Polyurethanes ionomer formation

Water-borne polyurethane coatings are formulated by incorporating ionic groups into the polymer backbone. These ionomers are dispersed in water through neutrali2ation. The experimental 1,12-dodecane diisocyanate (C12DI Du Pont) is especially well suited for the formation of water-borne polyurethanes because of its hydrophobicity (39). Cationomers are formed from IPDI, /V-methyIdiethan olamine, and poly(tetramethylene adipate diol)... 

In the prepolymer-ionomer process , the compound which contains the moieties which are the precursors of ionic groups is incorporated in the polymer chain already at the stage of urethane prepolymer formation. Then they are neutralised, which results in the formation of a prepolymer-ionomer which is emulsified in water and eventually crosslinked. In this process, the prepolymer-ionomer is usually dissolved in a small amount of water-miscible solvent of high boiling point, e.g., N-methylpyrolidone, which plays the role of coalescing agent in the process of film formation. It is then possible to obtain DPUR which contain either cationic DPUR with a pH of less than 7 (cationic moieties are attached to the polyurethane or polyurethane-urea chain) or anionic DPUR with a pH of greater than 7 (anionic moieties are attached to the polyurethane or polyurethane-urea chain). If non ionic hydrophilic moieties are attached to or incorporated in the polyurethane or polyurethane-urea chain, then a nonionic DPUR may be obtained. 

Crystallization provides the driving force for phase separation in these materials as well. These materials have especially low chemical permeability and can offer good properties at low temperatures. A commercial example of a copolyamide is PEBAX [7] marketed by Atofina. Copolyamides compete with polyurethanes and copolyesters for market share. lonomers are the final material that will be discussed. lonomers are materials where a small mole fraction of monomers, usually less than 10%, contain an ionic functionality. These materials are not segmented like most of the other materials discussed in this chapter, rather the ionic groups are distributed randomly along the polymer backbone. Incompatibility between the ionic groups and the nonpolar polymer backbone leads to the formation of ionic-rich domains. A commercial example of an ionomer is Surlyn [8] manufactured by DuPont, shown in Fig. 2. 

The strong stabilizing effect that polyurethane ionomers have on appropriately structured non-ionic polyurethanes, due to the formation of associated compounds, results in individual spherical particles instead of large jelly-like precipitations. This occurs when water is added to organic solutions of polyurethanes which contain 0 5-3% ionomers. 

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