Propylene Oxide Triblock Copolymer Research Articles

Crystalline Ethylene Oxide and Propylene Oxide Triblock Copolymer Solid Dispersion Enhance Solubility, Stability and Promoting Time- Controllable Release of Curcumin.

The design and development of an effective medicine are, however, often faced with a number of challenges. One of them is the close relationship of drug's bioavailability with solubility, dissolution rate and permeability. The use of curcumin's (CUR) therapeutic potential is limited by its poor water solubility and low chemical stability. The purpose was to evaluate the effect of polymer and solid dispersion (SD) preparation techniques to enhance the aqueous solubility, dissolution rate and stability of the CUR. The recent patents on curcumin SD were reported as (i) curcumin with polyvinylpyrrolidone (CN20071 32500 20071214, WO2006022012 and CN20151414227 20150715), (ii) curcumin-zinc/polyvinylpyrrolidone (CN20151414227 20150715), (iii) curcumin-poloxamer 188 (CN2008171177 20080605), (iv) curcumin SD prepared by melting method (CN20161626746-20160801). SD obtained by co-preciptation or microwave fusion and the physical mixture of CUR with Poloxamer-407 (P-407), Hydroxypropylmetylcellulose-K4M (HPMC K4M) and Polyvinylpyrrolidone-K30 (PVP-K30) were prepared at the ratios of 1:2; 1:1 and 2:1. The samples were evaluated by solubility, stability, dissolution rate and characterized by SEM, PXRD, DSC and FTIR. The solubility, stability (pH 7.0) and dissolution rate were significantly greater for SD (CUR:P-407 1:2). The PXRD,SEM and DSC indicated a change in the crystalline state of CUR. The enhancement of solubility was dependent on a combination of factors including the weight ratio, preparation techniques and carrier properties. The drug release data fitted well with the Weibull equation, indicating that the drug release was controlled by diffusion, polymer relaxation and erosion occurring simultaneously. Thus, these SDs, specifically CUR:P-407 1:2 w/w, can overcome the barriers of poor bioavailability to reap many beneficial properties.

PH induced tuning of size, charge and viscoelastic behavior of aqueous micellar solution of Pluronic ® P104–anthranilic acid mixtures: A scattering, rheology and NMR study

• SANS and rheology data for AA loaded P104 micelles at different pH are reported. • Uniaxial growth was seen with [AA] which suppressed in strongly acidic and alkaline pH. • The pH dependent growth in the presence of AA is accounted for charged micelles. • NOESY showed the location of AA in micelles at core–shell interface. A moderately hydrophilic ethylene oxide–propylene oxide triblock copolymer (EO 27 –PO 63 –EO 27 ) Pluronic ® P104 hereafter referred to as P104 forms spherical core–shell micelles in water. The pH dependence on the influence of anthranilic acid (AA) on P104 micelles was investigated by cloud point (CP), viscosity, dynamic light scattering (DLS), small angle neutron scattering (SANS), nuclear Overhauser enhancement spectroscopy (NOESY) and rheology. SANS results showed the remarkable effects on the structure of micelles and are discussed in terms of micellar growth and transition. NOESY revealed the location of AA close to the core–corona region of the micelle. These micelles develop ionic nature by changes in pH which affects micelle hydration and inter-micellar interaction. This was further supported by changes in viscosity, cloud point and DLS. The storage/loss modulus and other rheological parameters for selected viscoelastic solutions were evaluated and discussed.

Double cloud point of ethylene oxide–propylene oxide triblock copolymer in an aqueous solution

Anomalous double cloud point of ethylene oxide–propylene oxide triblock copolymer L62 in an aqueous solution is usually ascribed to impurities in the polymeric nonionic surfactant. In this article, the partial phase diagrams of block copolymers L62, L61, and L92 (including their mixtures) in aqueous solutions with and without the presence of 1-butanol have been determined, which indicates that double cloud point is not a peculiar character of L62 in an aqueous solution. Based on a further analysis of phenol solubilization in clear L62 aqueous solutions, a schematic phase diagram of polymeric nonionic surfactants in an aqueous solution is proposed. The schematic phase diagram was supported not only by our experimental results but also in line with the reported results in the literature.

Development of novel formulations for photodynamic therapy on the basis of amphiphilic polymers and porphyrin photosensitizers. Pluronic influence on photocatalytic activity of porphyrins

Effect of ethylene and propylene oxide tri-block copolymers (Pluronics) on the photocatalytic activity of tree porphyrins differing by their hydrophobicity was studied. It was shown that Pluronics induce considerable increase in the photocatalytic activity of the tetraphenylporphyrin, hematoporphyrin disodium salt (Dimegine) and relatively hydrophilic N-methyl-bis-glucamine salt of chlorine e6 (Photoditazine) in the reaction of photooxidation of tryptophan in water solution. This effect was maximal for Pluronics F127 and P85 with intermediate hydrophobicity, while more hydrophilic F68 and more hydrophobic L61 were less effective. Pluronic effect on the photocatalytic activity of tetraphenylporphyrin and dimegine is attributed to their disaggregation in water solution, while PD activity is elevated due to the local concentrating of the photocatalyst and the substrate within micellar volume. It was found by AFM that the structure of Pluronic F127 thin films prepared by water solution evaporation on mica surface significantly changed in the presence of porphyrin. This effect can be attributed to the interaction of Pluronics with porphyrins in water solution.

Effect of phenol on the aggregation characteristics of an ethylene oxide–propylene oxide triblock copolymer P65 in aqueous solution

The effects of phenol on the micellization, micellar growth, and phase separation of a poly(ethylene oxide)- block-poly(propylene oxide)- block-poly(ethylene oxide) (PEO–PPO–PEO) amphiphilic copolymer (Pluronic P65: EO 19PO 30EO 19) in aqueous solution have been studied by cloud point, viscosity, dynamic light scattering (DLS), differential scanning calorimetry (DSC), fluorescence spectroscopy, and small-angle neutron scattering (SANS). Various concentrations of P65 have been chosen to estimate the effect of phenol on different concentration regions of P65. Phenol interacts quite differently at low concentrations (0–2%) than at high concentrations (2–10%) of P65, as per the observation that phenol is more predominant at smaller concentrations of P65. A marked decrease in the cloud points of the P65 solutions is observed in presence of phenol. The critical micelle temperature (CMT) of P65 shows a synergistic effect of phenol on P65 aggregates. Micellar transitions, phase separation, and aggregation behaviours like micellization and micellar growth in the presence of phenol have been observed by combining viscometry, DLS, DSC, and CP. DLS shows that the effect of phenol is predominant at high temperatures. SANS shows a high increase in axial ratio and aggregation numbers in the presence of phenol at fixed concentrations of P65. Fluorescence data illustrate that addition of phenol makes micelles polar but at the same time its favours aggregation. Water-soluble phenol (present in low concentrations) forms aggregates with P65, which can be separated by cloud point extraction, making this study interesting for separation of phenol from the phenol–water system.

Micellization in aqueous solution of an ethylene oxide–propylene oxide triblock copolymer, investigated with 1H NMR spectroscopy, pulsed-field gradient NMR, and NMR relaxation

1H nuclear magnetic resonance (NMR) spectroscopy has been applied to study the temperature and concentration-induced micellization of a poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymer, Pluronic P105, in D 2O solutions in the temperature range from 5 to 45 °C and the concentration range from 0.01 to 15% (w/v). The intrinsic probes, the chemical shift, and the half-height width of the PO CH 3 signal are very sensitive to the local environment and can be used to characterize the temperature and concentration-dependent aggregation process. When the temperature approaches the critical micellization temperature or the polymer concentration reaches the critical micellization concentration, the chemical shift of the PO CH 3 signal moves toward lower ppm values and the half-height width of the PO CH 3 signal shows a sudden increase. It indicates that the methyl groups are experiencing a progressively less polar environment and transferring from water to the hydrophobic micellar core. The hydrodynamic radius of the unimers and the micelles are determined as be 1.8 and 5.0 nm by means of pulsed-field gradient spin-echo (PGSE) NMR. They were independent of temperature and concentration. The drastic shortening of spin–lattice relaxation time T 1 for the PO CH 3/ CH 2 protons in the transition region suggested that the PPO blocks are located in a “liquid-like” micellar core, whereas the exponential increase of T 1 for the PEO CH 2 protons implied that the PEO blocks are still keeping in contact with surrounding water. Thermodynamics analysis according to a closed association model shows that the micellization process is entropy-driven and has an endothermic micellization enthalpy.

Aggregation and clouding behavior of aqueous solution of EO–PO block copolymer in presence of n-alkanols

The aqueous solution behavior of an ethylene oxide–propylene oxide triblock copolymer Pluronic ® P123 [(EO) 20(PO) 70(EO) 20] was investigated in the presence of various n-alkanols (C 1–C 6) by cloud-point, viscosity, dynamic light scattering (DLS) and spectroscopic (FTIR, NMR) measurements. For lower alkanols (methanol, ethanol and 1-propanol), the cloud-points (CPs) increased with increase in alkanol concentration. The reverse effect was found for higher alkanols (C 4–C 6) where both the CPs and critical micelle temperatures (CMTs) decreased with increase in concentration. This behavior is explained in terms of a co-operative association of higher alkanols and block copolymers by replacing water molecules in the PPO core and inducing micellar growth in aqueous P123 solution. Lower alkanols are likely to be good solvents for both PEO and PPO blocks and the effect on PPO blocks predominates indicating an increase in CP and CMT with increase in alkanol concentration.

Unusual Micelle and Surface Adsorption Behavior in Mixtures of Surfactants with an Ethylene Oxide−Propylene Oxide Triblock Copolymer

Micellization and adsorption at the air-solution interface of binary mixtures of the triblock copolymer of ethylene oxide and propylene oxide, EO23PO52EO23 (EPE), and the surfactants sodium dodecyl sulfate (SDS), dodecyl trimethylammonium chloride (DTAC), and tetraethylene glycol monooctyl ether (C8EO4) have been studied by neutron reflectivity and surface tension. The synergistic attractive interaction between the polymer and the ionic surfactants has been analyzed in the framework of the pseudo phase approximation and gives rise to a stronger interaction for EPE/SDS than EPE/DTAC. In contrast, the interaction of the nonionic surfactant C8EO4 with the copolymer EPE shows an unexpected and rather different behavior, resulting in a strongly repulsive interaction, characterized by a positive interaction parameter. The neutron reflectivity measurements of the surface excess, where the predicted and measured surface excesses are directly compared, provide evidence that challenges the applicability of the pseudo phase approximation for describing the surface mixing behavior. Structural information on the mixed adsorbed layer provides evidence which in part explains the observed discrepancies between the measured surface excesses and the behavior predicted from the pseudo phase approximation. Furthermore the structural evidence can be use to rationalize the differences in behavior observed between the ionic and nonionic surfactants.

Examination of the adsorption of ethylene oxide–propylene oxide triblock copolymers to soil

The adsorption of 5 surfactants (P103, P105, F108, F127 and L92) to a sandy soil has been investigated. The surfactants are ABA block copolymers in which the A blocks are synthesised from ethylene oxide and the B block from propylene oxide. CMC values, for the block copolymers, as well as surfactant sorption to soil were measured by surface tension techniques. The adsorption of all five compounds can be described by the Freundlich adsorption isotherm. Adsorption, in each case, is related to the critical micelle concentration of the surfactant and the extent of adsorption appears to be linked also to the fraction of soil organic matter.

Effect of salt on the micellization of pluronic P65 in aqueous solution

Solutions of an ethylene oxide–propylene oxide triblock copolymer (PEO/PPO/PEO) pluronic® P65 (50–50 wt.% of each block with total molecular weight of 3400 g mol −1) in aqueous sodium chloride examined by different methods reveal salt-induced micellization. The critical micelle concentrations (CMCs) and critical micelle temperatures (CMTs) showed a marked decrease in the presence of added salt. Unimer-to-micelle transitions at low concentration (or temperature) and micellar growth at temperature close to cloud point are discussed.

Micellar Structure of an Ethylene Oxide−Propylene Oxide Block Copolymer: A Small-Angle Neutron Scattering Study

Micellar solutions of a highly hydrophilic ethylene oxide−propylene oxide triblock copolymer, pluronic F88 (EO103PO39EO103), in aqueous solution are examined by small-angle neutron scattering (SANS) at different concentrations and temperatures and in the presence of different salts. At temperature less than 30 °C, F88 solution in water (5 wt %) showed unimers which are fully dissolved Gaussian chains. The unimer-to-micelle transition takes place when the temperature or concentration is increased. Added neutral salt favors micellization of the copolymer at lower concentration/temperature. At temperature close to ambient, block copolymer forms micelles that consist of a central core, presumably dominated by the propylene oxide blocks, surrounded by a corona of highly hydrated ethylene oxide subchains. SANS analysis shows that the size of hydrophobic core increases as a part of PEO adjacent to the PPO core loses water with increasing temperature or salt (KCl) concentration. The micellar volume fraction incre...