Effect of syndiotacticity on the aqueous poly(vinyl alcohol) gel 4. X-ray diffraction analysis of gel

Summary The structure of syndiotacticity-rich poly(vinyl alcohol) (PVA)-water gel was investigated by the X-ray diffraction analysis. Diffuse haloes appeared in the gel prepared from lower aqueous solution of PVA (5 wt%) but diffraction pattern became sharper with increasing concentration of PVA. Thed-spacings of gels and films are agreed with each other. The half height width of value of peak position of (101) obtained by photodensitometer decreased with increasing syndiotacticity of PVA. The radius of gyration of gel obtained from theGuinier's plots by the small angle X-ray diffraction increases with increasing syndiotacticity. These results suggest that the syndiotactic sequence length increases with increasing content of syndiotacticity and the crystallites in gel networks become also larger with increasing syndiotacticity. The average size of gel junction is 73–89 Å (s-(diad)% = 49.₄-66.₂).

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Zusammenfassung Es wurden mit Röntgeninterferenzen die Strukturen von einem Polyvinylalkohol-Wasser-Gel mit syndiotaktisch angereichertem Polyvinylalkohol untersucht. Es erscheinen diffuse Halos in dem Gel, das aus niedrigeren wäßrigen Lösungen (5% PVA) präpariert wurde. Doch wurden die Beugungsinterferenzen schärfer mit steigender Konzentration an PVA. Died-Abstände in Gelen und Filmen stimmten miteinander überein. Die Halbwertsbreite der 101-Interferenzen, gemessen mit einem Photodensitometer, nahm mit steigender Syndiotaktizitat des PVA ab. Der Trägheitsradius des Gels aus Guinier-Auftragungen für die Kleinwinkelstreuung nimmt mit steigender Syndiotaktizitat zu. Diese Ergebnisse legen nahe, daß die syndiotaktische Segmentläange mit steigendem Gehalt an Syndiotaktizitat zunimmt und daß die Kristallite in den Gelnetzwerken mit zunehmender Syndiotaktizität gröBer wurden. Die mittlere Größe des Netzwerkabstandes ist 73–89 Å (s-(diad)% = 49.₄-66.₂).

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With 7 figures in 15 details and 3 tables     

Formation of poly(vinyl alcohol)–iodine complexes in solution

The effect of the dissolved state of poly(vinyl alcohol) (PVA) molecules in water on the color development due to PVA–iodine complexes was investigated at each given PVA and iodine concentration using two kinds of syndiotactic-rich PVA (S-PVA) which are unstable in water because of the formation of intermolecular hydrogen bonds and form the complex easily. In the reaction mixtures prepared by mixing PVA solutions and an iodine solution, the color development was constant and independent of standing time of the PVA solution before the addition of iodine up to a certain time, after which it decreased with the standing time. The color development obtained with use of the PVA solution allowed to stand for a fixed time was higher for S-PVA with a lower s-(diad)%. In the case of the reaction mixture prepared by dissolving PVA in an iodine solution, the color development was higher for S-PVA with a higher s-(diad)%. The initial ratio of the I₅⁻/I₃⁻ and the rate of decrease in the ratio of I₅⁻/I₃⁻ were larger than those in the preceding case. The color development decreased for the PVA with an s-(diad) % of 58, whereas it increased for the PVA an s-(diad) % of 61.3 with increasing propanol content, an inhibitor of gelation. From these results, the aggregates of PVA molecules have been assumed to play an important role in forming the complexes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1701–1709, 1997     

Sol‐gel technique for the preparation of β‐cyclodextrin gold nanoparticles as chiral stationary phase in open‐tubular capillary electrochromatography

A novel open‐tubular capillary electrochromatography column coated with β‐cyclodextrin was prepared using the sol‐gel technique. In the sol‐gel approach, owing to the three‐dimensional network of sol‐gel and the strong chemical bond between the stationary phase and the surface of capillary columns, good chromatographic characteristics and unique selectivity in separating enantiomers were shown. The influences of capillary inner diameter, coating time, organic modifier, buffer pH, and buffer concentration on separation were investigated. The sol‐gel‐coated β‐cyclodextrin column has shown improved enantioseparation efficiency of chlorphenamine, brompheniramine, pheniramine, zopiclone in comparison with the sol‐gel matrix capillary column. The migration time relative standard deviation of the separation of the enantiomers was less than 0.89% over five runs and 2.9% from column to column. This work confirmed that gold nanoparticles are promising electrochromatographic support to enhance the phase ratio of open‐tubular capillary electrochromatography column in capillary electrochromatography.     

Crystal growth in syndiotactic poly(vinyl alcohol) hydrogels

Aqueous solutions of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) form gels easily. The optimum condition of growth of the calcium tartrate crystal formed by diffusing calcium chloride into hydrogels containing tartaric acid was studied with use ofs- PVA of a syndiotacticity of 56 % and a degree of polymerization of 1460. The crystal grew in the gel of the concentrations of 2 % s-PVA and of 0.5 N tartaric acid at pH=4. The relation between the formation of Liesegang rings and shear modulus of a gel was studied by diffusing silver nitrate into gels containing potassium chromate. The distance between rings decreased with increasing shear modulus of a gel in the range from 670 to 7500 dyne/cm². The Liesegang rings were not formed for the shear modulus gel for 280 and 16200 dyne/cm₂.     

Shear influence on the phase behavior of systems containing a homopolymer A and a block copolymer AB

Cloud point temperatures (T_cp) and crystallization temperatures (T_l/s) of the ternary system tetrahydronaphthalene/poly(ethylene oxide)/poly(dimethyl siloxane-b-ethylene oxide) have been measured at different constant shear rates using a rheo-optical device and an advanced rheometer. The cloud points temperatures (UCST-type phase diagram) are reduced by several degrees as the system flows; i.e. the shear can suppress the phase separation and enlarge the homogenous region. The crystallization kinetics of PEO in the ternary mixtures has been investigated isothermally and non-isothermally at quiescent state and under shear. The shear could strongly enhance the crystallization i.e. the (T_l/s) shifts to higher temperatures and the induction time, t₀ (the time needs for the onset of crystallization) substantially decreases with increasing shear rate during the non-isothermal and isothermal crystallization processes, respectively. The isothermal crystallization kinetics at quiescent state and at different shear rates was analyzed on the bases of Avrami approach. The Avrami exponent which provides qualitative information about the nature of the nucleation and growth process, was found to be shear rate and temperature dependent. The Avrami exponent increased from ∼3 at the quiescent state to as large as 9 at &&ggr;dot; = 100 s⁻¹.     

Thermoreversible gelation and phase separation in aqueous methyl cellulose solutions

We derived typical phase diagrams for aqueous solutions of methyl cellulose (MC) of different molecular weights via micro‐differential scanning calorimetry, small‐angle X‐ray scattering, and visual inspection. The phase diagrams showed the cooccurrence of gelation and phase separation and qualitatively agreed with the theoretically calculated diagrams. The sol–gel transition line and phase separation line of a lower critical solution point type shifted toward lower temperatures and lower concentrations with an increase in the MC molecular weight. The sol–gel transition line intersected at a temperature higher than the critical point of the phase separation; therefore, both sol–gel phase separation and gel–gel phase separation were possible, depending on the temperature. Specifically, through visual inspection of a high molecular weight MC sample in the critical temperature region, we observed phase separation into two coexisting gels with different polymer concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 91–100, 2001     

Studies on the kinetics of growth of silver nanoparticles in different surfactant solutions

We produced gels using electrolytic-reduction ion water and magnesium aluminum silicates (smectone^®), and evaluated in detail gel properties in the presence of various types of salt (NaCl, KCl, CaCl₂, MgCl₂, and AlCl₃). Each salt was added to deionized-distilled water or electrolytic-reduction ion water, and phase diagrams for the smectone^® concentration (2.0–4.0%) were produced. The areas of the three phases of smectone^® (gel, sol, and separation) at each salt concentration were expressed as percentages of the total area. As a result, uni- and polyvalent cations (excluding Ca²⁺ ions) affected the stability of gels produced using electrolytic-reduction ion water, and, particularly, univalent cations (Na⁺, K⁺) markedly improved gel stability.Using electrolytic-reduction ion water as a dispersal medium, drug delivery systems (DDS) that can maintain the gelling state can be prepared. Thus, gel preparations with maintained functions or controlled-release transdermal drugs can be obtained.     

The role of precursors in the structure of SiO2-Al2O3 sols and gels by the sol-gel process

Binary sols and gels of SiO₂-Al₂O₃ were prepared using tetraethyl orthosilicate and each of four aluminum compounds; aluminum di (sec-butoxide) ethylacetoacetic ester chelate (AC), aluminum nitrate nonahydrate (AN), aluminum formoacetate (AF), and boehmite sol (BS) made from aluminum i-propoxide. The structure and the evolution of the Si-O-Al bonds in SiO₂-Al₂O₃ sols and gels were investigated by ²⁷Al nuclear magnetic resonance (NMR), Infrared absorption spectra, DTA, and X-ray diffraction. The formation of Si-O-Al bonds differs depending on the aluminum compounds used as raw materials. The ratio of Al(IV) to {Al(IV) + Al(VI)} is related to the microstructural homogeneity of the gels. When AC is used as a raw material, the Si-O-Al bonds are formed in the sol state and resultant gel shows good microstructural homogeneity. In case of AN, the Si-O-Al bonds are not formed either in the sol or the wet gel state. The bonds are formed by drying the gel before heat-treatment temperature reaches 300 400°C, resulting in good microstructural homogeneous gel. When AF is used, the Si-O-Al bonds are formed in the sol state but the ratio of Al(IV) to {Al(IV) + Al(VI)} is lower than when using AC. Microstructural homogeneity of the gel is ranked between AC or AN and BS. Using BS, the Si-O-Al bonds are not formed in the sol solution, and the change in the coordination number of the gel is similar to that of boehmite gel. The Microstructural homogeneity of the gel is the worst among the BS gels, which were prepared by using the four aluminum raw materials.     

Application of open tubular electrochromatography for acidic and basic analytes

Summary The separation of charged analytes by electrochromatography has been examined on porous-layer open tubular capillaries prepared using the sol gel method. An electroosmotic flow of about 2.10×10⁴ cm²V¹s¹ was obtained using between 10 and 30% acetonitrile in the mobile phase. Acidic diuretic drug compounds were successfully separated at high pH as were theN-alkylanilines in their basic and neutral forms. The limitation of open tubular columns was observed on separating some basic pharmaceutical drugs. These components showed severe peak tailing and were not resolved on a 20 μm i.d. porous silica layer open tubular column. Strongly acidic components could not be detected on these columns due to their higher counter electromobilities. The successful separation of neutral aryl alkyl ketones with an efficiency of 101,533 plates m¹ for butyrophenone was an indication of the improved phase ratio on this type of open tubular columns.     

Macroporous Morphology of the Titania Films Prepared by a Sol-Gel Dip-Coating Method from the System Containing Poly(ethylene glycol). IV. General Principle of Morphology Formation and Effect of Heat Treatment

The variation of macroscopic morphology of the titania (TiO₂) films has been studied at various dipping conditions for a sol-gel dip-coating system containing poly(ethylene glycol) (PEG). The variation of macroscopic morphology is understood consistently by considering both the volume fraction of solvent phase during the phase separation and the water to alkoxide ratio in the sol film. The gel film shrinks and the average pore diameter increases concurrently with the thermal decomposition of PEG while the morphology depends less on the crystallization of titania gel.     

Water based sol–gel methods used for Bi-222 thermoelectrics preparation

Three different water based sol?Cgel methods were compared in the synthesis of Bi₂Sr₂Co_1.8O_x thermoelectric ceramics. We chose methods that can stabilize a Bi³⁺ ion while solution and gel are formed: chelating method using combination of ethylenediamintetraacetic acid (EDTA) and triethanolamine (TEA) chelating agents and, further, synthesis using two different water soluble polymers??polyacrylamide or polyethylenimin. In each sol?Cgel process, we tested two gel decomposition atmospheres. The gels were decomposed either in air or in inert atmosphere (followed by treatment in pure oxygen). Additionally, a sample synthesized by solid state reaction was used for comparison with the sol?Cgel prepared samples. The grain size of precursors and also their phase composition were determined for methods used and different gels decomposition atmospheres. The sintered final samples did not differ in phase composition; on the other hand, they vary in volume density and microstructure. The differences were reflected in electric transport measurement (the temperature dependence of Seebeck coefficient, resistivity and thermal conductivity). The use of EDTA/TEA or PEI methods led to the samples with improved thermoelectric parameters in comparison to the solid state sample.     

Early Stages of Crystallization in Gel Derived ZrO2 Precursors

Three different precursor materials giving rise to contrasted nanostructures, xerogels, aerogels and precipitates, are prepared by a sol gel route in the Zrn -propoxide—acetylacetone—water—n-propanol system. Clear homogeneous gels are made by using a proper amount of acetylacetone and water. The gels are dried either by conventional processing (xerogels) or by supercritical evacuation of alcoholic solvent (aerogels). The complexation ratio (R = [acetylacetone]/[Zr(OR)₄]) is the main parameter controlling the size of ZrO₂ primary particles. WhenR = 0 , precipitates are obtained.Xerogels, aerogels and precipitates are characterized and their textures are compared through small angle X-ray scattering measurements. The fractal structure of gels is destroyed by conventional drying and is preserved in aerogels. On the other hand precipitates are described as homogeneous agglomerates of very small primary units.The first crystallization steps are studied by transmission electron microscopy and X-ray diffraction experiments. The contribution of crystallite size and microstrain effects are investigated by Rietveld whole pattern fitting. The crystallization of precipitate powders starts at the agglomerate scale with large crystal like distorted lattices.     

The influence of short chain branch on formation of shish‐kebab crystals in bimodal polyethylene under shear at high temperatures

Formation of shish‐kebab crystals due to the coil–stretch transition under shear in the molten state using a bimodal polyethylene system with high molecular weight (HMW) fraction having different branch content was investigated. In specific, in situ small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD) techniques were used to study the structure evolution of shish‐kebab crystals at high temperatures under simple shear. The SAXS results revealed that with the increase of branch content, shish‐kebab crystals became more stable at high temperatures (e.g., 139 °C). However, the shish length of the bimodal PE containing 0.11% branch was shorter than that with no branch. The WAXD results showed that the degree of crystallization for bimodal PE with HMW fraction having 0.11% branch increased with time but reached a plateau value of 1%, while that with no branch increased continuously till 11%. Furthermore, the crystal orientation of bimodal PE with HMW fraction having 0.11% branch was above 0.9 and maintained at a constant value, while that with no branch decreased from 0.9 to 0.1 upon relaxation. This study indicates that even though the crystallizability of the HMW fraction with branch content decreased, they could effectively stabilize the shear‐induced crystalline structure with shorter shish‐kebab crystals. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 786–794     

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     

Gel–sol transition for soluble polyimide solution

Copolyimides were synthesized in N‐methyl‐2‐pyrrolidone (NMP) to prepare polyimide (PI) solutions with various concentrations, and gels can form in PI/NMP solution with a suitable concentration or at a low temperature. Gel–sol transition in the PI/NMP solution has been investigated through a combination of polarized optical microscope, differential scanning calorimeter measurement, and rheological measurements. According to Winter–Chambon theory, the critical gel point is 12 wt %, and the loss tangent (tan δ) shows frequency independence. Gel–sol transition temperature (T_gel) for the 13 wt % solution is around 65 °C. Below the T_gel, the gel exhibits strong optical planar texture, indicating the formation of a fully anisotropic phase, which has a great importance for the fabrication of PI fibers by gel‐spinning. Dynamic temperature sweep measurements show that the formation of the gel from solution is thermoreversible and is significantly delayed in the cooling process. Under the favorable conditions, the tensile strength and modulus of the fibers derived from the solution are about 0.7 and 12.5 GPa using gel‐spinning method, which is believed to afford broad application potential in preparing high‐performance PI fibers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 450–459     

Rapid crystallization and thermoreversible gelation of poly(ethylene terephthalate) in polymer/oligomer binary system

Poly(ethylene terephthalate) (PET) was rapidly crystallized through thermoreversible gelation in a liquid ethylene glycol oligomer or in epoxy resin. The solutions formed gel rapidly on cooling. Polarized light microscopy and small-angle light scattering showed that these gels contain large, regular PET spherulites. The gels may be formed by two consecutive processes: the phase separation and crystallization, and gelation by formation of a three-dimensional PET network in the oligomer solvents, where the nodes of the network are PET spherulites. The crystallinity of PET recovered from polymer/oligomer gels is near 72% measured by wide-angle X-ray diffraction method, which is about 20% higher than PET samples crystallized by solution crystallization in small molecule solvent, high temperature annealing, and stretching techniques. It takes only a few minutes to form the highly crystalline phase PET in the PET/oligomer system, and the crystallinity of the dried gel is independent of the concentration of the original solution. Excimer-fluoresence and Raman spectroscopic studies indicated that PET recovered from the gels are in an ordered state with few chain entanglements. The entanglement density of the recovered PET recovered from a 20 wt % solution in ethylene glycol oligomer is as low as that of freeze-extracted PET from a 0.5 wt % solution in phenol. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1219–1225, 1998     

Thermoreversible gelation of helical polypeptide/single‐walled carbon nanotubes and their solid‐state structures

Single‐walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ‐benzyl‐L ‐glutamate)s (PBLGs) having well‐defined polymer molecular weight (M_n = 7.5–21.1 kg·mol^?1) and molecular weight distribution (PDI = 1.05–1.20) by a graft‐to method. Toluene solutions containing 5 wt % free PBLG and variable amounts of PBLG‐functionalized SWCNTs (PBLG‐SWCNTs) form gels at room temperature. Differential scanning calorimetry (DSC) analysis reveals that the gelation occurs thermoreversibly, in accord with previous studies on the pristine PBLG/toluene gels. The heat of gel melting (ΔH_m) is slightly elevated for the composite gels compared with the pristine gel, which suggests enhanced interactions between PBLGs in the former. But the gelation temperatures of the composites are unaffected by the presence of PBLG‐SWCNTs. Small‐angle X‐ray scattering (SAXS) analysis of the composite and pristine gels at different temperatures by the Guinier method suggests that PBLG‐SWCNTs promote interactions between PBLG rods, as indicated by the larger PBLG bundle size with increasing PBLG‐SWCNT content in the gel and the melt state. W/SAXS analysis of the dry gels reveals that PBLG‐SWCNTs induce significant changes in the PBLG packing order, resulting in a nematic phase, in contrast to a weakly ordered smectic C phase containing tilted PBLG rods that is observed in the pristine gel. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Effect of syndiotacticity on the aqueous poly(vinyl alcohol) gel 3. Mechanical property of gel

Summary The mechanical property of aqueous gel was studied using the PVA having the content of syndiotacticity in diad from 58.4 and 66.2%. The elastic modulus of gels was 105–106 dyne/cm2 and the variation of the elastic modulus of gel with the rise of temperature was corresponded with the variation of the concentration of PVA in gel accompanying syneresis. The elastic modulus of gel having the same content of syndiotacticity and concentration of PVA increased in the order as follows, the first is the gel chilled at room temperature, the second is the gel chilled at 60 °C and last is the gel chilled at 0 °C. The variation of the elastic modulus of gel with the rise of temperature became smaller with increasing content of syndiotacticity. The increase of elastic modulus is considered to be attributed to the further growth of stronger junctions through the recrystallization followed by syneresis rather than the entropic effect of polymer networks with the rise of temperature.

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Zusammenfassung Es wurden die mechanischen Eigenschaften wßriger Gele aus Polyvinylalkohol untersucht, mit Gehalten an Syndioaktizität in Diaden zwischen 58,4 und 66,2%. Die elastischen Moduln der Gele lagen bei 105 bis 106 dyn/cm2 und die Variation der elastischen Moduln der Gele mit Steigerung der Temperatur entsprach der Konzentrationsänderung von Polyvinylalkohol im Gele gemäß der stattgefundenen Synärese. Der elastische Modul des Gels mit konstantem Gehalt an Syndiotaktizität und Konzentration des PVA steigen in folgender Weise: Zuerst das Gel abgekühlt bei Raumtemperatur, dann das Gel abgekühlt bei 60 °C und zuletzt das Gel erstarrt bei 0 °C. Die Variation der elastischen Moduln mit steigender Temperatur wird kleiner mit steigendem Gehalt an Syndiotaktizität. Das Anwachsen der Moduln sollte vermutlich dem weiteren Wachstum strengerer Kopp lungen durch Rekristallisation infolge der Synärese zuzuschreiben sein mehr als einem Entropieeffekt der polymeren Netzwerke mit steigender Temperatur.

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With 6 figures and 2 tables

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Part 2. cf. reference 2.     

Thermally induced phase separation of poly(vinylidene fluoride)/diluent systems: Optical microscope and infrared spectroscopy studies

Thermally induced phase separation (TIPS) has been developed to prepare porous membranes. The porous structures are mainly dependent on diluents adopted in the TIPS process. We obtained two typical morphologies of poly(vinylidene fluoride) (PVDF) membranes using cyclohexanone (CO) and propylene carbonate (PC) as diluents, respectively. SEM observation displays that porous spherulites are formed from PVDF/CO system, whereas smooth particles result from PVDF/PC system. The TIPS processes of these two systems have been investigated in detail by optical microscope observation and temperature‐dependent FTIR combined with two‐dimensional infrared correlation analysis. Rapid crystallization of PVDF can be seen around 110 °C in the PVDF/CO system, which is consistent with the results of temperature‐dependent FTIR spectra. The spectral evolution indicates a transform of PVDF from amorphous to α‐phase after 110 °C. The ν_s(C?O) band at 1712 cm^?1 narrows and the ν_s(C? F) band at 1188 cm^?1 shifts to 1192 cm^?1 before crystallization, which implies the destruction of interaction between PVDF and CO. In contrast, the PVDF/PC system shows slow crystallization with all‐trans conformation assigned to β‐phase and γ‐phase below 60 °C but no obvious change of polymer?diluent interaction. We propose two mechanisms for the different phase behaviors of PVDF/CO and PVDF/PC systems: a solid?liquid phase separation after destruction of polymer?diluent interaction in the former, and a liquid?liquid phase separation process coupled with rich‐phase crystallization in the later. This work may provide new insight into the relationship among morphologies, crystal forms, and phase separation processes, which will be helpful to adjust membrane structure. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1438–1447     

Stimuli‐responsive reversible physical networks. I. Synthesis and physical network properties of amphiphilic block and random copolymers with long alkyl chains by living cationic polymerization

The living cationic polymerization of octadecyl vinyl ether (ODVE) was achieved with an 1‐(isobutoxy)ethyl acetate [CH₃CH(OiBu)OCOCH₃]/EtAlCl₂ initiating system in hexane in the presence of an added weak Lewis base at 30 °C. In contrast to conventional polymers, poly(octadecyl vinyl ether) underwent upper‐critical‐solution‐temperature‐type phase separation in various solvents, such as hexane, toluene, CH₂Cl₂, and tetrahydrofuran, because of the crystallization of octadecyl chains. Amphiphilic block and random copolymers with crystallizable substituents of ODVE and 2‐methoxyethyl vinyl ether (MOVE) were synthesized via living cationic polymerization under similar conditions. Aqueous solutions of the copolymers yielded physical gels upon cooling because of strong interactions between ODVE units, regardless of the copolymer structure. The product gels, however, exhibited different viscoelastic properties: A 20 wt % solution of a block copolymer (400/20 MOVE/ODVE) became a soft physical gel that behaved like a typical gel, whereas the corresponding random copolymer gave a transparent but stiff gel with a certain relaxation time. Differential scanning calorimetry analysis confirmed that the crystalline–amorphous transition of the octadecyl chains was a key step for inducing such physical gelation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1155–1165, 2005