Non aqueous dispersions NAD

Polyacrylic acid stabilised latices have been prepared by aqueous dispersion polymerisation. The method used is analogous to the non-aqueous dispersion (NAD) polymerisation methods originally used to prepare polymethyl methacrylate particles in aliphatic hydrocarbons (1. In effect the components of a NAD polymerisation have been replaced as follows aliphatic hydrocarbon by aqueous alcohol, and degraded rubber, the stabiliser, by polyacrylic acid (PAA). The effect of various parameters on the particle size and surface charge density of the latices is described together with details of their colloidal stability in the presence of added electrolyte. 

Examples of dispersion polymerizations using macromonomers are summarized in Table 4. Non-aqueous dispersion (NAD) polymerization of polar... 

The emulsion can be made in either (a) water or (b) some other nonsolvent. Emulsions based on b) are called organosols or non-aqueous dispersions (NADs). If aqueous emulsions are evaporated to dryness without coalescence of the polymer particles, these may be redispersed in some organic non-solvent to form an organosol However, if the polymer dispersion is produced by direct polymerization of monomers in organic non-solvent, then the product is an NAD. Methods of making emulsions, both aqueous and non-aqueous, will now be considered. 

Non-aqueous dispersion (NAD) The solvent analog of a latex the polymer is dispersed in a volatile organic hquid which is not a solvent for the polymer. NAD s have much higher solids than conventional high molecular weight solvent coatings. Like latices, the viscosity is independent of the molecular weight as opposed to solvent soluble resins. 

Polymer Polyols (BP Chemicals) are dispersions of polystyrene acrylonitrile copolymer particles of 0-5-F5/im in polyether polyols sterically stabilized with non-aqueous dispersants (NAD). Use of these with the conventional urethane polyols enables elastomers of relatively high hardness, high strength and exceptionally high elongation at break to be... 

My research group undertook as an objective to explore the utility of these methods in such systems. To begin, we needed to examine some complex material which might serve as a reasonable prototype for an industrial polymer material. Such an initial choice is always arbitrary. We were pursuaded by Dr. M.D. Croucher of the Xerox Research Centre of Canada to become involved in a project involving non-aqueous dispersions [NADs] of polymer particles. 

Non-aqueous dispersions [NADs] are said to be sterically stabilized. A surface coverage of stabilizer polymer, normally very soluble in the liquid medium but anchored into the particle surface, prevents close approach of two particles. The coils of the stabilizer are swollen in the solvent osmotic and entropic forces resist interpenetration of these coils. 

Non-aqueous dispersions (NAD) in which the dispersing medium is not water but an organic solvent may also be made by emulsion polymerization. Although such systems combine the advantages of high solids contents and adjustable drying rates, they find limited commercial use. 

In dispersion polymerisation (which is usually apphed to the preparation of non-aqueous polymer dispersions, commonly referred to as nonaqueous dispersion polymerisation, NAD), the monomer, initiator, stabihser (referred to as the protective agent) and solvent initially form a homogeneous solution. The polymer particles precipitate when the solubihty hmit of the polymer is exceeded, and the particles continue to grow until the monomer is consumed. 

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