Shin'ichi Yusa

To prepare amphiphilic diblock copolymers (M100Pm), a controlled radical polymerization approach was employed, incorporating hydrophilic poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) with hydrophobic poly(3-methoxypropyl acrylate) (PMPA). The synthesized diblock copolymers feature a PMPC block with a degree of polymerization (DP) of 100 and a PMPA block with DP (=m) values of 171 and 552. The hydrophilic PMPC block exhibits biocompatibility, such as inhibition of platelet and protein adsorption, because of its hydrophilic pendant zwitterionic phosphorylcholine groups that have the same chemical structure as cell membrane surfaces. The PMPA block exhibits hydrophilicity because of its hydrophilic ether groups; however, it is predominantly hydrophobic. In addition, PMPA exhibits biocompatibility. Because both blocks of M100Pm are biocompatible, M100Pm has potential applications in the biomedical field as an innovative material. Because of the hydrophobicity of the PMPA blocks, which were surrounded by hydrophilic PMPC shells, M100Pm aggregated when dispersed in water. M100P171 and M100P552 formed spherical micelles and vesicles, respectively. As the DP of the PMPA block increased, the aggregate size and number also increased. Doxorubicin was successfully encapsulated within the M100Pm aggregates. Given their biocompatible properties, M100Pm aggregates have potential applications in drug delivery systems.

This study investigates the stability and application of trithiocarbonate-based chain transfer agents (CTAs) in reversible addition-fragmentation chain transfer (RAFT) radical polymerization under harsh conditions. We evaluated the stability of 4-cyano-4-(2-carboxyethylthiothioxomethylthio) pentanoic acid (Rtt-17) and 4-cyano-4-(dodecylsulfanylthiocarbonyl) sulfanylpentanoic acid (Rtt-05) at 60 °C under basic conditions using 1H NMR and UV-vis absorption spectra, showing that Rtt-05 is more stable than Rtt-17. The greater stability of Rtt-05 is attributed to the hydrophobic dodecyl group, which allows it to form micelles in water, thereby protecting the trithiocarbonate group from the surrounding aqueous phase. In contrast, hydrophilic Rtt-17, without long alkyl chains, cannot form micelles in water. Following the stability assessment, Rtt-17 and Rtt-05 were employed for RAFT polymerization of hydrophilic monomers, such as N,N-dimethylacrylamide (DMA) and 2-(methacryloyloxy)ethyl phosphorylcholine (MPC). DMA can dissolve in both water and organic solvents, and MPC can dissolve in water and polar solvents. Both CTAs successfully controlled the polymerization of DMA, producing polymers with narrow molecular weight distributions (Mw/Mn) less than 1.2. Also, Rtt-17 demonstrated effective control of MPC polymerization, yielding Mw/Mn values of around 1.2. However, during the polymerization of MPC, Rtt-05 failed to maintain control, resulting in a broad Mw/Mn (≥1.9). The inability of Rtt-05 to control MPC polymerization is due to the formation of micelles, which disrupts the interaction between the hydrophilic MPC propagating radicals and the trithiocarbonate group in the hydrophobic core of Rtt-05 micelles. The findings provide critical insights into designing CTAs for specific applications, particularly for biomedical and industrial uses of hydrophilic polymers, highlighting the potential for precise molecular weight control and tailored polymer properties.