Nanoscale observation of morphological transformation during ageing of silica and silica-alumina

Atomic force microscopy (AFM) was used for in-situ observation of nanoscale morphological transformations during the ageing step in sol-gel synthesis. Silica, alumina and silica-alumina samples with different Si/Al ratios were prepared from inorganic salt precursors and geled at low pH. Silica and silica-alumina samples formed branch-like gel network made of nanometer-sized clusters. During ageing at room temperature, the overall structure of the gel network remained unchanged but the clusters underwent phase transformation, coaslesence, coarsening, fragmentation, as well as dissolution resulting in the internal restructuring of the gel material. Morphological transformation associated with crystallization of pseudo-boehmite phase was observed for the alumina samples. These nanometer-scale processes are expected to play a key role in dictating the material properties of the final sol-gel product.     

Hydrogel formation between enantiomeric B-A-B-type block copolymers of polylactides (PLLA or PDLA: A) and polyoxyethylene (PEG: B); PEG-PLLA-PEG and PEG-PDLA-PEG

A mixed suspension of the enantiomeric B-A-B triblock copolymers, polyoxyethylene-block-poly(L-lactide)-block-polyoxyethylene (PEG-PLLA-PEG) and polyoxyethylene-block-poly(D-lactide)-block-polyoxyethylene (PEG-PDLA-PEG), was found to induce reversible gel-to-sol transition depending on the polymer concentration and temperature. The storage and loss moduli of the gel formed at lower temperature were much higher than those of the gel prepared from the corresponding ABA-type triblock copolymers because of the higher polymer concentration in the former. Although the stereo-complexation of the PLLA and PDLA blocks occurred at higher temperature also in the B-A-B copolymers, it was not responsible for the gelation of the mixed suspension. The PEG chains, involved in the helix formation of the PLLA and PDLA, should form helices with opposite helical senses to aggregate and lead the gelation of the system.     

Supramolecular polymer gels from polystyrene bearing cyclic amidine Group and acrylic acid/n‐butyl acrylate copolymers

We have prepared supramolecular polymer gels by mixing solutions of a polystyrene bearing cyclic amidine pendant groups (Poly‐A) and copolymers of acrylic acid and n‐butyl acrylate (Poly‐C), followed by evaporation. FT‐IR analysis indicated that the gels were formed through three‐dimensional network of the amidinium‐carboxylate salt bridge. DSC study showed that the Poly‐A and the Poly‐C were miscible when the salt bridge content was high. On the other hand, the mixtures with small salt bridge content showed phase separation. Dynamic shear measurements showed that the gel prepared from Poly‐A and Poly‐C with acrylic acid unit content of 15% had G' higher than G″ over a temperature range of ?22 °C to 32 °C, in which the G' value reached almost 1 MPa. The gel had a crossover point of G' and G″ at 32 °C, very close to room temperature, which suggested facile processability. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 765–770     

Fast responsive poly(<Emphasis Type="Italic">N,N</Emphasis>-diethylacrylamide) hydrogels with interconnected microspheres and bi-continuous structures

We prepared thermo-responsive polymer hydrogels by γ-ray irradiation of aqueous solutions of N, N-diethylacrylamide at different temperatures below and above its lower critical solution temperature (LCST). Poly(N, N-diethylacrylamide) gel had a transparent and homogeneous structure when the radiation-induced polymerization and crosslinking were carried out below the LCST (25 °C) of the polymer. On the other hand, cloudy and heterogeneous gels were formed at temperatures above the LCST of the polymer (>35 °C). From environmental scanning electron microscopy observations, the gels prepared at 35 and 40 °C were seen to show sponge-like bi-continuous porous structures, while those prepared at 50 °C showed a porous structure consisting of interconnected microspheres. For temperature changes between 10 and 40 °C, gels with porous structures showed rapid volume transitions on a time scale of about a minute, not only for shrinking but also for swelling processes, which is in remarkable contrast to the porous poly(N-isopropylacrylamide) hydrogels.     

Gelation in aqueous solutions of carboxylated polyacrylamide in the presence of chromium(III) acetate,studied by oscillation rheometry

The time dependences of the elastic moduli and loss moduli of aqueous solutions of Alcoflood-254S carboxylated polyacrylamide, containing chromium(III) acetate as a cross-linking agent, were studied by oscillation rheometry in the temperature interval 50–80°?. The gel time increases with a decrease in the temperature, as well as in the concentration of the polymer and cross-linking agent. The elastic properties of hydrogels at the moment of the onset of their formation, characterizing the concentration of cross-links between the macromolecules, are due to the polymer concentration in the solution and are independent of the chromium(III) acetate concentration and temperature. Presumably, equal degree of conversion in the reaction between carboxylate groups of the polymer and chromium(III) ion, leading to cross-linking of macromolecules of carboxylated polyacrylamide, allows determination of the kinetic parameters of the gelation from data obtained by oscillation rheometry under nonisothermal conditions.     

A novel polymer gel electrolyte: Direct polymerization of ionic liquid from surface of silica nanoparticles

A novel polymer electrolyte is synthesized by directly grafting poly ionic liquids onto silica nanoparticles. The kinetic study of this surface‐initiated polymerization has also been included. A gel‐state electrolyte is formed by mixing this type of polymer/silica nanocomposite with ionic liquids under 60 °C, which exhibits an excellent conductivity of 0.8 mS/cm at room temperature and 14.7 mS/cm at 90 °C. In addition, the mechanism of gel formation has also been discussed in this article. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 121–127     

Thermoreversible gelation of solutions of vinyl polymers

The thermoreversible gelation of solutions of isotactic poly(methyl methacrylate) is investigated. Amorphous gels can be prepared in l-butanol by a combination of a liquid-liquid demixing with an upper critical demixing temperature and a glass transition. Annealing of the demixed solutions above their glass transition temperature T_G, results in the formation of a crystalline gel. In oxylene, crystalline gels are formed by a liquid-liquid demixing with an lower critical demixing temperature and an annealing at room temperature. Very fast gelation is observed to occur far below room temperature in solvents like 2-butanone.     

Stereocomplex Mediated Gelation of PEG-(PLA)2 and PEG-(PLA)8 Block Copolymers

Stereocomplex mediated hydrogels have been prepared by mixing solutions of polymers of opposite chirality of either PEG-(PLA)₂ triblock copolymers or PEG-(PLA)₈ star block copolymers. The critical gel concentrations of the mixed enantiomer solutions were considerably lower compared to polymer solutions containing only the single enantiomer. Moreover, gel-sol transition temperatures were increased and gel regions were expanded due to stereocomplexation. Rheology measurements showed that stereocomplexed hydrogels based on PEG-(PLA)₈ have higher storage moduli compared to those based on PEG-(PLA)₂. Stereocomplexed hydrogels prepared from 13 wt% PEG-(PLA)₂ solutions in PBS showed a storage modulus of 0.9 kPa at 37 °C, while at similar conditions stereocomplexed hydrogels of PEG-(PLA)₈ showed a storage modulus of 1.9 kPa at 10 wt%.     

Microporous poly(vinyl methyl ether) hydrogels prepared by γ-ray irradiation at different heating rates

We prepared thermoresponsive and microporous polymer hydrogels by γ-ray irradiation of aqueous solutions poly(vinyl methyl ether) (PVME) at different heating rates. Under all temperature programs, opaque and heterogeneous PVME gels formed, which swelled at temperatures below the lower critical solution temperature and shrank at temperatures above it. All of the samples contained porous and phase-separated structures. The shape and size of the gel pores varied depending on the temperature programs. Gels having a sponge-like continuous porous structure formed only when the radiation-induced crosslinking was carried out at an optimum heating rate, which we found to be 0.11–0.13°C min⁻¹. For temperature changes between 10°C and 40°C, gels with this structure showed rapid volume transitions on a time scale of about a minute.     

Supramolecular polymer gels formed from carboxy‐terminated telechelic polybutadiene and polyamidine through amidinium‐carboxylate salt bridge

In this article, we report the preparation and properties of the bulk supramolecular polymer gels prepared from a polybutadiene based on the amidinium‐carboxylate salt bridge, highlighting the difference from a well‐established network system based on carboxylic acid and amine. We have prepared the amidinium‐carboxylate salt bridge‐based supramolecular polymer gels from a carboxy‐terminated telechelic polybutadiene and a linear polyamidine having N,N′‐di‐substituted acetamidine group in the main chain. FTIR analysis along with Small angle X‐ray scattering measurements indicated that the salt bridge was attributed to the gelation through three‐dimensional network formation. Virtually no fluidity was observed for the supramolecular gel containing equimolar amounts of the carboxyl group and the amidine group, which showed a high G′ value of about 1 MPa at room temperature and a T_gel of 37 °C. For comparison, the supramolecular polymer gels crosslinked by ammonium‐carboxylate salt were prepared using a linear polyethyleneimine instead of the polyamidine. The gel with equimolar amounts of the carboxyl group and the secondary amino group showed liquid‐like fluidity with a G′ value of about 0.01 MPa at room temperature, which was attributed to the fact that a certain amount of the carboxyl group remained as its free form without salt formation, as evidenced by FTIR analysis. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1815–1824     

Thermal Decomposition and Crystallization of Aqueous Sol-Gel Derived Zirconium Acetate Gels: Effects of the Additive Anions

Zirconia powders were prepared by forming gels by desiccation of aqueous precursor solutions of zirconium acetate containing nitric or sulfuric acid at pH 2.4 and 1.4 and pyrolyzing the gels to temperatures up to 825°C. The structure development in the gels and solid pyrolysis products was investigated. The crystalline zirconia structures produced monoclinic (m), metastable cubic (c) and tetragonal (t) polymorphs. The structure transition temperatures were strongly dependent on the pH, the anions and the stoichiometry of the zirconium complex in the precursor solution. The monoclinic polymorph fraction in the zirconia formed by pyrolyzing the gel formed from the precursor solution containing sulfuric acid at pH 2.4 to 750°C approaches zero while this ratio in the zirconia formed by pyrolyzing the gel formed from the precursor solution containing nitric acid at pH 1.4 to 825°C is 0.7.     

Meticulous Doxorubicin Release from pH-Responsive Nanoparticles Entrapped within an Injectable Thermoresponsive Depot

The dual stimuli-controlled release of doxorubicin from gel-embedded nanoparticles is reported. Non-cytotoxic polymer nanoparticles are formed from poly(ethylene glycol)-b-poly(benzyl glutamate) that, uniquely, contain a central ester link. This connection renders the nanoparticles pH-responsive, enabling extensive doxorubicin release in acidic solutions (pH 6.5), but not in solutions of physiological pH (pH 7.4). Doxorubicin-loaded nanoparticles were found to be stable for at least 31 days and lethal against the three breast cancer cell lines tested. Furthermore, doxorubicin-loaded nanoparticles could be incorporated within a thermoresponsive poly(2-hydroxypropyl methacrylate) gel depot, which forms immediately upon injection of poly(2-hydroxypropyl methacrylate) in dimethyl sulfoxide solution into aqueous solution. The combination of the poly(2-hydroxypropyl methacrylate) gel and poly(ethylene glycol)-b-poly(benzyl glutamate) nanoparticles yields an injectable doxorubicin delivery system that facilities near-complete drug release when maintained at elevated temperatures (37 °C) in acidic solution (pH 6.5). In contrast, negligible payload release occurs when the material is stored at room temperature in non-acidic solution (pH 7.4). The system has great potential as a vehicle for the prolonged, site-specific release of chemotherapeutics.     

Thermodynamic properties of some polymeric forms of fullerite C<Subscript>60</Subscript> at temperatures ranging from 0 to 320 K

The temperature dependences of the heat capacityC ⁰ _p of fullerites C₆₀ were studied at temperatures ranging from 5 to 320 K in an adiabatic vacuum calorimeter with an accuracy of 0.4–0.2%. The fullerite C₆₀ samples were prepared by treating the starting fullerite C₆₀ under 8 GPa at 920 and 1270 K and “quenched” by a sharp decrease in pressure to −10⁵ Pa and in temperature to ∼300 K. Fullerite C₆₀(8 GPa, 920 K), a crystalline polymer with layered structure formed by polymerized fullerene C₆₀ molecules, was obtained at 920 K and 8 GPa. Fullerite C₆₀(8 GPa, 1270 K), a three-dimensional polymer with a graphite-like structure formed by fragments of decomposed C₆₀ molecules and containing many C(sp³)−C(sp³) bonds, was obtained at 1270 K and 8 GPa. Both polymers are metastable polymeric phases. The anomalous character of the temperature dependence of the heat capacity was revealed in the 49–66 K range for the polymer formed at 1270 K. The thermodynamic functions of the substances under study were calculated for the 0–320 K region along with entropies of their formation from graphite. The entropies of transformation of the starting fullerite C₆₀ into metastable phases and that of intertransformation of phases were estimated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 277–281, February, 2000.     

The synthesis and solution properties of some rigid-chain,water-soluble polymers: Poly[N,N′-(sulfo-phenylene)phthalamide]s and poly[N,N′-(sulfo-p-phenylene)pyromellitimide]

Poly[N,N′-(sulfo-phenylene)phthalamid]es and poly[N,N′-(sulfo-p-phenylene)pyromellitimide] were prepared in water-soluble form and were found to have unique solution properties, similar in some respects to xanthan. The polymer most investigated, poly[N,N′-(sulfo-p-phenylene)terephthalamide] (PPT-S), is produced as the dimethylacetamide (DMAC) salt by the solution polymerization of 2,5-diaminobenzenesulfonic acid with terephthaloyl chloride in DMAC containing LiCl. The isolated polymer requires heating in water to dissolve; the resulting cooled solutions are viscous or gels at concentrations as low as 0.4%. They are highly birefringent, exhibit circular dichroism properties, and are viscosity-sensitive to salt. Solutions of this polymer mixed with those of guar or hydroxyethyl cellulose give significantly enhanced viscosity. The polymer is relatively low molecular weight, ca. 5000 estimated from viscosity data. Some meta and para isomeric analogs of PPT-S were prepared; these polymers have similar properties except they are more soluble in water, and higher concentrations are required to obtain significant viscosity. Poly[N,N′-(sulfo-p-phenylene) pyromellitimide] (PIM-S) was prepared similarly from 2,5-diaminobenzenesulfonic acid and pyromellitic dianhydride. Its aqueous solution properties are similar to those of PPT-S. It appears that these relatively low-molecular-weight rigid-chain polymers associate in water to form a network that results in viscous solutions at low concentrations.     

Effects of preparation temperature on the conductivity of polypyrrole conducting polymer

An attempt has heen made to investigate the effect of temperature on the conductivity of polypyrrole conducting polymer films prepared by an electrochemical method in an aqueous medium using camphor sulfonate as the dopant. The polymer was grown from aqueous solutions employing a range of temperatures (l–60°C). It was found that with increase in temperature the conductivity decreased and the optimum temperature was found to be between 10 and 30°C. The results showthatthe polymer formed at low temperature has higher conductivity and is stronger than that formed at higher temperatures. Characterization by X-ray scattering shows that interlayer distance, d_Bragg (?), increases with increasing temperature. The morphology of the films formed was studied by using a scanning electron microscope (SEM). The changes in conductivity and physical appearance were interpreted as being due to compactness in the molecular packing and formation ofαβ linkages in the film.     

聚琥珀酸丁二酯的辐射交联和它的热变形行为

近年来 ,塑料废弃物污染环境的问题日趋严重 .对于环境的关心 ,已经使越来越多的科研人员对于研究环境友好化合物的发展产生了极大的兴趣 .发达国家先后制订了限制或禁止某些场合使用非降解性塑料 ,因此 ,多种可生物降解性塑料已经发展起来 .目前已经商业化的可生物降解性聚合物主要有脂肪族聚酯、聚醚、聚乙烯醇和聚多糖 .其中 ,利用化学合成法开发的可生物降解性聚合物是非常重要的 .脂肪族聚酯 ,例如聚乳酸(ＰＬＡ) .聚乙二酸 (ＰＧＡ)等被广泛地用于药物的载体[1] ,聚 (ε 己内酯 ) (ＰＣＬ)也已经被用作生产生物降解性薄膜 .脂肪族聚酯…     

Thermoresponsive terpolymers based on methacrylate monomers: Effect of architecture and composition

A series of amphiphilic thermoresponsive copolymers was synthesized by group transfer polymerization. Seven copolymers were prepared based on the nonionic hydrophobic n‐butyl methacrylate (BuMA), the ionizable hydrophilic and thermoresponsive 2‐(dimethylamino)ethyl methacrylate (DMAEMA) and the nonionic hydrophilic poly(ethylene glycol)methyl methacrylate (PEGMA). In particular, one diblock copolymer and six tricomponent copolymers of different architectures and compositions, one random and five triblock copolymers, were synthesized. The polymers and their precursors were characterized in terms of their molecular weight and composition using gel permeation chromatography and proton nuclear magnetic resonance spectroscopy, respectively. Aqueous solutions of the polymers were studied by turbidimetry, hydrogen ion titration, and light scattering to determine their cloud points, pK_as, and hydrodynamic diameters and investigate the effect of the polymers' composition and architecture. The thermoresponsive behavior of the copolymers was also studied. By increasing the temperature, all polymer solutions became more viscous, but only one polymer, the one with the highest content of the hydrophobic BuMA, formed a stable physical gel. Interestingly, the thermoresponsive behavior of these triblock copolymers was affected not only by the terpolymers' composition but also by the terpolymers' architecture. These findings can facilitate the design and engineering of injectable copolymers for tissue engineering that could enable the in situ formation of physical gels at body temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 775–783, 2010     

Temperature drop turbidity. IV. Polystyrene

The molecular weight distribution of fractionated and unfractionated polystyrene samples has been determined by temperature drop turbidimetry, in which polymer is precipitated from dilute solutions in cyclohexanol by progressively cooling from 388 to 310 K. Estimates of the molecular weight averages and the polydispersities, obtained by calibration of the temperature of initial onset of precipitation, T_i, and the weight-average molecular weight were low, but could be substantially improved by correcting for concentration changes during precipitation. An empirical procedure correlating the breadth of turbidity-temperature curves to the logarithm of the polydispersity, as measured by gel permeation chromatography, appeared to be a simpler method of characterizing the polymer samples and as accurate as the computational methods above.     

1,3-Butanediol as a co-solvent for the surfactant solutions

A biphasic solution containing water and precipitated phosphocholine (PC) is presented in order to investigate the consequences of 1,3-butanediol addition on the phase behavior of PC at different 1,3-butanediol concentrations and temperature values. With increasing the concentration of 1,3-butanediol in the mixed solvent at room temperature, the biphasic solution converts into turbid phase, two phase, and finally to a clear phase that is birefringent when viewed between two crossed polarizers. The birefringent phase moves to lower 1,3-butanediol contents at higher temperature values. The birefringent phase was observed via polarizing microscopy, and its rheological parameters were measured with cone plate method. In high 1,3-butanediol contents, solutions with 2.5% of PC behave as a gel with high yield stress value. The micellization of cetyltrimethyammonium bromide (CTAB) in a series of 1,3-butanediol/water mixed solvent at room temperature was also investigated. From the conductivity measurements, the critical micelle concentration and the degree of counterion dissociation of CTAB were obtained as a function of 1,3-butanediol. Standard free energy of micellization, as a function of 1,3-butanediol contents, was also estimated and discussed. Gibbs energies of micellization were found to have a good correlation with dielectric constant and Gordon parameters.     

Preparation and characterization of single-hole macroporous organogel particles of high toughness and superfast responsivity

Crosslinked macroporous polymer particles containing a single large hole in their surfaces were prepared by solution crosslinking of butyl rubber (PIB) in benzene using sulfur monochloride (S₂Cl₂) as a crosslinking agent. The reactions were carried out within the droplets of frozen solutions of PIB and S₂Cl₂ at −18 °C. Spherical millimeter-sized organogel beads with a polydispersity of less than 10% were obtained. The particles display a two phase morphology indicating that both cryogelation and reaction-induced phase separation mechanisms are operative during the formation of the porous structures. The beads exhibit moduli of elasticity of 1-4 kPa, much larger than the moduli of conventional nonporous organogel beads formed at 20 °C. The gel particles also exhibit fast responsivity against the external stimulus (solvent change) due to their large pore volumes (4-7 ml/g). The gel beads prepared at −18 °C are very tough and can be compressed up to about 100% strain during which almost all the solvent content of the particles is released without any crack development. The sorption-squeezing cycles of the beads show that they can be used in separation processes in which the separated compounds can easily be recovered by compression of the beads under a piston.