Extended Applicability of Classical Phenolphthalein: Color Changing Polymeric Materials Derived from pH-Sensitive Acrylated Phenolphthalein Derivatives

Polymerizable phenolphthalein derivatives with pH-sensitive properties were synthesized in the course of electrophilic aromatic substitution reactions. N -(2-hydroxy-5-(1-(4-hydroxyphenyl)-3-oxo-1,3-dihydroisobenzofuran-1-yl)benzyl)acrylamide ( 3 ) and N, N′ -(((3-oxo-1,3-dihydroisobenzofuran-1,1-diyl)bis(2-hydroxy-5,1-phenylene))bis(methylene))diacrylamide ( 4 ) were obtained and characterized. Copolymerization of 3 and 4 with acrylic acid ( 5a ), N -(isopropyl)acrylamide ( 5b ), and N, N -dimethylacrylamide ( 5c ) enabled the synthesis of color switchable materials. Thereby, water-soluble pH sensitive linear polymers 6 and 7 were prepared using monomer 3 . Additionally, cross-linked polymers 8 were prepared successfully by copolymerization of 4 and 5c . These pH-sensitive polymers form hydrogels in aqueous solution. Linear viscoelastic behavior depending on the concentration of the cross-linker was observed.