Use of multi-block copolymers as thermo-thickeners

Details Use of multi-block copolymers as thermo-thickeners Use of multi-block copolymers as thermo-thickeners

1998-09-08

2000-09-26

Dawson, Robert

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

524609, 528367, 528403, 528417, 528421, 528425, 528390, 558233, 558235, 558236, 558237, C08K 539

Patent

active

061243825

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to polymers having thermally-induced thickening properties in aqueous medium.
The term thermally-induced thickening polymers is understood to mean polymers whose viscosity in aqueous medium remains constant or increases over a wide temperature range, in contrast with standard polymers whose viscosity decreases substantially as the temperature increases.
EP-A-583,814 has described polymers having thermally-induced thickening properties, said polymers being in the form of copolymers consisting of a fully water-soluble chain on which other segments having a water-soluble transition at a critical temperature referred to as LCST (low critical soluble temperature) are grafted. Above the critical temperature, the segments which have become hydrophobic have a tendency to associate together, leading to the formation of a network of high molecular mass and thus to an increase in viscosity, or at least not to a decrease in viscosity, thereby generating the thermally-induced thickening property. Thus, in the prior art, it is possible to obtain thermally-induced thickening properties for polymers only at temperatures above the critical temperature (LCST) of the segments showing the water-soluble/hydrophobic transition.
Now, the critical temperature of the segments given as examples in the prior art can be high; it is, for example, above 100.degree. C. for polyoxyethylene. The thermally-induced thickening effect appears, in this case, only at temperatures for which this effect is not always sought. Thus, it is not possible to use certain thermally-induced thickening polymers in applications carried out at low temperature.
One solution is to use said thermally-induced thickening polymers in the presence of a salt which makes it possible to develop the thermally-induced thickening effect at a lower temperature. However, it is not possible to introduce a salt in the context of certain applications such as plant-protection applications or paper industry applications.
One object of the invention is thus to propose polymers having thermally-induced thickening properties at a temperature below the critical temperature LCST of the chain members.
Another object of the invention is to propose a means for controlling the temperature at which the thermally-induced thickening effect appears for a copolymer in which the nature of the water-soluble chain and of the chain members is given.
With this aim, the invention relates to the use, as thermally-induced thickening agents, of linear multiblock copolymers of general formula (I) or (II) ##STR2## in which: E represents a polyoxyalkylene block, each alkylene chain member having not more than 6 carbon atoms, monomer chosen from ethylenic monomers, atom and optionally a tertiary amine group, or greater than 250,000 g/mol, preferably greater than 270,000 g/mol and even more preferably greater than 400,000 g/mol.
The copolymers according to the invention are linear and have no side segments grafted onto the main chain of the type A. They have an alternation of polyoxyalkylene polymer blocks E and of water-soluble polymer blocks A derived from ethylenic-type monomers, joined together by a linking unit: ##STR3##
In the multiblock copolymers according to the invention, the polyoxyalkylene blocks E have a critical temperature (LCST), whereas the polymer blocks A are water-soluble in any temperature range.
The copolymers used must have a molecular mass of greater than 250,000 g/mol, said molecular mass being measured by gel chromatography (GPC) in aqueous phase, in polyoxyethylene equivalents.
In general, multiblock copolymers are used in which the polyoxyalkylene blocks E contain a number of units i of at least 25, preferably of not more than 1000, even more preferably of between 200 and 400.
According to the invention, and preferably, multiblock polymers are used in which the weight content T of polyoxyalkylene blocks E is at least 3%, preferably not more than 50%, even more preferably between 5 and 20%.
Among the copolymer blocks according to the invention, ment

REFERENCES:
Journal of Macromolecular Science, Chemistry, A27(6), pp. 791-806, Nair et al., 1990.

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