EFFECT OF HARD POLYMER FILLER PARTICLES ON POLYMER DIFFUSION IN A LOW-T-G LATEX FILM

The intercelluar diffusion of poly(butyl methacrylate) (PBMA; glass tr ansition temperature (T-g) = 21 degrees C) at 60 degrees C was monitor ed by fluorescence energy transfer in films formed from blends of PBMA latex and a high-T-g (hard) latex. Two types of hard latexes were use d in blends: one composed of poly(methyl methacrylate) (PMMA) and the other having a high-T-g shell made of styrene and acrylic monomer unit s with a large central void (Rohm & Haas Ropaque, ROP). The diffusion rate of PBMA is significantly decreased in the presence of hard partic les. The mean apparent diffusion coefficient (D-app) decreased from 0. 3 to 0.2 nm(2)/s when 35 vol % ROP particles (400 Mn) are present in t he film and to 0.1 nm(2)/s at 75 vol % ROP. The presence of similar-si zed PMMA (400 nm) particles showed a slightly larger effect than ROP o n the PBMA diffusion: D-app decreased by a factor of 2 at 35 vol % PMM A and a factor of 4 at 75 vol % PMMA. At a constant volume fraction of the hard particle additive, the PBMA diffusion rate decreases signifi cantly when the diameter of PMMA particles is reduced from 400 to 67 n m. These effects can be explained in terms of a model in which a more rigid PBMA layer forms, with a slower diffusion rate, near the hard pa rticle surface.