Polymerizing acrylic dispersions

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

Figure 1. Impact fracture surface of polymerized acrylic dispersion, no dimethacrylate, SEM 17.5X...

Figure 6. Flexural (0.05 in./min) fracture surface of polymerized acrylic dispersion containing 12% tetraeth-ylene glycol dimethacrylate, SEM 16 X...

Figure 7. Fracture surface of the interface of a molded acrylic artificial tooth with polymerized acrylic dispersion (60 vol % beads), SEM 850X...

Figure 9. Fracture surface of polymerized acrylic dispersion (67 vol % beads), polarized transmitted light microscopy 68 X...

Figure 12. Oscilloscope trace of impact fracture of polymerized acrylic dispersion time scale = 50 fisec per division...

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. 

Polymerizing acrylic monomers in the presence of oil-modified polyurethane leads also to a grafting onto the polyacrylics, resulting in dispersions suitable for stable water-borne latexes with good adhesion properties and fair hardness properties [103]. 

Potential health and safety problems of acrylic polymers occur in tlieii manufacture (159). During manufacture, considerable care is exercised to reduce the potential for violent polymerizations and to reduce exposure to flammable and potentially toxic monomers and solvents. Recent environmental legislation governing air quality has resulted in completely closed kettle processes for most acrylic polymerizations. Acrylic solution polymers are treated as flammable mixtures. Dispersion polymers are nonflammable. 

In emulsions, amine hydrochloride constitutes the aqueous phase and acrylic ester the organic phase. Cetyltrimethylanunonium bromide (CTAB) or span/twin (S/T)-type surfactants are used for emulsion polymerization. Solid dispersants such as talc and colloidal silica are often used to stabilize emulsions which are difficult to stabilize with usual surfactants. HydrophiUc colloidal silica (Aerosil 200) drastically increases the stability of some emulsions provided high amounts (up to 10%) of Aerosil are used. Random copolymers containing 10% hydroxyl groups can be used as polymeric dispersants for preparing w/o emulsions. 

Similar reports have appeared in the technology of polymerizing acrylic monomers such as acrylonitrile (753-759) or acrylamide (760-763), Korolev et al. (764) have used ascorbic acid as a reducing agent in the mixture to increase the polymerization rate. The kinetics of polymerization in the presence of oxygen has been studied in systems containing ascorbic acid (765), Recent patents (766,767) have been issued with ascorbic acid in the dispersion of acrylic aqueous resins. 

Sulphosuccinic acid diesters play a role above all in American polymerization formulations. They are rarely used as principal emulsifiers, but rather to control secondary properties, for example, for the production of highly concentrated low viscosity acrylate dispersions. The branched sodium di-2-ethyl hexyl sulphosuccinate is widely used, combining favourable emulsifier properties with excellent wetting power. Dicyclohexyl sulphosuccinate has a particularly high CMC and a particularly high surface tension [48]. 

The three fundamental techniques have been constantly improved and applied to the preparation of well-defined polymers from new monomers. For example, in SFRP, recently developed nitroxides have been successfully used to polymerize acrylates, acrylamides and most recently also methacrylates in the presence of small amoimts of styrene. Cobalt porphylines were originally used for CRP of acrylates but more recently for vinyl acetate. Both systems were successfully applied in aqueous dispersed media. 

Products of Emulsion Polymerizalion. This is the most useful process for polymerizing the acrylate esters, producing stable dispersions with excellent film-forming properties. These acrylate dispersions are employed in the paper, rubber, textile, leather, and paint industries. 

Section 19.S.1.2), and reported increases in toughness comparable to those achieved with CTBN. A further, but inconclusive, study compared pre-formed poly(n-butyl aciylate)-based particles made by emulsion and by suspension polymerization [97]. Dispersion polymerization in an epoxy resin has been used to give directly dispersions of acrylic rubber particles in the epoxy for subsequent use in toughening epoxy resins [98]. Core-shell toughening particles comprising 70 wt% of CFOSslinked polybutadiene cores, with a grafted functionalized shell have been claimed [99] to improve the fracture toughness of a methylene dianiline cured epoxy resin by a factor of 10. 

Uses DetergenL emulsifier, dispersant, wetting agent for laundry detergents, household and industrial cleaners, emulsions, dispersions, surf. treatmenL leather, pulp/paper, dyes and pigments, paints, building prods., emulsion polymerization (acrylic, vinyl, and styrene monomers) Properties Colorless clear or cloudy liq. sol. 10% in alcohols, aromatic hydrocarbons sp.gr. 0.98 vise. 90 mPa-s drop pt. 18 C solid, pt. 

Bulk Polymerization The polymerization of a monomer (mass polymerization) in the absence of any medium other than a catalyst or accelerator. The monomer is usually a liquid, but the term also applies to the polymerization of glass and solids in the absence of solvents or any other dispersing medium. Polystyrene, polymethyl methacrylate, low-density polyethylene, and styrene-acrylonitrile copolymers are examples of polymers most frequently produced by bulk polymerization. Acrylic monomers may be simultaneously polymerized and formed into products by conducting the polymerization in molds such as those for rods and sheets. (Odian GC, (2004) Principles of polymerization, Wiley, New York Mark JE (ed) (1996) Physical properties of polymers handbook. Springer, New York)... 

Polymeric dye dispersants Styrene Acrylic acid W. Germany 2,734,204 1979 BASF A.G. D o CD D... 

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