Preparation and self-assembly of thermosensitive triblock copolymers with N-isopropylacrylamide and 3-methacryloxypropyltrimethoxysilane as monomers

Well-defined triblock copolymers poly(N-isopropylacrylamide)-b-poly(3-methacryloxypropyltrimethoxysilane)-b-poly(N-isopropylacrylamide) (PNIPAM-b-PMEMO-b-PNIPAM) with varying block ratios were successfully synthesized via reversible addition–fragmentation chain transfer polymerization. The amphiphilic triblock copolymers showed surfactant-like behavior in aqueous solution and could easily self-assemble into dendritic micelles with hydrophobic PMEMO as the core and hydrophilic PNIPAM as the shell when the copolymer concentration exceeded the critical micelle concentration (CMC). Transmittance measurements showed the triblock copolymers were thermosensitive, and it was worth noting that the lower critical solution temperature (LCST) values of copolymers exceeded pure PNIPAM to about 35.3 °C, which was very close to physiological temperature of human body. This was attributed to the effect of Si–O–CH₃ hydrolysis in polymers. The effect of a series of inorganic salts on thermosensitivity of PNIPAM-b-PMEMO-b-PNIPAM was investigated, and our results suggested that the block copolymers maintained good thermosensitivity in all salt solutions. The LCST did not change significantly in different concentrations of NaCl, CaCl₂ and MgCl₂ solutions, which proved the polymer had good salt resistance. Dynamic light scattering experiments showed that the micelles were well dispersed at about 120 nm below LCST with a small polydispersity index. In addition, the drug-loading experiments of micelles showed high drug encapsulation efficiency indicating their potential as drug carriers.