Amphiphilic POSS-core dendrons for optically transparent thermoplastic films with tunable wettability

Abstract

Second- and third-generation hydroxy-terminated poly(amidoamine)-type heptaisobutyl-polyhedral oligomeric silsesquioxane (POSS)-core dendrons (that is, G2POSS-OH and G3POSS-OH, respectively) were prepared by ester-amide exchange reaction of G2 and G3 methyl acrylate-terminated POSS-core dendrons, which were synthesized from aminopropyl heptaisobutyl-T8-silsesquioxane via multiple Michael and ester-amide exchange reactions in excess amounts of methyl acrylate and ethanolamine, respectively. Carboxylic acid-terminated second- and third-generation poly(amidoamine)-type heptaisobutyl-POSS-core dendrons (that is, G2POSS-COOH and G3POSS-COOH, respectively) were quantitatively obtained by treatment of second- and third-generation t-butyl ester-terminated POSS-core dendrons with HCO 2 H. The hydrodynamic sizes of G2POSS-OH and G3POSS-OH micelles in methanol decreased from 18±10 to 6±4 nm, respectively. Casting of a methanol solution of G3POSS-OH onto a glass substrate followed by heating at 100 °C for 15 min provided optically transparent films. However, casting of a chloroform solution of G3POSS-OH resulted in the formation of an opaque whitish film. Both methanol and chloroform solutions of G2POSS-OH generated opaque whitish films. Casting of a 2.6 m formic acid solution of G3POSS-COOH and subsequent heating at 100 °C for 15 min resulted in a highly transparent self-standing film. The peripheral functional groups may have been exposed on the surface of the cast films, which enabled control of the wettability of the films via the polarity of the COOH groups.