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Thermoresponsive Behavior (thermoresponsive + behavior)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

N -Isopropylacrylamide/2-Hydroxyethyl Methacrylate Star Diblock Copolymers: Synthesis and Thermoresponsive Behavior

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2006
Zhiqiang Cao
Abstract Summary: Tri-arm star diblock copolymers, poly(2-hydroxyethyl methacrylate)- block -poly(N -isopropylacrylamide) [P(HEMA- b -NIPAAm)] with PHEMA and PNIPAAm as separate inner and outer blocks were synthesized via a two-step ATRP at room temperature. The formation, molecular weight and distribution of polymers were examined, and the kinetics of the reaction was monitored. The PDI of PHEMA was shown to be lower, indicating well-controlled polymerization of trifunctional macro-initiator and resultant star copolymers. The thermoresponsive behavior of diblock copolymer aqueous solution were studied by DSC, phase diagrams, temperature-variable 1H NMR, TEM and DLS. The results revealed that introducing a higher ratio of HEMA into copolymers could facilitate the formation of micelles and the occurrence of phase transition at lower temperatures. TEM images showed that I-(HEMA40 -NIPAAm320)3 solutions developed into core-shell micelles with diameters of approximately 100 nm. I-(HEMA40 -NIPAAm320)3 was used as a representative example to elucidate the mechanism underlying temperature-induced phase transition of copolymer solution. In this study we proposed a three-stage transition process: (1) separately dispersed micelles state at ,17,22,°C; (2) aggregation and fusion of micelles at ,22,29,°C; (3) sol-gel transition of PNIPAAm segments at ,29,35,°C, and serious syneresis of shell layers. Molecular architecture of Poly(HEMA- b -NIPAAm). [source]

Characterization of the physicochemical, antimicrobial, and drug release properties of thermoresponsive hydrogel copolymers designed for medical device applications

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2008
David S. Jones
Abstract In this study, a series of hydrogels was synthesized by free radical polymerization, namely poly(2-(hydroxyethyl)methacrylate) (pHEMA), poly(4-(hydroxybutyl)methacrylate) (pHBMA), poly(6-(hydroxyhexyl)methacrylate) (pHHMA), and copolymers composed of N -isopropylacrylamide (NIPAA), methacrylic acid (MA), NIPAA, and the above monomers. The surface, mechanical, and swelling properties (at 20 and 37°C, pH 6) of the polymers were determined using dynamic contact angle analysis, tensile analysis, and thermogravimetry, respectively. The Tg and lower critical solution temperatures (LCST) were determined using modulated DSC and oscillatory rheometry, respectively. Drug loading of the hydrogels with chlorhexidine diacetate was performed by immersion in a drug solution at 20°C (Thermoresponsive behavior was only observed with hydrogels composed of HEMA, NIPAA, MA, and NIPAA in which pulsatile drug release was obtained by elevating the temperature from below to above the LCST. A greater mass and enhanced pulsatile release of drug, with the associated greater antimicrobial properties (an 108 reduction in viability of Staphylococcus epidermidis in 15 min), was associated with poly(NIPAA- co -HEMA, 1:1). It is suggested that the pulsatile drug release and favorable antimicrobial and mechanical properties of candidate hydrogels, particularly poly(HEMA- co -NIPAA), offer promise as thermoresponsive, antimicrobial biomaterials that may be used as wound dressings, medical implants, or coatings of medical devices. Furthermore, it is suggested that drug loading may be effectively performed in situ by lowering the temperature of the device/dressing. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source]

Water-soluble, thermoresponsive, hyperbranched copolymers based on PEG-methacrylates: Synthesis, characterization, and LCST behavior

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2010
Mario Luzon
Abstract A series of water-soluble thermoresponsive hyperbranched copoly(oligoethylene glycol)s were synthesized by copolymerization of di(ethylene glycol) methacrylate (DEG-MA) and oligo(ethylene glycol) methacrylate (OEG-MA, Mw = 475 g/mol), with ethylene glycol dimethacrylate (EGD-MA) used as the crosslinker, via reversible addition fragmentation chain transfer polymerization. Polymers were characterized by size exclusion chromatography and nuclear magnetic resonance analyses. According to the monomer composition, that is, the ratio of OEG-MA: DEG-MA: EGD-MA, the lower critical solution temperature (LCST) could be tuned from 25 °C to 90 °C. The thermoresponsive properties of these hyperbranched copolymers were studied carefully and compared with their linear analogs. It was found that molecular architecture influences thermoresponsive behavior, with a decrease of around 5,10 °C in the LCST of the hyperbranched polymers compared with the LCST of linear chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2783,2792, 2010 [source]

Microwave and Ionic Liquids: Inverse Temperature Dependence of Viscosity in Aqueous Medium of Grafted Copolymers

MACROMOLECULAR REACTION ENGINEERING, Issue 9 2009
Ella Bezdushna
Abstract We elaborated a route to the thermosensitive polyelectrolyte system composed of 1-methyl-3-vinylimidazolium salt with , -cyclodextrin complexed counterions and mono-(meth)acrylic functionalized poly(N -isopropylacrylamide) as grafted side chains via a three-step synthetic procedure. The aqueous solution of the polyelectrolyte displays partially inverse thermoresponsive behavior; it exhibits enhancement of shear viscosity up to body temperature. Furthermore, based on classically prepared poly(NIPAAm) bearing terminal amino groups, corresponding (meth-) acrylamide-type of macromonomers were easily obtained under microwave conditions. [source]