Thermoresponsive and Flow Behavior of Hyperbranched Polymers from Monomer-Initiator Conjugates

Hyperbranched polymers (HBPs) offer unique structural and functional advantages due to their compact architecture, high density of terminal groups, and tunable solution properties. In this work, we synthesize a series of thermoresponsive HBPs via activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) using an initiator-monomer conjugate (inimer), 2-(2-bromoisobutyryloxy)ethyl methacrylate (EMABIB), in combination with oligo(ethylene glycol) methacrylate. These HBPs are benchmarked against linear copolymers prepared with isobutyryloxyethyl methacrylate (IBOEMA), a monofunctional structural analogue of EMABIB, to isolate the influence of branching on thermal and rheological behavior. We explore how the molar composition of the inimer modulates cloud point temperature (Tcp), complex viscosity, extensional flow behavior, and hydrolytic degradability. We leverage density functional theory (DFT) calculations and electrostatic potential (ESP) mapping to reveal connections between monomer polarity and their role in thermoresponsive behavior. Our findings show that hyperbranched architectures exhibit lower viscosity and Tcp, along with more consistent extensional flow behavior across concentrations, compared to their linear analogues at similar compositions. Moreover, the HBPs demonstrate selective and tunable degradation under basic conditions, highlighting their potential as responsive, degradable materials for potential future biomedical and industrial applications.