Self-association of hyperbranched poly(sulfone-amine) in water: studies with pyrene-fluorescence probe and fluorescence label

Both pyrene-fluorescence probe and fluorescence label techniques are used to investigate the association behaviors of hyperbranched poly(sulfone-amine) (HPSA) in aqueous solution. In the presence of HPSA, excimer emission peak evidently appeared, while no excimer peak was observed in the emission spectra in the absence of HPSA. The excitation spectrum monitored at excimer emission red shifts by about 38-40 nm compared to that monitored at monomer emission, which shows that the excimer is formed by preassociated pyrene chromophores. In the same concentration of pyrene, monomer emission of pyrene decreases but excimer emission increases with increasing the concentration of HPSA; the ratio of excimer-to-monomer emission intensity (I_E/I_M) gradually increases, reaches a critical point at 5-7 g/l, and sharply increases with the concentration. Pyrene-labeled hyperbranched poly(sulfone-amine) (Py-HPSA) was synthesized from 4-(1-Pyrene)butyroyl chloride and HPSA. The monomer emission and excimer emission of Py-HPSA show the concentration-quenching effect, while I_E/I_M increases monotonously, approaches a critical point, and then suddenly increases with increasing the concentration of Py-HPSA. Influences of acidity and solvents on the fluorescence emission were studied. In high concentrations of hyperbranched polymer, pH and DMSO significantly influence the emission of pyrene, and excimer peak disappears at 72% of DMSO fraction.     

Thermoresponsive surfaces by spin-coating of PNIPAM-co-PAA microgels: A combined AFM and ellipsometry study

Thermosensitive coatings are fabricated by spin-coating of microgels consisting of the cross-linked copolymer poly(N-isopropyl acrylamide-co-acrylic acid) (P(NIPAM-co-AA)) on silicon wafers. The microgels were synthesized with two different cross-linker molar ratios and the thin films were prepared at pH 2. At this pH the particles are negatively charged only due to the starter used for the polymerization. Scanning force microscopic (AFM) images indicate a dense packing of the particles and a strong flattening in the adsorbed state. This effect is stronger for microgels containing less cross-linker. Coatings consisting of these microgel particles show a reversible thermoresponsive swelling/shrinking in the region of the lower critical solution temperature (LCST) of NIPAM. For the ellipsometric study of this process a standard setup was modified in order to allow temperature dependent measurements of the optical thickness in a liquid cell. The temperature induced transition is sharper in the case of microgels with lower amount of cross-linker and smears out with increasing amount of cross-linker. No significant desorption of the particles occurs at pH 2, which was shown by AFM of the dried films before and after the ellipsometric measurements. In the dry state the average thickness of the prepared films is approximately 30 nm and a thickness of about 400 nm is reached in the swollen state.     

Novel polyion complex with interpenetrating polymer network of poly(acrylic acid) and partially protected poly(vinylamine) using N-vinylacetamide and N-vinylformamide

Poly(vinylamine), the simplest polycation with primary amines, was applied to interpenetrating polymer networks (IPN) with poly(acrylic acid). N-Vinylformamide (NVF) was employed for amino-protected monomers to control electrostatic balance. pH-responsivities of IPNs varied, depending on the hydrolysis conditions and acrylic acid (AAc) concentration of the second network. Poly(N-vinylacetamide)-co-poly(N-vinylformamide) (4/6, mol/mol) was employed for the first network, subsequently hydrolyzed with 50% amide groups, and the second network was polymerized with 0.25 mol L⁻¹ AAc, extremely shrunken hydrogels with polyion complex were formed at pH 7, showing that the controlled amount of highly active primary amines are available in IPN.     

Study of biomineralization of poly(vinyl alcohol)‐based scaffolds using an alternate soaking approach

The present work adds to the continuing efforts of designing a natural bone‐like structure by synthesizing a semi‐interpenetrating polymer network (IPN) of poly(vinyl alcohol)–poly[(acrylic acid)‐co‐acrylonitrile] and impregnating hydroxyapatite (HAP) into the polymer matrix by an alternate soaking process. The prepared HAP–polymer scaffolds were characterized using techniques like Fourier transform infrared spectroscopy, X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis and environmental scanning electron microscopy. The biomineralized semi‐IPN was evaluated for water sorption capacity and the data were utilized for calculating network parameters such as average molecular weight between crosslinks (M_c) and crosslink density (q). The impregnated HAP was quantified as a function of the chemical architecture of the semi‐IPN, number of reaction cycles and temperature of the swelling bath. Copyright © 2006 Society of Chemical Industry     

Synthesis of cross-linked poly(4-vinylpyridine) and its copolymer microgels using supercritical carbon dioxide: Application in the adsorption of copper(II)

Compared with conventional precipitation polymerization method, cross-linked poly(4-vinylpyridine) (P4VP) and its microgels copolymerized with α-methacrylic acid (MAA) were synthesized through a new route of stabilizer-free polymerization in supercritical fluids. The yellow, dry, fine powders were directly obtained from precipitation polymerization of 4-vinylpyridine in supercritical carbon dioxide (scCO₂) at pressures ranging from 70.0 to 230 bar, using N,N′-methylenebisacrylamide as cross-linker. The effects of the reaction pressure, cross-linker ratio, initiator concentration, and reaction time were investigated. The capacity of this microgel for adsorption of copper(II) was also studied. At higher cross-linker concentrations, a high yield of the cross-linked P4VP microgel was generated in scCO₂, and its particle size was less than 300 nm. Polymerization of cross-linked P4VP in scCO₂ was extremely sensitive to the density of the continuous phase. The adsorption followed the Langmuir isotherm. The adsorption capacities of cross-linked P(4VP-co-MAA) and cross-linked P4VP were 47.2 and 26.9 mg g⁻¹, respectively.     

Synthesis and properties of thermosensitive, crown ether incorporated poly(N-isopropylacrylamide) hydrogel

A crown ether derivative (4′-allyldibenzo-18-crown-6, CE) was covalently incorporated into the network of temperature sensitive poly(N-isopropylacrylamide) (PNIPA) hydrogels by copolymerization in a mixed solvent of water and tetrahydrofuran (H₂O/THF). The poly(N-isopropylacrylamide-co-4′-allyldibenzo-18-crown-6) (poly(NIPA-co-CE)) hydrogels exhibited dramatically faster deswelling rates than normal PNIPA hydrogels at a temperature (50 °C) above their lower critical solution temperatures. The effect of the solvent component ratio in the mixed solvent during the copolymerization on the swelling properties of the poly(NIPA-co-CE) hydrogel was investigated. The thermosensitive poly(NIPA-co-CE) hydrogels have potential applications in the extraction of cations and separation of chiral drugs.     

Swelling behavior of semi‐interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylamide‐co‐sodium methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(acrylamide‐co‐sodium methacrylate) poly(AAm‐co‐SMA) were prepared by the semi IPN method. These IPN hydrogels were prepared by polymerizing aqueous solution of acrylamide and sodium methacrylate, using ammonium persulphate/N,N,N¹,N¹‐tetramethylethylenediamine (APS/TMEDA) initiating system and N,N¹‐methylene‐bisacrylamide (MBA) as a crosslinker in the presence of a host polymer, poly(vinyl alcohol). The influence of reaction conditions, such as the concentration of PVA, sodium methacrylate, crosslinker, initiator, and reaction temperature, on the swelling behavior of these IPNs was investigated in detail. The results showed that the IPN hydrogels exhibited different swelling behavior as the reaction conditions varied. To verify the structural difference in the IPN hydrogels, scanning electron microscopy (SEM) was used to identify the morphological changes in the IPN as the concentration of crosslinker varied. In addition to MBA, two other crosslinkers were also employed in the preparation of IPNs to illustrate the difference in their swelling phenomena. The swelling kinetics, equilibrium water content, and water transport mechanism of all the IPN hydrogels were investigated. IPN hydrogels being ionic in nature, the swelling behavior was significantly affected by environmental conditions, such as temperature, ionic strength, and pH of the swelling medium. Further, their swelling behavior was also examined in different physiological bio‐fluids. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 302–314, 2005     

Monodispersed thermoresponsive hydrogel microspheres with a volume phase transition driven by hydrogen bonding

We report the synthesis and characterization of monodispersed thermoresponsive hydrogel microspheres with a volume phase transition driven by hydrogen bonding. The prepared microspheres, composed of poly(acrylamide-co-styrene) (poly(AAM-co-St)) cores and poly(acrylamide)/poly(acrylic acid) (PAAM/PAAC) based interpenetrating polymer network (IPN) shells, were featured with high monodispersity and positively thermoresponsive volume phase transition characteristics with tunable swelling kinetics, i.e. the particle swelling was induced by an increase rather than a decrease in temperature. The monodisperse poly(AAM-co-St) seeds were prepared by emulsifier-free emulsion polymerization, the PAAM or poly(acrylamide-co-butyl methacrylate) (poly(AAM-co-BMA)) shells were fabricated on the seeds by free radical polymerization, and the core-shell microspheres with PAAM/PAAC based IPN shells were finished by a method of sequential IPN synthesis. The microsphere size increased with increasing both AAM and BMA dosages. The increase of hydrophilic monomer AAM dosage resulted in a better monodispersity, but the increase of hydrophobic monomer BMA dosage led to a worse monodispersity. With increasing the crosslinker methylenebisacrylamide (MBA) dosage, the mean diameter of the microspheres decreased and the monodispersity became better. An equimolar composition of AAC and AAM in the IPN shells of the microspheres resulted in a more complete shrinkage for the microspheres at temperatures lower than the upper critical solution temperature. Both BMA and MBA additions depressed the swelling ratio of the hydrodynamic diameter of the microspheres.     

In situ characterization of moisture sorption/desorption in thin polymer films using optical waveguide spectroscopy

The kinetics of moisture sorption/desorption in poly(terephthalate-co-phosphate) thin films was investigated in situ at T = 25 °C using optical waveguide spectroscopy (OWS). At low water activities, Fickian diffusion was observed for the initial phase of the sorption process, while at high activities, due to the clustering of water, a complex sorption behavior was found. The moisture sorption isotherms were analyzed according to both the Zimm and Lundberg model as well as the Brown model, which suggests the formation of clusters of water molecules in poly(terephthalate-co-phosphate) at water activities of α₁ = 0.58 or higher. The water diffusion coefficient decreases with increasing water activity, which also suggests water cluster formation. A biphasic desorption behavior was also observed upon decreasing the water activity from α₁ = 1 to 0. This study demonstrated the unique advantages of OWS in characterizing in situ the sorption/desorption behavior of penetrants in polymer thin films.     

Highly crosslinked poly(glycidyl methacrylate-co-divinyl benzene) particles by precipitation polymerization

Stable and smooth surface poly(glycidyl metharylate-co-divinylbenzene) (GMA-co-DVB) microspheres composed of various concentrations of DVB from 20 to 90 mol% in acetonitrile medium were prepared without a significant coagulum by precipitation polymerization. The number-average diameter of the microspheres linearly increases from 2.63 to 3.34 μm and the particle size distribution becomes narrower by decreasing the uniformity from 1.10 to 1.02 with the DVB concentration from 20 to 90 mol%. The yield of polymerization increased from 28.9 to 79.7% with the DVB concentration as well. The FT-IR spectrum shows the characteristic peaks at 1725-1650 cm⁻¹ assigned to the confirmation of the polymerization between GMA and DVB. No glass transition temperature and the onset of the thermal degradation temperature at higher temperature indicate that the poly(GMA-co-DVB) is crosslinked; this is evidenced by the swelling ratio measurement relevant to the crosslinking density of the poly(GMA-co-DVB). The swelling test suggested that the poly(GMA-co-DVB) particles would be a core/shell type structure composing of a highly crosslinked DVB rich-phase in the core part and slightly crosslinked GMA rich-phase in the shell part.     

Synthesis and lithographic evaluation of poly[(methacrylic acid tert-butyl cholate ester)-co-(γ-butyrolactone-2-yl methacrylate)]

Poly[(methacrylic acid tert-butyl cholate ester)-co-(γ-butyrolactone-2-yl methacrylate)] was synthesized and evaluated as a new 193-nm chemically amplified photoresist. This polymer showed good thermal stability up to 240 °C and had a good transmittance at 193 nm. This material showed good resistance to CF₄-reactive ion etching. The resist patterns of 0.15 μm feature size were obtained at a dose of 11 mJ cm⁻² using an argon fluoride excimer laser stepper.     

Characterization of spatial inhomogeneities and dynamic properties of random cross-linked polystyrene networks by dynamic light scattering

The network inhomogeneity and the cooperative motion of the network chains of random cross-linked poly(styrene-co-maleic anhydride) gels were investigated by dynamic light scattering. Measurements were performed for gels in the preparation state as well as in the swelling equilibrium. Network inhomogeneities and cooperative motion were analyzed at varying the cross-linker concentration and the polymer volume fraction. While the cross-linker concentration has only a minor influence on the inhomogeneity and the diffusion constant D_coop, the polymer volume fraction clearly influences both measured properties. The concentration dependence of D_coop can be well described by a power law, as known for semi-dilute polymer solutions. In the preparation state the networks appear homogeneous, exhibiting dynamic contributions to the scattering intensity of 70-90%. Swollen to equilibrium stage, significant heterogeneities emerge, reducing the dynamic contributions to 10-20%.     

Rapid pH/temperature-responsive cationic hydrogels with dual stimuli-sensitive grafted side chains

Dual temperature- and pH-sensitive comb-type grafted cationic hydrogels are successfully synthesized by grafting polymeric chains with freely mobile ends, which are composed of both N-isopropylacrylamide (NIPAM) segments and N,N-dimethylamino ethyl methacrylate (DMAEMA) segments, onto the backbone of crosslinked poly(NIPAM-co-DMAEMA) networks. Equilibrium and dynamic swelling/deswelling properties of the prepared hydrogels responding to pH and/or temperature are investigated. The prepared hydrogels demonstrate a lower critical solution temperature (LCST) at about 34 °C and a pK_a value at about pH 7.3. At lower pH and lower temperature, both the swelling degree and the swelling rate of the comb-type grafted hydrogel are larger than those of the normal-type crosslinked hydrogel. The comb-type grafted poly(NIPAM-co-DMAEMA) hydrogel exhibits a more rapid deswelling rate than that of the normal-type hydrogel in response to a pH jump from 2.0 to 11.0 at a fixed temperature. The volume changes of the poly(NIPAM-co-DMAEMA) hydrogels are acute in a series of fixed buffer solutions with an abrupt increase of environmental temperature from 18 °C to a temperature higher than the LCST. The comb-type grafted poly(NIPAM-co-DMAEMA) hydrogels show quite fast shrinking behaviors in response to simultaneous dual temperature and pH stimuli. Drug-release in vitro from the prepared poly(NIPAM-co-DMAEMA) hydrogels is carried out when the environmental temperature and pH are changed synchronously. The results show that the model drug Vitamin B₁₂ is released much more rapidly from the comb-type grafted hydrogel than that from the normal-type hydrogel. The proposed dual temperature/pH-sensitive comb-type grafted cationic poly(NIPAM-co-DMAEMA) hydrogel in this study may find various potential applications, e.g., for fabricating rapid-response smart sensors, actuators, and chemical/drug carriers and so on.     

Physical and functional characterization of PHASCL membranes

Dense semicrystalline membranes of polyhydroxyalkanoates with medium change length (PHA_SCL), polyhydroxybutyrate (PHB) and poly β (hydroxybutyrate-co-hydroxyvalerate) [P(βHB-co-XβHV)] were characterized using wide-angle X-ray (WAXS) and scanning electron microscopy. PHB membranes showed a more rugged surface than those of copolymers (0-22%HV). Properties such as swelling capacity, vapor permeability and selectivity were investigated. Swelling percentage in water-ethanol mixtures was 34% for PHB as compared to 14% for copolymers membranes. The ethanol/water selectivity (α_s) of PHB was 5.8 which shows that it is more selective than copolymers.The water vapor and ethanol vapor permeability were determined by a gravimetric technique at different temperatures by static and dynamic methods. PHB permeability was 69.5 Barrer at 30 °C and a discreet increment was observed at temperatures (30-50 °C). The difference in permeability between PHB and [P(βHB-co-X%βHV)] could be interpreted in terms of the crystallization rate, crystallite size and distribution which impact to transport properties of amorphous phase.     

Effect of Mn content on the structure and electrochemical characteristics of La0.7Mg0.3Ni2.975−xCo0.525Mnx (x = 0-0.4) hydrogen storage alloys

The effect of Mn content on the crystal structure and electrochemical characteristics of La_0.7Mg_0.3Ni_2.975−xCo_0.525Mn_x (x = 0, 0.1, 0.2, 0.3, 0.4) alloys has been studied systematically. The results of the Rietveld analyses show that all these alloys mainly consist of two phases: the La(La,Mg)₂Ni₉ phase with the rhombohedral PuNi₃-type structure and the LaNi₅ phase with the hexagonal CaCu₅-type structure. The pressure-composition isotherms shows that the partial substitution of Mn for Ni results in lower desorption plateau pressure and steeper pressure plateau of the alloy electrodes. For a Mn content of x = 0.3, the electrochemical performances, including specific discharge capacity, high rate chargeability (HRC) and high rate dischargeability (HRD), of the alloy are preferable. Moreover, the data of the polarization resistance R_p and the exchange current density I₀ of the alloy electrodes is consistent with the results of HRC and HRD. The hydrogen diffusion coefficient D increases with increasing Mn content, and thereafter increases the low temperature dischargeability (LTD) of the alloy electrodes.     

Dilute solutions and phase behavior of polydisperse A-b-(A-co-B) diblock copolymers

The effect of polydispersity on dilute solution properties and microphase separation of polydisperse high-molecular-weight (M_w > 10⁵ g mol⁻¹) polystyrene-block-poly(styrene-co-acrylonitrile) diblock copolymers, PS-block-P(S-co-AN), was studied in this work. For experiments, a series of diblock copolymers with variable weight fractions of acrylonitrile units (w_AN = 0.08-0.29) and length of block P(S-co-AN) was synthesized using nitroxide-mediated radical polymerization (NMP) technique, namely, by chain extension of nitroxide-terminated polystyrene (PS-TEMPO). According to light scattering and viscometry measurements in dilute tetrahydrofuran (THF) solutions the studied diblock copolymers assumed random coil conformation with the values of characteristic structure factor R_g/R_h = 1.50-1.76. It was found that polydisperse diblock copolymers being in strong segregation limit (SSL) self-assembled into microphase-separated ordered morphologies at ordinary temperature. The long periods of lamellar microdomains were larger compared to theoretical predictions for hypothetical monodisperse diblock copolymers. It was demonstrated by means of SAXS and TEM that a transition from a lamellar (LAM) to irregular face-centered-cubic (FCC) morphology occurred with increasing volume fraction of P(S-co-AN) block.     

Investigation on the early and late stage phase-separation dynamics of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) blends through rheological and scattering functions

The phase-separation behavior of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) (PMMA/α-MSAN) blends with two different compositions was studied by time-resolved small angle light scattering (SALS) in the spinodal decomposition (SD) regime from 160 to 210 °C. The rheological function (WLF-like equation) was introduced into the processing of light scattering data. It was found that the WLF-like equation was applicable to describe the temperature dependence of apparent diffusion coefficient D_app and the relaxation time τ of normalized scattering intensity (I(t)−I(0))/(I_m−I(0)) at the early stage of SD, as well as the relaxation time τ of maximum scattering intensity I_m and characteristic scattering vector q_m with I_m at the late stage of SD for PMMA/α-MSAN blends with two different compositions. This is in consistence with the phase-separation behavior of PMMA/SAN reported in our previous paper.     

Characterization of blends of naphthalene-containing polymers with poly(alkyl methacrylates) by combined steady-state fluorescence spectroscopy and fluorescence decay measurements

The extent of mixing in two-component solution-cast films of poly(2-vinyl naphthalene) (P2VN) and poly(2-iso-propenyl naphthalene) (P2IPN) with poly(methyl methacrylate) and poly(n-butyl methacrylate) was studied by steady-state and time-resolved fluorescence spectroscopy. The steady-state fluorescence spectrum of 1% P2IPN in the two poly(alkyl methacrylates) evolves from 100% monomer emission (λ_max = 340 nm) to >70% excimer emission (λ_max = 390 nm) as its molecular weight increases from 1900 to 278000. Despite such clear-cut changes in the steady-state spectra on phase separation, the fluorescence decays were nonexponential for all mixed films. Triple-exponential decay functions were necessary to describe excimer decays at 430 nm and monomer decays at 340 nm. Moreover, the fluorescence decays varied slightly across the excimer emission band, and changed significantly when the polymer films were annealed. Studies on blends containing from 1 to 100% of P2VN and P2IPN established that this multicomppnent fluorescence decay behavior is intrinsicto the naphthalene-containing polymer phase, it is proposed that excimers formed between chromophores in meso and racemic dyads have different mean decay times and that imperfectly aligned chromophore pairs lead to an additional short-lived excimer decay component.     

The application of P(MMA-co-MAA)/PEG polyblend gel electrolyte in quasi-solid state dye-sensitized solar cell at higher temperature

A poly(methyl methacrylate-co-methacrylate acid)/poly(ethylene glycol) [P(MMA-co-MAA)/PEG] polyblend with viscoelasticity was synthesized by a copolymerizing reaction between methyl methacrylate (MMA) and methacrylate acid (MAA) using azobisisobutyronitrile (AIBN) as initiator in poly(ethylene glycol) (PEG) methanol solution. Then, a polyblend gel electrolyte was prepared by adding KI and I₂ to P(MMA-co-MAA)/PEG system. The influence of compositions of the polyblend gel electrolyte on the ionic conductivity and the effect of temperature on photoelectronic performance of quasi-solid state dye-sensitized solar cell (QS-DSSC) were discussed. It was found that the polyblend gel electrolyte was a good candidate as high-temperature electrolyte for QS-DSSCs. Under an optimized condition, the highest conductivity of the polyblend gel electrolyte was 2.70 mS/cm² at 30 °C. Based on the polyblend gel electrolyte, a light-to-electricity conversion efficiency of 4.85% for QS-DSSC was achieved under AM 1.5 simulated solar light illumination at 60 °C.     

Poly(d,l-lactide)/poly(methyl methacrylate) interpenetrating polymer networks: Synthesis, characterization, and use as precursors to porous polymeric materials

The use of semi-hydrolyzable oligoester-derivatized interpenetrating polymer networks (IPNs) as nanostructured precursors provides a straightforward and versatile approach toward mesoporous networks. Different poly(d,l-lactide) (PLA)/poly(methyl methacrylate) (PMMA)-based IPNs were synthesized by resorting to the so-called in situ sequential method. The PLA sub-network was first generated from a dihydroxy-telechelic PLA oligomer via an end-linking reaction with Desmodur^® RU as a triisocyanate cross-linker. Subsequently, the methacrylic sub-network was created by free-radical copolymerization of methyl methacrylate (MMA) and a dimethacrylate (either bisphenol A dimethacrylate or diurethane dimethacrylate) with varying compositions (initial MMA/dimethacrylate composition ranging from 99/1 to 90/10 mol%). Both cross-linking processes were monitored by real-time infrared spectroscopy. The microphase separation developed in IPN precursors was investigated by differential scanning calorimetry (DSC). Furthermore, the quantitative hydrolysis of the PLA sub-network, under mild basic conditions, afforded porous methacrylic structures with pore sizes ranging from 10 to 100 nm -at most- thus showing the effective role of cross-linked PLA sub-chains as porogen templates. Pore sizes and pore size distributions were determined by scanning electron microscopy (SEM) and thermoporometry via DSC measurements. The mesoporosity of residual networks could be attributed to the good degree of chain interpenetration associated with both sub-networks in IPN precursors, due to their peculiar interlocking framework.