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

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 wit h AIBN as radical initiator in a ethanol/water (4/1, v/v) mixed solvent. Th e correlation between compositions of the nanospheres and thermal propertie s was studied by Differential Scanning Calorimetry (DSC). The glass transit ion temperature (T-g) of the poly(styrene-co-alkylmethacrylate) core of the nanospheres was constant at 90 to 100 degreesC, even though the chemical c ompositions of the nanospheres differed. The melting temperature (T,) of th e PEG in the nanospheres was lowered compared with PEG itself. The T-g of p oly(styrene-co-alkylmethacrylate) in nanospheres composed of more PEG was l owered, although the T-m of the PEG in the nanospheres was higher than that of nanosphere containing small amounts of PEG. These results indicate that the thermal properties and compositions of the nanospheres were correlated . Freeze-dried nanospheres were annealed at 60 degreesC for 30 min in flask under nitrogen atmosphere. After the annealing, spherical form of the nano spheres consisting of a high percentage of polystyrene was maintained, alth ough the thermal properties dramatically changed by the thermal treatment. The T-g of the poly(styrene-co-alkylmethacrylate) segment and the T-m of th e PEG segment in the nanospheres were affected by composition of the graft copolymer and compatibility of the components of the graft copolymer.