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Thermoresponsive Polymers (thermoresponsive + polymer)
Selected AbstractsSalt-Induced Depression of Lower Critical Solution Temperature in a Surface-Grafted Neutral Thermoresponsive PolymerMACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2006Young K. Jhon Abstract Summary: Quartz crystal microbalance with dissipation monitoring (QCM-D) is employed to determine the effect of salt on the volume phase transition of thermoresponsive polymer brushes. Changes in mass and viscoelasticity of poly(N -isopropylacrylamide) (PNIPAM) layers grafted from a QCM-D crystal are measured as a function of temperature, upon contact with aqueous solutions of varying salt concentrations. The phase-transition temperature of PNIPAM brushes, TC,graft, quantified from the QCM-D measurements is found to decrease as the concentration of salt is increased. This phenomenon is explained by the tendency of salt ions to affect the structure of water molecules (Hofmeister effect). However, in contrast to the linear decrease in phase-transition temperature upon increasing salt concentration observed for free PNIPAM, the trend in TC,graft for PNIPAM brushes is distinctively non-linear. Schematic representation of the effect of salt concentration on the phase transition behavior of thermoresponsive polymer brushes. [source] Microfluidic Valves Comprising Nanolayered Thermoresponsive Polymer-Grafted Capillaries,ADVANCED MATERIALS, Issue 22 2005N. Idota Thermally regulated flow control using a thermoresponsive polymer grafted onto surfaces of capillary lumen facilitates rapid, reliable, and repeatable open,close cycles (see Figure). Hydration of the grafted polymer chains on the internal surfaces may increase the microviscosity of the hydration layers at the wall interfaces without physically occluding the lumen, producing complete and reversible on/off flow valving in microchannels under hydrostatic pressures relevant for microfluidics approaches. [source] Synthesis and characterization of thermoresponsive polymers containing reduction-sensitive disulfide linkageJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2009Lihua Li Abstract A novel class of thermoresponsive and reduction-sensitive polymer, p(PEG-MEMA- co -Boc-Cyst-MMAm), containing disulfide linkages and removable hydrophobic tert -butyloxycarbonyl side chains was synthesized. The cloud points (CP) of p(PEG-MEMA- co -Boc-Cyst-MMAm) in water determined by UV/VIS spectrometer were between 20 °C and 57 °C, which shows that the CP can be tuned by adjusting the copolymer composition. Moreover, the thermosensitive polymers p(PEG-MEMA- co -Boc-Cyst-MMAm) formed stable nanoparticles in neutral aqueous medium, but rapidly destabilized in an reductive environment mimicking the intracellular space making them suitable for cytoplasmic drug delivery. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5989,5997, 2009 [source] Preparation of novel acrylamide-based thermoresponsive polymer analogues and their application as thermoresponsive chromatographic matricesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2008Yoshikatsu Akiyama Abstract New thermoresponsive polymers based on poly(N -(N, -alkylcarbamido)propyl methacrylamide) analogues were designed with increased hydrophobic content to facilitate temperature-dependent chromatographic separations of peptides and proteins from aqueous mobile phases. These polymer solution exhibited a lower critical solution temperature (LCST) when the alkyl group is methyl, ethyl, isopropyl, propyl, butyl, and isobutyl. However, larger alkyl groups such as hexyl and phenyl were not soluble in aqueous solutions at any temperature. Phase transition temperatures were lower for larger alkyl groups and increased with decreasing polymer molecular weight and concentration in solution. LCST dependence on polymer molecular weight and concentration is more significant compared with well-studied poly(N -isopropylacrylamide) (PIPAAm). Partition coefficient (log P) values for N -(N, -butylcarbamide)propylmethacrylamide and N -(N, -isobutylcarbamide)propyl methacrylamide (iBuCPMA) monomers are larger than that for IPAAm monomer, suggesting higher hydrophobicity than IPAAm. Chromatographic evaluation of poly(N -(N, -isobutylcarbamide)propyl methacrylamide) (PiBuCPMA) grafted silica particles in aqueous separations revealed larger k, values for peptides, insulin, insulin chain B, and angiotensin I than PIPAAm-grafted silica beads. In particular, k, values for insulin obtained from PiBuCPMA-grafted silica separations were much larger than those from PIPAAm-grafted surface separations, indicating that PiBuCPMA should be more hydrophobic than PIPAAm. These results support the introduction of alkylcarbamido groups to efficiently increase thermoresponsive polymer hydrophobicity of poly(N -alkylacrylamides) and poly(N -alkylmethacrylamides). Consequently, poly(N -(N, -alkylcarbamido)propyl methacrylamide) analogues such as PiBuCPMA and poly(N -(N, -alkylcarbamido)alkylmehacrylamide) are new thermoresponsive polymers with appropriate hydrophobic partitioning properties for protein and peptide separations in aqueous media, depending on selection of their alkyl groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5471,5482, 2008 [source] Acid-labile, thermoresponsive (meth)acrylamide polymers with pendant cyclic acetal moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2008Xiao-Nan Huang Abstract Acid-labile, thermoresponsive polymers with pendant six-membered cyclic acetal groups were prepared by radical polymerization of two monomers, N -(2,2-dimethyl-1,3-dioxan-5-yl) methacrylamide (NDMM) and N -(2,2-dimethyl-1,3-dioxan-5-yl) acrylamide (NDMA). The aqueous solution properties of the polymers, PNDMM and PNDMA, were studied by turbidimetry, 1H NMR, fluorescence, and DSC measurements. It is found that both polymers show sensitive and reversible phase transitions with distinct lower critical solution temperatures (LCST). Below their LCSTs, there are still some polymer aggregates as evidenced by measurements of pyrene excitation spectra and urea effects on the cloud points (CP) of polymers. The salting effect of six inorganic sodium salts on the phase transition behavior of PNDMM was investigated by turbidimetric approach. The salting-out to salting-in effect is in the order of SO42, > F, > Cl, > Br, > I, > SCN,, following the Hofmeister's series. pH-dependent hydrolysis of PNDMM and PNDMA was studied by turbidimetric and 1H NMR methods. They are both pH-sensitive and their hydrolysis rates significantly increase with decreasing pH value. The CP of PNDMM gradually increases with the acid-triggered hydrolysis of the acetal groups and the hydrolyzed polymer with , 30% hydrolysis degree does not show thermally induced phase transition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4332,4343, 2008 [source] Hybrid Polymerization of Vinyl and Hetero-Ring Groups of Glycidyl Methacrylate Resulting in Thermoresponsive Hyperbranched Polymers Displaying a Wide Range of Lower Critical Solution TemperaturesCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2009Zhifeng Jia Dr. Abstract Hybrid polymerization of glycidyl methacrylate (GMA) with potassium hydride (KH) and various oligo(ethylene glycol)s as the initiating system, in which both vinyl polymerization and ring-opening polymerization occur simultaneously, generates hyperbranched poly(ether-ester)s. The reaction process has been followed by an in situ nuclear magnetic resonance technique. The experimental results indicate that both the vinyl and epoxy groups of GMA undergo polymerization, with the reactivity of the latter being much higher than that of the former. Interestingly, the resulting hyperbranched polymers exhibit a sharp phase transition in water at the lower critical solution temperature (LCST). Significantly, the LCST values can be accurately controlled from 0 to 100,°C by changing the hydrophilic/hydrophobic balance of GMA and various oligo(ethylene glycol)s or by modification of the precursor polymer through acetylation. This novel stimuli-responsive hyperbranched polymer is a promising candidate for a new generation of commercially viable thermoresponsive polymers following on from the widely used poly(N- isopropylacrylamide) (PNIPAM). [source] | ||||||||||