Reversible Thermoassociation of Water-Soluble Polymers

Abstract

TH ERMO ASSOCIATION RÉVERSIBLE DE POLYMÈRES HYDROSOLUBLESThe thermoassociative phenomenon was also studied by Small Angie Neutrons Scattering (SANS, using copolymers composed by a deuterated polyacrylate backbone and protonated polyethyl ene oxide grafts. The scattering properties of our system were studied by varying the temperature, the salinity and the polymer concentration of the solution. A good agreement between the microscopic characteristics of the solutions and their rheological properties was found. TERMOCOMBINACIÓN REVERSIBLE DE POLIMEROS HIDROSOLUBLESLos polimeros hidrosolubles se utilizan corrientemente corno agentes de espesamiento para controlar la reologìa de los fluidos acuosos, en distintos sectores de la industria. No obstante, sus propiedades se debilitan a medida que aumenta la temperatura. Para hacer trente a este problema se ha desarrollado el concepto de polfmeros "termocombinativos" solubles en el agua. Nuevos sistemas anfifilos de este gènero se pueden obtener por injerto en una estructura hidrófila de las cadenas laterales que dejan de ser solubles por encima de una temperatura critica infe rior de solución (Lower Critical Solution Temperature = LCST). Las soluciones semidiluidas de estos copolimeros presentan pro piedades de espesamiento reversibles a medida que aumenta la temperatura y alcanza un valor critico cercano de la temperatura de LCST de las cadenas laterales. Este comportamiento se puede poner en relación con la agregación de elementos de injertos por encima de su temperatura LCST en microsectores hidrófobos que conducen a la formación de una reticulación tridimensional. Con temperaturas màs elevadas, la viscosidad de la solución cizallada con valor constante alcanza un valor maximo. Esto se puede inter pretar en términos de reorganización de la red fisica debido al esfuerzo de cizallamiento, que pasa de una estructura con "combinaciones intermoleculares" principalmente a un sistema con un numero incrementai de "combinaciones intramoleculares". Habida cuenta de la diversidad de los polfmeros solubles en el agua que presentan una separación de fases al proceder a un recalentamiento (LCST), se han realizados distintos copolfmeros "termocombinados" [1] and [2], utilizando un polielectrolito, o sea una estructura hidrófila neutra. Con objeto de proceder a la aplicación de estos sistemas en la industria del petróleo, se han desa rrollado copolfmeros que contienen àcidos sulfónicos de propano 2-acrilamida 2-metil (AMPS) utilizando el óxido de polietilene (PEO) corno elemento de injerto LCST. En el presente artfculo figura una descripción generai de su comportamiento reológico. Sus propiedades se pueden controlar, ya sea variando las caracterfsticas de la solución (concentración de polimero, salinidad, etc.) o por modificación de la estructura quimica del copolimero (relación de injertos, masa molecular, etc.). Este estudio reológico ha demostrado la potencialidad de los sistemas "termocombinativos", particularmente para la industria del petróleo [3]. En la actualidad existe la po...

A novel thermoviscosifying water‐soluble polymer: Synthesis and aqueous solution properties

“…The thermoviscosifying behavior of P(AM-co-MPAD) solutions can be related to the thermoassociative interaction of macromonomer unit induced by an LCST type phase separation taking place at a local scale. 34,35,39 Nevertheless, the viscosity of PAM solution decreases with increasing temperature [ Fig. 5(b)], with a general trend following Arrhenius' law.…”

“…34,35 In these systems, some ''blocks'' or ''grafts'' with the character of lower critical solution temperature (LCST) were incorporated onto the hydrosoluble skeleton. The final copolymer is fairly water soluble and behaved as usual macromolecules at room temperature, but the thermosensitive sequences start to self-aggregate into hydrophobic microdomains upon heating to a critical associative temperature (T ass ), and reversibly switch off hydrophobic interactions when decreasing temperature to lower than T ass .…”

Thermoassociative graft copolymers based on poly(N-isopropylacrylamide): Relation between the chemical structure and the rheological properties

“…Phys. 201, 858-868 (2000) a water-soluble backbone (poly(sodium acrylate), PAA) and LCST side-chains which were initially poly(ethylene oxide), PEO 2,[6][7][8][9] . These copolymers exemplify very nicely the initial concept of thermoassociation and allow to clarify the general mechanism.…”

Synthesis and rheological properties of hydrophobically modified polyacrylamides with lateral chains of poly(propylene oxide) oligomers

“…However, as the temperature increases and reaches the side chains LCST, these units self-aggregate into hydrophobic microdomains. As was explained above, this aggregate effect on viscosity will depend on polymer concentration, thus, in the semi-dilute regime, the formation of hydrophobic clusters involving grafts covalently linked to different water soluble backbones can be expected [1]. Polymers which present a typical LCST phase diagram in aqueous solutions are, for example, polyethylene oxide, polypropylene oxide, poly(N-isopropylacrylamide), polyvinyl methyl ether and hydroxyalkyl cellulose [1].…”

“…To overcome these drawbacks, water soluble polymers which contain a relatively small number of hydrophobic groups attached along the polymer backbone (associative polymers), have been synthesized in the past few years. The incorporation of a few hydrophobic groups in a hydrophilic macromolecular chain can lead to a water soluble system which self-aggregates in water, resulting in thickening effects [1].…”