Hybrid dispersion Chemical structure

The results of investigations of the effect of method of hybrid dispersion synthesis (la, lb, 2 or 3 - see Section 3.2) on the properties of dispersions as well as of films and coatings made from them are presented in Tables 6.9 to 6.11 (dispersions prepared using water-soluble initiator) and in Tables 6.12 to 6.14 (dispersions prepared using redox initiating system). In all dispersions the chemical structure of the polyurethane-urea and acrylic/styrene polymer component was the same (see relevant tables in Section 6.5.2). All the dispersions contained a similar low level (2-3.6%) of NMP. 

The properties of hybrid dispersion prepared according to two different methods (la and 3 - see Section 3.2) and having the same chemical composition and differing only in the chemical structure of the acrylic/styrene polymer component are presented in Tables 6.24 to 6.26. All dispersions were synthesised using a water-soluble initiator. Dispersions prepared according to method la did not contain any coalescent while dispersions prepared according to method 3 contained 11.6% of NMP. 

Table 6.24 Properties of hybrid dispersions differing only in the chemical structure of the acrylic/styrene part of the hybrid ... 

As can be seen from Table 6.18, the chemical structure of the polyurethane-urea part of the hybrid does not affect the properties of hybrid dispersions, obviously not counting the MFFT which is much higher if polyesterdiol has been used as a starting material for the prepolymer-ionomer synthesis (compare MDPUR-ASD 300 and MDPUR-ASD 24). 

Here, the effect of chemical structure of the polyurethane-urea part of the hybrid is, of course, substantial (see Table 6.19). For hybrid dispersion synthesised without coalescent using polyesterdiol as a starting material for the prepolymer-ionomer, the Tg is so high that films cannot he obtained. On the other hand, if polyetherdiol is applied as a starting material in the synthesis of the same dispersion, films of very good mechanical properties are obtained. This was the reason for using polyetherdiol rather than polyesterdiol as the starting material for synthesis of dispersions in this study. 

Chemical Structure of the Acrylic/styrene Part of the Hybrid Properties of dispersions... 

Table 6.24 shows that the chemical structure of the acrylic/styrene part of the hybrid has no effect on the macroscopic properties of hybrid dispersions, although the appearance of the dispersion particles may be quite different (compare Figures 6.23 and 6.24). Difference in the appearance of particles may result from the degree of hydrophobicity of the monomer (this effect is explained in Section 6.3.2.1). 

The chemical structure of the acrylic/styrene part of the hybrid has a substantial effect on the properties of films made from hybrid dispersions (see Table 6.24). When the monomers that form polymers of high Tg (styrene or MM) are used and the synthesis is carried out according to method la, no film is obtained. For the same monomers but a different method of dispersion synthesis (method 3), a film was obtained only for styrene and only when a high level of coalescent was applied. In this case, the mechanical properties, water and solvent resistance of the film were quite good, but the film was not transparent, which... 

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