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 (T_{g}) in complex polymer systems. Here we characterize the T_{g} 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-T_{g} PBMA block, which lowers the homopolymer T_{g} 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 T_{g} for the homopolymers in the blends to T_{g} for diblock copolymers with equivalent labeled segment density profiles reveals that the homopolymer's T_{g} 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.