Physical Bond Breaking in Associating Copolymer Liquids.

We combine ideas from polymer and glassy liquid physics to construct a new model for the bond-breaking time scale of attractive sticker groups in associating copolymer liquids that form transient networks. The activated event is argued to be a two-step process, involving first the release of the nonsticker dynamic caging constraints that defines the primary alpha relaxation, followed by attractive stickers surmounting an association free-energy barrier subject to a local frictional resistance which can be strongly affected by relaxation-diffusion decoupling. The ideas embedded in the model produce a consistent and good description of the bond-breaking time scale for diverse polymer chemistries and architectures as a function of temperature and fraction of sticky groups. Chemically sensible values for association free energies are deduced. In strong contrast, the existing phenomenological models are shown to incur qualitative failures.