Fluorescence Probe Studies of Pluronic Copolymer Solutions as a Function of Temperature

Abstract

The temperature variation of the 11/13 ratio of pyrene vibrational fine structure has been studied in aqueous poly(ethy1ene oxide)-block-poly(propy1ene oxide)-block-poly(ethy1ene oxide) (PEO-PPO-PEO) copolymer solutions, in bulk PEO, PPO, and various organic solvents. Linear decreases were observed in organic solvents and in mixtures ofbulk PEO and PPO. The data in aqueous PEO-PPO-PEO copolymer solutions reveal three distinct solution conditions: at low temperatures, the linear decrease with temperature parallels that for water; over a small intermediate temperature range there is a sharp decrease in the ratio, attributed to the formation of micelles; and at higher temperatures, a linear decrease is again observed. Values in this region are strongly dependent on the PPO block and are consistent with the representation of micelles with a core dominated by PPO. These decreasing values for the intensity ratio in the latter region indicate a less polar environment for pyrene and were considered to be a linear combination of the temperature effects on the polarity observed in bulk poly(ethy1ene oxide) and poly(propy1ene oxide) homopolymers. The composition of the micelle core was estimated using these data and indicated an increase of poly(ethy1ene oxide) as the polymer becomes more hydrophilic. In addition, the size of the micelles and their aggregation numbers were determined using light scattering and pyrene luminescence decay studies, respectively. These data showed an increase of the aggregation number with temperature while the hydrodynamic radius remained constant and were interpreted in terms of dehydration of the PEO block.

Biodegradable Self-Assembling PEG-Copolymer as Vehicle for Poorly Water-Soluble Drugs

“…Increasing the concentration of the diblock copolymer mmePEG-CAP/TMC in an aqueous pyrene solution led to several changes in the fluorescence properties. Very small shifts were observed in the excitation (from 335 to 338 nm) and emission spectra (I 1: from 372 to 373 nm and I 3 : from 383 to 384 nm) of pyrene since the dye molecules moved from a water environment to a more hydrophobic medium (20,21). The I 1 /I 3 ratio decreased with increasing polymer concentrations to reach a constant base line (Fig.…”

“…This covers a wide range of polarity from water (I 1 /I 3 ‫ס‬ 1.9) to cyclohexane (I 1 /I 3 ‫ס‬ 0.6). This scale was used to evaluate the microenvironment in the micelle core (21).…”

Estudo de soluções aquosas de copolímeros em bloco de poli(óxido de etileno)-poli(óxido de propileno) utilizando calorimetria exploratória diferencial (DSC)

“…Copolímeros bloqueados com o grupamento C 12-14 apresentam valores mais baixos de TMC do que os encontrados para os copolímeros bloqueados com o grupamento C 4 . Este comportamento também é observado quando se analisa a solubilidade destes copolímeros: quanto maior o bloqueio, menor o ponto de turvação, e isso foi atribuído ao maior segmento hidrófobo presente nos copolímeros bloqueados com C [12][13][14] . Os valores de TMC para os copolímeros C 4 -(EO) 4 -(PO) 11 -OH e C 12-14 -(PO) 4 -(EO) 5 -OH não são detectados dentro da faixa de temperatura de trabalho o C) [20] .…”

“…Os parâmetros de maior importância estudados foram: a concentração na qual as micelas começam a se formar; fração de moléculas de copolímeros na forma micelar; e o tamanho e o número de agregados das micelas [8][9][10][11][12][13][14][15][16][17] .…”

Effect of the degree of neutralization on the micellization of block ionomers

“…Recently, considerable research has been pergle chains. Also, it was found that neutralized samples that formed on nonionic block copolymers that micellize in aquewe, recovered by freeze-drying and redissolved had a larger ous media (6)(7)(8)(9)(10)(11)(12) or in organic solvents (13)(14)(15)(16)(17). Research on aggregation number V) and R,, than those that were formed the micellization of ionic block copolymers, as compared to directly upon neutralization (25).…”