Synthesis and Characterization of Thermoresponsive Cationic Diblock Copolymers

Thermoresponsive cationic diblock copolymers have garnered significant attention due to their potential applications in drug delivery and biomaterials. This study focuses on the synthesis of a series of diblock copolymers incorporating both thermoresponsive and cationic segments. The copolymers were synthesized via a controlled radical polymerization technique (atom transfer radical polymerization) to achieve well-defined molecular weights and narrow dispersities. The nonionic block is a random copolymer of the thermoresponsive monomers, poly(ethylene glycol) methyl ether methacrylate and di(ethylene glycol) methyl ether methacrylate, while the cationic block is quarternized poly(2-(dimethylamino)ethyl methacrylate) offering tunable charge density and temperature sensitivity. The polymers were molecularly characterized by ¹H-NMR spectroscopy and gel permeation chromatography.

The thermal transitions were studied using high-sensitivity differential scanning calorimetry, revealing a demixing or cloud point temperature for the thermoresponsive block in aqueous solution, with modulation observed upon variation of its relative composition. The block copolymers self-assembled in water into micelles with increasing temperature, in which the hydrophilic cationic polymer chains protect a hydrophobic core composed of the nonionic blocks. Dynamic light scattering measurements provided insight into the self-assembly behavior and the results from small-angle X-ray scattering measurements offered detailed additional structural information.

In summary, this work demonstrates the successful synthesis of thermoresponsive cationic diblock copolymers and provides a comprehensive analysis of their phase behavior using a range of characterization techniques. The findings pave the way for the development of advanced polymer systems with programmable properties for a variety of functional applications.