Thermosensitive dendritic stars of tert-butyl-glycidylether and glycidol – Synthesis and encapsulation properties

Abstract

Dendritic block copolymers of hydrophobic core and hydrophilic shell were prepared by a multi-step process based on anionic ring-opening polymerization. In the first step, amphiphilic stars with four or six poly( tert-butyl-glycidylether)-block-polyglycidol arms were synthesized. The hydroxyl groups of polyglycidol after ionization served as initiation centers for sequential anionic polymerization of tert-butyl-glycidylether and 1-ethoxyethyl-glycidylether. Selective removal of protective groups of glycidol hydroxyls yielded amphiphilic, dendritic copolymers with a hydrophobic core and hydrophilic shell. The hydrophobicity of the dendritic core depended on the composition of the star macroinitiator. The number of reactive hydroxyl groups in the shell was controlled by the number and length of the outer polyglycidol blocks. The structure and molar mass of the copolymers obtained were characterized by GPC-MALLS and NMR spectroscopy. The aqueous solution properties of the copolymers were studied. Some of dendritic copolymers aggregated at elevated temperature. The dependence of phase transition temperature and dimension of aggregates on the copolymer composition were followed by light scattering techniques. The spherical aggregates were visualized by AFM. The encapsulation efficiency of a hydrophobic compound (pyrene) was followed by UV–VIS spectroscopy.