Upper Critical Solution Temperature Behavior of Linear and Star Polymers

This study explores the effect of molecular architecture (linear vs. star) on the upper critical solution temperature (UCST) behavior of ureido-modified polymers in solution. To that end, a series of linear and star poly(2-ureidoethyl methacrylate) (PUEM) polymers with the number of arms 2, 4, 6, and 8 were synthesized and studied. Our preliminary data showed that an increase in the number of arms of polymers with matched molecular weights leads to elevation of the transition temperature. This is likely due to a higher density of units and more extensive hydrogen-bonding between ureido-modified groups in the star polymers. In addition, we explored the effect of a hydrogen-bonded competitor on the UCST transition. Dimethyl sulfoxide (DMSO) – a hydrogen-bonded competitor – was demonstrated to efficiently control UCST transition for polymers with both molecular architectures by competing with polymer intramolecular hydrogen bonding. This work provides fundamental insight into the phase behavior of temperature-responsive star polymers which are potentially useful for controlled delivery applications.