Thermo-Responsive Polymer Colloids Prepared Using a Hybrid Polymer Synthesis Technique

Abstract

In the present study, we have designed a polymer colloid from a multi-block polymer chain composed of a hydrophobic and a hydrophilic segment. The hydrophobic segment consisted of the amorphous polymer poly(trimethylene carbonate) (PTMC) and was synthesized by ring-opening polymerization (ROP) of trimethylene carbonate. The hydroxyl terminal on the PTMC was functionalized for subsequent living radical polymerization of two functional vinyl monomers: N-isopropylacrylamide (NIPAAm) and 2-methacryloyloxyethyl phosphorylcholine (MPC), where poly-NIPAAm (PNIPAAm) shows thermo-responsive behavior, and poly-MPC (PMPC) is highly biocompatible. In this way, functional polymers were obtained via a hybrid polymer synthesis technique. The chemical structure of the resulting polymer was determined by 1 H-NMR and IR, and its solution properties were evaluated by UV spectroscopy, fluorescence spectroscopy, and dynamic light scattering (DLS). It was confirmed that the resulting polymers spontaneously self-aggregated in water by the Tyndall phenomenon, where the hydrophilic PNIPAAm and PMPC presumably covered the hydrophobic and amorphous PTMC domain. From DLS, we found that the diameter of the aggregation was changeable in terms of polymer sequence. Aggregates of the tri-block copolymer in water showed a diameter of 460 nm at 25°C, while at 35°C, the particle size decreased to 370 nm as a result of the increased hydrophobicity of the NIPAAm unit on the polymer. The polymer colloid could encapsulate a fluorescent probe proving the existence of a hydrophobic domain in the aggregate.