Role of Chain Connectivity across an Interface on the Dynamics of a Nanostructured Block Copolymer

Fluorescence labeling enables component- and location-specific measurements of the glass transition temperature (Tg) in complex polymer systems. Here we characterize the Tg of fluorescently labeled poly(methyl methacrylate) homopolymers (PMMA-py) blended at low concentrations into an unlabeled lamellar poly(n-butyl methacrylate-b-methyl methacrylate) diblock copolymer (PBMA-PMMA). In this system, the PMMA-py homopolymer is sequestered within the PMMA domains of the diblock copolymer and subject to soft confinement by the domains of the lower-Tg PBMA block, which lowers the homopolymer Tg by ∼5 K beyond the contribution of segmental mixing. In contrast to the PMMA block in the diblock copolymer, the PMMA-py homopolymer is not covalently bound to the interdomain interface. A comparison of Tg for the homopolymers in the blends to Tg for diblock copolymers with equivalent labeled segment density profiles reveals that the homopolymer's Tg is consistently ∼10 K higher than for diblock segments at the same location within the domain structure, highlighting the dominant contribution of a covalent bond across the interface to the perturbation of the chain dynamics in the block copolymer.