A Method for Controlled Radical Polymerization and for the Synthesis of the Solvent Free Dispersions

摘要

The search for versatile solvent-free dispersions for high performance Automotive coating applications led to the development of a new method of controlled radical polymerization. Using this technique, the synthesis of tailor-made polymer architectures for many different applications is possible. The new solvent free polymers can also function as dispersions and dispersants for many coating applications. This new technology, previously unknown in the field of controlled radical polymerization, is based on the use of diphenylethene (DPE) as the dominant species. In contrast to current methods of controlled radical polymerization, the DPE technology has numerous advantages and can be used with nearly all types of acrylates, methacrylates, vinyl and styrene monomers. The technique leads to high degrees of monomer conversion and is extremely 'user-friendly." The polymerization procedure, which is carried out in aqueous medium, is described in more detail below. In the first stage of the reaction a mixture of hydrophilic monomers and DPE are polymerized directly in water without the addition of an emulsifier or solvent. The oligomer that forms is water-soluble and has highly reactive bonds to the DPE species; these are susceptible to further free radical attack. As more monomers are added they are inserted into the labile DPE bond thus generating specific polymer architectures, the nature of which depends on the type of monomer used and its method of addition. The water-soluble oligomer segments ensure the stabilization of the micelles generated. Typical values for the synthesis include the use of approximately 5 percent active oligomer, monomer conversions of over 99 percent, and a latex particle size of less than 150nm. The dispersions which are solvent and emulsifier free, display several types of morphology from the micro-scale polymer block architecture to the macro-scale micelle superstructure. As well as their use as conventional coating binders, these dispersions have a high affinity for surfaces. This property makes them especially suitable for use as pigment wetting agents and stabilizers. In addition they show a very low film forming temperature, much below the conventional glass transition temperature of the polymer. In conclusion, diverse formulations for production-line automobile and industrial coatings using solvent-free primary dispersions are now possible with this versatile DPE chemistry.