Exclusion-to-Adsorption Transition of Hyperbranched Polymers in Liquid Chromatography: Governed by Configurational Diversity and High Fractal Dimension

The adsorption behavior of hyperbranched polymers in liquid chromatography under critical conditions (LCCC) remains a fundamental puzzle due to their complex nonlinear architecture and the absence of a theoretical framework. Here, we overcome this challenge by synthesizing a series of hyperbranched polystyrene (HB-PS) with controlled branching densities (ρ = 1/35–1/400) and using functionalized linear PS references to eliminate chemical interference. Our study unveils a distinct topological paradigm: HB-PS exhibits a nonuniversal exclusion-to-adsorption transition, and the elution behavior strongly depends on the branching density under LCCC, in sharp contrast to the unified coelution point (CEP) behavior of linear and cyclic chains. This behavior originates from the high fractal dimension of hyperbranched structures, which amplifies intrachain excluded volume effects and significantly raises the conformational energy barrier during the exclusion-to-adsorption transition. Consequently, the conventional scaling relationship between the adsorption free energy and molecular weight breaks down. For near-incompressible hyperbranched polymers, elution becomes governed solely by size exclusion, and the CEP and critical adsorption behavior cease to exist. This work fundamentally revises the understanding of polymer adsorption under critical conditions and provides a new framework for analyzing complex topological polymers, with implications for highly branched biological macromolecules such as starch and glycogen.