Unprecedented control over polymerization of n-hexyl isocyanate using an anionic initiator having synchronized function of chain-end protection

The living anionic polymerization of isocyanates carried out using conventional initiators is associated with side reactions due to rapid initiation rates as well as back-biting by the growing chain, resulting in a lack of control on the molecular weight (MW) and molecular weight distribution (MWD) of the polymers. Successful control over the reaction was possible by using additives that could prevent back-biting. We find an initiator in sodium benzanilide (Na-BA), which has a slow initiation rate combined with additive function, so that use of an external additive is eliminated. The initiator has resulted in polymers with high yields and an unprecedented control over the MW and MWD. It is possible to introduce a number of functionalities at the termini of the polymer by using Na-BA derivatives as well as suitable terminating agents, leading to macromonomer, reactive and chiral polymers, and chiral macromonomer in approximately 100% yields. In the process, the finding has expanded the scope of polyisocyanates in diverse applications.     

The Effect of Alkyl Side Chain and Additives on the Anionic Polymerization of Isocyanates with Carbamate Group

The synthesis of new isocyanate monomers and their polymerization by anionic route is reported. Reaction of 1,6-diisocyanatohexane with aliphatic alcohols such as methanol, n-propanol and n-pentanol in 1:0.5 molar ratios was carried out in the presence of pyridine such that one  NCO group remained unreacted. The anionic polymerization of n-alkoxycarbonylaminohexyl isocyanates was carried out using sodium napthalenide (Na-Naph) initiator in the presence of 15-crown-5 (15C5) and sodium tetraphenylborate as the additives. While polymerization of n-propyloxycarbonylaminohexyl isocyanate (PAHI) and n-pentanoxycarbonylaminohexyl isocyanate (PEAHI) was feasible that of methoxycarbonylaminohexyl isocyanate (MAHI) led to an insoluble material. The polymers were isolated in high yields with NaBPh₄ as the additive.     

Efficient Cellular Internalization and Transport of Bowl-Shaped Polydopamine Particles

In drug delivery applications, particle-based systems have been used widely due to their physicochemical properties such as size, shape, and surface charge to achieve desirable properties in intracellular environments. The way in which nanoparticles enter a biological cell is an important factor in determining their efficacy as drug carriers, their biodistribution, and toxicity. Most research thus far has focused on the comparison of spherical and rod-like particles on cellular internalization and transport. Here, the synthesis of bowl-shaped polydopamine (PDA) mesoporous nanoparticles with an average diameter of 200 nm and well-controlled radially oriented mesochannels are reported. By incubating bowl-shaped PDA nanoparticles and spherical nanoparticles with HeLa cells, their internalization behaviors are investigated using a suite of characterization techniques. Extensive experimental results demonstrate that bowl-shaped PDA nanoparticles adhere to the cell more efficiently and a faster rate of cellular uptake of bowl-shaped nanoparticles compared to their spherical counterparts. Overall, the cellular internalization behavior of particles is shape-dependent, and such information is crucial in designing nanoparticles for biomedical applications.