Dispersion at Single Unit TiO 2 Nanoparticles Reduced T g , Induced Chain Disentanglement and Reduced Tensile Modulus in Waterborne Acrylic Coatings

Spatially distributed TiO 2 nanoparticles induced an order of magnitude decrease of glass transition temperature, T g , and chain disentanglement in waterborne acrylic coatings. Acrylic/TiO 2 coatings are synthesized in situ by batch emulsion polymerization. The copolymer is based on butyl acrylate (BA), methyl methacrylate (MMA), and acrylic acid (AA) with composition 56:42:2 mol%, and nano‐TiO 2 (ca. 12 nm) is incorporated up to 3 wt% content. Transmission electron microscopy (TEM) showed that TiO 2 is dispersed at nearly single unit throughout the acrylic matrix. The nanoparticle reduced T g and broadened the temperature range of the glass transition, δT g . The considerable increase of δT g suggests gradients of dynamics. Shear rheometry demonstrated that TiO 2 induced chain disentanglement, the rubbery modulus G e decreased two orders of magnitude with only 1 wt% TiO 2 content thus increasing the packing length p (and the reptation tube diameter as d t = kp, k  > 1). Consequently, the tensile Young's modulus E decreased an order of magnitude, relative to the neat copolymer. The reduction of T g , the slowdown of macromolecular dynamics, the chain disentanglement and the increase of d t suggests dynamics modification due to intercalation of the entangled web by the TiO 2 nanoparticles, and these results may be ascribed to a nanoconfinement effect.