Direct nonradiative energy transfer (DET) experiments were carried out on five polyisoprene-poly(methyl methacrylate) diblock copolymers with polyisoprene volume fractions ranging from 0.07 to 0.5 (polyisoprene microdomains dispersed in a poly(methyl methacrylate) matrix). These experiments yield the ratio R/δ of the microdomain size R to the thickness of the domain-boundary interface δ as a function of the block copolymer overall chain length N. A plot of ln(R/δ) vs ln N indicates that the microdomain size varies as N 0.65 , close to the N 2/3 predicted by theory, while the interfacial thickness δ (26 Å) is independent of the degree of polymerization covered in this work. In addition, the Flory-Huggins interaction parameter χ for PI-PMMA was determined from the DET data (0.077). We conclude from these experiments that PI-PMMA belongs to the class of strongly segregated systems.

Six pairs of polystyrene-poly(methyl methacrylate) (PS-PMMA) diblock copolymers were prepared with a single fluorescent dye attached to the junction point. One partner contains phenanthrene (the donor), and the other, anthracene (the acceptor). Films were prepared, and nonradiative energy transfer measurements were carried out on these films. Analysis of these data yielded the local concentration of dyes within the interphase. This gives the volume fraction of the interphase in the system, from which we can calculate the ratio R/ , where is the thickness of the interphase and R is the length of the minor phase in the periodic structure of the system. Further analysis of the data in terms of the theory of Ohta and Kawasaki [Macromolecules 1986[Macromolecules ,19,2621 indicates that R/& varies as N010 (predicted, IV2/3) and is about 51Á. This value is remarkably close to that (50 ± 5 Á) reported by Russell [J. Chem. Phys. 1990,92,5677; Macromolecules 1991, 24, 5721] from specular neutron reflectivity experiments on similar PS-PMMA diblock copolymers.

The kinetics of direct nonradiative energy transfer between dyes confined to the 2.6 nm wide interface region of polyisoprene-poly(methyl methacrylate) block copolymer films are reported. This system differs from restricted geometry systems examined previously because of the diffuse nature of the edges of the confining space. The interface thickness is similar in magnitude to the characteristic distance for energy transfer (R 0 ) 2.3 nm) for the donor-acceptor dye pair (phenanthrene-anthracene) employed here. Samples were prepared from matched pairs of block copolymers, one containing a donor dye and the other an acceptor dye, at the PI-PMMA junction. Donor fluorescence decay profiles were fitted to the Klafter-Blumen expression [I D (t) ) A 1 exp{-(t/τ D ) -P(t/τ D ) } + A 2 exp(-t/τ D )] containing the additional A 2 term to account for donors (ca. 3%) outside the interface. The parameters obtained followed the predicted behavior, namely, that the preexponential term P was proportional to the acceptor concentration, whereas the stretched-exponential parameter was independent of the global acceptor concentration C A for acceptor-to-donor ratios C A /C D > 1. One of the most unusual features of the data is a crossover in observed as a function of a global acceptor concentration C A for a certain range of donor-acceptor composition, C A /C D < 1.