Ciba Specialty Chemicals Corporation (Tarrytown, NY) developed cationic alkoxyamines as polymerization initiators/regulators in a controlled stable free radical polymerization process to produce intercalated and/or exfoliated nanoparticles from natural or synthetic clays. The process results in improved nanocomposites and nanocomposite compositions for use in paints, inks, coatings, sealants, caulks, adhesives, reactive diluents and as plastic additives for thermoplastic materials, according to U.S. Patent 7,595,359.
One way of improving polymer properties is by adding a natural or synthetic clay material to polymers to form composite materials. However, incorporating clays into polymers may not provide a desirable improvement in the physical properties, particularly mechanical and optical properties of the polymer may be adversely affected. Nanocomposite compositions containing finely dispersed natural or synthetic clay with at least partially intercalated and/or exfoliated layers and mixtures of ethylenically unsaturated monomers and/or polymers have attracted much interest in recent years. According to Ciba inventors Andreas Muhlebach, Peter Nesvadba and Andreas Kramer, nanoclay materials combine the desired effects of dispersed clay bu avoid the negative influence on the mechanical or optical properties. The nanocomposite compositions can be optically almost transparent, indicating the fine distribution, on the nanometer scale, of the clay.
Ciba provides alkoxyamines, which can be anchored to natural or synthetic clays by a cationic anchor group and which have a high reactivity towards acrylates, methacrylates, styrene and other monomers resulting in a controlled molecular weight with narrow molecular weight distribution. With these compounds polymerization leads to high monomer to polymer conversions in short times and at relatively low temperatures. In contrast to conventional radical polymerization, controlled radical polymerization permits the adjustment of the molecular weight of all growing chains almost uniformly to a predetermined length (low polydispersity), resulting in an almost ideal dispersion of the intercalated and/or exfoliated clay particles.