Random copolymers of N-isopropylacrylamide (NIPA) and 4-vinylphenylboronic acid (VPBA) were obtained by solution polymerization using 2,2′-azobisizobutyronitrile as the initiator in ethanol at 65 °C. NIPA-co-VPBA copolymer exhibited both temperature- and pH-sensitivity. Thermally reversible phase transitions were observed both in the acidic and alkaline pH region for the copolymers produced with different VPBA/NIPA feed ratios. The pH dependency of the lower critical solution temperature (LCST) was stronger for the copolymers produced with higher VPBA feed concentrations. RNA was selected as a model biomolecule having vicinal-diol and amino groups that were potentially reactive with the boronic acid groups of NIPA-co-VPBA copolymer. The effect of RNA concentration on the LCST of NIPA-co-VPBA copolymer was investigated in aqueous media at different pHs. Although no significant effect was observed at pH 4, 7 or 10.5, the LCST decreased linearly with increasing RNA concentration at a pH approximately equal to the pKa of boronic acid. This behavior was explained by considering the binding of RNA onto the copolymer chains to occur via two types of complex formation. For the formation of these complexes, the amino and vicinal-diol groups of RNA should react with the boronic acid groups of the copolymer in the tetrahedral anionic form. The results indicated that NIPA-co-VPBA copolymer could be utilized as a new reagent for the determination of RNA concentration in aqueous media. The proposed method was valid for the RNA concentration range of 0–4 g · mL−1.
The schematical representation of the possible interactions between NIPA-co-VPBA copolymer and RNA. (A) A typical structure of single-stranded RNA. (B) Tetrahedral anionic form of boronic acid groups. (C) The interaction between the amino groups of the unpaired bases of RNA and the boronic acid groups of the copolymer. (D) Cyclic borate ester formation by the interaction between vicinal diol groups located at the 3′-end of RNA and boronic acid groups of the copolymer. 相似文献
A side-by-side diffusion cell was used to study the permeability of glucose through a temperature- and pH-sensitive poly(N-isopropylacrylamide-co-methacrylic acid) hydrogel membrane. At fixed temperature (37°C), lowering pH in one side of the cell induced hydrogel volume collapse and strongly attenuated glucose permeation across the membrane. Hysteresis was observed in the glucose permeability versus pH characteristic. 相似文献
Polyamides were synthesized by the direct polycondensation of aromatic diamines containing 4,5-imidazolediyl structure with aliphatic dicarboxylic acids, and the metal adhesive properties of these polymaides were studied. The inherent viscosity of the obtained polyamides was in the range of 0.28 to 0.71 dl g?1. The decomposition temperatures (Tds) of the obtained polyamides were above 400°C and their glass transition temperatures (Tgs) were from 168 to 198°C. These polyamides also showed good solubilities in polar solvents, such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc) and formic acid. A standard tensile test was performed in order to examine the adhesive property of these polyamides for stainless steel, and the obtained polyamides showed excellent tensile strengths, e.g. polyamide P1s derived from 4,5-di(4-aminophenyl)imidazole (DAPI) and sebasic acid had values of 212 kgf cm?2 at 20°C, 183 kgf cm?2 at 120°C, and 133 kgf cm?2 at 180°C. A commercially available epoxy resin was also examined, and showed great tensile strength at 20°C. However, the strength of the epoxy resin was found to decrease with increasing temperature, whereas polyamide having 4,5-imidazolediyl structure retains its strength at temperatures of up to 180°C. In addition, the polyamide was also derived from 4,4″-diamino-o-terphenyl(DAOT) (rather than DAPI) and sebasic acid, and the properties of the polyamides derived, respectively from DAPI and DAOT were compared. 相似文献
A poly(acrylamide) was synthesized from Nα -Boc-N? -acrolyl-l-lysylglycine methyl ester via radical polymerization. This polymer typically had Mn ~ 100,000 g/mol, Mw ~ 300,000 g/mol, and a Tg of 93°C. Removal of Boc with TFA and cyclization with DABCO? in DMSO at 65°C afforded a soluble piperazinedione-containing polymer that had a Tg of 157°C and thermal stability up to 300°C. These results demonstrate a viable and efficient synthetic route to piperazinedione-containing polyacrylamides of high molecular weight. Related polymers that incorporate substituted indane moieties could be useful high Tg materials for fabrication of LC and NLO devices. 相似文献
Poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends were prepared using melt processing. The effects of maleic anhydride grafted PLA (PLA-g-MA) and calcium carbonate (CaCO3) content on mechanical, thermal, and morphological properties of the blends were investigated. PLA-g-MA was synthesized by varying monomer and initiator contents using a reactive melt-grafting process. Tensile properties of PLA/PBAT blend were enhanced with adding 2 phr of PLA-g-MA. SEM micrographs exhibited the improvement of interfacial adhesion between PLA and PBAT in the compatibilized blend. Moreover, thermal stability of the blends improved with presence of PLA-g-MA. With increasing CaCO3 content, Young’s modulus of the composites increased. 相似文献
The construction and performance characteristics of a new potentiometric PVC membrane sensor for the determination of sodium dodecyl sulfate (SDS) are described. The sensor was based on the use of an N-cetyl-N,N,N trimethyl ammonium (CTA) dodecyl sulfate (DS) ion pair as ion exchange sites in PVC matrix in the presence of o-nitrophenyl octylether as plasticiser. The sensor exhibited a fast, stable, and near-Nernstian response for SDS over the concentration range of 1 × 10?3 to 10?6 M at 25°C and the pH range 4–8.5 with anionic slope of 52.5 ± 0.5 mV decade?1. The lower detection limit was 3 × 10?6 M, and the response time was 25 s. Selectivity coefficients of SDS with respect to a number of different species were investigated. There were negligible interferences caused by most of the investigated anions. The determination of 1.0–280.0 µg mL?1 of SDS in aqueous solutions showed an average recovery of 99.1%, and the mean relative standard deviation was 1.4 at 100 µg mL?1. The results obtained in the determination of SDS in liquid soap, water and in some pharmaceutical preparations compared favourably with those obtained by the Methylene Blue active substance method (MBAS). In the present investigation, the DS sensor has been used as an end-point indicator electrode for some precipitation titration reactions, e.g. titration of SDS with CTMABr and cetylpyridinium chloride with SDS. 相似文献
Summary: We are investigating an autonomous glucose-driven hydrogel/enzyme-based device prototype for rhythmic, pulsed delivery of gonadotropin releasing hormone (GnRH). The device employs a pH-sensitive hydrogel membrane in conjunction with the enzyme glucose oxidase. This system delivers GnRH in rhythmic pulses when exposed to a constant level of glucose. These pulses result from autonomous pH oscillations inside the device that are created by an unstable nonlinear feedback between hydrogel permeability to glucose and production of acid by glucose oxidase. Previous versions of this prototype utilized p(N-isopropylacrylamide-co-methylacrylic acid) p(NIPA-co-MAA) hydrogels, with 10 mol% MAA incorporated. With this membrane, which undergoes a volume transition (VT) near pH 5, pH oscillations centered around pH 5 are observed. This range is too low to sustain oscillations in physiologically buffered media. To shift the operating pH of oscillations closer to physiologic pH, we have sought ways to increase the pH of the volume transition. In this study we show that increasing the side chain length of the α-alkylacrylic acid (RAA) comonomer enhances the overall hydrophobicity of the copolymer, and shifts the VT pH closer to physiological pH values. We also demonstrate the ability of such membranes to affect an alkaline shift in the range of oscillations in the prototype oscillator device. 相似文献
Poly[lithium-N(4-sulfophenyl) maleimide -co- methoxy oligo-(oxyethylene) methacrylates] [P(LiSMOEn)s] with three different oligoether side chains and different salt concentrations were synthesized. The copolyelectrolytes are essentially random in structure, with blocks of methoxy oligo(oxyethylene) meth-acrylate (MOEnM) recurring sporadically in between the salt units of N(4-sulfophenyl) maleimide. They all show two glass transitions in the temperature range of ?100 to 100°C. The first one below ?30°C is assigned to the oligo(oxyethylene) side chain (Tg1), while the second one located between 20 and 50°C is attributed to the main chain of the polymer host (Tg2). The maximum ionic conductivity of the copolymer electrolytes, 1.6 × 10?7 S cm?1 at 25°C, occurs at lithium salt concentration [Li+]/[EO] = 2.2 mol%. The ionic conductive behavior of the copolyelectrolytes follows the Vogel-Tammann-Fulcher (VTF) equation. Moreover, a special VTF behavior exists in the copolymers with shorter oligoether side chain and higher salt concentration. Sweep voltammetric results indicate that these copolyelectrolytes have a good electrochemical stability window. 相似文献