Direct Energy Transfer Studies of the Domain−Boundary Interface in Polyisoprene−Poly(methyl methacrylate) Block Copolymer Films

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.