Physicochemical Properties of Poly(N-isopropylacrylamide-co-4-vinylpyridine) Cationic Polyelectrolyte Colloidal Microgels

Abstract

Aqueous colloidal poly (N-isopropylacrylamide-co-4-vinylpyridine) [poly(NIPAM-co-4-VP)] copolymer microgels have been synthesized using different percentages of 4-vinylpyridine (4-VP). A surfactant-free emulsion polymerization reaction using N-isopropylacrylamide (NIPAM) and 4-vinylpyridine comonomers cross-linked with N,N′-methylenebisacrylamide was utilized. The reaction was initiated using the cationic initiator 2,2′-azobis(2-amidinopropane) dihydrochloride. Transmission electron micrograph data show the copolymer microgels to be monodisperse spheres. The pH and electrolyte sensitivity of the copolymer microgels have been studied, as well as temperature sensitivity, since microgels undergo a reversible volume phase transition in response to heating and cooling. Changes in the hydrodynamic diameters in the system were monitored as a function of temperature (25-60°C), pH (3-8), and ionic strength (10 -3 -10 -1 mol dm -3 NaCl or NaClO4) using photon correlation spectroscopy. The hydrodynamic diameter of poly-(NIPAM-co-4-VP) microgels increases with decreasing pH, as the vinylpyridine units become more protonated. However, the hydrodynamic diameter decreases with increasing ionic strength (over the pH range 3-8) and with increasing temperature (at pH 3 and pH 6). UV-visible spectrophotometry measurements showed a good correlation between the molar absorption and the percentage of vinylpyridine incorporated. Potentiometric titrations were used to determine the pKa values of the copolymer microgels.

Preparation and Characterization of pH‐Sensitive Microgels of Poly((2‐dimethylamino) ethyl methacrylate)

“…These samples were dried in a vacuum oven at room temperature and then used to calculate the monomer conversion by a gravimetric method. 1 HNMR spectra of unpurified microgel dispersions were recorded on a JEOL JNM-EX90A spectrometer. A small amount of the unpurified latex was cast onto a Petri dish and dried in vacuum oven at room temperature.…”

“…[1] Depending on its degree of crosslinking, and on the nature of the solvent, the microgel will be more or less swollen. If an environmentally-sensitive polymer is used in the preparation of the microgel particles, they can be expected to have similar responsive properties to that of their linear counterpart.…”

“…If an environmentally-sensitive polymer is used in the preparation of the microgel particles, they can be expected to have similar responsive properties to that of their linear counterpart. In recent years, increasing attention has been paid to the synthesis and applications of stimulus-responsive microgels [1][2][3][4][5][6] among which, pH-and/or temperature-sensitive microgels are probably the most extensively studied classes. Essentially every property (e.g.…”

“…Recently, cationic microgels have received considerable attention primarily because of their potential for biomedical applications. [1,4,7] Poly((2-dimethylamino) ethyl methacrylate) (PDMAEMA) is a cationic polyelectrolyte which has been shown to be sensitive to both pH and temperature [12][13][14] and has been used in various biomedical applications such as gene delivery [15] and glucosesensitive controlled release systems. [16] To the best of our knowledge, there hasn't been any report on the preparation and pHsensitive characteristics of PDMAEMA microgels.…”

Core-Shell Microgels as Nanoreactors

“…Thus, acidic or basic comonomers, such as acrylic acid (AA) [23], vinylimidazole [24], or 4-vinylpyridine [25] have been often chosen for the formation of microgels with pH sensitivity. By incorporating charges into the microgel particles, electrostatic interactions will influence the volume phase transition and the immobilization of proteins and enzymes.…”