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The objective of this paper is to evaluate selected hydroxyl functional mono methacrylates, as well as reactive surfactants in emulsion polymerization (EP).
Some of the selected hydroxyl functional monomers are extensively used as reactive diluents for radiation-curable adhesives and coatings. They are also used as capping agents in urethane methacrylate oligomers for the production of photopolymer printing plates and dry film resists. In addition, they can be used in the production of acrylic polyols and urethane acrylate oligomers for use in photo imaging applications such as printed circuit boards. Other applications include the preparation of hydrogels, polyurethane dispersions, printing inks, waterreducible resins, etc. Now, the interest is to examine their incorporation characteristics, performance and benefits in emulsion polymerization.
Conventional (Non-Reactive) Surfactants
Emulsion polymerization technology has been discussed in a number of publications.1'4 The primary role of surfactants in EP is to lower the interfacial tension, which allows the emulsification of reactive vinyl monomers and the formation of stable colloidal dispersions of polymer particles. Conventional surfactants aid in the emulsification of monomers inside the micelles, stabilize the polymer particles during nucleation and growth, and promote the stability of the resulting latex.1'9 A fundamental property of surfactants is their ability to orient and adsorb at the interfaces. In latex systems, most of the surfactant is adsorbed at the interfaces between the particles and the water. This adsorption is a thermodynamic process favored by a decrease in the overall free energy of the system. The adsorbed layer of surfactant molecules is essential for the stabilization of latexes during polymerization and during post polymerization processes.
It is well known that the amount and chemical structure of the surfactant/s used in EP have a strong influence on conversion, particle size and distribution, viscosity, overall latex stability and cleanness. Surfactants also have an effect on final properties such as film formation, adhesion, wet ability, water resistance and foamability. A critical issue in the manufacture of commercial latexes is their stability during and after production.
As mentioned before, surfactants have an effect on overall latex stability. The appropriate selection of surfactants is an important consideration when designing a latex formulation. The most effective and widely used surfactants in EP are anionics and nonionics. Anionic surfactants prevent coagulation by electrostatic repulsions originated...