Papers by Keyword: Lower Critical Solution Temperature (LCST)

Abstract: Poly (N-isopropylacrylamide) (PNIPAAm) is one of the most well-known thermoresponsive polymers that exhibits a reversible coil-to-globule transition in aqueous solution at lower critical solution temperature (LCST) (32°C). PNIPAAm behave as an extended coil form in an aqueous solution below the LCST, meanwhile, above the LCST, it shrinks into a globule form. The LCST of PNIPAAm could be tune when it is chemically modified with hydrophilic and/or hydrophobic compound. In this study, modifications of PNIPAAm end-group with maleimide or phenyl maleimide compounds were prepared and their LCST behaviours were investigated. One end-group of synthesized poly (N-isopropylacrylamide)-chain transfer agent (PNIPAAm-CTA) was modified with maleimide or phenyl maleimide compound through aminolysis reaction to form PNIPAAm-Maleimide (PNIPAAm-M) and PNIPAAm-Phenyl maleimide (PNIPAAm-PhM). Maleimide is a hydrophilic compound, and phenyl maleimide is a slight hydrophobic compound were used in this study. The modification with hydrophilic compound will higher the LCST of PNIPAAm. The slight hydrophobic of phenyl maleimide compound will decrease the LCST. In this study, the successfulness of aminolysis process of PNIPAAm-CTA were determined through the fourier transform infrared (FTIR). Moreover, the LCST behavior of PNIPAAm-CTA, PNIPAAm-M and PNIPAAm-PhM were determined through light scattering intensity analysis. The results indicated that upon heating the solutions of PNIPAAm-CTA, PNIPAAm-M and PNIPAAm-PhM in 10 mM HEPES solution pH 7.4 at 25°C–40°C, PNIPAAm-CTA, and PNIPAAm-PhM solutions started to increase their light intensities at 35°C and PNIPAAm-M at 36°C, respectively. To conclude, modification of PNIPAAm end-group with hydrophobic and/or hydrophilic compound could tune their LCST.

Abstract: Novel thermoresponsive dendronized monomer bearing azobenzene moiety, 4-(4′-(3, 4, 5-tris (2-(2-methoxyethoxy) ethoxy) benzyloxy) phenylazo) benzyl methacrylate, has been successfully synthesized. The chemical structures of intermediate compounds and dendronized monomer were confirmed by FTIR and ¹H NMR. The phase transition behaviors of these intermediate compounds and dendronized monomer were investigated. These intermediate compound and dendronized monomer showed remarkably reversible thermoresponsive phase transition behaviors.

Abstract: Poly(N-isopropylacrylamide)(PNIPAM) with terminal aromatic groups were synthesized by atom transfer radical polymerization (ATRP), using N-isopropylacrylamide as monomer and phenyl 2-chloropropionate, (4’-phenyl)phenyl 2-chloropropionate and (2’,6’-diphenyl)phenyl 2-chloropropionate as initators. Then novel functional complexes of poly(N-isopropylacrylamide) and Eu(III) (PNIPAM-Eu(III)) with thermosensitive and fluorescent properties were synthesized and characterized by X-ray photoelectron spectroscopy (XPS), and fluorescence spectroscopy. Eu(III) was bonded to nitrogen and oxygen atoms in the polymer chain of PNIPAM and formed the complexes of PNIPAM-Eu(III). The lower critical solution temperatures (LCSTs) of PNIPAM-Eu(III) were slightly greater compared with that of PNIPAM. Europium(III) complexes had excellent fluorescence performance, the fluorescence spectrum present characteristic emission of Europium(III) at 613 nm.

Abstract: The ATRP of N-isopropylacrylamide (NIPAM) was carried out in DMF/water at 60 °C to afford a novel linear end-functionalized poly(N-isopropylacrylamide) with acetylated β-CD (AcCD-PNIPAM) and the structures of the products were characterized. The number-average molecular weight (M_n) and the polydispersity index (PDI) of the polymer were obtained from gel permeation chromatography (GPC) analysis. The end-functionalized PNIPAM with β-CD (CD-PNIPAM) was obtained by deacetylation from AcCD-PNIPAM. The lower critical solution temperature (LCST) for the aqueous solutions of CD-PNIPAM, measured by means of ultraviolet-visible spectroscopy (UV-vis), was 4~5 °C higher than that of AcCD-PNIPAM. Ferrocene was included into CD-PNIPAM with mole ratio of 1:1 and the inclusion complex was characterized by cyclic voltammetry (CV) technology.

Abstract: Novel Y-shaped amphiphilic block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide), PEG-b-(PNIPAM)2, were successfully synthesized through atom transfer radical polymerization (ATRP). A difunctional macroinitiator was prepared by esterification of 2,2-dichloroacetyl chloride with poly(ethylene glycol) monomethyl ether (PEG). The copolymers were obtained via the ATRP of N-isopropylacrylamide (NIPAM) with CuCl/Me6TREN as catalyst and DMF/H2O (v/v = 3:1) mixture as solvent. The resulting polymers were characterized by gel permeation chromatography (GPC) and 1H NMR. These block copolymers show controllable molecular weights and narrow molecular weight distributions (PDI <1.15). Their phase transition temperatures and enthalpy changes in aqueous solution were measured by differential scanning calorimetry (DSC). The results indicate a significant influence of the macromolecular architecture on the phase transition. This is the first study into the effect of molecular architecture on the phase transition using Y-shaped amphiphilic block copolymer composed of PEG and PNIPAM.