In-Line Molar Mass Determination in Semidilute Polymer Solutions

Molar mass directly governs polymer properties, yet its routine measurement remains slow, offline, and largely confined to dilute solution conditions. This limitation restricts the rapid structure–property mapping needed for data-driven materials discovery and emerging self-driving laboratory workflows. Here we integrate semidilute polymer solution theory with practical in-line measurement to enable rapid determination of polymer weight-average molar mass (Mw) at concentrations typical of polymerization and processing (i.e., above the overlap concentration, c*). Building on modern scaling concepts that treat semidilute solutions as strings of correlation blobs, we establish a quantitative calibration linking solution specific viscosity to Mw for a concentration range c > c*. This framework allows Mw to be determined for unknown samples using a conventional rheometer in as little as 2 min. We implemented the same viscosity to Mw calibration under continuous flow by converting real-time pressure drop in a tubular module into solution viscosity and hence Mw. Together, the theory-grounded calibration and its flow-compatible implementation provide a practical route to rapid, Mw readout in a semidilute solution regime, enabling high-throughput synthesis and characterization workflows for materials development.