Poly(acrylic acid)-grafted Poly(N-isopropyl acrylamide) Networks: Preparation, Characterization and Hydrogel Behavior

Abstract

Poly(acrylic acid)-grafted poly(N-isopropylacrylamide) co-polymer networks (PNIPAAm-g-PAA) were prepared via the reversible addition-fragmentation transfer (RAFT) polymerization of N-isopropyl- acrylamide (NIPAAm) with trithiocarbonate-terminated PAA as a macromolecular chain-transfer agent in the presence of N,N-methylenebisacrylamide. The PNIPAAm-g-PAA co-polymer networks were characterized by means of Fourier transform infrared spectroscopy, differential scanning calorimetry and small-angle X-ray scattering. It is found that the PNIPAAm-g-PAA co-polymer networks were microphase-separated, in which the microdomains of PNIPAAm-PAA interpolymer complexes were dispersed into the PNIPAAm matrix. The PNIPAAm-g-PAA hydrogels displayed a dual response to temperature and pH values. The thermoresponsive properties of PNIPAAm-g-PAA networks were investigated. Below the volume phase transition temperatures, the PNIPAAm-g-PAA hydrogels possessed much higher swelling ratios than control PNIPAAm hydrogel. In terms of swelling, deswelling and reswelling tests, it is judged that the PNIPAAm-g-PAA hydrogels displayed faster response to the external temperature changes than control PNIPAAm hydrogel. The improved thermoresponsive properties of hydrogels are ascribed to the formation of PAA-grafted PNIPAAm networks, in which the water-soluble PAA chains behave as the hydrophiphilic tunnels and allow water molecules to go through and, thus, to accelerate the diffusion of water molecules.

Injectable hydrogels for cartilage and bone tissue engineering

“…To date, the most common explanation of the phase transition mechanism of temperature-sensitive injectable hydrogels is that when the temperature changes, there is a change in the hydration state favoring intra- and inter-molecular hydrogen bonding, thus eventually changing the hydrogel solubility. 196,197 Therefore, to make injectable hydrogels that are sensitive to temperatures, temperature-sensitive polymers such as poly(lactic- co -glycolic acid)–PEG, 194 poly( N , N -diethylacrylamide), 195 PNIPAAm, 197 and poly(ethylene glycol-b-[ DL -lactic acid- co -glycolic acid]-b-ethylene glycol) 198 are needed.…”

Stimuli-Responsive Hydrogels: An Interdisciplinary Overview

“…Surface modification of cotton fabric with pH and temperature dual-responsive hydrogels of chitosan and pNIPAAm improved air and moisture management activities of functionalized textiles [83]. Dual-responsive hydrogels made of pNIPAAm as thermoresponsive polymer and PAA as pH-responsive polymer found drug delivery applications [77,140]. The hydrogel system made from copolymer of NIPAAm and itaconic acid [NIPAAmco-itaconic acid] showed dual responsiveness to external stimuli temperature and pH and was proposed as effective drug delivery system [141].…”

“…Biomedical application of dualresponsive hydrogel References pNIPAAm (temperature), glycidyl methacrylated chitosan (pH) Drug delivery application [135] pNIPAAm (temperature), chitosan (pH) Drug delivery application [136] pNIPAAm (temperature), chitosan (pH) Textile application (water and moisture management) [138,139] pNIPAAm (temperature), PAA (pH) Drug delivery application [77,140] pNIPAAm (temperature), PDMAEMA (pH) Drug delivery application [142,143] p(NIPAAm-co-hydroxyethyl methacrylate) (temperature), poly(L-glutamic acid) (pH)…”

Comb-Type Grafted Hydrogels of PNIPAM and PDMAEMA with Reversed Network-Graft Architectures from Controlled Radical Polymerizations

“…For the practical applications of stimuli-responsive hydrogels, the high response rate is usually expected to be as fast as possible. To meet this target, several strategies have been proposed: (1) the utility of micro-hydrogels since their response rate is inversely proportional to the dimensional size of hydrogels [18,19]; (2) bulky hydrogels with micro/nano-porosity [20,21]; (3) bulky hydrogels with phase-separated structure [22,23]; (4) adjusting hydrophilic/hydrophobic balance of bulky hydrogels [24,25]. Besides, the most important factors to dominate the performance of responsive hydrogels are their chain structural parameters, such as the cross-linkage density and network architecture.…”

“…Through RAFT polymerization, Zheng et al obtained the hydrogels of the PNIAPM network grafted with PAA by using trithiocarbonate-terminated PAA as a macromolecular chain-transfer agent. [22] In the above cases, the cross-linkage density can be controlled by the amount of small molecular cross-linker, such as N , N -methylenebisacrylamide. In our previous report, we developed a macro-cross-linker of PNIPAM with two azido groups at one chain and performed an azido-alkynyl click reaction with alkynyl-pending PDMAEMA to prepare network-graft hydrogels [45].…”