Micellization of poly(2-vinylpyrridine)-b-poly(cyclohexyl methacrylate) (P2VP-b-PCHMA) block copolymers and their interpolymer complex formation in non-aqueous medium.

HYPOTHESIS: The interpolymer complex formation between poly(vinylpyridine)-based polymers with poly(acrylic acid) (PAA), in aqueous or organic medium, is driven by the hydrogen-bonding complexation. Well-defined nanostructures, with specific practical applications, may be obtained by taking advantage of such non-covalent interactions. EXPERIMENTS: Poly(2-vinylpyridine)-b-poly(cyclohexyl methacrylate) (P2VP-b-PCHMA) and poly(2-vinylpyridine)-b-poly(t-butyl methacrylate)-b-poly(cyclohexyl methacrylate) (P2VP-b-PtBuMA-b-PCHMA) copolymers were synthesized by sequential anionic polymerization. Their micellar characteristics were examined as a function of their molecular characteristics in methylcyclohexane and toluene respectively, as cycloaliphatic and aromatic solvents for the selective solubilization of the PCHMA sequence. The size of interpolymer complexes was determined by DLS, in 1,4 dioxane, and their structural composition was characterized by 1H NMR. FINDINGS: The scaling relationship between the molecular composition and the micellar characteristics, such as particle size and aggregation number, could be established for the PCHMA-based copolymers in methylcyclohexane. It was further demonstrated that controlled micellization in 1,4 dioxane, as a non-selective organic solvent, could be achieved by hydrogen bond type interpolymer complex formation between P2VP-b-PCHMA and PAA-b-PCHMA under stoichiometric P2VP/PAA conditions. Finally, the size of the PCHMA-b-PAA/P2VP block copolymer/homopolymer complexes as well as of the PCHMA-b-PAA/PCHMA-b-P2VP block copolymer/block copolymer complexes was correlated with the molecular characteristics of the copolymers.

Self-Assembly of Block and Graft Copolymers in Organic Solvents: An Overview of Recent Advances.

This review is an attempt to update the recent advances in the self-assembly of amphiphilic block and graft copolymers. Their micellization behavior is highlighted for linear AB, ABC triblock terpolymers, and graft structures in non-aqueous selective polar and non-polar solvents, including solvent mixtures and ionic liquids. The micellar characteristics, such as particle size, aggregation number, and morphology, are examined as a function of the copolymers' architecture and molecular characteristics.

Effect of poly(vinyl alcohol-co-vinyl acetate) copolymer blockiness on the dynamic interfacial tension and dilational viscoelasticity of polymer-anionic surfactant complex at the water-1-chlorobutane interface.

Poly(vinyl alcohol-co-vinyl acetate) (PVA) copolymers obtained by partial hydrolysis of poly(vinyl acetate) (PVAc) are of practical importance for many applications, including emulsion and suspension polymerization processes. Their molecular characteristics have a major influence on the colloidal and interfacial properties. The most significant characteristics are represented by the average degree of hydrolysis D̅H̅, average degree of polymerization D̅P̅w̅ but also by the average acetate sequence length n(VAc)(0) which designates the so-called blockiness. Colloidal aggregates were observed in the aqueous PVA solutions having a D̅H̅ value of 73 mol%. The volume fraction of these aggregates at a given D̅H̅ value is directly correlated to the blockiness. Three PVA samples with identical D̅H̅ and D̅P̅w̅ but different blockiness were examined. By pendant drop and oscillating pendant drop techniques it was shown that the PVA sample having the lowest blockiness and thus the lowest volume fraction of colloidal aggregates has lower interfacial tension and elastic modulus E' values. On the contrary, the corresponding values are highest for PVA sample of higher blockiness. In the presence of sodium dodecyl sulfate (SDS), the colloidal aggregates are disaggregated by complex formation due to the hydrophobic-hydrophobic interactions. The PVA-SDS complex acts as a partial polyelectrolyte that induces the stretching of the chains and thus a reduction of the interface thickness. In this case, the interfacial tension and the elastic modulus both increase with increasing SDS concentration for all three PVA samples and the most significant effect was noticed for the most "blocky" copolymer sample.

Block copolymer stabilized nonaqueous biocompatible sub-micron emulsions for topical applications.

Polyethylene glycol (PEG) 400/Miglyol 812 non-aqueous sub-micron emulsions were developed due to the fact that they are of interest for the design of drug-loaded biocompatible topical formulations. These types of emulsions were favourably stabilized by poly (2-vinylpyridine)-b-poly (butadiene) (P2VP-b-PBut) copolymer with DPBut>DP2VP, each of these sequences being well-adapted to the solubility parameters of PEG 400 and Miglyol 812, respectively. This type of block copolymers, which might limit the Ostwald ripening, appeared to be more efficient stabilizers than low molecular weight non-ionic surfactants. The emulsion characteristics, such as particle size, stability and viscosity at different shear rates were determined as a function of the phase ratio, the copolymer concentration and storage time. It was further shown that Acyclovir, as a model drug of low water solubility, could be incorporated into the PEG 400 dispersed phase, with no significant modification of the initial emulsion characteristics.

Micellization of pH-stimulable poly(2-vinylpyridine)-b-poly(ethylene oxide) copolymers and their complexation with anionic surfactants.

The micellization behavior was examined for a series of 3 pH-stimulable poly(2-vinylpyridine)-b-poly(ethylene oxide) (P2VP-b-PEO) copolymers, with a constant composition of 67.5±1.5wt% PEO and increasing molecular weight. The micellar characteristics were determined by dynamic, static and electrophoretic light scattering, fluorescence spectroscopy, as well as by (1)H NMR in the pH range of 2-7 and in the presence or in the absence of the anionic surfactant sodium dodecylsulfate (SDS). In the absence of SDS, two pH regimes were investigated. For the pH range below 5, the micellar characteristics, such as C.M.C., particle size and zeta potential, were determined. For the first time, it could be shown that the micellization range could be extended to low pH values for relatively high copolymer concentrations. Above pH 5, correlations between the molecular characteristics and the aggregation number as well as the hydrodynamic diameter were established. A fair agreement could be demonstrated with the theoretical predictions for star-like micelles having a P2VP core and a PEO corona. Another original aspect of these double hydrophilic copolymers is their complex formation by electrostatic interaction between the protonated P2VP and SDS. At low pH and low copolymer concentrations, where only protonated unimers are present, the SDS induces the micellization at a given neutralization degree (DN). The process of complex formation was analyzed as a function of DN and pH by DLS, fluorescence spectroscopy, zeta potential measurements and by (1)H NMR, this last technique providing information on the mobility of the P2VP/SDS micellar core. A model for the micelle formation mechanism was suggested.

Original stimuli-sensitive polysaccharide derivatives/N-isopropylacrylamide hydrogels. Role of polysaccharide backbone.

This article compares the properties of a novel class of unsaturated Xanthan and Gellan derivatives/N-isopropylacrylamide stimuli-responsive hydrogels synthesized by free radical polymerization. Xanthan and Gellan Gum were partially functionalized by esterification with maleic anhydride under various conditions. By copolymerization of these maleate polysaccharides with a N-isopropylacrylamide known temperature sensitive precursor, water-swollen hydrogels with interpenetrating polymer networks (IPN) were obtained. The hydrogels were characterized for their temperature and pH-responsive behaviour by equilibrium swelling experiments and differential scanning calorimetry. The investigation of these materials also includes solid-state (13)CP/MAS NMR and elemental analysis of the nitrogen content. Morphology was visualized by scanning electron microscopy. Depending upon composition and the nature of the base-polysaccharide, the hydrogels showed different response rates to the external changes of temperature as well as pH. By changing the feed composition ratio of precursors and crosslinking agent (ß-cyclodextrin acrylate or N,N'-methylenebisacrylamide respectively) the phase transition temperature (lower critical solution temperature) could also be adjusted near to the body temperature for biomedical and biotechnological applications. The role of the rigidity and the charge density of the polysaccharide chain, its ability to form hydrogen bonding on these properties are more particularly considered.

Stimuli-sensitive xanthan derivatives/N-isopropylacrylamide hydrogels: influence of cross-linking agent on interpenetrating polymer network properties.

This article first describes the preparation and characterization of a novel class of unsaturated polysaccharide derivatives/ß-cyclodextrin acrylate/N-isopropylacrylamide stimuli-responsive hydrogels synthesized by free radical polymerization. Xanthan gum was partially functionalized by esterification with maleic anhydride under various conditions. By copolymerization of these maleate polysaccharides with a known temperature sensitive precursor (N-isopropylacrylamide) water-swollen hydrogels with interpenetrating polymer networks (IPN) were obtained. The hydrogels were characterized for their temperature and pH-responsive behavior by equilibrium swelling experiments and differential scanning calorimetry. The investigation of these materials also includes solid-state (13)CP/MAS NMR, elemental analysis of the nitrogen content and thermogravimetric measurements. Morphology was visualized by scanning electron microscopy. Depending upon composition, the hydrogels showed different response rates to the external changes of temperature as well as pH. By changing the feed composition ratio of precursors and cross-linking agent (ß-cyclodextrin acrylate or N,N'-methylenebisacrylamide, respectively) the phase transition temperature (lower critical solution temperature) could also be adjusted near the body temperature for the potential applications in biomedical and biotechnology fields. The role of the cross-linking agent on these properties is more particularly discussed.

[New ophthalmic insert]. / Nou insert oftalmic pe baza de hidrogel termosensibil.

UNLABELLED: Controlled release of drugs on ocular level is an important care for modern pharmacology. New studies targets are medical ophthalmic products with prolonged action (controlled release, target release). The hydrogel is an important segment in these studies. The purpose of this study is to assess a monolithic thermosensible hydrogel for releasing a certain medical product. MATERIAL AND METHOD: We used several materials for making thermosensible ophthalmic inserts that were processed (hydrogel synthesis, establish the inflation degree, hydrogel drug inclusion, establish the kinetics of in vitro drug releasing, in vivo studies). RESULTS: The study show that MA-G and PNIPAm basis hydrogel is a smart one that have the ability to collapse on a temperature closed to the physiological one, the result is the drug release in a desired doses. The hydrogel is perfectly tolerated, an experimental study prove that. CONCLUSIONS: Controlled release of active drug that are highly adequate to have a clinical response is based on small doses, without adverse effects. Is a target release.

Synthesis and characterization of poly(ethylene oxide)-block-poly(methylidene malonate 2.1.2) block copolymers bearing a mannose group at the PEO chain end.

A poly(ethylene oxide)-block-poly(methylidene malonate 2.1.2) block copolymer (PEO-b-PMM 2.1.2) bearing a mannose moiety at the poly(ethylene oxide) chain end was synthesized by sequential anionic polymerization of ethylene oxide (EO) and methylidene malonate 2.1.2 (MM 2.1.2), followed by a coupling reaction between its poly(ethylene oxide) amino- or aldehyde-end group and a sugar derivative. Different coupling procedures, either in organic media or in aqueous micellar solutions, were examined in order to optimize the poly(ethylene oxide) end-glycosylation yield. The micellar size of the functionalized block copolymers was determined by dynamic light scattering.

Non-aqueous emulsions stabilized by block copolymers: application to liquid disinfectant-filled elastomeric films.

The emulsifying and stabilization efficiency of polybutadiene-b-poly(ethylene oxide) and poly(ter butylstyrene)-poly(ethylene oxide) diblock copolymers is examined in non-aqueous emulsions. These emulsions are formed by a dispersion of polyethylene glycol mixed with a cationic surfactant acting as a biocide, in a continuous phase of a thermoplastic elastomer (SEBS) dissolved in methylcyclohexane. Emulsions with controlled droplet size and excellent stability could be obtained, which by solvent evaporation lead to elastomeric films containing droplets of confined disinfecting liquids.

Biocide squirting from an elastomeric tri-layer film.

Protective layers typically act in a passive way by simply separating two sides. Protection is only efficient as long as the layers are intact. If a high level of protection has to be achieved by thin layers, complementary measures need to be in place to ensure safety, even after breakage of the layer-an important issue in medical applications. Here, we present a novel approach for integrating a biocide liquid into a protective film (about 300-500 microm thick), which guarantees that a sufficient amount of biocide is rapidly released when the film is punctured. The film is composed of a middle layer, containing the liquid in droplet-like compartments, sandwiched between two elastomeric boundary layers. When the film is punctured, the liquid squirts out of the middle layer. A theoretical model was used to determine the size and density of droplets that are necessary to ensure a sufficient quantity of biocide is expelled from an adequately elastic matrix to provide protection at the site of damage. We demonstrate the utility of this approach for the fabrication of surgical gloves.