Fluorescence Study on the Swelling Behavior of Comb-Type Grafted Poly(N-isopropylacrylamide) Hydrogels

Abstract

The shrinking mechanism of comb-type grafted poly(N-isopropylacrylamide) gel due to temperature jump across its volume transition temperature has been investigated. Grafted chains or gel networks were labeled by a dansyl probe, and the temporal change in microenvironment of the dansyllabeled gel was investigated by means of fluorescence spectroscopy. The comb-type grafted poly(Nisopropylacrylamide) gel exhibited a rapid shrinking compared to normal-type NIPA gel, and the change in its microenvironment was found to become hydrophobic more than 10 times faster than normal-type poly(N-isopropylacrylamide) gel by observation of temporal change in the maximum emission wavelength, λ em, of the dansyl group. The freely mobile characteristics of grafted chains are expected to show the rapid dehydration to make tightly packed globules with temperature, followed by the subsequent hydrophobic intermolecular aggregation of dehydrated graft chains. The dehydrated grafted chains created the hydrophobic cores, which enhance the hydrophobic aggregation of the networks.

Monodisperse Thermoresponsive Microgels with Tunable Volume‐Phase Transition Kinetics

“…Another well-known method is to chemically graft linear side chains of the same stimuli-sensitive polymer onto the cross-linked polymer network. [31][32][33][34][35] The linear side chains, with one free end each, respond to stimulus faster than the cross-linked network, and this leads to a shorter response time for the entire hydrogel as compared with a hydrogel with ungrafted polymer networks. However, the process of chemically grafting linear side chains onto a polymer network is complicated, which limits the widespread use of this technique.…”

Molecular‐Recognition‐Induced Phase Transitions of Two Thermo‐Responsive Polymers with Pendent β‐Cyclodextrin Groups

“…These materials are supposed to be able to respond to environmental changes such as temperature, [1][2][3][4][5][6][7] pH, [8][9][10] light, [11] electric field, [12] magnetic field, [13,14] and chemical or biological species [15][16][17][18][19] at the most optimum conditions and manifest their own functions according to the changes.…”

Synthesis and properties of pH and temperature sensitive P(NIPAAm-co-DMAEMA) hydrogels

“…As the representative one, poly(N-isopropylacrylamide) (PNIPAAm) is a well known temperature sensitive polymer, which exhibits phase separation at a lower critical solution temperature (LCST) of ∼32 • C in aqueous solution [9,10]. Below this temperature, PNIPAAm is hydrophilic and exists in individual chain with a coil conformation; while above the LCST, it undergoes a sharp coil-to-globule transition to form inter-and intrachain association, resulting in hydrophobic aggregation and depositing from the aqueous solution [11][12][13][14]. Up to now, because of this reversible phase transition, PNIPAAm has been widely used to prepare temperature sensitive hydrogels [15][16][17][18].…”