Graft Copolymers Having Hydrophobic Backbone and Hydrophilic Branches XXXI. A DSC Study of Internal Structures and Thermophysical Properties of Core-Corona Polymeric Nanospheres

Abstract

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 (Tgl 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 (T ml 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 thermal 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.KEY WORDS Nanospheres / Macromonomer Method I Core-Corona I Thermal Property I Internal Structure I Annealing/ The free radical dispersion copolymerization of hydrophilic macromonomers and hydrophobic comonomers in a polar solvent gave water dispersible polymeric particles by our "Macromonomer Method". 1 The particles called "core-corona nanospheres", and variety of polymeric particles have been prepared. 2 -4 Nanospheres assembled with functional groups on the surface are great scientific interest for various applications as foundations for catalyst, 5 captures of human immununodeficiency virus-1 (HIV-1), 6 and peptide drug carriers via oral administration.7-9 Using various polymers as macromonomers, such as poly(N-vinylisobutyramide)(PNVIBA) or poly(methacrylic acid)(PMAA) as a polyelectrolytes, thermosensitive or pH sensitive nanospheres were obtained. 2-4,10In the macromonomer method, particles size is affected by molecular weight of the macromonomer, the concentration of monomer, the composition of solvent and the ratio of hydrophobic monomer to hydrophilic macromonomer in the feed. In addition, also the particle size affected by polymerization conditions, such as the concentration of initiator, polymerization time and temperature.11,12 The surfaces of nanospheres accumulate hydrophilic components of the graft copolymers, supported by the results of electron spectroscopy for chemical analysis (ESCA). 2 -4 Very recently, direct observation was made of the internal structure of na...

Cross-sectional Morphologies of Polystyrene Nanospheres with Hydrophilic Corona Surfaces

“…6,9,10 On the other hand, differential scanning calorimetric study of PSt nanospheres with PEG coronas demonstrated melting peaks of PEG crystals presented in nanosphere cores. 25 These observations suggest that PMAA and PNIPAAm segments were also located in cores. Hydrophilic branches of graft copolymers seem to be partially incorporated in cores during copolymerization.…”

Cholesteryl moiety terminated amphiphilic polymethacrylates containing nucleic acid bases for drug delivery

“…In recent decades, there has been a growing interest in self-assembled polymeric micelles, which can be prepared in two ways: One is to self-assemble micelles as random copolymers, [1][2][3][4][5] block copolymers, [6][7][8][9][10][11][12] and graft-copolymer 13 made up of hydrophilic and hydrophobic segments. The other one is to self-assemble polymers soluble in water containing a few hydrophobic substituent per chain and hydrophobic groups attached to the polymer ends.…”