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Recently, a variety of amphiphilic block copolymers for water-based color inks as pigment dispersants have been developed. Although such dispersants require both high adsorption of pigments and dispersion-stability in water, the most crucial issue is the difficulty in controlling the affinity balance of the polymeric dispersants between the pigments and aqueous media. Therefore, it is important to increase the solubility of the hydrophobic polymers with low acid-value for ink design. Amphiphilic block copolymers containing styrene-based blocks as hydrophobic segments and methacrylic acid blocks as hydrophilic segments were prepared. The polymers with low acid-value could not dissolve in the alkaline solution directly. They could dissolve in methyl-ethyl-ketone (MEK) at room temperature and diethylene glycol (DEG), with heating. Polymer aqueous solutions were successfully prepared using polymer solutions in DEG as the pre-solutions. Because they were also unable to dissolve directly even in an alkaline solution containing DEG, the existence of DEG is not important, but the process employing the pre-solution is important. The influence of pre-solution viscosity on solubility in water was evaluated. The result suggests that the high viscosity of the DEG solution would work to slowly disperse the polymers in the alkaline solution, efficiently converting polymers into an aqueous soluble state, owing to there being enough time for the neutralization of the carboxylic acids of the polymers. Note that in the pre-solution of a lower concentration, the aqueous solution did not become clear, and the larger particle sizes were detected. These results showed that the viscosity of the pre-solution is an essential factor in solubilization in water. Using this method, the polymeric dispersants with low hydrophilicity were well dissolved in water, up to a high concentration.

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