Upper or lower critical solution temperature, or both? : Studies on cationic copolymers of N-isopropylacrylamide

The solution properties of statistical copolymers of N-isopropyl acrylamide (NIPAm) and cationic (3-acrylamidopropyl) trimethylammonium chloride (AMPTMA) have been studied. The phase behavior of the copolymers in aqueous solutions is strongly affected by the addition of lithium bis(trifluoromethane)sulfonimide (LiNTf2), NaCl, or both. Hydrophobic NTf2 counter ions bind to the AMPTMA repeating units. By adjusting the balance between hydrophobic and electrostatic interactions the transition temperature of the copolymers may be tuned over a wide temperature range. It was observed that a homopolymer PAMPTMA undergoes an UCST-type phase separation in an aqueous solution in the presence of both NaCl and LiNTf2. When AMPTMA and NIPAm are present in the copolymer in nearly equal amounts both LCST and UCST can coexist. It was observed that the effect of LiNTf2 is similar to that of the salts in the kosmotropic end of the Hofmeister series for PNIPAm.Peer reviewe

Influence of photo-isomerisation on host-guest interactions in poly(azocalix[4]arene)s

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Microgel-like aggregates of isotactic and atactic poly(methacrylic acid) chains in aqueous alkali chloride solutions as evidenced by light scattering

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Mucoadhesive Properties of Gellan and Its Modified Derivatives

This review is devoted to recent achievements in the development of macromolecular therapeutic systems with the participation of a polysaccharide, gellan, that possesses conformational and sol–gel transitions. The main attention is paid to the mucoadhesive properties of gellan and its derivatives. Various applications of gellan in biotechnology, bioengineering, and nanomedicine are briefly considered.Peer reviewe

Tough Materials Through Ionic Interactions

This article introduces butyl acrylate-based materials that are toughened with dynamic crosslinkers. These dynamic crosslinkers are salts where both the anion and cation polymerize. The ion pairs between the polymerized anions and cations form dynamic crosslinks that break and reform under deformation. Chemical crosslinker was used to bring shape stability. The extent of dynamic and chemical crosslinking was related to the mechanical and thermal properties of the materials. Furthermore, the dependence of the material properties on different dynamic crosslinkers-tributyl-(4-vinylbenzyl)ammonium sulfopropyl acrylate (C4ASA) and trihexyl-(4-vinylbenzyl)ammonium sulfopropyl acrylate (C6ASA)-was studied. The materials' mechanical and thermal properties were characterized by means of tensile tests, dynamic mechanical analysis, differential scanning calorimetry, and thermogravimetric analysis. The dynamic crosslinks strengthened the materials considerably. Chemical crosslinks decreased the elasticity of the materials but did not significantly affect their strength. Comparison of the two ionic crosslinkers revealed that changing the crosslinker from C4ASA to C6ASA results in more elastic, but slightly weaker materials. In conclusion, dynamic crosslinks provide substantial enhancement of mechanical properties of the materials. This is a unique approach that is utilizable for a wide variety of polymer materials.Peer reviewe

Phase Separation of Aqueous Poly(diisopropylaminoethyl methacrylate) upon Heating

Poly(diisopropylaminoethyl methacrylate) (PDPA) is a pH- and thermally responsive water-soluble polymer. This study deepens the understanding of its phase separation behavior upon heating. Phase separation upon heating was investigated in salt solutions of varying pH and ionic strength. The effect of the counterion on the phase transition upon heating is clearly demonstrated for chloride-, phosphate-, and citrate-anions. Phase separation did not occur in pure water. The buffer solutions exhibited similar cloud points, but phase separation occurred in different pH ranges and with different mechanisms. The solution behavior of a block copolymer comprising poly(dimethylaminoethyl methacrylate) (PDMAEMA) and PDPA was investigated. Since the PDMAEMA and PDPA blocks phase separate within different pH- and temperature ranges, the block copolymer forms micelle-like structures at high temperature or pH.Poly(diisopropylaminoethyl methacrylate) (PDPA) is a pH-and thermally responsive water-soluble polymer. This study deepens theunderstanding of its phase separation behavior upon heating. Phase separationupon heating was investigated in salt solutions of varying pH and ionicstrength. The effect of the counterion on the phase transition upon heating isclearly demonstrated for chloride-, phosphate-, and citrate-anions. Phaseseparation did not occur in pure water. The buffer solutions exhibited similarcloud points, but phase separation occurred in different pH ranges and withdifferent mechanisms. The solution behavior of a block copolymer comprisingpoly(dimethylaminoethyl methacrylate) (PDMAEMA) and PDPA wasinvestigated. Since the PDMAEMA and PDPA blocks phase separate withindifferent pH- and temperature ranges, the block copolymer forms micelle-likestructures at high temperature or pHPeer reviewe

Well-dispersed clay in photopolymerized poly(ionic liquid) matrix

This contribution presents a methodology for combining the solvating power of ionic liquids with polymer composite synthesis. A polymerizable ionic liquid was used as solvent to disperse clay, after which the mixture was polymerized into a solid polymer-clay composite. Polymer-clay composites were prepared with filler load-ings up to 10 wt%. The addition of clay as filler enhanced mechanical properties; tensile strength and stiffness of the materials exhibited appreciable improvements. The glass transition temperature of the materials shifted to slightly higher temperatures due to the hindered segmental motions of the polymer chains. The improvements were the highest at approximately 5 wt% filler content. When the filler content was increased further, excessive aggregate formation impaired the material properties.Peer reviewe

Polycation-PEG Block Copolymer Undergoes Stepwise Phase Separation in Aqueous Triflate Solution

A block copolymer poly(ethylene glycol)-b-poly(vinylbenzyltrimethylammonium triflate), PEG-PVBTMA-OTf, and a homopolymer PVBTMA-OTf were synthesized through RAFT reactions. The polymers were studied in aqueous triflate solutions with varying temperatures, changing also the polymer and salt concentrations. The hydrophobic triflate anion turns polycations thermoresponsive, and they show an UCST. In the block copolymer, the interaction between the PEG and the cationic block makes the phase separation occur in distinct steps. Upon cooling, transparent solutions first turn turbid and then partially clear at T-cL. The T-cL is not observed in a mixed solution of PVBTMA-OTf and PEG macro-CTA. By considering the interplay between ionic, hydrogen bonding, and hydrophobic interactions, an overall picture of the complex phase separation processes is suggested.Peer reviewe

Ophthalmic drug delivery system based on the complex of gellan and ofloxacin

Complex formation between a natural polysaccharide – gellan and an antimicrobial drug – ofloxacin was studied in aqueous solution. Conductimetric and potentiometric titration curves revealed that gellan and ofloxacin forms a water-soluble complex of composition 2:1 mol/mol stabilized by ionic and hydrogen bonds. The formation of the gellan-ofloxacin complex was confirmed by FTIR spectroscopy, dynamic light scattering, zeta-potential and thermogravimetric analysis. The average hydrodynamic size of the complex was found 307±5 nm and its zetapotential was negative and equal to -15 mV. Thin films of the gellan-ofloxacin complex, gelled in 0.3 wt.% of CaCl2, were used to study the release kinetics of ofloxacin in distilled water and phosphate buffer. The drug release kinetics evaluated by UV-Vis spectroscopy at λmax = 289 nm and calculated by the Ritger-Peppas model correspond to non-Fickian diffusion in distilled water and Case II transport (zero-order kinetics) in phosphate buffer. The cumulative release of ofloxacin from the gellan-ofloxacin films was equal to 96±2% and 36±2% in phosphate buffer and distilled water, respectively. It is expected that the gellan-ofloxacin complex is able to form in situ gel on the surface of the eye and to prolong the drug residence time in the tear fluid.Peer reviewe