Graft copolymers having hydrophobic backbone and hydrophilic branches XXXI. A DSC study of internal structures and thermophysical properties of core-corona polymeric nanospheres

Abstract

Polystyrene core nanospheres having poly(ethylene glycol) (PEG) polymers on the corona were prepared by the free radical polymerization of hydrophilic methacryloyl group terminated PEG macromonomer and hydrophobic styrene with AIBN as radical initiator in a ethanol/water (4/1, v/v) mixed solvent. The correlation between compositions of the nanospheres and thermal properties was studied by Differential Scanning Calorimetry (DSC). The glass transition temperature (Tg) of the poly(styrene-co-alkylmethacrylate) core of the nanospheres was constant at 90 to 100°C, even though the chemical compositions of the nanospheres differed. The melting temperature (Tm) of the PEG in the nanospheres was lowered compared with PEG itself. The Tg of poly(styrene-co-alkylmethacrylate) in nanospheres composed of more PEG was lowered, although the Tm of the PEG in the nanospheres was higher than that of nanosphere containing small amounts of PEG. These results indicate that the t hermal properties and compositions of the nanospheres were correlated. Freeze-dried nanospheres were annealed at 60°C for 30 min in flask under nitrogen atmosphere. After the annealing, spherical form of the nanospheres consisting of a high percentage of polystyrene was maintained, although the thermal properties dramatically changed by the thermal treatment. The Tg of the poly(styrene-coalkylmethacrylate) segment and the Tm of the PEG segment in the nanospheres were affected by composition of the graft copolymer and compatibility of the components of the graft copolymer.