomer droplets can be achieved. 

---