Thermosensitive Behavior of Poly(N-isopropylacrylamide) Grafted Polystyrene Nanoparticles

Abstract

ABSTRACT:We analyzed the thermosensitive behavior of monodisperse polystyrene (PSt) nanoparticles having different densities and chain lengths of grafted poly(N-isopropylacrylamide) (PNIPAAm) on their surfaces. The PSt nanoparticles were synthesized by free radical copolymerization of styrene monomer with PNIPAAm macromonomers in mixed ethanol/water solvents. The grafted PNIPAAm densities on the PSt nanoparticle surfaces can be controlled by varying polymerization conditions such as reaction temperature and initiator concentrations. The nanoparticle sizes and densities of grafted PNIPAAm on their surfaces significantly affected temperature-response, which was investigated by dynamic laser light scattering. The larger PSt nanoparticle sizes and higher grafted PNIPAAm densities showed a more significant decrease in hydrodynamic diameters when temperature of dispersed solutions was raised above lower critical solution temperature of the linear PNIPAAm. The molecular weight of grafted PNIPAAm on nanoparticle surfaces had no relationship with a visible decrease in hydrodynamic diameter.KEY WORDS Poly(N-isopropylacrylamide) / Macromonomer / Polystyrene Nanoparticle / Thermosensitivity / Dispersion Copolymerization / There has been a geometric increase in the number of publications involving water-soluble poly(Nisopropylacrylamide) (PNIPAAm), because it exhibits a remarkable phase transition in the aqueous solution when temperature is raised above the lower critical solution temperature (LCST). 1-5 For these ingenious applications, the phase transition behavior of PNIPAAm has been also described in the metal colloids 6 and protein conjugation systems. 7 Copolymers containing PNIPAAm with hydrophilic-hydrophobic segments can exhibit the similar phase transition properties in a large range of temperature. 8 The copolymers with acrylic acid units show a pH sensitive property as well as a thermosensitive one. 9 PNIPAAm-based gels also exhibit thermo-reversible swelling properties. 10 They have been exploited to control enzymatic reactions 11 and drug delivery of biomolecules such as proteins of human gamma globulin. 12 On the other hand, when PNIPAAm was grafted on the external surfaces of substrates such as polymeric films and silicons, it acts as a reversible thermovalve for the separation column. 13 The water absorption and electrostatic charge of surfaces can be controlled for a temperature stimulation. 14 Based on the thermosensitivity of PNIPAAm, it may be used as other material fields in order to develop other functionalities.Polymeric particles that have an extremely large surface area are useful because of their potential application, not only in the technological, but also biomedical fields. In order to expand functions of particle surfaces, Okano et al. prepared thermo-responsive polymer nanoparticles with a core-shell micell structure, in which PNIPAAm chains show the coil-to-globule transition at their surface. 15 Makino et al. reported the particle synthesis with the crosslinked PNIPAAm layer by seed polymer...

Controlled post‐synthesis grafting of thermoresponsive poly(N‐isopropylacrylamide) on mesoporous silica nanoparticles

“…The H D of the polymer‐grafted nanoparticles is reduced to 142 nm upon heating the sample and overcoming the LCST of the polymer. These results confirm the typical thermoresponsive behavior of PNIPAM on the particles as reported for the homopolymer and also for PNIPAM grafted on various nanoparticles …”

Preparation and Characterization of Thermoresponsive Poly(N-isopropylacrylamide-co-acrylic acid)-Grafted Hollow Fe3O4/SiO2 Microspheres with Surface Holes for BSA Release

“…Hence, the HD of the particles decreases at this temperature. These results confirm the thermoresponsive behavior of the grafted polymer and also prove the good dispersibility of nanoparticles [37,38]. The zeta potential value for the p-Fe 3 O 4 /SiO 2 at pH 6.8 was −21.4 mV, which upon polymer grafting was −16.8 mV.…”

To aggregate, or not to aggregate? considerations in the design and application of polymeric thermally-responsive nanoparticles

“…To the best of our knowledge the collapse transition temperature as a function of grafting density has not yet been studied in detail, although some observations have been made (vide infra). 54 This interplay between grafting density, curvature and elongation of the polymer chains is complicated when considering particles, particularly in terms of the macroscopic consequences of the polymers passing through their transitions. As discussed above for polymer brushes, a transition (in terms of partial collapse of the polymer chains) can occur without significant changes in the contact angle, implying there is still hydration-solvation.…”