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New stimuli-responsive cationic hydrogels based on N-acryloyl-N′-propyl piperazine (AcrNPP) were prepared using two types of chemical crosslinkers, viz., N,N-methylene bisacrylamide (Mba) and 1,4-butanediol diacrylate (Bda), respectively. The solubility parameter of the hydrogels was evaluated by equilibrium swelling experiment in a series of twelve solvents with well-distributed range of solubility parameters. The hydrogels exhibited maximum equilibrium swelling ratio in 1-butanol. The experimental swelling data were analyzed by two methods, (1) non-linear curve fitting and (2) least-square regression to determine the solubility parameter of the hydrogels. The solubility parameter determined by the two methods was in the range 11.45–11.85 (cal cm−3)1/2. The solubility parameter of the hydrogel containing the hydrophilic crosslinker (Mba) was higher than the hydrogel with a hydrophobic crosslinker (Bda), in all cases. This showed that the nature of chemical crosslinker influences the swelling and thus the solubility parameter of the hydrogels. The partial solubility parameter of the hydrogels related to the cohesive energy was evaluated by plotting the equilibrium swelling data against dispersion forces, polar forces, and hydrogen bonding. It was observed that both polar forces and hydrogen bonding play an important role in the swelling of these cationic hydrogels. The solubility parameter and the related forces were also estimated theoretically using group contribution methods and compared with the experimental results.

New polyampholyte linear polymers and hydrogels based on N -acryloyl- N ′-ethyl piperazine (AcrNEP) and maleic acid (MaA) were prepared by free-radical solution polymerization. The microstructure of copolymers was statistically estimated by the terminal copolymerization model. A maximum tendency (80%) of alternating sequence of monomers units occurred at about 85 mol % of AcrNEP in the reaction feed. The copolymers at definite monomer compositions (40 mol % of AcrNEP and 59.6 mol % of MaA) exhibited lower critical solution temperature (LCST) behavior in water. The LCST was dependent on monomer composition, pH of external solution, type and concentration of simple salts. The isoelectric points (IEP) of copolymers were found to be influenced by the overall composition of ionic monomer units. The influence of high maleic acid content (14 mol % and 59 mol %) and the type of chemical crosslinker on pH-responsive swelling behavior, water diffusion and dye sorption properties of the hydrogels were studied in detail. The gels exhibited interesting swelling behavior as function of pH (ionic strength = 0.01 M) due to a combination of factors such as pK a of the monomers, charge density, and type of crosslinker. The IEP of the gels were also determined from swelling experiments. The swelling ratio of the gels increased at the IEP with increase in ionic strength of the solution due to anti-polyelectrolyte effect. However below the IEP, the swelling ratio decreased considerably. Dynamic swelling properties of the amphoteric gels in water without added salt were measured. The swelling behavior was found to depend on the ionization state of the monomers, and the swelling followed non-Fickian (anomalous) mechanism. The swelling process of the hydrogels in water followed second-order kinetics. The amount of bound and unbound water in swollen gels was quantified using differential scanning calorimetry. Dye adsorption capacity of the new hydrogels was investigated using a Congo red as a model dye and was in the range 8.37–11.45 mg g −1 . This corresponds to an absorption efficiency of range 68–93%.

Stimuli-responsive cationic hydrogels based on N-acryloyl-N′-propyl piperazine (AcrNPP) crosslinked with N,N′-methylenebisacrylamide (Mba) and 1,4-butanedioldiacrylate (Bda) were prepared by UV light-initiated free-radical polymerization in bulk. The effect of external stimuli and type of crosslinker on the equilibrium swelling behavior and dynamic swelling was investigated in detail in buffer solution of various pH and temperatures. The equilibrium swelling capacity of the gels was large in swelling medium at pH 3.0 than at pH 10.0 due to ionization of polymer network under acidic conditions. With increase in temperature from 25 °C to 45 °C, the gels exhibited negative temperature-responsive (thermo-shrinking/thermophobic) behavior with negative activation energy for diffusion of water. The thermodynamic parameters such as Gibbs' free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) for the swelling of gels as function of temperature were negative indicating an exothermic swelling process. Water (media) transport mechanism and diffusion process in thin rectangular gels was studied. At pH 3.0, the diffusion process was non-Fickian (anomalous) while at pH 10.0 it was quasi-Fickian. The transport mechanism was partly influenced by the type of crosslinker in the gel. The dynamic swelling data was analyzed using early-time, late-time and Etters diffusion models. From the equilibrium swelling studies the average molecular weight between crosslinks (Mc), the crosslink density (ρc), and the mesh size (ξ) were determined. The Mc was large at pH 3.0 due to ionization of polymer and chain expansion. The experimental Mc was much larger than the theoretical Mc which implied that the gels were loosely crosslinked real networks. The mesh size of gels were between 447 and 786 A in the swollen (ionized) state (pH 3.0), and between 100 and 231 A in the collapsed (non-ionized) state (pH 10.0). The mesh size increased between three to four times during the pH-dependent swelling transition. The state of water in fully swollen hydrogels which influences many important biomaterial properties was determined by differential scanning calorimetry. The bound water content of gels increased linearly with increase in pH of the swelling medium while the unbound water decreased. These hydrogels have potential to be used as controlled drug delivery systems and sorbents for removal of pollutants from water.

New multi-stimuli responsive cationic copolymers based on N-acryloyl-N′-ethyl piperazine (AcrNEP) and N-isopropylacrylamide (NIPAM) were prepared by thermal free-radical solution polymerization in dioxane at 75 °C. The chemical composition of the copolymers was determined by 1H NMR spectroscopy and was found that the copolymers were slightly rich in NIPAM content than that of AcrNEP. The reactivity of the two monomers for the copolymerization reaction was evaluated by the extended Kelen-Tudos method. The distribution of monomer sequence in the copolymer chain was estimated using the terminal copolymerization model. The maximum tendency to alternation (∼ 70%) was at 60 mol % of AcrNEP in the monomer feed. The copolymers were readily soluble in water at room temperature at all compositions and exhibited well-defined lower critical solution temperature (LCST) phenomenon. The influence of various stimuli such as pH, temperature, simple inorganic salts, and surfactants on the LCST of the copolymers was studied in detail. Simple inorganic salts such as sodium chloride, sodium bromide, and sodium sulfate showed a salting-out effect while sodium iodide showed a salting-in effect. The salting-out coefficient of the salts were calculated using the Sestchenow method, and the salting trend followed the order SO42− > Cl− > Br− > I−. The divalent salt was more effective in lowering the LCST than the monovalent salts. The cationic surfactant hexadecyl trimethylammonium bromide at concentrations above the critical micelle concentration caused a gradual increase in the LCST of the copolymer solutions. The intrinsic viscosity and light scattering behavior of the copolymers in water and in sodium chloride solutions were studied in detail. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1175–1183

New functional linear copolymers and crosslinked gels based on a disubstituted heterocyclic acrylamide, i.e., N-acryloyl-N′-phenyl piperazine (AcrNPhP) with acrylic acid (AA) and hydroxyethyl methacrylate (HEMA) were prepared by thermal free-radical polymerization. The composition of the linear copolymers was analyzed by infra-red spectral analysis and elemental analysis methods. The reactivity parameters of the monomers were determined by the Finemann-Ross and Kelen–Tudos linearization methods. Using the values obtained from the Kelen–Tudos linearization methods, the reactivity or resonance stabilization (Q) and polarity (e) of AcrNPhP with AA and HEMA were calculated (AcrNPhP–AA system Q = 1.9, e = −0.6, and AcrNPhP–HEMA system Q = 2.5, e = −1.2). Crosslinked copolymer hydrogels of AcrNPhP with AA and HEMA were prepared by bulk and solution polymerization methods. The method of preparation, the type of crosslinker and monomers showed a profound impact on the pH responsive swelling of the gels. The hydrogels were highly responsive to changes in external pH. The gels composed of AcrNPhP and AA swelled more than 1,200 % above the pK a of acrylic acid. Interestingly, no significant swelling (about 1 %) was observed in solution of low pH (acidic) despite the presence of an ionizable tertiary amine function in the polymer network. This is attributed to the presence of a bulky phenyl group at the tertiary amine function of AcrNPhP which sterically hinders the protonation and thereby the final swelling of the gel. The gels composed of AcrNPhP and HEMA did not display a significant pH responsive behavior due to the same effect. The AcrNPhP–HEMA gel-containing 70 % AcrNPhP swelled to only 50 % despite the presence of a large fraction of the ionizable unit.

Poly(N-acryloyl-N0-ethyl piperazine-co-N-isopropyla- crylamide) hydrogels were prepared by thermal free-radical copolymerization of N-acryloyl-N 0 -ethyl piperazine (AcrNEP) and N-isopropylacrylamide (NIPAM) in solution using N, N 0 - methylene bisacrylamide as the crosslinking agent. The gels were responsive to changes in external stimuli such as pH and temperature. The pH and temperature responsive character of the gels was greatly dependent on the monomer content, namely AcrNEP and NIPAM, respectively. The gels swelled in acidic (pH 2) and de-swelled in basic (pH 10) solutions with a response time of 60 min. With increase in temperature from 23 to 80 � C the swelling of the gels decreased continuously and this effect was different in acidic and basic solutions. The tem- perature dependence of equilibrium water content of the gels was evaluated by the Gibbs-Helmholtz equation. Detailed anal- ysis of the swelling properties of these new gels in relation to molecular heterogeneity in acidic (pH 2) and basic (pH 10) solu- tions were performed. Water transport property of the gels was studied gravimetrically. In acidic solution, the diffusion process was non-Fickian (anomalous) while in basic solution, the diffusion was quasi-Fickian. The effect was more evident in solution of pH 2 than in pH 10. Various structural parameters of the gels such as number-average molar mass between crosslink (Mc), the crosslink density (qc), and the mesh size (n) were evaluated. The mesh sizes of the hydrogels were between 64 and 783 Ain the swollen state in acidic solution and 20 and 195 Ain the collapsed state in basic solution. The mesh size increased between three to four times during the pH-depend- ent swelling process. The amount of unbound water (free water) and bound water of the gels was also evaluated using differential scanning calorimetry. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000-000, 2012

The formation and growth of titania (anatase) nanoparticles in benzyl alcohol from TiCl4 was studied in situ at 85 °C via powder X-ray diffraction (PXRD), small-angle X-ray scattering (SAXS), and turbidimetry. The results provide new information on the kinetics of this process and allow for better control of particle size, shape, and aggregation. Rietveld refinement of ex situ PXRD data shows that the final crystals are anisotropic in shape and elongated along the crystallographic c-axis. In situ SAXS and PXRD show that the crystals form suddenly after a lag period. The crystals are initially isotropic in shape and the growth is isotropic; thereafter, the growth proceeds predominantly along the crystallographic c-axis to form anisotropic crystals, in agreement with the ex situ PXRD results. The relative lattice strain, which is determined as the lattice deformation relative to the lattice constants found late in the growth process, is positive along the c-axis and negative, but smaller, along the a-axis. ...

A clear and stable nonionic model microemulsion consisting of pentaoxyethylene glycol dodecyl ether (C(12)E(5)), water, and 1-chlorotetradecane (CLTD) was prepared. This system was subjected to a systematic temperature quench (perturbation out of equilibrium) in steps of 1.0 degrees C from 20.4 to 15.3 degrees C in the unstable region of its phase diagram. The change in turbidity (for droplet volume fractions of 0.02 and 0.08) and hydrodynamic radius (R(h)) (for a droplet volume fraction of 0.02) of the system on its way to its new equilibrium was measured at each quench temperature. For small systematic temperature quenches just below the emulsification failure boundary (EFB) the turbidity decreases and remains constant indicating quick changes in the microstructures. Further lowering of temperature brings the system to the unstable region where the turbidity and light scattering increase sharply as function of time because of expulsion of excess oil from the microemulsion droplets. The newly formed oil-rich droplets grow in size as a function of time. These observations indicate the existence of a narrow but observable metastable region en route to the new equilibrium where both microemulsion droplets and larger oil-rich droplets coexist. The region in which microemulsion droplets are metastable is very narrow and is concentration-dependent. The presence of a metastable region is as for other similar systems attributed to the presence of a free energy barrier for the formation of the larger oil-rich droplets associated with curvature free energy of the surfactant film. The turbidity-time curves were converted to the radius-time curves using a model assuming monodisperse spherical droplets. The obtained results are in good agreement with the results for the hydrodynamic radius. The observed average radius from both type of measurements decreases in the metastable region. By performing calculation of the influence of eccentricity and size polydispersity on the observed radius, we have shown that the distribution of the microemulsion droplets becomes more homogeneous in the metastable region.

Copolymers of N-acryloyl-N′-methylpiperazine (AcrNMP) and 2-hydroxyethyl methacrylate (HEMA) were synthesized by free radical solution polymerization in dioxane at 70 ± 1 °C, using 2,2′-azobisisobutyronitrile (AIBN) as initiator. The copolymer compositions were analyzed by the methods of FTIR spectroscopy and elemental analysis. Both the method of analysis yielded results that agreed reasonably well. The monomer reactivity ratios of the copolymerization were determined by the linearization methods of Finemann–Ross (FR) and Kelen–Tudos (KT). The reactivity parameter results derived using FTIR analysis showed that the copolymerization yielded mainly alternating structure with reactivity ratios, r1(AcrNMP) = 0.263 ± 0.011 and r2(HEMA) = 0.615 ± 0.097 by F–R method and r1 = 0.227 ± 0.074 and r2 = 0.53 ± 0.15 by KT method. Microstructure data calculated by the method of Igarashi also supports the alternating structure (tendency) of the copolymer. Crosslinked polymer gels of this system exhibited remarkably high swelling of more than 500% in water at ambient temperature.

The phase behavior and phase separation kinetics of a model ternary nonionic microemulsion system composed of pentaethylene glycol dodecyl ether (C12E5), water, and 1-chlorotetradecane were studied. With increasing temperature, the microemulsion exhibits the following rich phase behavior: oil-in-water phase (L1+O), droplet microemulsion phase (L1), lamellar liquid crystalline phase (Lproportional), and sponge-like (liquid) phase (L3). The microemulsion with a fixed surfactant-to-oil volume fraction ratio (Phis/Phio) of 0.81 and droplet volume fraction of 0.087 was perturbed from equilibrium by a temperature quench from the L1 region (24 degrees C) to an unstable region L1+O (13 degrees C), where the excess oil phase is in equilibrium with the microemulsion droplets. The process of phase separation in the unstable region was followed by time-resolved small-angle X-ray scattering (TR-SAXS) and time-resolved turbidity methods. Due to the large range of scattering vector (q=0.004-0.22 A(-1)) that is possible to access with the TR-SAXS method, the growth of the oil droplets and shrinking of the microemulsion droplets as a result of phase separation could be studied simultaneously. By using an advanced polydisperse ellipsoidal hard-sphere model, the experimental curves have been quantitatively analyzed. The microemulsion droplets were modeled as polydisperse core-shell ellipsoidal particles, using molecular constraints, and the oil droplets are modeled as polydisperse spheres. The radius of gyration (Rg) of the growing oil droplets, volume fraction of oil in the microemulsion droplets, and polydispersity were obtained from the fit parameters. The volume equivalent radius at the neutral plane between the surfactant head and tail of the microemulsion droplet decreased from 76 to 51 A, while the radius of oil drop increased to 217 A within the 160 min of the experiment. After about 48 min from the temperature quench, the system reaches a steady state and continues to coarsen at a constant fraction of the oil of 0.51 in the oil phase by Ostwald ripening with the power law dependence of Roil proportional, variant t1/3. The size of the oil droplets determined by the time-resolved turbidity method is in good agreement with that of the TR-SAXS, highlighting the usefulness of the method in the size determination of oil-in-water microemulsions on an absolute scale.

Monoquaternary cationic polymerizable surfactants of type N-acryloyl-N'-methyl-N-alkyl piperazinium bromide based on piperazine heterocycle was synthesized by reacting N-acryloyl-N'methyl piperazine with the corresponding n-alkyl bromide (decyl, dodecyl, tetradecyl, and hexadecyl) in anhydrous acetone at room temperature. The resulting surfactants were deliquescent to display any sharp melting points. The surface activity was studied by surface tension measurements. Due to the complex head group geometry of these surfactants, the critical micelle concentration value was high in comparison to the analogous alkyltrimethyl ammonium bromides of similar alkyl chain length. The surfactants were polymerized by micellar (in water) and isotropic (in benzene) conditions and the resulting polymers were characterized by solubility and viscosity studies. The polymers prepared in water showed higher viscosity than the ones prepared in benzene as a result of micellar aggregation in water. The reduced viscosity of the polymers in polar solvents such as methanol and dimethyl formamide (DMF) showed polyelectrolyte-like behavior, whereas nonelectrolyte behavior was observed in chloroform. pH-responsive hydrogels were prepared by polymerizing the surfactants in the bicontinuous phase of a microemulsion. The resulting polymers did not exhibit any definite micro/nanostructure due to cross-polymerization of the hydrophilic oil in the bicontinuous network structure. The gels were highly responsive to changes in pH of the medium and showed high-swelling degree in acidic media owing to the protonation of the tertiary nitrogen of the piperazine ring.

Linear homopolymers of N-acryloyl-N′-alkyl piperazine (N′-alkyl: methyl, ethyl, or propyl) and their corresponding crosslinked hydrogels were prepared. The polymers showed good responses to changes in the pH of the medium due to the presence of tertiary amine functions that could be protonated at a low pH. The nature of the N′-alkyl group attached to the piperazine amino nitrogen greatly affected the pKa of the amino group. This in turn influenced the solution behavior of the polymers and was studied with light scattering, potentiometry, and viscosity measurements. The basicity of the polymers increased with an increase in the chain length of the N′-alkyl substituent. The intrinsic viscosity of the polymers in a good polar organic solvent such as dimethylformamide decreased slightly with increasing temperature because of decreased thermodynamic affinity (interaction) at high temperatures. The viscosity behavior of the polymers in sodium chloride solutions was similar to that of classical polyelectrolytes. The swelling property of the hydrogels was studied with water sorption measurements, and the swelling was by anomalous (non-Fickian) transport. The diffusion coefficient of the gels in solutions of pH 2.6 increased with increasing N′-alkyl chain length, whereas at neutral pH, the effect was reversed. This behavior was attributed to the increase in both the basicity and hydrophobicity of the gels with an increase in the chain length of the N′-alkyl groups. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

‘Stimuli’ responsive copolymers of N-acryloyl-N′-ethyl piperazine (AcrNEP) and methyl methacrylate (MMA) were synthesized by free radical solution polymerization. The copolymers were analyzed as thin films by FTIR spectroscopy. The monomer reactivity ratios were determined by linearization methods of Fineman–Ross (F–R) and Kelen–Tudos (K–T) giving the results r1 (AcrNEP)=0.58 and r2 (MMA)=0.91 by the F–R method and r1=0.72 and r2=1.08 by the K–T method. The latter r values in turn yielded Q=0.59 and e=−0.12 for AcrNEP. Crosslinked copolymer hydrogels of AcrNEP and MMA with various compositions were prepared in bulk and solution by photo-initiated free-radical polymerization. The gels were dual responsive to pH and temperature. The response to pH was reversible with a response time of 100 min with good reversibility and with no loss in swelling capacity. Water sorption of the gels was investigated gravimetrically and the collective diffusion coefficients were determined at 10, 25, and 50 °C. The water sorption of the gels in water was Fickian. The temperature dependence of the equilibrium water content was studied by the Gibbs–Helmholtz equation. The enthalpy of mixing decreased with an increase in the hydrophilic content (AcrNEP) of the gel. Other parameters such as type and amount of crosslinker, preparative conditions, nature of buffers, and salts were found to influence the swelling behavior.

An oil-in-water microemulsion of the system C12E5/water/ n-decane with a fixed surfactant-to-oil volume fraction ratio φs/φo of 0.85 is studied. This clear microemulsion is temperature-quenched from a clear one-phase region (26 °C) with spherical microemulsion droplets to an unstable region (13 °C) where the excess oil phase is in equilibrium with the microemulsion droplets. Using a high-resolution version of a laboratory small-angle X-ray scattering (SAXS) instrument, the evolution of the excess oil and its growth as a function of time is studied. Unlike coarsening in alloys and polymer blends, a maximum in the intensity at a finite scattering vector is not observed. This clearly indicates that the droplet of the excess oil is formed homogeneously and that there is no depletion zone around the formed droplets. The scattering curves are quantitatively analysed as a function of time. The microemulsion droplets are modeled as polydisperse core-shell ellipsoidal particles, using molecular constraints and the oil droplets are modeled as polydisperse spheres. The average radius of the oil droplets increases with a scaling exponent in agreement with that of coarsening of precipitates in alloys and phase separations in polymer blends, suggesting some degree of universality of coarsening processes.

By using a powder method, a new method for producing semiconductor/polymer nanocomposites, lead sulfide (PbS) nanoparticles were prepared and dispersed in either poly(methylmethacrylate-co-methacrylic acid) or poly(styrene-co-styrenesulfonic acid). The size of the nanoclusters was less than 2 nm, and the size distribution was rather sharp, determined by UV–vis absorption spectroscopy. The absorption spectra of the PbS-containing sheets showed a blue shift and the absorption edges were steep, reflecting the formation of nano-sized PbS clusters. The spectra also exhibited an absorption maximum, which is an indication of a narrow particle size distribution. The glass transition temperature (Tg) of the PbS-containing nanocomposites was higher than that of the corresponding ionomer. The effect of heat treatment on the aggregation of PbS is also discussed. The dissolution of powder samples, followed by neutralization of acidic groups, led to reduction of particle sizes, suggesting the usefulness of ionic groups for stabilizing PbS nanoclusters.

A piperazine-based cationic surfactant, N , N ′-dimethyl- N -acryloyloxyundecyl piperazinium bromide (DAOUPB) was synthesised by a two-step procedure. The monomer was polymerised in two new microemulsion systems: (i) DAOUPB/water/methyl methacrylate (MMA):hydroxyethylmethacrylate (HEMA) and (ii) DAOUPB/water/acrylonitrile with ethyleneglycol dimethacrylate (EGDMA) as the crosslinking agent. Transparent solid polymeric materials were obtained by photo-initiated polymerisation of some of these microemulsion compositions. Most of the bicontinuous microemulsions investigated gelled within 10 min resulting in transparent solid polymers. The electron micrographs of the polymers obtained from microemulsion compositions containing MMA:HEMA did not show any micropores, while those obtained using acrylonitrile revealed the existence of open-cell type micropores and also of the bicontinuous nature of the system. The width of the bicontinuous structure (micropores) was about 33 nm in the dry state, with long and winding channels of random distribution. The swelling of the gels was highly sensitive to pH.

New crosslinked copolymer hydrogels of N -acryloyl- N ′-methyl piperazine and methyl methacrylate in various compositions were prepared in bulk and solution by photo-initiated free-radical polymerization. The gels exhibited both pH and temperature sensitivities. The response to pH was reversible with a response time of 150 min. The water sorption of the gels was investigated gravimetrically and the collective diffusion coefficients were determined according to the Fickian kinetics at 10°C, 25°C, and 50°C. The apparent activation energy was independent of the composition of the gel networks with a value of 6.26 kJ mol −1 corresponding to a typical diffusion process. The temperature dependence of the equilibrium water content was analyzed by the Gibbs–Helmholtz equation. The enthalpy of mixing decreased with an increase in the hydrophilic content of the gel.

Hydrogels based on N-acryloyl-N'-methylpiperazine (AcrNMP) swelled extensively in solutions of low pH due to the protonation of the tertiary amine. The water transport in the gels under an acidic condition was non-Fickian and nearly Fickian in neutral pH with the collective diffusion coefficients determined as 2.08 x 10 -7 and 5.00 x 10 -7 cm -2 s -1 , respectively. These gels demonstrated good metal-uptake behavior with various divalent metal ions, in particular, copper and nickel, with the uptake capacity increased with increasing pH. The swelling ratio of the gel in the presence of metal ions decreased with increasing metal ion uptake. The results suggest that high metal ion uptake can lead to physical crosslinking arising from the interchain metal complex formation. The metal-loaded gels could be stripped easily with 1M H 2 SO 4 without any loss in their uptake capacity.

Erbium (III) oxalate nanoparticles dispersed titania/y-Glycidoxypropyltrimeth-oxysilane composite materials for photonic applications were prepared by a chemical approach combining the microemulsion technique and the sol-gel method at low temperature. Transmission electron microscopy observation shows that the size of the erbium (III) oxalate nanoparticles is in the range from 10 to 40 nm. A relatively strong room-temperature green up-conversion emission at 543 nm (4S3/2→4I15/2) has been measured for the composite thin films with different erbium oxalate content and heat treatment temperature upon excitation at 993 nm. The lifetime of the visible up-conversion emission has been measured. UV-visible transmission spectroscopy results showed that a relatively high transparency (in the visible range) composite thin film could be obtained at a suitably low heat treatment temperature.

Water-soluble copolymers of N-acryloyl-N′-alkylpiperazine (alkyl: methyl, ethyl) with methyl methacrylate were synthesized and the lower critical solution temperatures (LCSTs) of the copolymers which depend on the compositions and pH of the aqueous solutions are described. The effects of cationic surfactants and simple inorganic salts on the LCSTs are also reported. The influences of pH and temperature on the swelling of the ionizable and thermosensitive hydrogels are studied.

A new water-soluble stimuli-responsive poly(N-acryloyl-N‘-propylpiperazine) (PAcrNPP) was synthesized and characterized. The polymer exhibited a lower critical solution temperature (LCST) in water ...

Copolymers of N -acryloyl- N′ -methylpiperazine (AcrNMP) and methyl methacrylate (MMA) were synthesized in 1,4-dioxane using benzoyl peroxide as initiator at 70 ± 1 °C. The copolymers were analyzed by FTIR spectroscopy. The monomer reactivity ratios were determined by the methods of Fineman-Ross (F-R) and Kelen-Tudos (K-T), yielding the results r 1 (AcrNMP) = 0.552 and r 2 (MMA) = 1.074 by the F-R method and r 1 = 0.466 and r 2 = 0.980 by the K-T method. The latter r values in turn yielded Q = 0.56 and e = −0.49 for AcrNMP.

Structures of poly(ethylene propylene)–poly(ethylene oxide) (PEP–PEO) block copolymer micelles were determined from small-angle X-ray scattering and static light scattering and compared to predictions from a thermodynamic model. Both the corona block length and the solvent water–ethanol ratio were changed, leading to a thorough test of this model. With increasing ethanol fraction, the PEP core–solvent interfacial tension decreases, and the solvent quality for PEO changes. The weight-average block masses were 5.0 kDa for PEP and 2.8–49 kDa for PEO. For the lowest PEO molar mass and samples in pure water (except for the highest PEO molar mass), the micelles were cylindrical; for other conditions they were spherical. The structural parameters can be reasonably well described by the thermodynamic model by Zhulina et al. [Macromolecules2005, 38 (12), 5330–5351]; however, they have a stronger dependence on solvent composition and PEO molar mass than predicted.

Copolymers of N -acryloyl- N ′-methylpiperazine and methyl methylacrylate were synthesized and characterized. The monomer ratio in the copolymer was analyzed by FTIR spectroscopy. The copolymer was found to form a complex with Hg(II) ions. A chemically modified electrode (CME) fabricated by attaching a copolymer film to a glassy carbon electrode for the detection of Hg(II) ions is described. The polymer swelled in aqueous solution, allowing easy access of Hg(II) ion for binding. Anodic stripping voltammetry was employed for the detection of Hg(II) ions. The effects of pH of the measurement and deposition solutions, deposition time and the Hg(II) concentration were studied. The limit of detection was estimated to be 0.23 μg/ml.