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We examine the influence of small (56 nm diameter) cross-linked poly(butyl acrylate) (xPBA) particles as fillers on the diffusion rate of poly(butyl methacrylate) (PBMA) molecules in PBMA latex films. For the high-M PBMA sample (Mw = 400 000), the presence of soft, elastic particles strongly decreases the diffusion rate of the PBMA molecules across the intercellular boundaries. The retardation effect increases linearly with xPBA content, with the surface-to-volume ratio for xPBA particles of different size, and is best explained as an obstacle effect on the PBMA diffusion rate. For the low-M PBMA sample (Mw = 35 000), the presence of 30 vol % cross-linked PBA particles increases the diffusion rate of the PBMA polymer, whereas in the presence of 60 vol % cross-linked PBA particles, the PBMA diffusion rate is the same as that in the latex film without filler. Thus, the overall effect of soft filler particles on polymer diffusion is a combination of an obstacle effect, which retards polymer diffusion, and a second effect, probably a free volume effect, which promotes polymer diffusion. This effect is much smaller for the high-M PBMA sample. Depending on which of these effects dominates, one can observe an increase or decrease in the polymer diffusion rate.

We describe the miscibility of blends involving poly(ethylhexyl methacrylate) [PEHMA] latex copolymers using the direct nonradiative energy transfer (DET) technique. When the polymers in both components of a blend are PEHMA homopolymers, we obtain a fully mixed film. When one of the components in the blend is replaced with a PEHMA copolymer containing 5 mol % tert-butylcarbodiimidoethyl methacrylate (tBCEMA), we also obtain a fully mixed film. However, if a PEHMA copolymer containing 11 mol % methacrylic acid (MAA) is mixed with PEHMA homopolymer, the miscibility between the polymers is limited and is reduced further when the amount of MAA is increased to 20 mol %. Using a distribution model for energy transfer, we were able to determine the evolution of the interface thickness with annealing time. The maximum interface thickness attained in these blends decreases from δ = 15 nm to δ = 8 nm when the content of MAA in the blends increases from 11 mol % to 20 mol %. A freshly formed solvent-cast film prepared from a 1:1 blend of the PEHMA copolymer containing 11 mol % MAA and the PEHMA copolymer containing 5 mol % tBCEMA exhibits some polymer segregation. This persists in the solid film when the film is annealed for short times (20 min) at 60 °C. Over longer times, mixing of the copolymers occurs and reaches completion. We attribute this increase in miscibility to the formation of graft copolymer, which serves as a compatibilizing agent, through the reaction between the −COOH and −N&dbd;C&dbd;C− groups. When a film of the same composition is prepared from a blend of the two latex dispersions and annealed, a fully mixed film also results.

We report pyrene fluorescence probe experiments which examine the association in aqueous solution of a hydrophobically modified hydroxyethylcellulose (HMHEC) of Mw ≈ 300 000 containing on average 1 C16H33 group/143 anhydroglucose units as well as the transformation of this polymer into a pyrene-labeled derivative HMHEC-Py-1 containing 1 pyrene/200 glucose units. Fluorescence studies of mixtures of HMHEC-Py-1 + HMHEC in water demonstrate that both pyrene−pyrene and pyrene−C16 associations occur, and we are able to infer that even in the most dilute solutions that we can examine these polymers exist as small aggregates of several polymer molecules. HMHEC-Py-1 exhibits excimer emission at concentrations as low as 0.01 g/L. As the polymer concentration is increased, one observes a sharp increase in the reduced viscosity at 1.5−2.0 g/L. Over the same range of concentrations HMHEC-Py-1 exhibits an increase in IE/IM values, indicating that the viscosity increase is due to a substantial increase in polymer association. HMHEC solubilizes pyrene as a fluorescent probe. The limiting solubility, approximately 1 pyrene/35 C16 alkyl groups, and the partition coefficient (5 × 10⁴) are much smaller than those found for other more flexible associating polymers, yet the I1/I3 value is consistent with solubilization of pyrene in domains large enough to minimize exposure of the probe to water. We infer that HMHEC in water forms hydrophobic domains with a large size polydispersity. The mean aggregate size is small, but hydrophobic probes such as pyrene and bis(1-pyrenylmethyl) ether are solubilized preferentially in the largest hydrophobic domains.