Poly[(N-isopropylacrylamide-co-acrylamide-co-(hydroxyethylmethacrylate))] thermoresponsive microspheres: An accurate method based on solute exclusion technique to determine the volume phase transition temperature

Poly[(N-isopropylacrylamide-co-acrylamide-co-(hydroxyethylmethacrylate))] [poly(NIPAAm-co-AAm-co-HEMA)] copolymer was synthesized as a new thermoresponsive material possessing a lower critical solution temperature (LCST) around 37 °C in phosphate buffer, pH 7.4, at a solution concentration of 1%, w/v. The influence of polymer concentration on LCST was determined by cloud point measurements and by microcalorimetric analysis. The copolymer was transformed in hydrogel microspheres by suspension reticulation of OH groups with glutaraldehyde. The volume phase transition temperature (VPTT) of microspheres was determined by a new approach, which involves measurement of the increase in concentration of a blue dextran (BD) solution at different temperatures in the presence of dry microspheres. The minimum BD concentration that gives reliable and reproducible results was determined to be 1 mg/ml. However, the higher is the concentration of BD in solution the smaller is the error. Contrary to solution of the linear polymer which displays a sharp phase transition temperature, the dependence of water regain of the hydrogel with temperature lasts from 4 °C to 50 °C.     

Environmentally sensitive hydrogel functionalized with electroactive and complexing‐iron(III) catechol groups

Thermoresponsive pNIPA (poly (N‐isopropylacrylamide)) gels modified with dopamine methacrylamide were synthesized using free‐radical polymerization. In this way, the catechol groups were introduced into the polymer network. The presence of dopamine in the gel led to a significant shift in the volume phase transition temperature (VPTT). It was found that hydrogels were electroactive and that oxidation of catechol groups also led to a strong shift in the VPTT. The temperature window, that is, the range of temperature where volume of the gel could be substantially changed by oxidation of the catechol groups, for the gel formed from the polymerization solution containing 5% of the dopamine derivative, was 30–40 °C. Additionally, the influence of Fe³⁺ ions, which form the most stable complexes with dopamine, on swelling behavior of the gels was investigated at various pH. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3236–3242     

Synthesis and characteristics of poly(N‐isopropylacrylamide‐co‐methacrylic acid)/Fe3O4/poly(N‐isopropylacrylamide‐co‐methacrylic acid) two‐shell thermosensitive magnetic composite hollow latex particles

In this study, the poly(N‐isopropylacrylamide‐methylacrylate acid)/Fe₃O₄/poly(N‐isopropylacrylamide‐methylacrylate acid) (poly(NIPAAm‐MAA)/Fe₃O₄/poly(NIPAAm‐MAA)) two‐shell magnetic composite hollow latex particles were synthesized by four steps. The poly(methyl methacrylate‐co‐methylacrylate acid) (poly(MMA‐MAA)) copolymer latex particles were synthesized first. Then, the second step was to polymerize NIPAAm, MAA, and crosslinking agent in the presence of poly(MMA‐MAA) latex particles to form the linear poly(MMA‐MAA)/crosslinking poly(NIPAAm‐MAA) core–shell latex particles. Then, the core–shell latex particles were heated in the presence of NH₄OH to dissolve the linear poly(MMA‐MAA) core to form the poly(NIPAAm‐MAA) hollow latex particles. In the third step, the Fe₃O₄ nanoparticles were generated in the presence of poly(NIPAAm‐MAA) hollow polymer latex particles and formed the poly(NIPAAm‐MAA)/Fe₃O₄ magnetic composite hollow latex particles. The fourth step was to synthesize poly(NIPAAm‐MAA) in the presence of poly(NIPAAm‐MAA)/Fe₃O₄ latex particles to form the poly(NIPAAm‐MAA)/Fe₃O₄/poly(NIPAAm‐MAA) two‐shell magnetic composite hollow latex particles. The effect of various variables such as reactant concentration, monomer ratio, and pH value on the morphology and volume‐phase transition temperature of two‐shell magnetic composite hollow latex particles was studied. Moreover, the latex particles were used as carriers to load with caffeine, and the caffeine‐loading characteristics and caffeine release rate of latex particles were also studied. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2880–2891